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GBT Observer`s Guide - NRAO - National Radio Astronomy

1. 81 ohne Us QoS RCRUM ede e po Oe Rd 81 Point Map 4 da Pe Oe Gee qe ueste ded ax 82 eS E PREG asoees es4eneeee 82 TEENEST eee EEEE EE EEE ae 83 Po Oe a ERR OE Pa ta Oe eee OP v Pea EROS 83 ks suce uu a 85 6 2 4 1 Getting Your Catalog Into Astrid 85 6 2 4 2 The Format of the 86 Ge eee A Os ae a cet 86 6 2 4 3 SPHERICAL format 88 CL c ae at aks Mek 2 Ree 89 6 2 4 5 Catalog Functions 2 e 90 6 2 4 6 EPHEMERIS format Tables for moving objects 91 Comets 2 REPRE ATR EER QUE XO ow vow ER RT 93 II 98 jog Reb RR E EES bed BOR OR Rok Rok 08 08 odo cR es 99 6 2 5 4 Annotation 4 ma ck eorr E E wo RR OE X w vov wok RO S 99 6 2 5 2 BalaeeQ ot IRR EE op AS 99 62 5 3 Break s ssi eeu SR dee ee EO Ru E RE RH TRIS brad 100 6 2 54 Comment ss pea nen e dE e444 Sub ed domos eee eas 100 6 2 5 5 GetUTO ea dunk wee ae BORE GR UAE RR mmm E es 100 6 2 5 6 GetLST Rh ros 101 6 2 5 7 4 CAO bata Race ba OO OES Eee a ee eS 101 6 2 5 8 WaitborO o co a a lE eee O3 RE we E 101 6 2 5 9 ChangeAttenuation 102 EP 102 6 2 6 1 Location Object eA 102 6 2 6 2 Offset Object
2. 94 8 1 GBT IF system routing s s siaaa eee en nn 117 8 2 GBT IF system flow 118 8 3 IF system 119 9 1 Orientation of feeds on the GBT 122 126 de aie telah tah ee Fey se 128 10 3 Dual Beam Receiver to VEGAS Mapping 2e 128 10 4 Four Beams to VEGAS Mapping RR 129 10 5 KPFA seven beam to VEGAS 129 ML C D C TTITIT 133 I nE E E a a a y Gn ee ah eet 134 la TTL Bm GSR A a eh eh eee ee a RA AS GO Oe eS 135 C Sid Bits tives Bo Ee ea eR AE Ee a A OE ERAS Ge aS ee e 136 the bandpass for mode 4 modes 4 9 all show a similar bandpass mode 17 representing denoting the locations of the spurs as dictated by Equation 11 1 The GUPPI ADC histogram 149 11 2 The GUPPI monitor 150 11 3 The GUPPI status 153 12 1 Data from a CCB beamswitched OTF NOD showing data and model versus time through one B1 B2 B2 B1 scan The white line is the CCB beamswitched data and the green line is the fit for source amplitude using the known source and telescope as a function
3. T cC r EA 8 eee a Ge ah hae ee 8 11 3 1 Overview ofthe 5 11 5 2 DSS Terminology lt s e ho wok oe ox ke PEPPER ewe ea ee M MOM SERE 11 3 3 Controlling the Scheduling of a 12 TL PRETI 13 pup hae ues Gdn pp 13 3 5 The DSS 13 D r Responsibilities Rub wo de ec PRR Se ee i RO RR ORO o set wur ue d 16 4 4e xw xvm Ve TPTEESSS4 2055 16 sa gh Ak ah ae eee Fe Be eee 17 Cee ghee eee ee Bak hs eee 17 Ped 4444 Lbs 4454414749393 444 PS S3 dg dus 18 jog SU ee de PIS Pd b EROR S 18 3 13 Other DSS Control 19 4 Introduction To Astrid 21 A1 Wbatls Astrid cs esc R Robb ae a cs RE 4 e 21 42 How Start Astrid oro oom o d ooh EAE ob ee eee o RR RR 22 4 2 1 Running Astrid u aen Rem ec Rex ee eR 3 Er ea 22 TETTE 23 4 2 21 Drop down 23 Ig UU 23 eh eee de eee ee ee ee Tr 24 1 TP 24 LOOMS ts 5 ode ee Se gy v AER etu e e de ee RR 24 ca eae ie ee EL 25 42 2 2 oolb r 4 2 4 o4 oe OO OAS oe eme OSG OEE S334 SAS 25 4 2 2 3 Application Component
4. 195 16 4 Weather Restrictions ooa aaa 199 ba a he be aR ERR ee DEER A 199 P 200 oR cis te Ak GAGA Om AAR EROS SS 200 oS Stak oh ee ee ee es a A A 200 16 4 5 heed Blowers s s soe b ooo eee S P S EGER a A 200 201 17 1 Remote Observing Guidelines for Approved Projects 17 2 VNC Setup Instructions iadaaa dan les 202 18 Planning Your Observations And Travel 203 OG tee ho nine oo bebe at he eS 203 18 2 Travel SUppOrtl 2 2 4 a dere Se run ONES qe ec db te 203 EEG Ecole yd et ae ake Bien lela Be ee TT 204 18 4 Housing s ca saatat RR RR bee eee eR AAA ERE eee es Rta dt edie 204 18 5 Getting To Green Bank 204 18 5 1 Where is Green 204 18 5 2 Directions to Green Bank 204 P44 ba ie ek ee ee ee ee a eS 204 Pittsburgh to Green 206 CT 206 Charlottesville to Green 206 DLE TTC TZ 206 18 5 3 Once You Green Bank 0 000000 00 000004 206 19 After Your Observations 209 19 1 Taking your data home s s s iaa da d a a eee 209 19 2 Installing 209 19 3 Keep Your Contact Person Informed
5. 1 File Edit View Scrollback Bookmarks Current VEGAS st Settings DAQPULSE _SNPH PFBRATE FILENUM 0 ODE M Last update Fri Nov 21 08 19 32 2014 lil vegas hpcl Help DAQSTATE PKTFMT NPOL GPUSTAT PFBBLKIN STTOFF ACCBLKIN q to quiti Figure 10 9 The VEGAS shared memory screen e Because of the way VEGAS writes it s data the filler cannot start filling until the scan has finished For immediate inspection of data Observers are urged to use the real time display Section e For large scans the filler could potentially fall behind the data acquisition process To avoid this the filler will skip scans that it cannot keep up with The rule is If integration time total number of spectra per integration lt 0 00278s skip the scan Except if integration length gt 0 9s it will be filled The total number of spectra per integration is the total across all banks So for example 2 banks 8 subbands 2 polarizions and 4 switching states e g frequency switching with calibration will produce 2 8 2 4 128 spectra and so if the integration time is lt 0 356s the online filler will not fill that data The 0 9s limit is because for that integration time the online filler can almost keep up even in the worst case and interscan latencies pauses for pointing and focus scans and so on will nromally allow it time to catch up The online fi
6. 22e 209 19 4 Press Releases and News worthy Items 209 19 5 Publishing Your Results ss 210 A The GBTSTATUS IF Path Nomenclature 211 B Introduction to Spectral Windows 213 B 1 Array Receiver Spectral 213 C Usage of vlow and vhigh 215 D Location and Offset Objects 217 E A Note on Angle formats and units in Astrid and Catalogs 219 F Advanced Utility Functions 221 E L General Functions lt amp 4x wow a aod ROG Re Re d X omm mm S 221 FE GetValue ee bee ed REX S RU EX XE A UE Y 221 1 2 S tValuesO lt e Rr Pee E Eee had p ded n n RE 221 L3 DetneScan 4 4 4 tor ck SEA OR RE ROS 6 o9 wp WR 222 1 4 GetCurrentLocation 4 4 4 e 222 1 5 SetSourceVelocity ee ee 222 F 2 Specialty Scan Types Submitted By Observers 222 Ed BSES 439433 EEE EE RE Re Roy do Y x Y 222 2 2 Spiders 43 ob ep eh eee eee bob de dc EME dad d dod mop Ros YR od 223 eB ZIG 5 478 ar d els Sedis us ai at Rd 223 G Advanced Use of the Balance Command 225 H Operator Run Observing Guidelines 227 ist of Acronyms 229 Glossary 233 List of Figures a 3 sta ete thd eee head bm GOGH oS Rae a ed AS 5 3 1 sample DSS 14 eu te Se te BE at ache ee acetate Oe a ede oe gs eee oe 22 4 2 Astrid startup pop
7. 9 0 cg 6 LI TZ Z618 6 9T 8 LM g 1 8T 9 OPON 9 0 cg 6 8 Uv 960 6 9 8 LMd1 8T 9 6 0 43 I 26 vo 9899 vr es 8 TM 1 81 9POIN 8 0 Ze TS 20 8947 pret 8 LM g 1 8T 9 0 Ze 8 ce VI PSE9T Prez 8 7 81 OPON 8 0 cg ZI ZI 6 618 8 7 871 OPON 8 0 cg ZI 9 279 9607 vvec 8 LM amp 1 81 0c OPON psepom pueq qng 8 8 0 ZE 6 27 z0 0 88ZPZS ZL TT T 8 6T 8 0 ce 6 EZZ v0 0 1 9 ZL IT I LM g I 8T 8T 0 cg c9 EZI TO ZLOTET ZL IT I LM g I 8T LI 8 0 cg 6 gg 9999 I LM g 1 8T 9T 80 Ze 6 22 vo 8947 CL TI I LAAG I 8 T ST 9POIN oT ZE GZ OFZ v0 O 88ZPZS I LMg I 8T FT 8 0 cg 6 vel 1 9 1 LMg 1 8T 9 0 cg GL eL ZLOTST pV e I 7 871 80 ze 6 vo 9899 vr es I 97 871 IT 9POIN 8 0 Ze 6 91 20 8947 vr es I 97 871 OT 9 0 Ze 69 oF 80 ZLOTET OOT I 7 7 6 PON Vo cg IG GZ SI 9899 001 I 7 7 8 vo cg Ig rg 8942 001 I 7 7 4 OPO 9 0 69 ce VI ZLOLET LET I LAAS I T I 9 9POIN 0 6 9 999 281 1 7 7 amp PON vo Ze ZG II Lg 8947 q 48T I 7 7 PON cg OST Y 99 V8 91 080T I AAHH M91H cg 281 6 V8 91 0081 I AAHH MO9TH 0 e e I VOL OOST I A HH MIH
8. FEM Model Off DC Focus Y mm 0 IAS Zernike Model off AS offsets On H E ObservationManagement Log 1 DataDisplay Log 1 GbtStatus Log 1 Command Console Figure 4 7 The Gbt Status Tab showing the top portion of the status To see the rest of the status screen you will need to use the scroll bar The default status screen displays all of the currently supported items of the gbtstatus program These are Duration The scan length in seconds Remaining The time remaining in the scan Scan A derived field composed of the scan number and PROCNAME PROCSIZE and PROCSEQN keywords from the GBT Observing GO FITS file Scan Start Time If scan has started it is the UTC scan start time if the scan has not started then it is the countdown until the start of scan On Source Yes or displays a countdown until the antenna is on source 34 CHAPTER 4 INTRODUCTION TO ASTRID gt Sill C Eile Edit View Tools Help ee ObservationManagement 1 DataDisplay 1 GbtStatus 1 Scan 306 26 of 173 in RALongMap Source pol E Observation State Duration sec 420 Vel Def Radio Scan Start Time 18 26 55 Vel Frame KinematicalLSR GBT State n Source Yes Source Vel km s 360 000 Remaining 00 00 17 Time To Set N A H Receiver Revrl 2 Obs Freq MHz 1419 622198 CRI Status Polarity polLinear Rest Freq MHz 1420 406 al State O
9. The expected wait time is printed in the observation log including a warning if the wait is longer than 10 minutes WaitFor will immediately return if the specified time has already passed and is within the last 30 minutes While WaitFor has the Observing Script paused it does not prevent the user from aborting a script However if the user chooses to continue once the abort is detected then the WaitFor abandons the wait and returns immediately Using a Horizon object defined in 6 2 6 3 WaitFor can be used to have an Observing Script wait for a source to rise above an elevation of 10 WaitFor Horizon 10 0 GetRise 15324 3421 or to wait for a source to set WaitFor Horizon 10 0 GetSet sun If WaitFor s argument is None then it aborts with an error message to the observation log This can occur when the commands GetRise or GetSet detect an event which will never occur such as the rise time for a circumpolar source 102 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS 6 2 5 9 ChangeAttenuation ChangeAttenuation allows the observer to change all the attenuators in the IF Rack or the Converter Rack by the same ammount ChangeAttenuation takes two arguments devicename A string that can be either IFRack or ConverterRack This specifices the device in which the attenuators will be changed attnchange A float This specifies how much the attenuators should be changed This v
10. Observing With The Green Bank Telescope by GBT Scientific Staff November 3 2015 Version 3 3 This guide provides essential information for the preparation of Observing Scripts for observations with the Green Bank Telescope Authors Contributors and Editors This Guide is the product of many of the GBT Scientific Staff with major contributions from Dana Balser Jim Braatz David Frayer Frank Ghigo Amanda Kepley Adam Kobelski Karen O Neil Glen Langston Ryan Lynch Ron Maddalena Brian Mason Toney Minter Dan Perera Richard Prestage Scott Ransom Contents 1 How Use This Manual 1 3 3 2 1 1 Main Features of the GBT 4 TT 4 213 Front Ends 43x44 PE ER wee aA a 4 2 1 3 1 Prime focus receivers 5 2 1 3 2 Gregorian focus 6 2 1 3 3 The MUSTANG 6 2 1 4 Backends aww eae ee ee ae OE ees eA wa we 6 2 1 4 1 Digital Continuum Receiver DCR 6 2 1 4 2 Caltech Continuum Backend 6 2 1 43 VEGAS BR ee ae ee ee e a WO PA ER 7 CUT uS S3 94h ee 7 Ma ee Oe aaa ade OES ESE Is eae 7 2116 S VEBI BD 7 21 471 Radar si 4440 ou ESR eee PRES Hees BAGS SRE a 7 2 1 5 Polarization Measurements
11. center of map Offset J2000 4 8 60 0 0 0 False 4 8 wide Offset Offset J2000 0 0 12 0 60 0 cosv False 12 tall 12000 0 24 60 0 0 0 False 0 24 stripe spacing Offset J2000 3 0 2 0 cosv False 2 2 deg ref offset 3 ref every 3rd column 10 0 10 seconds per row Note that the above example does not create a map which is rectangular when plotted in RA vs Dec You would have to use cosv True to get a rectangular map DecLatMap A Declination Latitude map or DecLatMap does a raster scan centered on a specific location on the sky It is similar to DecLatMapWithReference except that it does not make periodic observations of a reference position Syntax DecLatMap location hLength vLength hDelta scanDuration beamName unidirec tional start stop DecLatMap does not have referenceInterval as a parameter otherwise it is the same as DecLatMap WithReference See DecLat MapWithReference for information on the parameters for DecLatMap Point MapWithReference A PointMapWithReference constructs a map by sitting on fixed positions laid out on a grid This scan type allows the user to periodically move to a reference location on the sky Please see PointMap if no reference location is required The starting point of the map is defined as hLength 2 vLength 2 Syntax PointMapWithReference location hLength vLength
12. fastdump py A special 256 channel fast dump mode at X band for Crab Giant Pulses users sransom astrid GUPPI astrid 350MHz fastdump py A way to dump at 81 92us for 100MHz BW mode data for searching users sransom astrid GUPPLastrid_slew takedata py The Slew and Track example from above e users sransom astrid GUPPL_astrid_driftscan py The Track for driftscans example from above 156 CHAPTER 11 PULSAR OBSERVING WITH GUPPI Chapter 12 The CalTech Continuum Backend CCB The Caltech Continuum Backend CCB is a dedicated continuum backend for the GBT Ka band re ceiver built in collaboration with A C S Readhead s radio astronomy instrumentation group at Caltech and commissioned on the GBT in 2006 The driving consideration behind its design is to provide fast electronic beam switching in order to suppress the electronic gain fluctuations which usually limit the sensitivity of continuum measurements with single dish radio receivers To further improve stability it is a direct detection system there are no mixers before the conversion from RF to detected power The Ka band receiver provides eight simultaneous directly detected channels of RF power levels to the CCB one for each feed times four frequency channels 26 29 5 GHz 29 5 33 GHz 33 36 5 GHz and 36 5 40 GHz Astronomical information and labels for these 8 channels or ports in GBT parlance is summarized in Table 12 The following sections outline
13. path and again to set the power levels just before collecting data Allowed values are True or False The default is True configure A Boolean This argument causes the scan type to configure the telescope for continuum observing for the specified receiver The default is True Note because AutoPeakFocus is self configuring one must re configure the for your normal observing after the pointing and focus observations are done unless the configure parameter is set to False Also be aware that setting configure to False means the observer must ensure the DCR is properly configured and included in the Scan Coordinator as the AutoPeakFocus procedures will not check the configuration of the beamName A string It specifies which receiver beam will be the center of the cross scan beamName can be 1 2 3 4 etc up to 7 for the receiver The default value is the recommended value for the receiver If you configure for one beam and point with another using the beamName parameter you can have very very bad data Make sure that if you choose Configure False and beamName that the two are compatible refBeam A string It specifies which receiver beam will be the reference beam for subtracting sky contribution to the pointing observations The name strings are the same as for the beamName argument Two beams used for pointing should be at the same elevation ie beamName 7 refBea
14. WR BOE a 33 37 5 1 Astrid Data Display Tab 2 3T Tr 37 38 5 1 3 Pointing and Focus Data 38 5 1 3 1 Fitting Acceptance 5 39 5 1 3 2 Heuristics Options secs s reco a enan ERE ERREA 40 5 1 3 3 Data Processing Options 41 5 1 8 4 Send Corrections a ssena a a 42 5 1 4 OOF Data Display e sa 22h 43 5 1 5 Continuum Data Display 45 5 1 6 Spectral Data Display ooa a 45 47 48 5 2 The CLEO Utilities a 49 5 2 1 Talk and Draw 44 62 244 base dd ea dead S PR ewe ead 49 a Mok he amp eee eB 49 523 a PR RO De A 49 524 Weather tgrt ho o RR te db E Sia eae ad 50 22 5 Glock 5 uut dva dun Gk SR SUA UR Red Rete a a ae AR S 50 9 2 6 Messages x sob do dow we xc SE RR E ERR ROS X de wo ok 50 5 2 7 Other screens 22 4e es 50 6 Introduction To Scheduling Blocks And Observing Scripts 51 6 1 What Are Scheduling Blocks and Observing 5 8 52 6 1 1 Making An Observing Script s sssaaa 2e 52 6 2 Components of an Observing Script 52 LOT 52 6 2 1 1 Overview a xoc kom xXx RR A SEE DEEN eS RR RE du du 52 6 2 1 2 Example Configurations
15. When implementing a NNTLE catalog the scantype function will pass the 3 lines to a program that will calculate positions for the antenna given the scan start time and duration The source name is the string that appears on the first of the three lines and that is what one would pass to the scan function Because it may be convenient to download a Two Line Element TLE file from we provide an option to use such a TLE file as is by using the FILE keyword as shown in the following example An example of this format follows i NNILE catalog referring to an unedited TLE file E FORMATZNNTLE USERADVEL 0 FILE users fghigo tlecatalogs goes txt Name GOES 6 Name GOES 10 Name GOES 11 The first set of orbital elements whose name matches the name listed in the file will be used for calculating the satellite position Note that the generation of tracks for satellites is based on an implementation of xephem in Python 4One might load a catalog through the web site http www celestrak com NORAD elements 6 2 COMPONENTS OF AN OBSERVING SCRIPT 99 6 2 5 Utility Functions Utility functions are used in Observing Scripts to control various aspects of the other than data taking scans This includes such things as balancing the pausing the Observing Script or waiting for a source to rise Please note that the syntax for all utility functions is case sensitive
16. sp switched power with cal sp_nocal switched power without cal The default value is tp The switching schemes Total Power With Cal The noise diode is periodically turned on and off for equal amounts of time Total Power Without Cal The noise diode is turned off for the entire scan Switched Power With Cal The noise diode is periodically turned on and off for equal amounts of time while another component is in a signal state and then again in a reference state This is used in frequency switching where the signal state is one frequency and the reference state is another frequency Similarly beam switching and polarization switching change the beams or polarizations so that their signals are sent down two different IF path Switched Power Without Cal The noise diode is turned off while another component is switched between a signal and reference state swtype This keyword is only used when swmode sp or swmode sp_nocal and specifies the type of switching to be performed This keyword s values are none fsw frequency switch ing bsw beam switching and psw polarization switching Default values are fsw for all single beam receivers except receiver Rcvr 26 40 The default for re ceiver Rcvr 26 40 is swtype bsw 1500 1000 187 5 100 23 44 15 625 11 72 6 2 COMPONENTS OF AN OBSERVING SCRIPT 63 swper This keyword defin
17. 25 T TID TT 25 Tcr 25 4 2 2 0 Observational Status c ose ee 25 de Hate ee UE d PUT Ree ee 25 Tv ccr 26 i ar ar r E PP OD eee OS Se EE SG 26 4 2 2 T Queue Control 2822 RR eek a Ra REED 27 4 2 2 8 Observation Control 2 2 eee 27 4 2 3 Resizing Astrid Display 5 27 4 2 4 Changing Modes Within 27 4 3 Observing Management Tab 2s 28 43 The Edit Tab eee eae 4m ee QR d ee Y 28 4 3 1 1 Project ID and List of Observing Scripts 28 43 12 Editor ooo ae ke ASR REE A RR RRR x X X eR A 29 T 29 Saving an Observing Script to the 29 Selecting an Observing Script eee 30 ZI 30 43 1 4 Validator sek xo ux GS XO ERRORS 4 a E eode 30 432 The R n ab s 624 ees Ae Ros Neb RU 30 4 3 2 1 Header Information 3l Project s eso Re xoc OR UR ee PR e ee p Ah RA 31 TTC PES Ree eee eee 31 TI c GES ee ad 32 T 32 4 3 2 2 Submitting An Observing Script to the Run Queue 32 4 3 2 3 Run Queue and Session History 2l less 32 4 3 2 4 The Observing Log s aa IR 32 44 Data Display Tab 2 22 33 4 5 The Gbtstatus Tabi e ee a ae deed oe oe ee s
18. Clear Info or Warning then there are no significant problems with the If the status is Error then there is potentially something wrong that may need attention If the status is Fault or Fatal then something has definitely gone wrong with the observations Time To Set The time till the current source sets Receiver The receiver being used Polarity The receiver polarity Obs Freq The observational frequency in MHz Rest Freq The rest frequency in MHz Cal State ON if the noise diode is firing during the scan Sw Period The switching period in seconds Center Freq The center frequency in MHz Vel Def The velocity definition Vel Frame The velocity frame Frequency State The switching type total power or frequency switching Coordinate Mode The coordinate mode Major and Minor Coord The telescope position in the current Coordinate Mode Major and Minor Cmd Coord The telescope position in the current commanded Coordinate Mode Antenna State The telescope state T he most common antenna states are e Disconnected e Dormant Stopped Guiding Tracking e Slewing If the antenna software is not running the state will be Disconnected If the antenna software is running but with its control of the antenna turned off then the state is Dormant If the antenna is not moving then the state will be Stopped If the antenna is moving and data are being taken then the state is
19. Configuring for spectral line with L band 110 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS We recommend that the following should be avoided within a single Observing Script as it will make the block too long Multiple configurations Multiple configurations peak focus and science observations should opti mally be done in separate Observing Scripts Changing Receivers You should use only a single receiver within an Observing Script Multiple Maps You should perform only a single map within any Observing Script Chapter 7 Observing Strategies 7 1 Balancing Strategies The has many ways to add gain and or attenuation in the IF path depending upon the desired configuration Before taking data with the the observer must ensure that all components along the IF path have optimum input power levels this process is referred to as balancing This will ensure for example that no components saturate and that amplifiers are in the most linear part of their dynamic range The system automatically adjusts power levels to optimum values when you issue the Balance command in an Astrid script i e Balance The following discussion gives guidelines for when and how often to use the Balance command Strategies for balancing the IF power levels depend upon the backend the observing frequency the observing strategy the weather and the objects being observed The DCR has a dynamic range of about 1
20. Guiding and if data are not being taken the state is Tracking If the antenna is moving to a new commanded position the state is Slewing Az commanded The commanded azimuth position of the telescope in degrees El commanded The commanded el position of the telescope in degrees Az actual The actual azimuth position of the telescope in degrees El actual The actual elevation position of the telescope in degrees 36 CHAPTER 4 INTRODUCTION TO ASTRID Az error The difference between the commanded and the actual azimuth position of the telescope in arc seconds This value does not contain a cos el correction El error The difference between the commanded and the actual elevation position of the telescope in arc seconds LPCs Az XEI El The Local Pointing Correction LPC offsets in arc seconds DC Az XEI El The values in arc seconds The has temperature sensors attached at various points on the backup structure and the feed arm These are used in a dynamic model for how the flexes with changing temperatures This model is used to correct for pointing and focus changes that occur from this flexing AS FEM Model The state of the Finite Element Model FEM correction for the Active Surface AS The predicts how the surface changes due to gravitional flexure versus the elevation angle AS Zernike Model The state of the Zernike model correction model The Zernike model is a set of Zernike polynomial coefficients determined
21. d uu RUE d a ee ae eee NR UR REGE 102 6 2 6 3 Horizon Object ooh o RUE PE m e 103 6 264 Time Object i aw oe Sa a a a a ae ee b a a ag 103 6 2 7 Example Observing 8 104 6 2 7 1 Frequency Switched Observations Looping Through a List of Sources 105 6 2 7 2 Position Switched Observations Repeatedly Observing the Same Source 105 6 2 7 4 Frequency Switched On The Fly Mapping 107 6 2 7 5 Position Switched Pointed 108 6 3 What Makes a Good Observing Script o en 109 Choose the Optimal Size for your Observing Script 109 111 Lid Oe ea eRe eB we eee eg 111 7 2 Active Surface AS Strategies 112 3 AutoOOP Strategy so om sae cE a a ee DOS eS 4 112 7 4 Strategies For Pointing and 112 tuos Soa 4 CP Ree ie RE A ek 114 7 6 Balancing The Converter 114 a eked E E E 115 a 115 9 VLBlIhp Oe hee qued eese COE eee dee doe bec 115 117 8 1 From the Receiver to the IF 118 8 2 From the Converter Rack to the 119 83 Combined 119 121 a havea 121 0 2 Point
22. n a RAD 800 Al 7 225261D 10 A2 1 525012E 9 A3 3 798639D 10 58 a Mi 14 6 M 17 L5 PHCOF 030 E e EEG RR k k k k k k k k k Date UT HR MN R A ICRF J2000 0 DEC dRAxcosD d DEC dt delta deldot SOE 2012 May 09 00 00 x 12 08 16 10 08 47 03 0 12 7258 11 35837 3 88454176735642 25 3429284 2012 May 10 00 00 x 12 07 56 54 08 42 31 9 12 2131 11 15479 3 89940183197388 25 7105007 2012 May 11 00 00 x 12 07 37 82 08 38 05 7 11 6978 10 94757 3 91446891960406 26 0708444 2012 May 12 00 00 x 12 07 19 94 08 33 44 6 11 1801 10 73683 3 92973877575586 26 4237848 2012 May 13 00 00 x 12 07 02 91 08 29 28 7 10 6602 10 52273 3 94520704145659 26 7691331 Now that you have your ephemeris it needs to be converted to a form that Astrid can read You can do this by running the Python script jpl2astrid from any directory in your area on the Green Bank 6 2 COMPONENTS OF AN OBSERVING SCRIPT 97 computer system If you just type jpl2astrid and give it no arguments it lists instructions like this Usage jpl2astrid cometfilename txt output will have astrid extension Include in Astrid with e g Catalog fullpath cometfile astrid Access the JPL Horizons web interface http ssd jpl nasa gov horizons cgi Set up Horizons web interface as follows ephemeris type OBSERVER target body select the object Observer Location
23. 189 16 1 Night time forthe 196 16 2 Wind speed statistics 2l ee 197 16 3 Opacity statistics oo oem a a eae ee ee 198 16 4 Typical system temperatures 199 18 1 Directions to Green Bank 205 18 2 Green Bank Site 207 ii List of Tables 2 1 Prime Focus receiver properties 2s 4 2 2 Gregorian Focus receiver properties 4 22 2 lll ls 5 6 1 GBT receivers and frequencies 61 6 2 GBT backends 4 4 2 444405 Be eee a he Pe ae NL e m e OR Re o ob ko Row 9 Rd 62 6 3 Allowed bandwidths ls 62 VELIT hk ah ah gh ve he Re eee ne Me ay a TL 67 6 5 Peak and Focus recommendations oa e e 70 6 6 Available catalogs enn 90 7 1 Observing wind requirements ooa 113 7 2 VLBI Pointing 115 9 1 Nominal Beam Offsets 20 00 0000 000000000 2 122 are for the 2010 2011 observing season 14 1 4mm Channel Definitions 190 14 2 Effective Cold Load Temperature for 191 iii iv Chapter 1 How Use This Manual This document provides the necessary information to be able to perfor
24. 2 3 4 5 1 0 0010 0 0100 0 3200 0 3300 2 0 0028 0 0280 0 3200 0 3480 3 0 0040 0 0400 0 3200 0 3600 4 0 0114 0 0280 0 3200 0 3480 5 0 0227 0 0559 0 3200 0 3759 6 0 0357 0 1118 0 7600 5200 7 0 0128 0 0524 0 3200 0 3724 8 0 0256 0 1049 0 7600 5200 9 0 0406 0 2097 0 7600 5200 0 0 0168 0 2237 0 7600 5200 1 0 0336 0 4474 0 7600 5200 2 0 0727 0 8948 0 8948 7896 13 0 1342 1 7896 1 7896 3 5791 4 0 2461 3 5791 3 5791 7 1583 5 0 0280 0 4474 0 7600 5200 6 0 0559 0 8948 0 8948 7896 T 0 1230 1 7896 1 7896 3 5791 8 0 2237 3 5791 3 5791 7 1583 9 0 4474 7 5383 7 1583 14 3166 20 0 0065 0 0280 0 3200 0 3480 21 0 0129 0 0559 0 3200 0 3759 22 0 0357 0 1118 0 7600 1 5200 23 0 0517 0 2237 0 7600 1 5200 24 0 0979 0 4474 0 7600 1 5200 25 0 0090 0 0388 0 3200 0 3588 26 0 0180 0 0777 0 7600 1 5200 27 0 0476 0 1553 0 7600 1 5200 28 0 0699 0 3107 0 7600 1 5200 29 0 1320 0 6214 0 7600 1 5200 Col 1 VEGAS mode Col 2 Recommended minimum switching period swper for Doppler tracked total power on the fly maps with no noise diode tp_nocal These values will yield less than 10 blanking overall These values assume that the maps are sampled at twice Nyquist in the scanning direction and that there are four integrations per switching period Col 3 Recommmended minimum switching period swper for Doppler tracked total power on the fly maps with the noise diode tp These values will yield less than 10 blanking overall These
25. 2005 06 23 or 2005 Jun 23 form UTC The UTC time in the form hh mm ss DRA DHA DDEC DAZ DEL DLON DLAT The coordinate rate keywords given in arc seconds per hour DVEL The radial velocity rate in km sec hour Additional keywords used by the NNTLE format are see 6 2 4 7 on NNTLE format below for examples FILE For use in NNTLE format only This keyword value may refer to a file or a URL containing a 2 line element set USERADVEL For use in the NNTLE format only If this is set to 1 then the radial velocity tracking will be performed Otherwise if this is set to 0 or is missing then radial velocity tracking will not be performed 6 2 4 3 SPHERICAL format Examples Here is an example of a simple catalog My source list format spherical coordmode J 2000 HEAD NAME RA Objectl 09 56 16 98 Object2 10 56 16 98 Object3 11 56 16 98 Object4 12 56 16 98 My source list Objectl 09 56 16 98 Object2 10 56 16 98 Object 11 56 16 98 Object4 12 56 16 98 My source list with radial velocities format spherical coordmode B1950 head name ra velocity Objectl 09 56 16 98 2 29 Object2 08 56 16 98 28 24 Object3 07 56 16 98 ioe DO 2 s Object4 06 56 16 98 30 26 is an example Catalog where one may omit the format line but not the coordmode line 6 2 COMPONENTS OF AN OBSERVING SCRIPT 89 Warning setting the velocity or rest fre
26. 5 Page 08 16 45 GMT 0500 EST is balanced correctly the ADC counts should be approximately Gaussian centered around zero with a full width half maximum of approximately 50 counts If the ADC counts are very centrally peaked there is not enough power going into VEGAS while if the ADC counts have peaks at 127 counts VEGAS is being over driven The final tab of VEGASDM gives an overview plot of the total power for all eight banks on a single screen 134 CHAPTER 10 VEGAS X vecas File Managers Help Filter BW Noise ew Int Time Switching Bank Power Mode MHz SaaS Tone Polarization Subbands ES EE 950 8 self 1 4 internal 950 8 self 1 4 internal 950 8 self 1 4 internal 950 8 self 1 4 internal 950 NH self 1 4 internal 5 950 self 1 4 internal ETE 950 NH self 1 4 internal H BEEN 12 950 on 8 self 1 4 intemal 20 49 _ Phase Tables Requested Actual Master Switching Bank A Blanking Source internal VEGAS Power Monitor VEGAS Status clear State Ruming ual Locked SutoPrepara Quit Bank Status fclear State Pu al Bank E Status clear State Running Bank Status clear State Ruming Pula Bank F Status clear State Ruming Pull Bank C Status clear state Running
27. If is not communicating with the M amp C system such as in its offline mode then you will see Not Connected If Astrid is communicating with the M amp C system and there isn t a Scheduling Block SB being executed then you will see Idle and if a Scheduling Block is running or has been paused then you will see SB Executing SB Paused GBT State The GBT State indicates the state of the M amp C system The GBT state is either e Not In Service e Not Connected e Unknown e Ready Activating Committed e Running e Stopping e Aborting If the M amp C system is not working properly you will see Not In Service or Not Connected Un known indicates that the M amp C system is working but does not know the state of any of the hardware devices You will see the state be Ready when the GBT is not doing anything It will be Activating or Committed when the GBT is preparing to perform an observation etc While taking data during a scan the state will be Running At the end of a scan you will see the state become Stopping If the scan is ended for any abnormal reason the state will be Aborting GBT Status The GBT status gives the error status of the M amp C system The GBT status is either e Not Connected e Unknown e Clear e Info e Notice e Warning e Error e Fault e Fatal If the M amp C system is not communicating properly with the hardw
28. In Location and Offset objects a quantity given as a decimal number is always understood as being in units of degrees of arc regardless of the type of unit However in Catalogs a decimal number for RA or HA is assumed to be hours for other angles DEC Az El Glon Glat it is degrees of arc For example if one is specifying an Offset object as in the following Astrid directive OnOff 3C286 Offset J2000 00 04 00 0 5 60 1 The offset will be 4 minutes of time in RA and 0 5 degrees of arc in DEC The coordinate mode J2000 means the coordinate pair is RA DEC hence sexegesimal RA is assumed to be in hours Alternately if one says OnOff 3C286 Offset J2000 1 0 0 5 60 1 The offset will be one degree of arc in RA and 0 5 degrees of arc in DEC 219 220 APPENDIX E A NOTE ON ANGLE FORMATS AND UNITS IN ASTRID AND CATALOGS Appendix F Advanced Utility Functions There are a few advanced utility functions that once can use in an Observing Script F 1 General Functions F 1 1 GetValue The GetValue function can be used to retrieve any parameter value within the Monitor and Control system The syntax is value GetValue ScanCoordinator source which returns a string which in the above example is stored in value If you need for the value to be another data type such as an integer or a float please consult your favorite Python manual to find out how to use conversion ope
29. Step 3 Make sure that the header information fields all have entries Step 4 Select the Observing Script you wish to execute from the list of available Observing Scripts Step 5 Hit the Submit button below the list of Observing Scripts Your Observing Script is then automatically combined with the header information to produce a Schedul ing Block that is then sent to the Run Queue Note that double clicking on an Observing Script is the same as selecting the Observing Script and then hitting the Submit button 4 3 2 3 The Run Queue and Session History When an Observing Script is submitted for execution it is first sent to the Run Queue This contains a list of submitted Observing Scripts that will be sequentially executed in the future When an Observing Script begins execution it is moved to the Session History list So the Session History list contains the currently executing Observing Script on the first line and all previously executed Observing Scripts that have been run while the current instance of Astrid has been running on subsequent lines If there are not any Scheduling Blocks in the Run Queue when a new Observing Script is submitted for execution it may appear that the Observing Script just shows up in the Session History However it has indeed gone through the Run Queue albeit very quickly 4 3 2 4 The Observing Log The observing log is always visible at the bottom of the Observation Management Tab It shows information fr
30. VEGAS We wish to take data on multiple spectral lines nwin 9 each having a 23 44 MHz bandwidth band width 23 44 with 8192 spectral channels nchan medium low The eight subband mode of VEGAS see Table is selected by default The spectral windows will be centered on the rest frequencies of the lines at 9816 867 9487 824 9173 323 8872 571 9820 9 9821 5 9822 6 9823 4 9824 6 MHz rest freq 9816 867 9487 824 9173 323 8872 571 9820 9 9821 5 9822 6 9823 4 9824 6 We wish the cycle time to go through a full switching cycle of 1 second swper 1 0 We want VEGAS to record data every 30 seconds tint 30 We wish to Doppler track the spectral line with rest frequency 8873 1 MHz dopplertrackfreq 8873 1 in the commonly used Local Standard of Rest velocity frame vframe lsrk vdef Radio We would like to use the low power noise diode noisecal lo Finally we wish to take the data using circular polarization pol Circular Multiple Spectral Lines Multi beam Nodding Observations configuration definition for spectral line observations using a multi beam receiver for nodding observations 99 90 99 vegas_nod_config receiver RevrArray18_26 beam 1 9 obstype Spectroscopy backend VEGAS nwin 41 restfreq 23694 495 23722 633 23870 129 25056 025 deltafreq 0 0 0 0 bandwidth 100 swmode swtype 56 CHAPTER 6 INTRODUCTIO
31. command 6 2 2 2 Configuration Keywords So far we have shown you how to use the configuration Now we need to discuss what keywords and values are allowed in a configuration definition Keywords That Must Always Be Present The following keywords do not have default values and must be present in all configuration defini tions receiver This keyword specifies the name of the receiver to be used The names and frequency ranges of the receivers can be found in Table 6 1 The value of the receiver keyword is a string and should therefore be placed within quotes when used 6 2 COMPONENTS OF AN OBSERVING SCRIPT 61 obstype This keyword specifies the type of observing to be performed The allowed values are one of the following strings Continuum Spectroscopy Pulsar Radar VLBI backend This keyword specifies the name of the backend data acquisition system to be used The value for this keyword is a string Valid backends are listed in Table 6 2 restfreq In the simplest case this keyword specifies the rest frequencies for spectral line observations or the center frequencies for continuum observations Up to 64 different frequencies can be given in a comma separated list Values are floats and are given in MHz The Doppler track frequency can be specified using the dopplertrackfreq keyword Otherwise the first restfreq value will be Doppler tracked For more advanced configurations one can also inp
32. encountered during the daytime with particularly unfavorable solar illuminations may produce pointing and axial focus errors which unless corrected will approach the limits for successful ob servations We recommend you perform peak and focus measurements every few hours during night time increasing to perhaps once per hour around local noon and into the afternoon Strategy C Appropriate for good all and useable performance at K band Ensure that the wind speeds do not exceed the limits listed in T able 7 1 Daytime thermal gradients may easily produce pointing and axial focus errors which unless corrected will approach or exceed the limits for successful observations under some conditions these gradients may also extend well into the evening We recommend that you perform peak and focus measurements at least once an hour initially The spacing between peak focus checks may be extended during the night time if the results appear stable Remember to increase the frequency of pointing and focus checks again after dawn Strategy D Appropriate for good or any or MUSTANG observing Ensure that the wind speeds do not exceed the limits listed in Table Uncorrected thermal gradients will certainly cause unacceptably large pointing and focus corrections Perform peak and focus checks at least every half hour initially The spacing between peak focus checks may be 114 CHAPTER 7 OBSERVING STRATEGIES extended during the night time if t
33. pop ups 22 Source Name Make Map F Scan numbers 83 Feeds Select Scans 21 Append Data No Yes Show Current Nap Map Nane rap 0 Store Nap Show Coverage Hap Pathi users bmason Tot Disk Henory Show calibration Show Time Stream Select r From Disk Fit map ATV Save FITS image Export Image lew Error Clear Data Show Help 85 2010 04 05 11 10 11 fits 84 2010 04 05 11 15 53 fits 05 11 18 12 f 05 11 ot 20 05 PE 05 11 31 20 ae 32 201010405 11 33 59 Fits 93 2010 04 05 11 36 11 Fits R amp LongMap ScanType out of 1 1 1 1 1 1 m 1 2 1 1 1 quickdaisy lllissdais SB SrcName WindsHin Humid Temp T DP Elev az LPC el LPC LFC Y arcm s cal 74 fu 1 fulllissdais 1 fulllissdais 1 fulllissdais 2 1 fulllissdais Z 1 fulllissdais Z 1 fulllissdais 718 1 ulllissdais ulllissdais 0 86 D 94 9 0 egaN 1 36 70 BBPEPSSESAE ioo s tt ooi to 992999922222 fofotofotofo foto fo foto Figure 13 3 Selecting the CAL scan in the MUSTANG IDL GUI 173 The GUI will also now have a list of valid CAL scans in the drop down CAL SCAN box see below There are some latencies involved in getting all the FITS files written to disk so the current scan may not be accurately reflected in the summary For this reason y
34. users bmason mustangPub sb mustangfull conf 13 6 2 autooof mySrc 1159 2914 Catalog Slew mySrc AutoOOF source 2mySrc 13 6 3 calandblank This SB runs a 15 second scan with the cal diode firing on and off allowing the bolometer responsivities to be measured and a 30 second scan tracking blank sky allowing a check on the detector noise duration of cal and blank scans in seconds calduration 15 blankduration 30 uncomment these lines to do the calibration at a given az el myAz 260 myEl 78 myLoc Location Encoder myAz myEl or use this one to use the current az el myLoc Get CurrentLocation Encoder do not modify from here down extra information source names caltags etc is added for the sake of data analysis software which depends on these tags THHHHHHHHHHHE Slew myLoc Configure users bmason mustangPub sb mustang conf execfile users bmason mustangPub ygor relockAstrid py Configure users bmason mustangPub sb calon conf Annotation CALTAG DIODE Set Values ScanCoordinator source cal 178 CHAPTER 13 MUSTANG Track myLoc None calduration Configure mustang init cal swmode tp_nocal tint 0 001 Annotation CALTAG BLANK Set Values ScanCoordinator source Blank Track myLoc None blankduratio
35. 3C286 point and focus on 3C286 AutoPeakFocus location Location J2000 16 30 00 47 23 00 find a pointing source near ra 16 30 00 dec 47 23 00 Normally AutoPeak and AutoPeakFocus will choose reasonable scanning rates and lengths Table 6 5 gives the standard parameters If you need to use non standard values for a peak or focus use the Peak or Focus commands explicitly AutoPeak AutoPeak is the same as AutoPeakFocus except that it does not perform a Focus scan Step 11 above AutoFocus AutoFocus has the same parameters as AutoPeakFocus However it does not do a pointing and only does a Focus scan skipping Step 10 in AutoPeakFocus AutoFocus should not be used with Prime Focus receivers The prime focus receivers have pre determined focus positions and there is not enough travel in the feed to move these receivers significantly out of focus Peak The Peak scan type sweeps through the specified sky location in the four cardinal directions Its primary use is to determine pointing corrections for use in subsequent scans Note that the hLength vLength and scanDuration should be overridden as a unit since together they determine the rate Peak assumes that the user has executed a continuum configuration Syntax Peak location hLength vLength scanDuration beamName The only required parameter for Peak is location The parameters for peak are 70 CHAPTER 6 INTRODUCTION TO SC
36. Advanced utility functions are found in Appendix 6 2 5 1 Annotation The Annotation function allows you to add any keyword and value to the GBT Observing GO FITS file This could be useful if there is any information you would like to record about your observation for later data processing or for record keeping The syntax is Annotation KEYWORD Value where KEYWORDS must be written completely in capital letters and can be no longer than eight characters in length An example use of the Annotation function is if you wish to specify what type of source you are observing Your sources might include H II regions and Planetary Nebulae for example You could specify each type with Annotation SRCIYPE HII Annotation SRCIYPE PNe The information in a FITS KEYWORD created via the Annotation function will be ignored by the standard data reduction package GBT Data Reduction Package GBTIDL 6 2 5 2 Balance Balancing changes the various attenuator levels and gain levels in the GBT receivers the IF and the back ends so that each device is operating in its linear response regime The Balance function is used to balance the electronic signal throughout the GBT IF system The Balance function will work for any device with attenuators and for a particular backend Indivdual devices can be balanced such as the Prime Focus receivers the the Spectrometer and or the Spectral Processor The Gregorian re
37. OffOn The OffOn scan type is the same as the OnOff scan except that the first scan is offset from the source location Syntax OffOn location referenceOffset scanDuration beamName The following example does an OffOn scan with reference offsets of 1 degree of arc in Right Ascension and 1 degree of arc in Declination and a 60 second scan duration using beam 1 78 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS OnOffSameHA The OnOffSameHA scan type performs two scans The first scan is on the source and the second scan follows the same HA track used in the first scan Syntax OnOffSameHA location scanDuration beamName The parameters for OnOff are location A Catalog source name or Location object It specifies the source upon which to do the On scan beamName A string It specifies the receiver beam to use for both scans beamName can be C 1 2 8 4 or any valid combination for the receiver you are using such as MR12 and MR34 The default value for beamName is 1 scanDuration A float It specifies the length of each scan in seconds The following example does an OnOffSameHA scan with a 60 second scan duration using beam 1 OnOffSameHA 0137 3309 60 1 Nod The Nod procedure does two scans on the same sky location with different beams Nod should only be used with dual beam receivers Syntax Nod location beamNamel beamName2 sca
38. Optionally preset observer quantities selection using one of the following planets satellites small bodies default all none 1 viAstrometric RA amp DEC 15 Sun sub long amp sub lat 29 Constellation ID 2 Q Apparent RA amp DEC 16 Sub Sun Pos Ang amp Dis 30 O Delta T CT UT 3 M Rates RA amp DEC 17 Pole Pos Ang amp Dis 31 OD Obs eclip lon amp lat 4 AZ amp EL 18 Q Helio eclip lon amp lat 32 North pole RA amp DEC 5 L Rates AZ amp EL 19 Q Helio range amp rng rate 33 Q Galactic latitude 6 OSat X amp Y pos ang 20 YI range amp rng rate 34 Local app SOLAR time 7 Local app sid time 21 One Way Light Time 35 Earth Site It time 8 22 Speed wrt Sun amp obsrvr gt 36 LIRA amp DEC uncertainty 9 Vis mag amp Surf Brt 23 JSun Obsrvr Target angl gt 37 POS error ellipse 10 Illuminated fraction 24 Sun Target Obsrvr angl gt 38 OPOS uncertainty RSS 11 O Defect of illumin 25 LJ Targ Obsrv Moon Illum gt 39 Range amp Rng rate sig 12 Sat angle separ vis 26 Obsr Primary Targ angl gt 40 Doppler delay sigmas 13 Target angular diam 27 Q Pos Ang radius amp vel 14 Obs sub Ing amp sub lat 28 Orbit plane angle Notes affected by apparent position estimation atmospheric refraction model see below gt requires object orbit covariance Figure 6 3 Selecting qu
39. The GBT has two continuum backends the Digital Continuum Receiver and the Caltech Con tinuum Backend The spectral line backend is Pulsar observations can be done with GUPPI There is a single dish mode for the Very Long Baseline Array backend that is available for high time resolution observations Planetary radar uses a specialized backend For more information on backends please see the Proposer s Guide which is available http www gb nrao edu gbtprops man GBTpg GBTpg tf htm 6 at 2 1 4 1 Digital Continuum Receiver DCR The digital continuum receiver is the GBT s general purpose continuum backend It is used both for utility observations such as pointing focus and beam map calibrations as well such as for continuum astronomical observations including point source on offs extended source mapping etc 2 1 4 2 Caltech Continuum Backend CCB The is a sensitive wideband backend designed exclusively for use with the 26 40 GHz receiver It provides a carefully optimized Radio Frequency not an Intermediate Frequency IF detector circuits and the capability to beam switch the receiver rapidly to suppress instrumental gain fluctuations There are 16 input ports only 8 can be used at present with the Ka band receiver hard wired to the receiver s 2 feeds x 2 polarizations x 4 frequency sub bands 26 29 5 29 5 33 0 33 0 36 5 and 36 5 40 GHz The CCB allows the left and right noise diodes to be
40. astro aotms performance 2001 02 ps d Another issue is finding a proper IF balance that allows both the on and off source positions to remain in the linear range of the backend being used This means that one must find the IF balance in both the on and off position and then split the difference assuming that the difference in power levels between the on and off do not exceed the dynamic range of the backend The BalanceOnOff see 8 6 2 3 1 can be used to accomplish this type of balancing 7 8 High Frequency Observing Strategies When observing at frequencies above 10 GHz you should be aware that additional calibration measure ments may be necessary The telescope efficiency can become elevation dependent atmospheric opacities are important and the opacities can be time variable You should contact your GBT support person to discuss these issues All the high frequency receivers have at least two beams pixels on the sky You should make use of both of these during your observations if possible For example if you are doing position switched observations and your source is not extended then you can use the Nod procedure to observe 7 9 VLBI T he GBT is different from the standard VLBA stations 1 Changing between Gregorian receivers in the receiver turret takes 1 2 minutes and 2 Changing between Gregorian and prime focus requires about 10 minutes Changing from one prime focus receiver to ano
41. gentle way to stop a scan The Abort button stops the current scan immediately This may lead to corrupted data The Interactive button when selected will cause to automatically answer any pop up query Astrid will always choose what it deems to be the safest answer This is useful when you have to leave the control for an extended period of time such as when you go to the cafeteria to eat etc 4 2 3 Resizing Astrid Display Areas It is possible to resize some of the display areas within If you put the mouse over the bar separating two display areas you will get a double arrowed resize cursor If you then hold down the left mouse button you can use the mouse to move the border and resize the display areas 4 2 4 Changing Modes Within Astrid Observers should login and setup for their observations before their scheduled time begins Under these circumstances the observer will have already brought up in the offline mode or the Work online but only monitor observations mode When the observer s scheduled time on the GBT begins the Astrid mode can be changed without having to exit out of This is done with the following steps Confirm with the Operator that you can go online Step 1 Click on File in the drop down menus section Step 2 Click on Real time mode in the drop down menu Step 3 The pop up window shown in Figure appears Step 4 Click the radio button for the desired mode in the pop up window
42. observing The weather affects observations in three ways winds affect the telescope pointing differential heating cooling affect the telescope pointing and efficiency and atmospheric opacity affect the received signal and the system temperature 16 1 Time of Day Differential heating and cooling of the telescope alters the surface of the telescope resulting in degrada tion of telescope efficiencies and bends the telescope resulting in pointing changes At high frequencies these effects are important The current recommendations are that for best work observing above 40 GHz should only be done at night from 3 hours after sunset to 2 hours after sunrise At 40 GHz and above it is recommended to use AutoOOF see at the start of an observing session Use AutoOOF for daytime observing at 27 GHz or higher Low frequency observers may want to consider night time observing for two reasons is usually lower at night and in some cases the sun has a slight negative impact on baseline shapes By default we assume that daytime observing will be acceptable for all observations below about 16 GHz Figure depicts the range of UT EST and LST for our definition of night time observing 16 2 Winds Winds tend to buffet the telescope and to a lesser extent set the feed arm into motion The current recommendations for wind limits can be found in specifically in Table ma The fraction of time when wind speeds are low is
43. ual Bank G Status clear State Running Bank D Status clear State Ruming Bank H Status clear State Ruming Maa More Info More Info More Info More Info More Info More Info More Info More Info T2222 Figure 10 7 The VEGAS CLEO Screen vegas status This section is only relevant for advanced diagnosis of VEGAS problems It may be skipped by the average Observer VEGAS utilitizes eight high performance computers HPCs one for each Bank Each HPC contains a Graphics Processor Unit GPU which is used to perform much of the digital processing for modes 4 and above These HPCs are also responsible for collating metadata and writing this plus the actual spectra to disk These machines are called VEGAS HPC1 through VEGAS HPC8 VEGAS meta data is stored in shared memory on these machines and it is possible to monitor the status of this meta data as follows ssh into the machine of interest then 4 source home gbt gbt bash or csh vegas status This will bring up a terminal status display as shown in Figure Observer s should not normally need to use this t
44. 0 2 5 We want VEGAS to record data every 2 seconds tint 2 0 We wish to Doppler track the spectral line with the rest frequency 1420 MHz in the commonly used Local Standard of Rest velocity frame vframe lsrk vdef Radio We would like to use the noise diode with the lower cal temperature noisecal lo Finally we wish to take the data using linear polarization pol Linear Multiple Spectral Lines Position Switching Observations configuration definition for multiple spectral line observations using position switching 6 2 COMPONENTS OF AN OBSERVING SCRIPT 55 2525 7 vegas ps config receiver Rcevr8_10 obstype Spectroscopy backend VEGAS nwin 9 restfreq 9816 867 9487 824 9173 323 8872 571 9820 9 9821 5 9822 6 9823 4 9824 6 dopplertrackfreq 8873 1 bandwidth 23 44 swmode ip swtype swper 1 0 tint 30 vlow vhigh E vframe eile vdef noisecal lo pol Circular nchan medium low 907 This configuration definition has the name vegas_ps_config and can be used for spectral line obser vations obstype Spectroscopy using position switching swmode tp swtype none For these observations we wish to use the single beam 8 to 10 GHz receiver receiver Rcvr8_10 beam B1 and VEGAS as the backend detector without cross polarization products backend
45. 1 0 2 cosv True which represents an offset of 0 1 degrees in and 0 2 degrees in DEC cosv True the default means the RA offset is divided by cosine Dec before applying the offset Two Offsets may be added together but they must have the same coordinate type For example offi Offset J2000 0 1 0 2 cosv True off2 Offset J2000 1 0 1 0 totaloffset offi off2 BUT off3 Offset B1950 1 0 1 0 totaloffset offi off3 result in an error In Astrid scripts one may add an Offset to a Location if they have the same coordinate types Here is an example of how to add an Offset to a Location myoffset Offset B1950 00 00 30 00 00 45 mysrclocation Location B1950 16 30 00 47 23 00 mynewposition mysrclocation myoffset But note that addition is not commutative for Astrid The following produces a validation error in Astrid mynewposition myoffset mysrclocation ERROR 217 218 APPENDIX D LOCATION AND OFFSET OBJECTS Appendix E A Note on Angle formats and units in Astrid and Catalogs There are two formats for angles in Observing Scripts and Catalogs sexegesimal e g hh mmc ss ss dd mm ss ss decimal numbers e g ddd ddd When the quantity is RA or HA an angle given in sexegesimal is hours minutes seconds of time For all other angle quantities e g dec az el glon glat an angle given in sexegesimal is degrees minutes seconds of arc
46. 10 log log P2 111 112 CHAPTER 7 OBSERVING STRATEGIES 7 If you are observing target sources and calibration sources then try not to balance between observations of the targets and calibrators Whenever you balance the GBT IF you almost always change variable attenuator settings Each attenuator setting has a unique bandpass shape So if you change attenuators then you will likely see changes in the bandpasses and baseline of the raw data If during your observing you expect to see a change in power levels on the sky that are roughly equivalent to the system temperature then you should contact your support person to discuss balancing strategies There are no global solutions or formulae to follow and each specific case must be treated independently 7 2 Active Surface AS Strategies If you are observing at a frequency of 8 GHz or higher then you should use the At frequencies below 8 GHz the does not provide any improvements to the efficiency of the Due to Radio Frequency Interference RFI considerations the AS may be turned off for lower frequency observations You do not need to do anything to turn on or off the use of the AS The telescope operator performs these tasks 7 3 AutoOOF Strategy AutoOOF is recommended for observing at frequencies of 26 GHz and higher For a description of this procedure and strategies refer to Section 6 2 3 2 For the associated data display see Section 7 4 Strategies For Poin
47. 10 0 The following example generates subscans through 12584 6126 starting the first leg 40 arc minutes from the source s right Spider 1258 6126 Offset AzEl 00 40 00 00 00 00 30 0 F 2 3 717 717 executes two circles of point subscans around location at 45 degree intervals The first circle with a radius of startOffset and the second circle at a radius of sqrt 2 startOffset The initial subscan is at the angle specified by the startOffset After circling twice the procedure executes a subscan on location The entire set of 17 subscans each of length scanDuration is sandwiched between two cal subscans of lengths calDuration which consist of equal parts calibration noise signal on and off Syntax Z17 location startOffset scanDuration beamName calDuration The parameters for Z17 are 224 APPENDIX F ADVANCED UTILITY FUNCTIONS location A Catalog source name or Location object It specifies the source which is to be tracked startOffset An Offset object It specifies the angle from location of the initial subscan as well as the radius of the inner circle scanDuration A float It specifies the length of the subscans in seconds beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 2 3 A or any valid combination for the receiver you are using such as MR12 and MR34 The default value for beamName is 1 calDuration A float It
48. 140 CHAPTER 10 VEGAS is caused by the Finite Impulse Response FIR filter used in the digital processing of low bandwidth modes This pattern is stable and as long as the amplification within the IF system is kept in the linear regime see Section 10 3 3 this pattern will not effect the final calibrated data Modes 10 29 show a similar pattern with just a single ripple Secondary ripples 10MHz wide are visible in the mode bandpass shown in the upper right of Figure These ripples are due to a standing wave in the cabling between the Converter Rack and VEGAS Placing attenuation on the cables at the converter rack minimizes these standing waves while leaving the signal strength and signal to noise ratio of the signal intact The ripples in the mode 2 image upper left have a lower amplitude since this data was taken with the attenuation in place In the next version of this guide we will replace the mode 3 figure with one taken after the attenuators were in place As mentioned previously the stability of the baseline is more important than the overall baseline shape The thermal stability of the system greatly impacts the temporal stability of the baselines We have attempted to isolate all cables and VEGAS itself to minimize these impacts and are currently in the process of further improving the thermal isolation of the system The calibration of the digital systems within VEGAS can also affect the temporal stability of the baselines
49. 2 and MR34 The default value for beamName is 1 start Time A time string with the following format hh mm ss It allows the observer to specify a start time for the Tip stopTime A time string with the following format hh mm ss It allows the observer to specify a stop time for the Tip Scan timing may be specified by either a scanDuration a stopTime a startTime plus stopTime or a startTime plus scanDuration The following example tips the from 6 0 degrees in elevation to 80 0 degrees in elevation over a period of three minutes using beam 1 Tip Location AzEl Offset AzEl 0 300 0 6 2 COMPONENTS OF AN OBSERVING SCRIPT 73 BalanceOnOff When there is a large difference in power received by the GBT between two positions on the sky it is advantageous to balance the IF system power levels to be at the mid point of the two power levels Typically this is needed when the source position is a strong continuum source This scan type has been created to handle this scenario one should consider using it when the system temperature on and off source differ by a factor of two or more BalanceOnOff slews to the source position and then balances the IF system It then determines the power levels that are observed in the IF Rack Then the telescope is slewed to the off position and the power levels are determined again The change in the power levels is then used to determine attenuator settings
50. 28 Gtr 0 128 Tsys 15 982 28 ctr 0 196 Tsys 15 953 26 Hgt 12 743 26 Hgt 12 735 Observation Control T 24r amp 2r 18 18 lt AL iia 80 60 40 20 0 20 40 60 80 80 60 40 20 0 20 40 60 80 Offset arcmin Offset arcmin Rcvrl 2 Feeds 1 TotalPower Polarizations Center Sky Frequency 1 40 GHz m Scans 300 303 145947140 Az El 337 081 36 028 pazcEl 0 557 dazCEL 0 277 1 0 280 pazCE2 0 558 dazCE2 0 107 tazCE2 0 451 peli 4 911 dell 0 128 tell 5 039 pel2 4 910 del2 0 196 tel2 5 106 OldAz2 0 000 OldEl 0 000 dAz2 0 192 dEl 0 162 n 192 NewEl 0 16 z ObservationManagement Log 1 DataDisplay Log 1 eE Log 1 Command Console Staring scan 305 in project AGBTO7A_104_03 Figure 5 1 The Data Display Tab showing pointing data 5 1 THE ASTRID DATA DISPLAY TAB 39 The focus scan data will appear under the Focus Tab see Figure Again the data will be processed automatically They will be calibrated have a baseline removed and a Gaussian will be fit to the data The focus offset will automatically be sent to the M amp C system d O NE Elle Edit View Tools Help 2 M 5 IP ARIERO R ObservationManagement 1 DataDispla
51. 3C286 Offset J2000 1 0 0 0 cosv True scanDuration 65 Consult Chapter 6 for other useful observing tricks such as Horizon objects and using start Time or stopTime to control scan duration If you need to stop a scan early you can use Stop or Abort in Astrid 152 CHAPTER 11 PULSAR OBSERVING WITH GUPPI 11 5 Monitoring GUPPI During an Obser vation When you first start an observing session it is a good idea to have several terminals open on beef and to set up your shell for the GUPPI environment by using either source opt 64bit guppi guppi_daq guppi bash or source opt 64bit guppi guppi_daq guppi csh as appropriate Once this is done you can use guppi_adc_hist and guppi monitor as described above as well as other tools described here 11 5 1 Monitoring Incoherent Data Taking To check the status shared memory use guppi status This will display the current GUPPI configura tion Check that the observing mode source integration time parfile etc are all correct When data is being taken you will see the NETSTAT key turn to Receiving and the DISKSTAT keyword change to either waiting or writing Figure l1 3 shows an example of this screen You should also follow the data acquisition server log by typing This will update when scans start or end new files are open or closed and sub integrations are written to disk You should also check this log for warnings about large fractions of dropped packets This can occur
52. Figure 3 1 where they see a list of active projects on which they appear as co investigator From the DSS home page users can 14 CHAPTER 3 INTRODUCTION TO THE DYNAMIC SCHEDULING SYSTEM Active Projects Fi B Support Center GBT Schedule Weather My Home Preferences Docs Logout Upcoming Observations Project ID Title IGBT10B 501 M amp C Regression J Upcoming Reservations Dynamic Contact Information Static Contact Information None To update edit your profile at my nrao edu check in check out Email s edit n Other Personal Phone s m Work Other Postal Address es NRAO PO Box 2 Green Bank West Virginia 24944 USA Office Other Affiliation s National Radio Astronomy Observatory Oregon University of Blackout Dates America New York Begin End Repeat Until Description dd Completed Projects Project ID Title Figure 3 1 A sample DSS home page 3 6 THE DSS SOFTWARE 15 e Access the project page for each of their affiliated projects e See a list of upcoming observations e See a list of upcoming Green Bank room reservations e See their static contact information as entered in the NRAO services system http my nrao edu e Set dynamic contact information e Set blackout dates e Follow a link to the current GBT fixed schedule e Follow a link to the weather forecasts page e fo
53. I psepom pueq qng ep Sutg gm zm CHIN oeds 8 oremyos Aq od sod MOpUIM jod smopurm 1 9381 49019 qut uorn oso1 e132eds 1od e132eds e132ods XEN ayer eyed XEN e132odg sjeuueyp jo iequinN jo qQyptMpuegq jo 19quin N oureN e qe3 oq poj3si GV 54A Jo s193euro132eds oy Jo yore Aq pog1oddns suorjyeunS uoo ou T SOPOIN SVOGA TOT 91991 128 CHAPTER 10 VEGAS 10 2 IF Configuration The GBT IF system introduces some constraints on routing signals from the receivers to VEGAS AII single beam receivers see Table and KFPA beam 1 can be routed to all eight spectrometers see Figure 10 2 For all dual beam receivers see Table 6 1 including the two beam mode of the KFPA the signal from one beam can only be routed to a maximum of four spectrometers see Figure 10 3 For the KFPA in four beam mode each beam can be routed to no more than two VEGAS spectrometers see Figure 10 4 When using all seven beams of the KFPA each beam can map to a single spectrometer with an optional second copy of beam 1 being routed to the eighth VEGAS spectrometer see Figure 10 5 Spectral resolution is not gained with VEGAS by using only one beam of a multi beam receiver 1 Ee 1 Figure 10 2 A graphic demonstration of how single beam receivers and beam 1
54. N 873 10 m To set the location to Green Bank first click change then select Observatories click Display List and select Green Bank GBT 9 radar Time Span CHOOSE YOUR RANGE The ephemeris table should contain enough entries to cover a period longer than that required by a particular observing session The observing system selects the portion of the table needed for the current scan start time and duration If the position of the comet is changing rapidly you should select a step range of 5 mins or shorter If the comet is further out in the solar system and is not moving as rapidly with respect to the sidereal rate a step range of 10 15 mins may be adequate to track the comet Consult your observatory friend if you are unsure of the step range you should choose Table Setting QUANTITIES 1 3 20 Figure shows the quantities that should be selected through the web interface to properly generate an ephemeris for tracking a comet NOTE The dates and times are required to be in UTC The dates and times can be specified in any legal python form for example a YY YY MM DD hh mm ss where MM is month number e g August 09 or b YYY Y MMM DD hh mm ss where MMM is the abbreviated month name such as Jan Feb etc see below Display Output download save Table Settings Select observer quantities from table below switch to manual entry list of numbers form Use Settings Below Cancel
55. PAR cryoAutoCycle He3 Set Values Revr PAR cryoDAQPowerSafety On Set Values Revr_ PAR cryoDAQPower Off Set Values PAR cryoTowerPower Off Set Values PAR fireCal Off Set Values Revr PAR hlDetBias column all Set Values Revr PAR hlDetBias value 0 Set Values gt Revr_PAR scan Type Default SetValues state Prepare 184 CHAPTER 13 MUSTANG Chapter 14 The 4mm 68 92 GHz Receiver 14 1 Overview The 4mm receiver W band is a dual beam dual polarization receiver which covers the frequency range of approximately 67 93 GHz The performance degrades significantly outside of this range After the amplifier upgrade in the fall of 2012 typical system temperatures are under 100 K over much of the band Figure 14 1 A key difference between the 4 mm receiver and other GBT receivers is that there are no noise diodes for the 4mm receiver This impacts the observing and calibration techniques for the receiver Users need to take a calibration sequence whenever the configuration changes or whenever the IF system is balanced for any data that needs to be calibrated The receiver has an optical table with an ambient and cold load that is used for calibration Figure 14 2 The optical table can also convert linear polarizatio
56. Script and then save it to the Astrid database A pop up window will notify you if the Observing Script did not pass Validation A second pop up window will allow you to set the name that the Observing Script will be saved under in the Astrid database Delete from Database This button will delete the currently selected Observing Script from the database Import from File This button will allow you to load an Observing Script from a file on disk Export to File This button will allow you to save the edited Observing Script displayed in the editor to a file on a disk This does not save the Observing Script into the Astrid database The first time you select either of the Import from File or Export to File buttons you will have a pop up window that lets you select the default directory to use After selecting the default directory you will get a second pop up window that shows the contents of the default directory so that you can select or set the disk file name to load from or export too 4 3 1 3 Adding Observing Scripts to the Database and Editing Them We will first describe how to add an Observing Script to the Scheduling Block list i e database and then we will describe how to manipulate and edit Observing Scripts in the list Saving an Observing Script to the Database If you have already created an Observing Script outside of you should go to the Edit Tab in and then use the Import from File button to load yo
57. Step 5 Click the OK button in the pop up window If problems occur inform the Operator who will clear them up At the end of an observing session the observer should change the mode to offline imme diately after their observing session ends 28 CHAPTER 4 INTRODUCTION TO ASTRID 4 3 The Observing Management Tab The Observation Management Application consists of two sub GUIs the Edit Tab and the Run Tab see Figures and 4 6 In the Edit Tab you can create load save and edit Observing Scripts You can also Validate that the syntax is correct The Run Tab is where you will execute observations 4 3 1 The Edit Tab The Edit Tab has three major areas a list of Project IDs Observing Scripts that have been saved into the database for that project an editor a Validation area and a log summarizing the observations This is shown in Figure Chapter 6 covers the contents and creation of Observing Scripts Editor for Validation Observing Scripts Area v Acind OFFLINE File View Toos Help BX WED Project ID Editor 19 w OW Project GRTOSR_ONYSP pulsar HI absorption of 81508455 itch theu nning users tminteopulsar abs hs pulsarahs my Scheduling Blocks 3 s We observe biank sky with the noise cals switching s EVI M Then we observe the program pulsar for an hour or so unti the specifi 1420 4057519939959 E stop tne 62 L
58. URL is only accessible to machines inside the observing network This will bring up a display as shown in Figure 10 3 4 Any bank may be selected by clicking on the boxes labelled A through H For multi subband modes a sub band may then be selected by clicking on a box through 7 The main display will then show a false color display building up integration by integration The right hand plot shows total power as a function of time while the bottom plot shows the latest integration as a function of frequency A particular integration frequency channel versus time may be displayed by clicking in the main display this can be reset to the default by clicking the Reset Crosshairs button Below this top display the latest spectrum is shown for each sub band for each bank Observers are urged to use the real time data display any time they are observing with VEGAS to monitor the data quality in real time The VEGAS CLEO screen This can be launched from the backend list of the CLEO launcher An example of the VEGAS CLEO screen is show in Figure 10 3 4 The VEGAS CLEO screen follows standard CLEO conventions and is fairly self explanatory As for all backend screens IF information for a selected bank can be displayed by clicking on the blue square to the right of the Bank label The VEGAS CLEO screen can be used to launch the VEGAS Data Monitor described in the next section by clicking on the VEGAS Pow
59. a bolometer Given a nominal detector calibration mapping data can be made into images by entering the desired scans in the box labelled Scan Numbers and clicking Make Map see Figure 13 4 This uses the default imaging parameters which should be suitable for most situations but which can be changed in the Advanced tab The coverage map can also be displayed by clicking the Show Coverage Map button this results in an image of weight per pixel units of inverse Janskys squared and is approximately proprtional to integration time and inversely proportional to map noise variance The map can be saved to a FITS file by clicking on Save FITS Image These files can be manipulated by standard astronomy imaging packages e g ds9 fv For monitoring the amplitude and beam width of the twice hourly pointing calibrator observations the GUI provides the facility to fit each map to a Gaussian To reduce the calibrator observations you can use the default Right Ascencion Declination coordinate system but it is often more useful to make the map in Elevation Cross Elevation coordinates i e offset relative to the source nominal True position in order to monitor the telescope pointing offset This can be done by selecting EL XEL coordinates in the Advanced tab see Figure 13 5 A given map can be fit to a Gaussian with the Fit Map button the amplitude and beam width FWHM are shown in the terminal windo
60. a technique for measuring large scale errors in the shape of the reflecting surface by mapping a strong point source both in and out of focus The procedure derives surface corrections which can be sent to the active surface controller to correct surface errors The procedure is recommended for high frequency observing at frequencies of 30 GHz and higher The AutoOOF procedure will obtain three on the fly maps each taken at a different focus position Processing will occur automatically upon completion of the third map and the result will be displayed in the OOF plugin tab of Astrid see Figure 5 7 Astrid OFFLINE lt anewton gt AER File Edit View Tools Help ew ObservationManagement 1 DataDisplay 1 GbtStatus 1 Pointing Focus OOF Spectral Line Beta Observation State 20 0423 0120 RALongMap 38 21 0423 0120 RALongMap 4 Zernike Solutions LPCs az2 el LFCy 22 0423 0120 RALongMap sia 1 1 db 001 26 e notilt fits 22 GBT State 23 cal Track 1 of 1 23 40 24 40 02 3 71 mm 24 cal Track 1 of 1 c 40 25 40 02 5 36 mm GBT Status 25 Blank Track 1 of 1 26 0423 0120 RALongMap 7 27 0423 0120 RALongMap 2 28 0423 0120 RALongMap i 27 0 24 0 02 7 75 mm 29 0423 0120 RALongMap 4 30 0423 0120 RALongMap 5 31 cal Track 1 of 1 32 Blank Track 1 of 1 33 0423 0120 RALongMap 1 34 0423 0120 RALongMap 2 35 0423 0120 RALongMap 36 cal Track 1
61. all catalogs are available and referenced by name within the scope of the Observing Script with the exception that for duplicate source names only the last entry of that name will be recognized After loading a Catalog any scan function may be run by giving it the source name for example Track TMC 1 60 Nod ORI KL 120 Slew SGR B and so forth 6 2 4 2 The Format of the Catalog A Catalog typically has two sections a header section followed by a table of information for all the sources The header section consists of the KEYWORD VALUE pairs The KEYWORD VALUE pairs tell the Scheduling Block interpreter how to read the information in the table section of the Catalog Once a keyword value is given its value will persist until re set or the end of the Catalog is reached The keywords are case insensitive The values for a keyword must not contain any embedded blanks except source names in NNTLE and CONIC formats A Catalog can contain comments with the beginning of a comment being denoted by the hash symbol All information on a line after the hash symbol is considered to be part of the comment After the header each source in the Catalog occupies a single line You should not use the hash symbol in source names Here is an example of a simple catalog Catalog Header Keywords Catalog Header Keywords are used to define how the catalog entries should be read The keywords and their valu
62. beams 5 6 7 have a rest frequency of 23400 and the second beam 1 IF band has a rest frequency of 25000 All delta frequencies are set to 0 for this observation The bandwidth used is 187 5 MHz bandwidth bandwidth 187 5 with the lowest value for the number of spectral channels 32768 nchan low We wish the cycle time to go through a full total power switching cycle to be 1 second swper 1 0 We want VEGAS to record data every 30 seconds tint 30 We wish to Doppler track the spectral lines with rest frequency 25500 0 MHz in the commonly used Local Standard of Rest velocity frame vframe Isrk vdef Radio We would 58 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS like to use the low power noise diode noisecal lo Finally we wish to take the data using circular polarization pol Circular 6 2 2 Advanced Configuration Examples This section gives some example configurations using the advanced restfreq keyword syntax This key word syntax can be used to more precisely configure the GBT system Note that the routing limitations for VEGAS listed in the Proposer s Guide still apply configuration definition for spectral line observations with KFPA vegas_kfpa_aconfig receiver RevrArray18_26 obstype Spectroscopy backend swmode swtype swper tint vlow vhigh vframe vdef Radio noisecal lo pol dopplertrackfreq 25500 bandwidth 187 5 nchan delt
63. calibdat which we can pass into subsequent invocations of the calibration indexscans si readccbotfnod si 13 q calibtokelvin q dogain calibdat calibdat fitccbotfnod q the scan index si must be updated to read in scans collected after it was first created indexscans si readccbotfnod si 14 q and calibrate to kelvin using the information we just derived calibtokelvin q calibdat calibdat 3 dn plo fitccbotfnod q 5 Gu CSWGPe oo Example OTF NOD data for bright sources under good and poor conditions and a weak source under good conditions are shown in Figures through Mapping data can also be imaged using the IDL tools make a map from scans 7 10 using port 11 data note the port must be specified valid ports are 9 16 img makedcrccbmap 7 8 9 10 isccb port 11 replot the map plotmap img int make a png copy of it grabpng mymap png 162 CHAPTER 12 THE CALTECH CONTINUUM BACKEND CCB Figure 12 2 CCB data from an OTF NOD observation of a bright source showing data and model versus time through one B1 B2 B2 B1 scan The white line is the CCB beamswitched data and the green line is the fit for source amplitude using the known source and telescope as a function of time positions The close agreement between the data and the fit indicate that neither fluctuations in atmospheric emission nor pointing fluctuations typically due to the wind on these tim
64. does not have referenceInterval as a parameter otherwise it is the same as RA LongMapWithReference See RALongMapWithReference for information on the parameters to RA LongMap Daisy The Daisy scan type performs a scan around a central point in the form of daisy petals also sometimes called rose curve Examples of these curves are shown in Figure 3from the Greek meaning as the ox plows i e back and forth 84 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS Jo r acos26 acos38 r acos 48 r acos 66 Figure 6 1 Examples of rose curves The area of the sky covered will be circular with a diameter equal to twice the specified radius For map radii of a few arc minutes a radial oscillation period of 60 seconds or longer is recommended a scanDuration of 20 radial oscillation period s will result in an approximately closed pattern For beam sizes of 20 arcsec or so the circular area mapped will be fully sampled if the map radius is less than 6 It is not an especially useful observing mode for general purpose single beam mapping since the largest hole in the map is approximately 0 3 x map radius However it is useful for focal plane arrays Syntax Daisy location map_radius radial_osc_period radial_phase rotation_phase scanDuration beamName cos_v coordMode calc_dt This command scans around a central point in the form of a daisy petal or a The following explanati
65. either disable all sessions until they are ready to resume with the observing or enter blackout dates to cover the period they do not wish to observe The project page includes a panel with project team members listed Using a checkbox team members can select or deselect those identified as observers They can also rearrange the order observers are listed The top observer in the list is expected to observe the next scheduled session If there is a change in schedule this person will be called first 16 CHAPTER 3 INTRODUCTION TO THE DYNAMIC SCHEDULING SYSTEM 3 7 Responsibilities Each project has a Principal Investigator PI and optionally a list of additional investigators An investigator is eligible to be an observer for a given project if that person is qualified for remote observing or is on site in Green Bank It is essential that one of the observers for a scheduled project contact GBT operations at least 30 minutes prior to the start of the observation Observers can contact the GBT operator by telephone 304 456 2341 by the CLEO chat program for qualified remote observers or by showing up in the GBT control room If the GBT operator has not been contacted within 30 minutes of a session s start time the operator will phone observers in the order they are listed on their project web page The PI is responsible for e Managing the project e Identifying all associated observers e Working with project team members and the GB
66. en 53 Continuum Observations en 53 Juss wis obe dung uid 54 54 T 55 56 57 58 6 2 2 1 Executing A Configuration 59 6 2 2 2 Configuration 5 60 SRR Raha eS hee ERE REA ES 60 62 P 64 PREMIERE bene eres been an 65 6 2 2 3 Resetting Astrid remo RR RR eee 66 6 2 3 Scan sa es 9 9 Be Seed O3 X Ro eee wee ae eae eae eed 66 6 2 3 1 Utility Scans s 2 a a EUR bes Sa ee ey PGR Rees 66 s 5c SSS OLOR P oR B boe RR P1S SE weg dim eee EE ES 66 GG ee era ate SG ee ee ak hn ee Ee 69 E Pp alia a ae PES ey aE a 69 oec hw SEAR Gre ee TO Re ehe s ew a 69 Slew go seer Pda eee en 9 9 x 4 a Rex 6445 p54 won needed 71 HOCUS 4 6 MAS ea Bo SOS X EON RR e x RR moe m 71 aia a as eo eae ete A ee ete oe a a ee 72 ee ee re ee eae 73 0232 AUtoOOB 2222 d hehe ee ee Aa ee Be EEE S 73 E 73 Oe Bee ee eed 74 74 6 2 3 3 Observumig Scans xm deg xav wx Rd 76 Lode mean astir 6 4 oR cR ded boh Ghat 0 redo4 wow vada 76 Sse Chad a 45524942 TU Brae AAA OP RE eS 78 TTC eae ee tee Oe a 78 SubBeamNod s o s oe eho Eee SOO EAS GG ae E 79 gh A Ae Poe eet 80 80
67. exist and are available within the Green Bank computing environment 6 2 COMPONENTS OF AN OBSERVING SCRIPT 105 6 2 7 1 Frequency Switched Observations Looping Through a List of Sources In this example we perform frequency switched observations of the HI 21 cm line towards several different sources This example is available as home astro util projects 6D01 example one py Frequency Switched Observations where we loop through a list of sources Us first we load the configuration file execfile home astro util projects 6D01 configurations py 7 now we load the catalog file c Catalog home astro util projects 6D01 sources cat i now we configure the IF system for frequency switch HI observations Configure vegas_fs_config Us now we balance the IF system Balance 7 now we use a Break so that we can check the IF system Break Check the Balance of the IF system i get the list of sources sourcenames c keys Us now loop the sources and observe each one for 10 minutes for srcs in sourcenames Track srcs None 600 6 2 7 2 Position Switched Observations Repeatedly Observing the Same Source In this example we perform position switched observations of a single source We observe the source for two minutes and the off position for two minutes This is repeated twenty times This example is available as home astro util projects 6D01 example two py from any computer within the Gre
68. favor of coherent fold mode cal Incoherent cal mode i e data are folded at a constant 25 Hz frequency used in con junction with the pulsed noise diodes for each receiver coherent search Coherent search mode i e spectra are coherently dedispersed at a DM specified using the guppi dm keyword before being channelized accumulated and written to disk coherent fold Coherent fold mode i e spectra are coherently dedispersed at the DM specified in the ephemeris file before being written to disk Since the DM is read from the ephemeris file the guppi dm keyword is not needed coherent cal Coherent cal mode i e data are taken as in coherent fold mode although no dedispersion is applied since the noise diode is not dispersed guppi polnmode controls whether Full Stoke s or total intensity data are recorded Allowed values are full stokes and total intensity though total intensity can only be used in incoherent search mode guppi numchan sets the number of spectral channels Allowed values are any power of two between 64 and 4096 though care must be taken not to exceed the maximum data rate guppi outbits controls the number of bits used for output values The only allowed value is 8 11 2 DETAILS OF GUPPI CONFIGURATION 147 e guppi scale controls the internal scaling so that the output data is properly scaled for 8 bit values This value is typically chosen from experience with the observing set up Contact
69. for the central d 1 area covered 13 3 3 Establishing amp Monitoring Good 3mm Per formance of the Antenna It is imperative to establish good 90 GHz performance of the GBT at the start of your observing run and monitor it carefully throughout This entails determining any corrections to the GBT subreflector focus 170 CHAPTER 13 MUSTANG Figure 13 2 4 box scan trajectory position that are needed and determining any corrections for thermal deformation of the GBT surface that are needed To do this we use the technique of Out of Focus or phase retrieval Holography also known as OOF The phase retrieval technique uses data from a series typically three of beammaps collected at different focus settings to reconstruct low order phase errors at the dish surface which can then be corrected with the GBT s active surface The same data are used to derive a consistent set of corrections to telescope pointing and focus which are also applied online via the telescope control system The ASTRID AutoO0F procedure will acquire and analyze these data and give you the option to send them to the telescope Acquiring the OOF data should take about seven minutes analyzing them will take another five to seven When complete send the surface correction to the telescope from the AUTOOOF tab and collect a single in focus scan to verify that the beam shape is still reasonable not larger than before and that the source amplitude is equal to o
70. from Out Of Focus holography that improve the shape of the AS versus the elevation angle AS Offsets The state of the AS zero offsets The zero offsets are the default positions for the AS This should always be if the AS is being used LFCs XYZ mm The Local Focus corrections for the offset focus position in millimeters This value is determined from a Focus observation see Chapter 6 LFCs XYZ deg The Local Focus Tilt offset in degrees DC Focus Y mm The Y subreflector offset in millimeters The has temperature sensors attached at various points on the backup structure and the feed arm These are used in a dynamic model for how the GBT flexes with changing temperatures This model is used to correct for pointing and focus changes that occur from this flexing Temp The current air temperature in Celsius Wind Vel The current wind velocity in m s The Intermediate Frequency paths IF path in use are always displayed in the last section of the status screen An example screen is shown in Figure Each line represents the IF path for a single polarization path from the Rack to the backend Each line contains only the devices in use for the listed path A path may include a subset of the devices and values listed below Details on information presented for the path can be found in Appendix A Chapter 5 Near Real Time Data and Status Displays 5 1 The Astrid Data Display Tab The Data Display T
71. from location of the initial subscan That is if you were to use startOffset Offset AzEI 00 40 00 00 00 00 cosv True then the first leg of the scan would start at 40 arc minutes in azimuth from the location and would complete at 40 arc minutes in AZ If instead you used startOffset Offset AzEI 00 40 00 00 40 00 cosv True the first leg would start at AZ 40 arc minutes EL 40 arc minutes and would go to the opposite AZ 40 arc minutes EL 40 arc minutes scanDuration A float It specifies the length of the subscans in seconds slices An integer It specifies the number of subscans through location The default is 4 making a spider shape i e eight legs beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 27 3 A or any valid combination for the receiver you are using such as MR12 and MR34 The default value for beamName is 1 unidirectional A Boolean It specifies whether each slice is scanned once in one direction or twice in both directions The default is True one direction cals A string It specifies the order of calibration subscans i e at the beginning of the slice subscan begin at the end of the slice subscan end or both both The default is both calDuration A float It specifies the length of the calibration subscans in seconds The default is
72. full conversion rate Use of these ADCs require a number of calibration steps Mixed mode Clock Management MMCM The ADC clock is driven by the FPGA on the Roach II card The MMCM phase calibration consists of calibrating the FPGA clock phase relative to the ADC inputs to avoid glitches when the FPGA captures the data samples The MMCM calibration depends on the mode FPGA clock frequency and BOF file in use 10 3 GENERAL OPERATION 131 MMCM calibration is performed automatically by the VEGAS Manager whenever a new mode is selected This calibration step is stable and routine Offset Gain and Phase OGP Each core of the ADC may have a separate Offset Gain and Phase Currently these are calibrated off line by injecting a test tone and adjusting the offset gain and phase of the ADC counts to match the injected tone as closely as possible Once the OGP calibration has been performed the optimum values are stored in the VEGAS config file and downloaded by the Manager to the firmware whenever the mode changes The OGP values also depend on the mode the FPGA clock frequency in use Integral non linearity INL INL is a measure of the deviation of each individual 8 bit value from a straight line through the input to output transfer function The deviation of any given value from a straight line is measured from the center of that value INL calibration is also done off line It is independent of VEGAS Mode so the
73. hDelta vDelta referenceOffset ref erenceInterval scanDuration beamName start stop The parameters for PointMapWithReference are location A Catalog source name or Location object It specifies the center of the map hLength An Offset object It specifies the horizontal width of the map vLength An Offset object It specifies the vertical height of the map hDelta An Offset object It specifies the horizontal distance between points in the map vDelta An Offset object It specifies the vertical distance between points in the map referenceOffset An Offset object It specifies the position of the reference source on the sky relative to the Location specified by the first input parameter i e the center of the map referenceInterval An integer The number of points that should be completed in the map before moving to the reference offset position and to perform a reference scan e g 4 means every four points 82 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS scanDuration A float It specifies the length of each scan in seconds beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 2 3 4 or any valid combination for the receiver you are using such as 12 Default is 1 start An integer It specifies the starting point for the map The default value for start is 1 Note in PointMap this counts points not stripes stop An integer
74. have been invoked are available within an Observing Script If the same name appears in two or more catalogs the name from the most recently invoked catalog will prevail Name comparisons are case insensitive hence b2322 16 and B2322 16 are equivalent 6 2 4 1 Getting Your Catalog Into Astrid Although one can include any number of Catalogs into an observing script the standard practice is to put all the Catalogs into separate files that are then brought into the Observing Script via the Catalog command This a keeps the Observing Scripts simple and without clutter and b allows changes to be made to the Catalog without having to validate and re save the Observing Scripts The best way to learn about how to bring Catalogs into the Observing Script is through an example Lets suppose that there are two Catalogs that you need for your observations These two catalogs are in the following files 86 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS home astro util projects 6D01 sources cat home astro util projects 6D01 pointing cat To bring these Catalogs into your Observing Script you would need the following lines in your Observing Script first load the catalog with the flux calibrators cata Catalog home astro util projects 6D01 sources cat now load the catalog with the pointing source list catb Catalog home astro util projects 6D01 pointing cat All sources from
75. illustrated in Figure which shows the cumulative percentages when wind speeds are below a certain value Figure is from Ries PTCS project Note 68 1 The DSS Dynamic Scheduling System see Chapter uses forecasted wind speeds when it determines what projects are suitable for scheduling one should rarely see any negative impacts from winds 16 3 Atmospheric Opacities The frequency range covered by the extends from low frequencies where the opacity is relatively low 0 008 nepers to high frequencies where opacity is very high gt 1 nepers Atmospheric opacity 195 196 CHAPTER 16 HOW WEATHER CAN AFFECT YOUR OBSERVING Sunset 3h to Sunrise 2 LST gh Jun Jul Aug Sep LST Feb 8 12 16 20 24 4 UT Figure 16 1 The range of UT EST and LST used in the definition for night time observing 16 3 ATMOSPHERIC OPACITIES 197 Hourly Max winds from August 2008 July 200 1 0 0 8 5 0 6 9 All year 5 Oct 1 1 Z 0 4 Oct 1 May 1 Nights o 10 GHz Limit 22 GHz Limit i 30 GHz Limit 45 GHz Limit 86 GHz Limit 115 GHz Limit 205 5 10 15 20 25 30 35 40 45 Station 2 max wind speed mph Figure 16 2 The cumulative fraction when wind speeds are below a certain value Data from the year August 2008 to July 2009 are shown in blue green shows winter data and red shows winter nights hits observing twice it attenuates the astronomical signal and it increases the system temperature and
76. lt i lt 32 meaning there will never be more than 33 spurs in a given data 142 CHAPTER 10 VEGAS Ol 10 Counts e d apa lt 5 n 41 6 41 8 42 0 42 2 42 4 GHz Figure 10 12 Spectra of a noise source centered near 42 4 GHz black A high pass filtered version of the data offset by 1 and scaled by a factor of 100 for visibility is shown in red showing the spurs Note that these frequencies are relative to the intermediate frequency input into VEGAS so they should be offset by the centered VEGAS specific intermediate frequency and the center sky frequency such that the spurs will occur at sky frequencies Vspurs sky Vs c Vspurs Vy 10 2 as shown in Figure 10 13 It is important to keep in mind that vs D vs the central sky frequency may be shifted by a function D from the requested sky frequency v e g via doppler tracking The value of is dependent on which mode is used and is not as straightforward when using the low bandwidth higher resolution modes 11 29 For modes 4 29 the FFT of the raw time series from the ADCs is not performed on the FPGA but on external GPUs which further filter the bandwidth allowing higher resolution and thus all 33 spurs are not be present in these modes This filtering in the GPU modes also causes Vv to not simply equal to f 4 in these cases as it is in modes 1 3 Ad
77. not necessary to perform an AUTOOOF just to correct pointing which has drifted assuming the beam shape and source amplitude are stable The pointing offsets can be corrected after the fact in the data analysis using your periodic calibrator monitoring observations 13 3 4 Calibration It is essential to observe a flux calibrator during each observing session and to do this only after the initial set of active surface OOF corrections have been applied Changes in gain due to subsequent OOF corrections if any can be tracked with the secondary calibrator The recommended MUSTANG flux density scale is ultimately based on the WMAP 7 year Wieland et al 2010 measurement of Mars however Mars is often not visible and is resolved by the GBT at 90 GHz complicating its use A list of secondary flux calibrators sufficiently compact and stable or have modelable light curves is shown in Table Other sources may also be suitable given appropriate bootstrapping observations Custom ephemeris can be obtained from the JPL online HORIZONS system and translated into the ASTRID format Work is under way to increase the number of secondary bootstrapped from planets flux calibrators A catalog of 27 compact 90 GHz bright sources is at users bmason mustangPub mustangpnt cat These sources are suitable for peak focus OOF check observations and for monitoring the antenna performance but are not suitable for flux calibration 13 3 5 Observing Summary Example Obse
78. process the pointing scans It will calibrate the data remove a and fit a Gaussian to the data After the two azimuth scans it will then automati cally update the system with the new azimuth pointing offset values that it determined It will then automatically update the elevation pointing offset after the two elevation scans unless certain criteria are not met see 6 1 3 1 A sample of the Data Display Application after a pointing is shown in Figure 5 1 Astrid ONLINE MONITOR ONLY 0x File Edit View Tools Help PASEI aI ARIERO R ObservationManagement 1 DataDisplay 1 GbtStatus 1 00 1459 7140 Peak 1 c Pointing Focus Continuum Spectral Line Beta Observation State 301 1459 7140 Peak 2 302 1459 7140 Peak 3 9 30 300 1L 1459 7140 azimuth _301 1L 1459 7140 azimuth GBT State 303 1459 7140 Peak 4 Wid 8 513 Eware wT Wid 9 157 EWId EEIU 28 Tsys 16 785 28 Groio7 Tsys 15 946 Running 304 14597140 FocusSul 26 12 040 _ 26 Hot 12 666 305 pol RALongMap 25 d 23 B 23 GBT Status AES E noice 18 18 i it Lu uu EFE 80 60 40 20 0 20 40 60 80 80 60 40 20 0 20 40 60 80 Queue Control Offset arcmin Offset arcmin 30 302 1L 1459 7140 elevation 303 1L 1459 7140 elevation 9093 99079
79. rate User defined parameters may also be added The dates and times are required to be in UTC The dates and times can be specified in any legal python form for example a YYYY MM DD 92 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS hh mm ss where MM is month number e g August 09 or b YYYY MMM DD hh mm ss where is the abbreviated month name such as Jan Feb etc The ephemeris table should contain enough entries to cover a period longer than that required by a particular observing session The observing system selects the portion of the table needed for the current scan start time and duration Here is an example of a valid ephemeris file Us Richard s sample ephemeris catalog Us i FORMAT EPHEMERIS i NAME MyMovingObject COORDMODE J2000 VELDEF VRAD LSR 2004 07 16 00 10 00 09 56 16 98 915 QUT RAD Bel 2004 07 16 00 20 00 09 56 17 76 27 456345 2004 07 16 00 30 00 09 56 18 55 27 568233 2004 07 16 00 40 00 09 56 19 32 16 57 27 623423 2004 07 16 00 50 00 09 56 20 10 21 723456 Us Note that the HEAD line has been omitted because the default is DATE UTC RA DEC VEL Here is a more complicated example for a comet that specifies the coordinate rates FORMAT EPHEMERIS NAME C 2002T7 dec dra ddec vel 2004 Jun 13 2155 46 23 35 2004 Jun 13 20 46 23 89 2004 Jun 13 52 55 46 24 44 2004 Jun 13 30 46 24 98
80. readily removed by the standard calibration schemes Note the high frequency ripples shown in the mode 3 plot were caused by a standing wave in the cable between the IF Rack and VEGAS attenuators have been added to the cable to remove this ripple hence it is not seen in the mode 2 data taken later 10 5 Baseline Performance Gain variations across the large bandpasses desired in radio astronomy require significant efforts to balance and stabilize These variations create baselines that are not perfectly flat and can potentially vary with time Thorough data calibration helps to mitigate these effects but calibration can only be effective if the baselines are stable With this in mind developing the VEGAS infrastructure has focused on the temporal and spectral stability of these baselines It has served as an interesting engineering problem to create an IF system that is capable and stable for all receivers In this section we will discuss the status of the baselines as recorded by VEGAS The baseline shapes come from two main causes variations due to the receiver and IF system and shapes due to digital filters within VEGAS Figure 10 10 shows the baselines types expected from VEGAS While not flat all of these baseline shapes have been found to be stable out to at least 30 minutes and are easily removed with standard calibration techniques When looking at Figure 10 10 the ripples in the mode 4 9 data lower left stand out This pattern
81. routed to the back end device one for each polarization if you specify two windows you get 4 IFs and so forth The configuration software tries to put the midpoint of the total frequency range spanned by all windows at the center of the nominal IF1 band so as to use the narrowest I F bandpass filters that will pass the desired range of frequencies In some uncommon cases this is not possible so the IF bandwidth must be increased to pass the desired range of frequencies For prime focus receivers the total bandwidth is 240 MHz for the Gregorian receivers up to 4 GHz is possible depending on the receiver The user specifies the rest frequencies restfreq keyword and a range of radial velocities vlow and vhigh keywords The various IF filters are set to include the required range of frequencies in the local frame required by the radial velocity range The configuration software predicts the local frequency for each spectral window based on the rest frequencies and the radial velocity During observing the tracking Local Oscillator will correctly track the velocity of spectral window number 1 Because there is only one tracking L O the other spectral windows are set up with frequency offsets in the local frame with respect to window number 1 When observing at a variety of high velocities one should run a configuration for each change of velocity i e do not rely on just changing the velocity in the manager and one should set
82. scan types are discussed in Appendix Location Most Scan commands require a location parameter This may be either a Location object see 8 and Appendix D or it may be the name of a radio source given in a Catalog see 6 2 4 beamName Most Scan commands use a beamName parameter This should not be confused with the beam keyword in Configurations see Section 9 2 2 2 This indicates the tracking beam i e the beam that is pointed at the specified location It may have values 1 2 3 up to the maximum beam number for the specified receiver The beam numbers and their relative locations depend on the receiver A value of C means the center of the receiver box where there may or may not be a feed Syntax such as MR12 or MR34 means halfway between beams 1 and 2 or 3 and 4 respectively These are used for subreflector nodding see SubBeamNod in Section 6 2 3 3 6 2 3 1 Utility Scans AutoPeakFocus The intent of this scan type is to automatically peak and focus the antenna for the current location on the sky and with the current receiver Therefore it should not require any user input However by setting any of the optional arguments the user may partially or fully override the search and or procedural steps as described below AutoPeakFocus should not be used with Prime Focus receivers The prime focus receivers have pre determined focus positions and there is not enough travel in the feed to move them sign
83. scans 5 through 25 PROJECT SESSION gt is what you d expect e g AGBTIAA 252 04 lt OUTPUT PREFIX gt is the leading part of the output directory name e g scan5to25 would result in a directory named scan5to25 raw vegas 138 CHAPTER 10 VEGAS 10 4 Blanking While the observing system is switching between states such as switching the noise diodes on or off switching frequencies running doppler updates etc the collected data is not valid and thus must be blanked by VEGAS VEGAS allows the user to switch states frequently enough that the required blanking time can become a non negligible percentage of the total observing time For efficient observing It is important to choose switching periods that are long enough for the total amount of blanking to be negligible The amount of blanking per switching signal is dependent on the VEGAS mode used Conservative values are shown in Table 10 4 For a more thorough description of the appropriate switching periods for a given amount ofblanking and more accurate estimates of the minimum switching periods we refer the interested reader to http library nrao edu public memos gbt GBT_288 pdf Table 10 2 Minimum Recommended Switching Periods for Mapping Observations with Doppler Tracking Total Power Total Power Frequency Switched Frequency Switch ed No Noise Diode Noise Diode No Noise Diode Noise Diode tp_nocal tp sp_nocal sp Mode s s s s 1
84. signficant amounts due to firmware configuration glitches that may occur after reseting the manager updates to receiver parameters and power failures Users can calibrate their data by carrying out NOD observations between pairs of beams on a known flux calibrator It is also possible to use the sky at different elevations to flat field the relative gains of the beams and then absolute calibrate the data with an ONOFF NOD observation of one reference beam using a known flux calibrator Calibration using resolved sources such as planets or the Moon adds the requirement for an accurate temperature model of the source plus a model for coupling the GBT beam to the planet disk Observers should consult the Friend of their project to devise the best strategy for calibration 9 5 Mapping Strategies The KFPA beam is small about 30 For high angular resolution images the sky should be sampled five times across the beam i e the scan rate and integration times should be set such that there are five integrations recorded in the time the telescope scans across an angle equal to the beam FWHM and there should be four switching periods per integration see Mangum Emerson and Greisen 2007 A amp A 474 679 for details The user should consult the GBT Proposer s Guide for minimum recommended switching periods and integration times It is important to take account of the overheads involved with mapping scans For example it takes approximately 25 s
85. size of 10 8 at 77 GHz and derived na 31 and m 50 in good nighttime conditions with the application of the thermal AutoOOF corrections Without the AutoOOF corrections the beam size increased to 12 5 and the aperture efficiency decreased to 2396 but the main beam efficiency remained nearly constant at about 50 ox 02 pna Therefore extended sources may be observed during the day without the AutoOOF corrections if the science is not impacted by the primary beam variations 14 4 Calibration and Data Reduction For accurate calibration users are recommended to run a CalSeq before and after each set of source data Users are also recommended to take a short nod observation on their pointing amp focus source every hour to track the relative efficiency of the system If users only want absolute calibration done 190 CHAPTER 14 THE 4MM 68 92 GHZ RECEIVER Table 14 1 4mm Channel Definitions Channel Polarization Beam 1 beaml fdnum 0 X or L plnum 0 ch3 beaml fdnum 0 Y or R plnum 1 ch5 6 beam2 fdnum 1 X or plnum 0 ch beam2 fdnum 1 Y or plnum 1 Table Notes The GBT IF channel numbers 1 3 5 7 and their corresponding beam and polarization definitions The parameters fdnum and plnum are GBTIDL keywords to within 20 3096 then the default calibration from the cold amp ambient loads may be used For more accurate absolute flux calibration a source of known flux density should be use
86. specialized interaction with the system This is to be used by expert observers and is currently only used during some pulsar observations 4 2 How To Start Astrid 4 2 1 Running Astrid From any Linux computer in Green Bank just type astrid to start the program It usually takes Astrid between 10 20 seconds to launch from the command line The first thing you will see is the astrid splash screen which is shown in Figure 4 1 Figure 4 1 The Astrid splash screen will now ask you what mode you would like to operate in This will be done via a pop up window which is shown in Figure v Real Time Mode Work offline f Work online but only monitor observations Work online with control of the telescope Figure 4 2 When you start you will see this pop up window which will allow you to choose which mode of that you would like to use There are three different modes in which you can run Astrid Work online with control of the telescope In this mode you can run Observing Scripts and you are in full control of the observations In this mode you can also see near real time data from the 4 2 HOW TO START ASTRID 23 Work online but only monitor observations In this mode you can actively watch what is currently happening in for the current observations However you will not be allowed to submit any Observing Scripts for execution or to affect the current observing in any manner Y
87. switching cycle to be 1 second swper 1 0 We want VEGAS to record data every 30 seconds tint 30 We wish to Doppler track the spectral lines with rest frequency 25500 0 MHz in the commonly used Local Standard of Rest velocity frame vframe Isrk vdef Radio We would like to use the low power noise diode noisecal lo Finally we wish to take the data using circular polarization pol Circular Multiple Spectral Lines KFPA Observations configuration definition for spectral line observations with KFPA vegas kfpa config receiver RcvrArray18 26 beam alll obstype Spectroscopy backend VEGAS restfreq 24000 1 2 3 4 23400 5 6 7 25500 DopplerTrackFreq 25500 deltafreq 24000 0 23400 0 25500 0 bandwidth 187 5 swmode swtype swper 1 vlow vhigh vframe vdef Radio noisecal pol Circular nchan low vegas vpol cross 929999 22 29 29 Fa 7 The configuration has the name vegas_kfpa_config and can be used for spectral line observations obstype Spectroscopy using cal switching observations swmode tp swtype none with the multi beam 18 to 26 5 GHz all beams receiver receiver RevrArray18_26 beam all and VEGAS as the backend with cross polarization products backend VEGAS vegas vpol cross We request that beams 1 2 3 and 4 have a rest frequency of 24000 that
88. that you reduce your imaging data as you go along so that you can catch problems should they develop For monitoring ongoing observations observers should use the GUI interface to the MUSTANG IDL code This can be started from the UNIX command line on any Green Bank UNIX machine as follows The first step is to select the project you are working with via the Browse Projects button selecting Online will select the most recently updated project in home gbtdata probably your project if you are observing on the GBT You can also for inspection of already acquired data type in the full path to the data directory in the box for instance home gbtdata AGBT11C 033 or home archive science data tape 030 AGBT07B_012 note the trailing slash Once this is done the area at the bottom of the GUI will display a summary of your telescope period so far This summary can be updated with the Update Scan Summary At this point IDL will read all files in the project directory so far and generate a summary in the GUI window and also in the terminal window the IDL GUI was launched from 13 4 QUICK LOOK DATA REDUCTION vw Um Basic Options Advanced Options Online Browse Projects Yhone gbtdata RGBTOBC 026 06 Update Scan List DISPLAY OPTIONS Change Color Calibration Focus list Allowed Values z JSet mei screen 13 4 5 80 81 82 v Full Screen Show
89. the Second LO LO2 signal Each copy of the signal can be mixed with a different LO2 since there are eight different synthesizers The resultant signals are then sent through a filter to make sure it has a bandpass of no more than 1 85 GHz A final mix with a fixed frequency of 10 5 GHz then gets the signal within the input band passes of the backends There is a final set of filters that ensures the signal has the correct bandwidth for the backend LO2 T 5 9 7 7 GHZ ge S18 26 5 GHz Fibers 6 8 Fibers 2 4 Fibers 5 7 C Rack B Selected LO 1A LO 1B 4 8 26 5 GHz 5 9 7 7 GHz dimid ru AL Fibers 1 3 Beam 6 gt 1 2 7 7 GHZ Beam 7 Beam 1 Duplexer 1 2 3 0 GHz eeeee8 KFPA Feeds Figure 8 3 A simplified KFPA diagram showing the combination of beams onto fiber modems and their selection in the Converter Rack Modules A and B 8 3 Combined IF The KFPA receiver with 7 beams is the first GBT receiver with more IF signals than there are Optical Fibers from the GBT to the Jansky Lab In order to bring the IF signals to the control room pairs of signals from different beams were combined on single fibers The signal combination was accomplished by an analog addition of the IFs of pairs of beams Beams 1 2 3 and 4 have IF signals centers at 6800 MHz The IF signals from beams 5 6 and 7 are down converted to 2100 MHz center frequency Beam 2 is paired with 6 beam 3 with 7
90. the antenna slews to the indicated position plus the specified offset 3 If only an offset is given the antenna slews to the current location plus the specified offset The following example slews to 3C 48 using the center of all the receiver s beams Slew 3048 beamName C Focus The Focus scan type moves the subreflector or prime focus receiver depending on the receiver in use through the axis aligned with the beam Its primary use is to determine focus positions for use in subsequent scans Syntax Focus location start focusLength scanDuration beamName The only required parameter for Focus is location The parameters for Focus are location A Catalog source name or Location object It specifies the source upon which to do the scan start A float It specifies the starting position of the subreflector in mm for the Focus scan See Table 6 5 for the recommended value for each receiver focusLength A float It specifies the ending position of the subreflector relative to the starting location also in mm See Table 6 5 for the recommended value for each receiver scanDuration A float It specifies the length of each scan in seconds See Table 6 5 for the recom mended value for each receiver 72 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 2 3 A or
91. the software digital team has worked diligently to successfully track down and alleviate these issues Removal of all baseline shapes is not feasible so it is important to account for these shapes in data calibration This is most often accomplished by using position switching obtaining data when pointing on and off source and or frequency switching shifting the central frequency such that the desired spectral lines appear at different locations within the bandpass shape If the shape of the baseline is still of concern after these types of calibration it is recommended to look into vectorized baseline removal such as described in Winkel Kraus amp Bach 2012 http adsabs harvard edu abs 20124 264 540A 140W 10 6 VEGAS and Deep Integrations At the time of writing December 2014 we have not extensively tested the performance of VEGAS for deep integrations However some science observations have been performed with VEGAS at Q band looking for high redshifted CO lines Figure shows the result of four and a half hours of effective integration time using the sub beam nod observing technique D Frayer private communication The previous vector calibration as applied for example to the GBT spectrometer yields bad baselines with VEGAS However a simple scalar Tsys calibration works well when applying an appropriate high pass filter to remove large scale smooth frequency structures The sub beam nod observations were taken
92. then decide to cancel a telescope period and substitute an alternate backup observation in its place Note that the observer may decide that the weather conditions are too poor even after beginning the observation Equipment failure can also lead to cancellations If GBT staff must change the 24 hour schedule for these reasons affected observers will be notified immediately by email or telephone 3 10 Backup Projects When a scheduled telescope period is cancelled a backup project will fill the time Backup projects can come in two categories observer run and operator run Observer run backup projects are those for which observers have volunteered to be called on short notice The notice could be as little as 15 minutes although the GBT staff will attempt to make the lead time as long as possible Backup project observers should be ready to take control of the telescope at any time of the day or night consistent with their observing program and blackout dates These call outs are expected to be rare By volunteering as a backup project observers improve their project s chances of getting observing time Note that identifying a project as a backup does not penalize that project during the normal scheduling procedure The project will compete for regular scheduling on an equal footing with all other projects but the PI is agreeing to make the project available as a backup in addition to regular scheduling Note that observer run backup projects w
93. this is the case can be determined by inspecting the MUSTANG CLEO screen see Section 5 2 The detector array array G0 should be under 400 milliKelvin and shouldn t be changing by more than a milliKelvin or two per reading there is one reading every few minutes the series array should be under 5 Kelvin The bolometer array is kept cold by a closed cycle helium fridge consisting of two separate closed pots one with liquid He3 and one with liquid He4 The liquid in these pots boils away thereby cooling the 13 2 PREPARING FOR AND CLEANING UP AFTER OBSERVATIONS 167 detectors and is captured internally when it has all boiled away it must be re condensed or cycled The MUSTANG CLEO screens present conservative estimates of how much time remains for the and 4 fridges Ideally there will be enough of both to cover your entire observing run Only He3 is required to operate MUSTANG although if He4 runs out in the middle of a run the detectors will warm up slightly and need to be re biased 13 2 Observatory staff are responsible for delivering appropriate cryogenic conditions but due to external factors it will occasionally not be possible at the start of a run If this has occured the operator or support scientist will inform you of the situation and recommend a course of action Time lost to cryogenic failures like other lost time from hardware failures will not be charged to the balance of your project time
94. those in Table Default value is low dopplertrackfreq Rest frequency in MHz used to compute the velocity for Doppler tracking The default value of this keyword is the first restfreq value vegas vpol Keyword to specify which spectral product to record in the FITS file It assumes values selfl self2 self and cross They value selfl corresponds to the spectrum of signal connected to port A of the vegas and self2 corresponds to that connected to port B Default value is self vegas subband Keyword used by config tool to select between single and multiple spectral window VEGAS modes with 23 44 MHz bandwidth It assumes values 1 or 8 Default value is 8 10 3 2 VEGAS ADC MMCM OGP and INL Cal ibration An understanding of VEGAS ADC calibration is not necessary in order to be able to observe with the instrument It is included here as background information only those who are not interested in it may safely skip to section n The precise method of calibrating the ADCs is still evolving this description is correct as of December 2014 Each VEGAS Bank contains two Analog to Digital converter ADC cards one for each polarization The ADC cards used are National Semiconductor now Texas Instruments ADC083000s which perform 8 bit sampling at 3 Gigasamples per second Gs s The ADC083000 has a 1 4 demultipexer data is output on four busses at a quarter of the ADC sampling rate The outputs are interleaved to provide output words at the
95. thus the noise in the observation due to atmospheric emission Figure ma shows opacities atmospheric contributions to the system temperature and number of air masseg the astronomical signal must pass through vs elevation under three typical weather condi tions as calculated using the method described on the High Frequency Weather Forecasts web page http www gb nrao edu rmaddale Weather index html Typical total system temperatures are shown in Figure The opacities shown in Figure are for planning purposes only and observers should not use them at high frequencies for calibrating data Instead one should use the actual opacities and the air mass from the bottom of Figure 16 3 to approximate the amount of attenuation a signal will experience at the expected elevation of the observation The signal is attenuated by 16 1 where r is the opacity the total number of air masses Since opacity is very weather dependent please consult with a local support staff on how best to determine opacities for your observing run 1 airmass curve in Figure 16 3 is a better approximation than the csc elevation approximation which is only correct above about 20 degrees elevation 198 CHAPTER 16 HOW WEATHER CAN AFFECT YOUR OBSERVING Zenith Opacity For Typical Winter Weather Conditions 0 40 5 0 35 o 0 30 amp 0 25 D g 0 20 015 0 10 0 05 0 00 0 10 20 30 40 50 Frequency GHz Z
96. to do two of these back to back since they each take less than a minute which will also give you a check of the photometric accuracy of your measurements every half hour some good sources are 1642 3948 22534 1608 0927 3902 0319 4130 08544 2006 mysSrc Ceres Catalog users bmason gbt obs par ceres ephem TITT TEITT TT TT CATALOGS none needed for planets standard pointing source catalog 1 home astro util pointing pcals4 0 pointing cat Catalog or user defined catalog Catalog users rfeynman gbt obs nobel cat Configure users bmason mustangPub sb mustang conf Daisy Params nominal 1 5 30sec 0 120sec better coverage 0 8 30 sec 100 sec daisyScanDur 75 daisyRad 1 5 daisyRadPd 15 0 Coord Sys in which to execute trajectory eg J2000 Encoder coordSys J2000 Do not modify below here Slew mySrc relock detectors execfile users bmason mustangPub ygor relockAstrid py Daisy mySrc daisyRad daisyRadPd 0 0 daisyScanDur beamName C cos_v True coord Mode coordSys cale_dt 0 2 13 6 EXAMPLE ASTRID SCRIPTS 181 13 6 7 parfulldaisy does a sequence of five daisy scans phased appropriately relative to each other to provide good coverage of a circular region in this case with a radius of r 2 8 Th
97. up window 22 4 3 Initial Astrid screen upon startup 4 23 4 4 Components of the Astrid 24 4 5 Astrid Observation Management Edit Tab 28 4 6 Astrid Observation Management Run 31 HT Astrid Status Tab top 4 4 22255 baw Oe xS SR RU x WE m Oe aS 33 4 8 Astrid Status Tab 34 5 1 Astrid Data Display 38 39 5 3 Pointing and Focus acceptance 40 5 4 Pointing and Focus heuristics 41 5 5 Pointing and Focus change fitting 41 5 6 Send Corrections 42 5 7 Astrid Data Display OOF 4 43 5 8 Good raw data OOF plot 44 5 9 Bad row data 45 DX PELLIT 46 bth deeded dak bd bo gos oe eee be aed 46 thas ey eases aera ae gh ee eed LP 47 5 13 Astrid Data Display plot 4T 0 1 Hose Curvel o e s awam eee ee De Eee OEE eee eee ean es 84 6 2 JPL Horizons website 93 6 3 Selecting quantities to generate an
98. values being output by the ADCs Both histograms should have a roughly Gaussian shape with a FWHM of about 30 The two histograms do not need to be identical but they should be reasonably close Figure shows a well balanced example Note that guppt adc hist will only update when there is no scan in progress lf you try to run it while taking data you will only see the results of the last run which will not be up to date For this reason is usually a good idea to put a Break statement in your scheduling block which will pause Astrid and give you a chance to check the ADC levels If the ADC histogram looks extremely narrow then GUPPI is probably not getting signal If it is very broad then the input power is too high In both cases stop the scheduling block and resubmit so that you configure and balance again If the problem persists after one or two attempts ask the operator to contact the on duty support scientist Once the IF LO system is properly balanced you will need to check the internal GUPPI internal scaling controlled via the guppi scale parameter The only way to do this is via the guppi monitor command while data is being taken This command will plot the bandpass The mean bandpass level should be around 20 30 and less than 50 Figure shows a well scaled example If the level looks too high or too low you should adjust the guppi scale parameter accordingly the relationship is linear and then resubmit your scheduling block b
99. vlow vhigh Note that the deltafreq keyword gives frequency offsets that are applied in the local or topocentric frame For example if Vframe is velocity of the reference frame V is source velocity in that frame Vrest 18 the rest frequency of the line and we use the Radio definition of velocity then the topocentric frequency will be V Vtrame C Vtopo Vrest deltafreq B 1 Finally note that the expert user may specify any of the IF conversion frequencies and total IF bandwidth overriding the calculations done by the configuration software ifbw ifOfreq lolbfreq lo2freq and if3freq keywords This option may be needed in some peculiar cases Of course one needs a good knowledge of the IF to make use of this option B 1 Array Receiver Spectral Windows Array Receivers can be configured with a variety of spectral windows The configtool part of ASTRID sets up these spectral windows and a new syntax was required to specify more complex configurations 213 214 APPENDIX B INTRODUCTION TO SPECTRAL WINDOWS Each feed has the potential to be tuned to a different rest frequency For the KFPA receiver a special all beam mode is defined which uses all 7 beams plus one beam tuned to a second different spectral window This stretches the current syntax of the configtool restfreq and deltafreq keywords In order to support these modes within the configtool expanded values and intepretation
100. want to write your Nobel Prize winning paper can help you with your page charges see Chapter 19 You should also notify your scientific contact person of your paper to help the Observatory keep track of how successful all observing projects have been Chapter 3 Introduction to the Dynamic Scheduling System by Jim Braatz and Dana Balser July 15 2010 edited by Karen O Neil October 5 2011 This document gives an introduction to the Dynamic Scheduling System DSS for the Robert C Byrd Green Bank Telescope GBT The GBT has been scheduled with the DSS since October 1 2009 Observers can access the DSS through this site https dss gb nrao edu 3 1 Overview of the DSS The primary goal of the Green Bank Telescope Dynamic Scheduling System DSS is to improve the efficiency of GBT observations by matching the observing schedule to predicted weather conditions while allowing each observer to retain interactive control of the telescope Each day the DSS will examine the weather forecast equipment availability observer availability and other factors and set an observing schedule for the 24 hour period beginning the next day Observers will therefore get about 24 48 hours notice before their project will observe Observers will have the opportunity to pause their observing program set blackout dates indicating when they are unavailable for observing and back out of current observations if they find the observing conditions are not suit
101. which can bleed through to the final product Due to the limited and often negligible effect of these spurs we do not automatically interpolate across them but let the user decide how to handle those channels A tool for locating these spurs within GBTIDL is forthcoming 10 8 Known Bugs and Features vegasdisplay is not updating or is running very slowly This occasionally happens The cure is to ask the Operator to restart the display 144 CHAPTER 10 VEGAS TaskMaster gbtdata stop 15 TaskMaster gbtdata start 15 Data is not filling The online filler checks for project changes when it is not actively filling a scan This means that if the previous project was a VEGAS one and it ended on a long scan the filler may still be filling that project when the VEGAS scan has finished in your project If you suspect that this is the case the only solution is to ask the Operator to restart the online filler task There is a square wave and or divot in my VEGASDM display The samples which are taken to produce the VEGASDM total power display run asynchronously to the switching signals Hence the sampling may occur during the Cal on phase at one point in time and then drift into the Cal off phase sometime later This may produce an apparent square wave in the VEGASDM output with an amplitued of a few tenths of a dB and a period of seconds Similarly it is possible for the VEGASDM data to be acquired when the LO is updating
102. will be done for each table position The user can input a list of calibration table wheel positions with the tablePositionList argument auto default dwell fraction 0 33 0 33 0 34 and default three positions Observing Cold1 Cold2 The user can specify a list of positions and dwell times with the tablePostion List and dwellFractionList arguments autocirc dwell fraction 0 25 0 25 0 25 0 25 and four positions Observing Posi tion2 for beamName 1 or Position5 for beamName 2 for use with circular VLBI observa tions Cold1 Cold2 e scanDuration scan exposure time in seconds For manual mode each specified position will be observed for the scan exposure time i e separate scans for each position For auto modes the total scan exposure time will be divided between positions based on the dwell fractions i e one scan for all positions e location a Catalog source name or Location object default is None use current location e beamName Beam name associated with pointing location This argument is a string Default beam is 717 e fixedOffset offset sky position used in cases when observing a bright source and want to measure the system temperature of the sky off source This argument should be an Offset object Default sky offset is 0 e tablePositionList user specified variable length ordered list of cal table positions for the manual or auto modes The default sequence is O
103. with GUPPI 145 ILI Summary a a 9 3o o9 m om RO A ER osos a 145 Lou Sono e Gea Gt ea eae 146 D a d Huet Gea SO Rod ate ROS GSR Qo 148 Mowe ee eae TOUT cx 151 2 dem oe ew ooo gos d 9 152 11 5 1 Monitoring Incoherent Data Taking 152 11 5 2 Monitoring Coherent Data 152 PUR y WU Ce EE EU ede oe Ny 154 154 11 8 Warnings Be te ee er 155 11 9 More Information oaa ss 155 12 The CalTech Continuum Backend CCB 157 2c boe EERE OO dede de e 3e Gp CRURA SORES DDD X ox x OY ESS 158 sex pb cR RR Used pow p Rated ae ee e e dew vod ror b bo 158 TT 7 777 159 12 1 8 Observing Modes amp Scheduling Blocks 6 159 both hh ae Hf 160 B4 VA OW YE Y OY XOU eed Y RI Y Y XE d d d eus 160 ADIT eee dadieedaddwmerddaokddedaideses 164 TET 164 165 a A E A a a e 165 T 165 jd ee ht 9 Pork RR RR ugs P ee Red 166 166 DD 167 TTD eet bb ee UTC 168 ee BE eee 168 Sensitivity cw 44 e Ro one ee bee ee ee e ee D S 169 169 es gt ir de ee Gest Pe he Ae Ree oe ae E 171 Tr 171 TTL 172 13 5 l
104. your location during the observations e Prepare ASTRID observing scripts in advance e Contact the telescope operator 30 minutes before the start of your setup time The number to call is 304 456 2346 or the Operator s direct line at 304 456 2341 x2346 connects to a speaker phone and is the preferred number to use Provide the operator with all the appropriate contact information in case they need to contact you during the run e We strongly recommend VNC network displays of observing applications Suggested VNC setup procedures are provided below If you have not run VNC before you are strongly urged to run a test VNC session several days before your observations e Start up your observing applications immediately after contacting the operator These usually include cleo Open at least the Talk amp Draw windows then any other cleo application you need You can use Talk amp Draw to communicate with the operator during the run and after you have finished with the phone astrid The GBT observing interface gbtidl The GBT data reduction package Or another data reduction program to be used 201 202 CHAPTER 17 REMOTE OBSERVING WITH THE GBT e At the start of your observing time again call the telescope operator at 304 456 2346 who will put you on a speaker phone The line should stay open at least through the setup period The backup line in case x2346 is busy is the Operator s direct line at 304 456 2341 This line does not
105. 0 in its ability to handle changes in the brightness of the sky as seen by the GB The Spectrometer has the dynamic range to handle up to a factor of 4 change in the sky brightness The spectral processor can handle changes of about a factor 15 in the observed sky brightness The sky brightness can change because of continuum emission of a source or a maser line as you move on and off the source It can also change due to changes in the atmosphere s contribution to the system temperature as the elevation of the observations change There are not any set in stone rules for when an observer should balance the However there are some guidelines which will allow you to determine when you should balance the Here are the guidelines 1 You should balance the IF after performing a configuration 2 You should minimize the number of times you balance when observing 3 If you know Tsys Tsrc will change by more than a factor of two 3 dH when you change sources not between and on and off observation you should consider balancing 4 If VEGAS reports errors in excess of 5 dB then you should consider balancing 5 Iry to avoid balancing while making maps 6 Never balance between signal and reference observations such as during an on off observation lFrom about 0 5 to 5 Volts of IF power in the IF Rack A factor of 2 from its optimal balance point in each direction change in power from to P2 can be represented in dB by
106. 0 to 17 30 ET If all observers for a given project are blacked out at a given time that project will not get scheduled If at least one observer is not blacked out the project is eligible for scheduling The default time zone used for entering blackouts is set on the Preferences tab which is linked at the top of every DSS web page Observers can also override the default by selecting a time zone when making a blackout entry Observers with more than one project will find that they need to enter blackout dates only once and the dates will be applied to all their projects Those visiting Green Bank to observe should use blackout dates to mark the periods of their travel before and after the run to ensure they are scheduled only when available and ready on site Guidelines for the use of blackouts While blackout dates give observers control of the scheduling process efficient GBT operation requires that not too much time be blacked out or disabled It is especially important that projects with large observing allocations not have too much time unavailable for scheduling because of blackouts As a guideline projects with more than 20 hours of allocated observing should limit time that cannot be scheduled to no more than 20 of the total eligible observing time over the course of a trimester If a project cannot meet this guideline the PI is encouraged to increase observing opportunities by enlisting additional observers who are qualified for remote obse
107. 01 0 14 5 2 Status clear State Ready 20 45 35 cate 23 4 508 ons 018 009 Gate 10 22 0 05 0 11 0 13 Figure 14 3 The 4mm Receiver CLEO window Users can manual move the wheel by using the Desired Position button The temperature of the ambient load used for calibration is given by the Ambient temperature sensor value shown at the right 277 83 K in this example 14 3 3 AutoOOF Thermal Corrections Optimal point source observations should be carried out with regular AutoOOF measurements every 2 4 hours during the nighttime when the thermal stability of the dish is best Based on commissioning tests with the 4mm receiver the AutoOOF corrections improves the point source aperture efficiency by 30 5096 Application of these corrections during the day are typically not practical for the 4mm receiver given the thermal environment of the dish is generally not sufficiently stable During the day the measured beam sizes can vary significantly e g 10 14 but the beam shape typically remains well behaved fairly symmetric and Gaussian Although the variation of beam size has a direct impact on the point source aperture efficiency 7 it has less of an impact on the effective main beam efficiency r5 used for the calibration of extended sources For example during the commissioning of the instrument we measured beam
108. 1 E cede followed by a short vertical space more header information and then the date the time and a pair of coordinates for an Ephemeris as shown below Optional parameters are coordinate rates geocentric distance and geocentric radial velocity 96 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS xk ok OK K K K ok ok ok ok ok K K K K 2K OK ok oe K ok K FK OK OR oe K K K I K I a 2K a FK FK FK FK FK I a I a K a K a aK aK aK aK K ak K ok K K FK FK oe ok ak ok ak ok ak ak K ak ok ak K K Ephemeris WWWUSER Wed May 9 13 53 04 2012 Pasadena USA Horizons SKK K OR ok ok OR OK k k ok ok K K K K OR K K K K K K GI ok ok OO K K K K K K K ok ok OO IK IG IG I K K K K I K K K K K K 3k ak ok ak ok ak ok ak ok Target body name 103P Hartley 2 source JPL 183 Center body name Earth 399 source DE405 Center site name Green Bank GBT FKK K K ROR 2K 2K ok ok OK FK ok oe ok ok ok ok ok K K K OK 2K 2K K ok oe FK K a ok a FK oe ok K K I K aK 2K aK ok aK a FK aK K aK FK aK FK ak K K K K a K oe ok ak ok ak FK ak ak ak ak ak ak ok ak ok ak ok Start time A D 2012 May 09 00 00 00 0000 UT Stop time A D 2012 Jun 08 00 00 00 0000 UT Step size 1440 minutes kk KK ok KOK ok K K ok K K ok oko KOK ok oko ok OK ok K 2K ok K K ok oko ok K K ok oko ok 2K FK ok K K ok K K ok 2K FK ok K K ok K K K 2K FK ok K K FK K K K koe K K K K K K K K
109. 1 South Option 1 Take l 81 South for 3 miles exit at Strasburg exit 296 to Route 55 Stay on Route 55 through Wardensville WV Moorefield and Petersburg then Rt 28 South to Green Bank From Washington DC Via l 66 West to l 81 South Option 2 Take l 81 South to Harrisonburg exit 247 take the truck bypass around Harrisonburg to US 33 West Take US 33 West through Franklin then take Rt 28 South at Judy Gap to Green Bank Figure 18 1 Direction to Green Bank From Charlottesville Richmond Via l 64 West to Staunton then l 81 North for 3 miles to Exit 225 Woodrow Wilson Parkway Take the Parkway around Staunton to US 250 West Stay on US 250 West to Monterey VA At Monterey take Rt 220 South 3 5 miles to Rt 84 West Take 84 West to Frost WV At Frost take Rt 92 North to Green Bank 206 CHAPTER 18 PLANNING YOUR OBSERVATIONS AND TRAVEL Pittsburgh to Green Bank From the Greater Pittsburgh International Airport go east on route 60 to US 22 30 Follow 22 30 east to Interstate 79 Take I 79 south through Clarksburg WV to the US 33 exit exit 99 near Buckhannon WV Go east on US 33 through Buckhannon to Elkins WV Turn south on US 250 219 to go to Huttonsville In Huttonsville take US 250 route 92 southeast to Bartow Follow route 92 28 south to Green Bank Washington Dulles or National to Green Bank From the Washington Dulles International Airport go south on route 28 to Interstate 66 Fro
110. 13 2 Preparing for and Cleaning up after Observations Your GBT friend or support staff will have MUSTANG tuned up and ready to go at the start of your run These settings should have been saved to home gbt etc config mustang config current conf From a terminal s on a 32 bit machine on the gbt network As for other GBT observations start ASTRID and CLEO Within CLEO select Launch Receivers MUSTANG The housekeeping tab is most useful to have up during observations Start the MUSTANG data monitor To do this first source home gbt gbt bash or source gbt csh if using C shell Then type mustangdm e Run the mustanginit scheduling block SB This scheduling block sets up ASTRID and performs basic initialization of MUSTANG e Run the TweakTargets and FindBestBiases SBs in that order These SB s find and set usable detector biases and optimize the SQUID tuning they will require about 5 minutes to execute e Run savetuning SD This will save the tunings so that they can be restored if needed later e Collect a cal file to check that everything is in working order using the calandblank SB This will collect two scans one with the cal diode flashing on and off to check for optical responsivity and one file with the cal off the check detector noise Fire up the MUSTANGIDL GUI and check the cal data as described in 8 e Proceed with observing as described in 8 As the last scheduling block SB in your program please ru
111. 1500 0 in MHz backend GUPPI bandwidth 800 in MHz 100 200 or 800 search mode script 80 for 100MHz Linear for no cals RevrA 6 EU 0 for gt 100MHz BW modes tint 40 96e 6 sample time in seconds very flexible swmode tp_nocal for cals tp_nocal noisecal off if no cals set to off else The following are boilerplate until guppi section You should probably not change them swtype swper 0 04 swfreq 0 0 0 0 nwin 1 deltafreq 0 vlow 0 vhigh 0 vframe topo vdef Radio GUPPI specific params ji obsmode can be search fold cal or coherent cal guppi obsmode search coherent search numchan can be a power of two between 64 to 4096 guppi numchan 2048 coherent fold 148 CHAPTER 11 PULSAR OBSERVING WITH GUPPI 11 3 Balancing and Checking Levels Before balancing the system you must configure it for your observing set up as described above Once that is done slew to your source of interest using the Slew command and then issue a Balance command Note that these can and should all be included in the same scheduling block Once the system has finished balancing you should run the guppi adc hist command on beef As the name implies this will plot two histograms one for each polarization channel of the data
112. 2004 Jun 13 46 25 52 2004 Jun 13 40 46 26 06 2004 Jun 13 pal ye 46 26 2004 Jun 13 50 3010522 T 757540 758070 758760 759620 760650 761850 763220 764740 Oo OO OO OO OO OO OO OO Here is an example for tracking a satellite PRN14 tracking table angles in degrees visible 01 30 to 3 00 UT format ephemeris name PRN14 coordmode azel head date utc AZ 2004 05 16 01 30 06 103 1822 2004 05 16 01 30 14 103 2464 2004 05 16 01 30 22 103 3105 2004 05 16 01 30 30 103 3745 6 2 COMPONENTS OF AN OBSERVING SCRIPT 93 Comets Tracking a comet which does not track at the sidereal rate will require the use of an external file generated from the NASA JPL Horizons website which holds a database of all the orbital parameters of all major and minor bodies in the solar system First you must download the ephemeris file for your object of interest from the website http ssd jpl nasa gov horizons cgi Then you will have to convert the file into the CATALOG format for astrid When you go to http ssd jpl nasa gov horizons cgi you should see something like what is shown in Figure 6 2 California Institute of Technology Near Earth Object NEO Project JPL HOME ERW O SOLAR SYSTEM STARS amp GALAXIES TECHNOLOGY Jet Propulsion Laboratory View the NASA Portal Search JPL HORIZONS Web Interface This tool provides a web based limited interface
113. 40 26 0 31 0 30 5 37 0 36 0 40 0 Revr40_52 40 5 47 0 Rcvr PAR 80 0 100 00 Mustang Bolometer Array NoiseSource N A 62 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS Table 6 2 backends Name Notes The Digital Continuum Receiver directly from the One frequency available DCR_AF The Digital Continuum Receiver from the Four two frequencies maximum for single dual beam receivers VEGAS Spectral line backend with up to 524288 channels and 64 frequencies with large bandwidths VLBA_DAR Very Long Baseline Array Data Acquisition Recorder Radar For bi static radar observations Private backend GUPPI Green Bank Ultimate Pulsar Processor CCB CalTech Continuum Backend Zpectrometer Wide band Spectrometer Table 6 3 Bandwidths for Very Long Baseline Interferometer VLBI and Radar backends Backend Receiver Possible Bandwidths MHz VEGAS Any IDCR VLBI or Radar Prime Focus 20 40 80 240 DCR VLBI or Radar 1 2 Revr4_6 Revr8_10 Revr12_18 20 80 320 1280 DCR VLBI or Radar Revr2_3 RevrArray18_26 Revr40_52 80 320 1280 Any 12 5 50 200 800 Keywords With Default Values swmode This keyword specifies the switching mode to be used for the observations This keyword s values are given as a string Values are tp total power with cal tp_nocal total power without cal
114. 95 Frequency GHz Figure 14 1 The derived main beam nmb and aperture na efficiencies from 2012 are given by the solid and dotted line respectively These estimated efficiencies are based on measurements made after an AutoOOF and the a values are slightly less than expected measurements correspond to surface errors of 280um instead of the advertised 240um errors for the dish The squares and diamonds show the measured system temperatures for the original amplifiers 2012 June and the upgraded amplifiers 2012 December respectively Both sets of data were collected under similar conditions with 7 0 2 at 86 GHz e receiver Rcvr68_92 name of the receiver e beam B12 B1 or B2 dual beam receiver e swmode tp nocal or sp_nocal There are no noise diodes with this receiver polarization linear or circular Default is linear If user selects circular then the 1 4 wave plate is placed in front of the chosen beam There is only one 1 4 wave plate so users can have circular polarization for only one of the beams 14 3 Observing In general observations should be carried out during the night under stable thermal conditions to max imize the observing efficiency for targets smaller or similar in size to the beam 10 During the daytime the effective point source aperture efficiency decreases significantly since the beam shape in creases in size Depending on the science goals successful d
115. ANG IDL GUL GUI text output window Since an elliptical Gaussian is used there are two parameters for the width The imaging routines produce diagnostic feedback primarily intended for support staff Many IDL routines also produce a floating point exception which can be safely ignored In the unlikely event that the beam degrades AutoOOF does not fix it and you have acquired parFocusDaisies data to check it you may enter the scan numbers of the focus maps in the Focus list box Each scan will be imaged and fit to a Gaussian and the beam width and amplitude as a function of focus offset LFC will be plotted Choose the LFC that minimizes the beamwidth and maximizes the source response and enter this into the Antenna Manager CLEO screen or have the operator do so The amplitude does not always peak at the same focus position that minimizes the beam shape but it should be within a few millimeters Choose a focus position that for your purposes is a good compromise between these two In the lower beam width or FWHM plot the two widths are represented by a dot and a diamond Therefore a circular beam which is a good indication of being in focus will correspond to the dot and the diamond coinciding This is illustrated in Figure When processing focus data note that it can often take up to a minute for the most recently completed scan to become readable on the filesystem so exercise some patience when processing your data on line Y
116. Continuum and Spectral Line data are only updated when these displays are being viewed Pointing and Focus data are always automatically updated whether or not their displays are being shown or not The list of scans will always automatically update 37 38 CHAPTER 5 NEAR REAL TIME DATA AND STATUS DISPLAYS 5 1 2 Working Offline You can look at data that have already been taken with the by running in its offline mode To view data in this mode you need to follow these steps Step 1 Change the mode to offline see 84 2 4 Step 2 Select the Data Display Tab Step 3 Go to the menu bar click on File and then Open A dialog window will appear containing all of the project directories in home gbtdata Select your project from the list Once you have entered the directory for that project double click on ScanLog fits to access your data Step 4 Depending upon how much data you have in your project it will take several seconds to a few minutes to access all of your scans The load process is complete when you see the list of your scans displayed sequentially on the left hand side of the display Step 5 Click on a scan in the scan list window to process it 5 1 3 Pointing and Focus Data Display We will describe the details of pointing and focus observations in Chapter 6 8 6 2 3 1 Pointing scans from Peak AutoPeak and AutoPeakFocus see below will appear under the Point ing Tab The data display will automatically
117. Display Log 1 GbtStatus Log 1 pol RALongMap pol RALongMap 32 Plot Color Scan Int Beam Pol IF Phase Sampler Source Procedure Major Minor Epoch El deg TSys K Ctrfq MHz red 313 0 1X 0 o A9 pol RALongMap 33 121 63854 24 349895 GALACTIC 39 319 17 247 1 420e 03 green 313 io o A13 pol RALongMap 33 121 63854 24 349895 GALACTIC 39 319 16 855 1 420e 03 17 289 1 420e 03 17 007 1 420 03 32 128 35850 24 291565 GALACTIC 850 24 291565 GALACTIC Command Console Observation State GBT State GBT Status Queue Control Halt Queue Observation Control Pause Stop i Abort Interactive Idle Offline Figure 5 11 The Data Display Tab showing spectral line data As spectra are plotted information about each plot is printed in the console window Each line is color coded to match the color of that spectrum in the plotting window the information for the very first spectra are used to annotate the plot The plot title is parsed as project name scan_number integration_number In addition some of 5 1 THE ASTRID DATA DISPLAY TAB AT The options panel also includes three buttons and a radio box for plot viewing The Views radio box offers options for plotting the bandpass vs Channels and the bandpass vs Sky Frequency for all backends In addition Spectrometer data will include the option to display the raw auto correlation lags
118. E keyword in the HEAD line since we have sources whose positions are given in different coordinate modes J2000 and B1950 VEL or VELOCITY The radial velocity in km sec The Default is to use any previous setting or 0 0 if there is none VELDEF Velocity definition in the FITS convention see https safe nrao edu wiki bin view GB Data VelDefFits e g VOPT BAR VRAD LSR etc The default is the velocity definition or reference frame that was previously set In the above example we put the VELDEF keyword in the HEAD line since we have sources whose velocity definitions are different RESTFREQ The rest frequency in MHz The default is to use the previous setting Again we put the RESTFREQ keyword in the HEAD line since we are defining two different spectral line rest frequencies for each source RA HA DEC AZ EL GLON GLAT A pair of coordinates must be given RA DEC HA DEC AZ EL or GLON GLAT Angle formats may be either in sexegesimal with colons e g dd mm ss ss or in decimal format RA and HA are in hours all other angles are in degrees EQUINOX Used if the Coordmode is MEAN The value is a float e g 2006 December 1 12 00 UT would be 2006 919178082192 An example of the use of the EQUINOX Catalog Header Keyword is 88 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS Additional keywords used when the Ephemeris format is active are see 8 6 2 4 6 for examples DATE The UTC date either
119. F Power 10 and special care should be taken in calibration of such data The target power level for w band is 1 5 and the software adjusts the attenuation to reach this level If the channel s are saturated with maximum attenuation 31dB users can decrease the bandwidth of the observations e g avoid using All Pass or choose a smaller filter to decrease the power levels If the channels s do not have enough power with the no attenuation 0dB users can increase the filter bandwidth or choose All Pass to increase the power levels In general manual changes of the default configuration values for the IF rack should not be needed for most configurations e Users must run the CalSeq procedure to calibrate the data see 8 14 3 1 During the calibration sequence users can watch the movement of the calibration wheel from the Rcvr68 92 cleo page Figure 14 3 14 3 1 CalSeq The CalSeq procedure is used to calibrate w band data This procedure should be run after every configuration and balance This is needed to convert instrumental voltages into antenna temperatures The syntax for the Calseq command is the following CalSeq type scanDuration location beamName fixedOffset tablePositionList dwellFraction List where the arguments in are optional e type string keyword to indicate type of calibration scan manual auto autocirc 188 CHAPTER 14 THE 4MM 68 92 GHZ RECEIVER manual A separate scan
120. Green Bank select from list of observatories Time Span put in desired values Table Settings QUANTITIES 1 3 20 i e 1 Astrometric RA amp Dec 3 rates RA amp Dec and 20 Range and range rate Display Output plain text Use the web browser file menu to save the output file as for example cometfilename txt If you give it a file name say by typing jpl2astrid jplephemfile txt it produces another file in the form for Astrid Catalogs You should verify that the first non comment line of the resulting catalog file contains FORMAT EPHEMERIS You now have a valid catalog file that Astrid will be able to use When you load the catalog into Astrid make sure you have the correct path and that the name of the comet is exactly what is in the astrid catalog file in quotations The catalog file should look something like this FORMAT EPHEMERIS VELDEF VRAD TOP COORDMODE J2000 HEAD date utc ra dec dra ddec vel 1 soln ref JPL 183 NAME 103P Hartley 2012 May 09 01 00 12 08 15 24 08 46 51 6 12 8622 11 3666 25 4420 2012 May 09 01 05 12 08 15 17 08 46 50 7 12 8638 11 3674 25 4507 2012 May 09 01 10 12 08 15 10 08 46 49 8 12 8651 11 3682 25 4595 2012 May 09 01 15 12 08 15 03 08 46 48 8 12 8663 11 3690 25 4683 For long tracks it is suggested to use OffOn position switching to minimize possible baseline effects For shorter tracks 15 20mins it is possible t
121. HEDULING BLOCKS AND OBSERVING SCRIPTS Table 6 5 Recommended lengths and times for performing peak and focus observations Peak Focus Band Av Beam Focus Length Time Length Time Notes MHz MHz FWHM Beam FWHM sec mm sec 340 20 36 1 3 2m 180 30 415 20 30 1 2 6m 180 30 A C 680 20 18 1 1 6m 90 15 A C 770 20 16 1 1 4m 80 15 A C 970 20 13 1 1 1m 65 15 A C IL 1400 80 8 8 1 76cm 130 30 480 60 B D E 2000 80 6 2 1 54cm 90 30 480 60 B D E 5000 80 2 5 1 22cm 40 30 480 60 B D E 9000 80 1 4 1 12cm 20 30 480 60 B D E 14000 320 53 1 76mm 18 30 320 60 B D F 25000 800 30 1 43mm 10 30 240 30 B D F 32000 320 23 1 32mm 8 30 180 60 B D F 43000 320 17 1 25mm 6 30 120 60 B D F 77000 320 10 1 14mm 3 30 120 60 B D A Prime Focus Peak Lengths are chosen to be 5 x with a scan time of 15 seconds to have good sampling across the beam B Gregorian Focus Peak Rates are chosen to give 2 seconds across the FWHM Peak Times to give a scan time of 30 seconds to allow vibrations to settle C Prime Focus Axial focus measurements are not recommended for prime focus receivers since the gain changes only slightly over the entire focus range D Gregorian Focus The optimal focus length is 2 x but to allow for varying baseline we currently recommend 3x focus FWHM plus 40mm at each end to
122. ING SCRIPTS the size of the map along the major axis majorSize Offset Galactic 5 0 0 0 5 degrees in galactic longitude the size of the map along the minor axis minorSize Offset Galactic 0 0 5 0 5 degrees in galactic latitude the size between two rows of the map rowStep Offset Galactic 0 0 0 05 3 arcminutes expressed in degrees the time to scan each row time majorSize rowStep integration time per pixel scanTime 5 0 0 05 2 2 seconds per pixel row start and stop number only do part of the map here rowStart 10 rowStop 20 now observe for the map RALongMap srcs majorSize minorSize rowStep scanTime start rowStart stop rowStop 6 2 7 5 Position Switched Pointed Map In this example we perform position switched observations to map a 0 5 by 0 5 degree region of the sky We use pixels that are arc minutes in size and have an integration time of 120 seconds per pixel We observe the reference Off position after every second point in the map This example is available as home astro util projects 6D01 example five py Position Switched Observations where we repeatedly observe the same source first we load the configuration file and the catalog file execfile home astro util projects 6D01 configurations py Catalog home astro util projects 6D01 sources cat jii now we configure the IF sys
123. It specifies the stopping point for the map The default value for stop is None which means go to the end The following example does a 4x4 point map using beam C that moves to a reference source every 2 points PointMapWithReference 202342223 map center location Offset B1950 1 50 0 00 cosv True 9 Offset B1950 0 00 1 50 cosv True 9 Offset B1950 0 50 0 00 cosv True 3 3 arcmin cos dec size arcmin of deg size arcmin cos dec step Offset B1950 0 00 0 50 cosv True arcmin step spacing Offset J2000 3 00 3 00 cosv True ffset reference dist 25 reference every 2nd pnt 2 0 2 seconds per point 0 0 0 0 Point Map A PointMap constructs a map by sitting on fixed positions laid out on a grid It is similar to PointMapWithReference except that it does not make periodic observations of a reference position Syntax PointMap location hLength vLength hDelta vDelta scanDuration beamName start stop PointMap does not have referenceInterval as a parameter otherwise it is the same as PointMap WithReference See PointMapWithReference for information on the parameters for PointMap RALongMapWithReference A Right Ascension Longitude RALong map performs a raster scan centered on a sky location Scans are performed in the right ascension longitude or azimuth coordinate depending on the desired coordinate system This sc
124. J 6 sult 1420 5578663084418 804 2 This uses a custom made procedure Prrack which allows setting trying 10 nun makepalyco Juy 8 the cals onor off and also allows tracking urti the source sets 7 01 22 01 25 56 73 2007 01 22 23 20 12 82 80158146 July 26 5 80458446 July 27 our observing script is syntactically corect H H 458446 May 14 1 11 Define generic names here that way you only have to Observing Scripts reseed May 18 11 12 change the settings here in order to observe differen End Validation 2007 01 22 13 18 58 20 13 sources with the same script Saved in Astrid 80458446 May 2821 ga Database 80159 46 May 3 1 c You are currently editing 01 05 2007 1506 55 zor Save to Datahase Delete from Database Import fram File Fxpart to Fite Validate Export Observation Log Opeians 4 Commern Trace C Export Log ObservanonManagemer Log 1 DataDisplay Log 1 GbtStatus Log 1 Command Corsale Figure 4 5 The Observation Management Edit Tab 4 3 1 1 Project ID and List of Observing Scripts When you first go to the Edit Tab you will select your project name using the pull down menu in the upper left part of the Edit Tab under the window labeled Project You may also just type in the 4 3 THE OBSERVING MANAGEMENT TAB 29 project code Your project name is the code that your proposal was given After doing this you will see in the window labeled Sc
125. N TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS swper 1 0 tint M vlow vhigh vframe vdef Radio noisecal lo pol meu es nchan low bleh ie The configuration has the name vegas nod config and can be used for spectral line observations obstype Spectroscopy using nodding observations swmode tp swtype none with the multi beam KFPA 18 to 26 5 GHz beams 1 and 2 receiver receiver RevrArray18_26 beam 1 2 and VEGAS as the backend without cross polarization products backend VEGAS We wish to take data on multiple spectral lines awin 4 each having a 100 MHz bandwidth bandwidth 100 with the lowest value for the number of spectral channels nchan low Each spectral window will be centered on the rest frequencies of the lines at 23694 495 23722 633 23870 129 and 25056 025 MHz restfreq 23694 495 23722 633 23870 129 25056 025 We wish the cycle time to go through a full total power switching cycle of 1 second swper 1 0 We want VEGAS to record data every 30 seconds tint 30 We wish to Doppler track the spectral lines with rest frequency 23694 495 MHz default is first specified rest frequency in the commonly used Local Standard of Rest velocity frame vframe lsrk vdef Radio We would like to use the low power noise diode noisecal lo Finally we wish to take the data using circular polarization pol Circular Multi
126. T project Friend to ensure that observing scripts are properly and promptly prepared e Enabling each session by clicking the enable button on the project s web page Sessions should be enabled only if they will be ready for observing in the next 24 hours e Ensuring that all associated observers have provided contact information including a current telephone number and an email address for each observer e Ensuring that a project s scheduling information is current This includes checking the hours remaining on the project and ensuring that the session parameters are up to date and accurate e Ensuring that each scheduled telescope period has an observer who is available at least 30 minutes before the session is scheduled to begin Observers are responsible for e Ensuring that the DSS project web page has their current contact information For remote ob servers this includes entering telephone numbers where they can be reached at the time of obser vation e Contacting GBT operations 30 minutes prior to the start time of an observation e Attending to observations during a scheduled telescope period e Notifying GBT operations if they find conditions unsuitable for their session 3 8 Remote Observing To use the GBT remotely observers must first be trained and certified by Green Bank staff In general astronomers must observe at least once in Green Bank before being certified for remote observing Please note that students shou
127. Target pole equ No model available Target radii 0 8 km Center geodetic 280 160200 38 4331406 0 8751417 E lon deg Lat deg Alt km Center cylindric 280 160200 5003 37558 3943 7589 E lon deg Dxy km Dz km Center pole equ High precision EOP model East longitude Center radii 6378 1 x 6378 1 x 6356 8 km Equator meridian pole Target primary Sun source DE405 Interfering body MOON Req 1737 400 km source DE405 Deflecting body Sun EARTH source DE405 Deflecting GMs 1 3271E 11 3 9860E 05 km 3 s 2 Small perturbers Ceres Pallas Vesta source SB405 CPV 2 Small body GMs 6 32E 01 1 43E 01 1 78E 01 km 3 s 2 Atmos refraction NO AIRLESS RA format HMS Time format CAL EOP file eop 120508 p120730 EOP coverage DATA BASED 1962 JAN 20 TO 2012 MAY 08 PREDICTS 2012 JUL 29 Units conversion 1 AU 149597870 691 km c 299792 458 km s 1 day 86400 0 s Table cut offs 1 Elevation 90 0deg NO Airmass gt 38 000 NO Daylight NO Table cut offs 2 Solar Elongation 0 0 180 0 NO FOI ik kk kk kok Initial FK5 J2000 0 heliocentric ecliptic osculating elements AU DAYS DEG EPOCH 2455456 5 2010 Sep 17 0000000 CT Residual RMS 40404 EC 6951452964967095 QR 1 058690085281137 TP 2455497 756967203 OM 219 7626609177958 181 1954811299036 IN 13 61716956119923 Comet physical amp dynamic parameters KM SEC A1 A2 A3 AU d 2 DT days
128. The Keep Zoom toggle button will maintain the current zoom even as new spectra are plotted Using the unzoom command mouse right click or viathe tool bar will return the plot to its original scale The Overlay toggle button can be used to overplot spectra from different integrations or scans Finally the Clear button erases the plot 5 1 7 Creating PNG and Postscript Plots Note that the Print option in the File menu and the printer item in the toolbar do not work Instead you select the export option or the E uparrow symbol in the toolbar You can create postscript encapsulated postscript or PNG copies of the plots displayed To do this Step 1 Select the Data Display Tab Step 2 Display the data for which you would like a plot Step 3 Click on the plot button This button has an E followed by and up arrow see Figure 5 12 Step 4 Select the directory in which to save the file Step 5 In the pop up window see Figure 5 13 enter the desired file name for the plot The name must have an extension of either png ps or eps Step 6 Hit the Save button Figure 5 12 The Astrid Data Display plot button Save Plot Name Save in folder gt Browse for other folders Figure 5 13 The Astrid Data Display pop up plot window 48 CHAPTER 5 NEAR REAL TIME DATA AND STATUS DISPLAYS 5 1 8 Use of Plotting Capabilities A User Manual is available at http deap sourceforge net help index html that descr
129. U S government to provide protection from RFI Ortho Mode Transducer OMT This is part of the receiver that takes the input from the wave guide and separtes the two polar izations to go to separate detectors PulsaR Exploration and Search TOolkit PRESTO A software package used to analyze pulsar observations Mainly used for spigot card data p Radio Frequency RF The frequency of the incoming radiation detected by the GBGT 6 Radio Frequency Interference Light polution at radio wavelengths 112 Telescope Allocation Committee TAC The group that decides how much observing time your proposal will get Two Line Element TLE 85 08 Very Long Baseline VLB A general acronym for VLBI or VLBA Very Long Baseline Array VLBA An interferometer which unconnected elemets run by the NRAO Very Long Baseline Interferometer VLBI The use of unconnected telescopes to form an effective telescope with the size of the separation between the elements of the inteferometer Virtual Network Computer VNC A GUI based system that is platform independent that allows you to view the screen of one computer on a second computer This is very useful for remote observing 9 232 List of Acronyms Glossary The number of air masses along the line of sight One air mass is defined as the total atmospheric column when looking at the zenith Analog Filter Rack A rack in the GBT IF system that provides contains filter
130. ab provides a real time display of your GBT data so that you can check that you are getting valid data The Data Display is actually running an application called GBT Fits Monitor This application provides sub scan based display and analysis of GBT data either in real time as the data is being collected or in an offline mode where it can be used to simply step through the sub scans from an observation Users are encourage to run GFM offline for reanalyzing data during observations A separate application can be launched from the Linux prompt via the gfm command or astrid could be switched to offline mode Some of the features of are e Automatically detects the type of scan observing e g Focus Pointing Spectral Line and calls the relevant analysis modules e Knows how to handle groups of scans properly for example the four scans within a pointing obser vation e Supports multi beam dual polarization multiple and multiple phases e Supports dynamic focus corrections e Graphics export to Portable Network Graphics PNG and Postscript PS and EPS formats is sup ported e Playback feature allows you to quickly review the plots within a range of sub scans Playback should be done in offline mode while observing 5 1 1 Working Online If you are using Astrid s online or monitor mode and have selected the DataDisplay tab then the data display will update as new data are obtained
131. able to their science goals The DSS readily accommodates remote observing but by being on site in Green Bank observers increase their likelihood of being scheduled during the period of their visit Visits to Green Bank should be arranged in advance with the project s Friend and observers should ideally spend one two weeks in Green Bank to give enough opportunity for their project to get scheduled at least once Projects observing at high frequencies 20 GHz and higher typically require staying in Green Bank for two weeks or longer 3 2 DSS Terminology The process of scheduling GBT observations begins with the preparation of the proposal using the NRAO Proposal Submission Tool PST Proposals accepted by the NRAO Time Allocation Committee become GBT projects that appear in the DSS system and are identified by an assigned project ID e g GBTO09C 001 Projects are divided into sessions which have associated parameters that define how the observation should be scheduled These parameters include sky position time allocated observing frequency and 11 12 CHAPTER 3 INTRODUCTION TO THE DYNAMIC SCHEDULING SYSTEM minimum and maximum durations preferred for a single contiguous block Sessions for monitoring observations have additional parameters describing how often to repeat the observation The project investigators initially define the session parameters in the proposal but the parameters may be modified during the refereeing proce
132. actual instrument configuration but are necessary to set up internal variables and insure the recorded FITS files are accurate The following keywords configure the CCB itself The meaning of these keywords is as follows e The first four specify the cal firing pattern e ccb bswfreq specifies the beam switching frequency in kHz 4 kHz is standard the gt 10 blanking warning which results is also standard and may be safely ignored e tint is the integration time in seconds 12 1 OBSERVING WITH THE CCB 159 12 1 2 Pointing amp Focus The online processing of pointing and focus data is handled by GFM which runs within the Astrid Data Display window similarly as for other GBT receivers and the DCR A few comments e because the Ka band receiver currently only has one polarization per beam GFM will by default issue some complaints which can be ignored These can be eliminated by choosing Y Right polarization in the Astrid Data Display window see Chapter 5 section under Tools gt Options gt Data Processing e in the same menu Tools gt Options gt Data Processing choosing 31 25 GHz as the frequency to process instead of the default 38 25 GHz can improve robustness of the result e The results shown in the Astrid Display are in raw counts not Kelvin or Janskys e Choosing Relaxed heuristics is also often helpful There is a template pointing and focus SB for the CCB in users
133. afreq 0 vegas vpol cross restfreq restfreq 24000 beam 1 2 3 4 restfreq 25000 beam 1 restfreq 23400 beam 5 6 7 Y 97 The configuration has the name vegas kfpa aconfig and can be used for spectral line observations obstype Spectroscopy using cal switching observations swmode tp swtype none with the multi beam 18 to 26 5 GHz all beams receiver receiver RevrArray18_26 and VEGAS as the backend with cross polarization products backend VEGAS vegas vpol cross The bandwidth used is 187 5 MHz bandwidth bandwidth 187 5 with the lowest value for the number of spectral channels 32768 nchan low We wish the cycle time to go through a full total power switching cycle of 1 second swper 1 0 We want VEGAS to record data every 30 seconds tint 30 All delta frequencies are set to 0 deltafreq 0 for this observation We wish that beams 1 2 3 and 4 have a rest frequency of 24000 that beams 5 6 7 have a rest frequency of 23400 and the 2nd beam 1 IF band has a rest frequency of 25000 We wish to Doppler track the spectral lines with rest frequency 25500 0 MHz in the commonly used Local Standard of Rest velocity frame vframe lsrk vdef Radio We would like to use the low power noise diode noisecal lo Finally we wish to take the data using circular polarization pol Circular configuration d
134. akcatalog Save to Database Delete from Database import from File Export to File Validate Observation Lag Options Comment Trace Export Lag ObservationManacement Log 1 Figure 4 4 The different components on the GUI GUI The Real Time Mode option allows you to change between the operational modes of Edit Under the Edit drop down menu you will find standard Windows View cut and paste options The options under the View drop down menu allow you to turn on or off the display of the drop down menus and the toolbar You can also toggle between having the Astrid GUI taking up the full screen or not Tools The Tools drop down menu is only active when the Data Display Application is being shown in the Astrid GUI You can zoom and pan within the data plots shown in the Data Display Application using the Tools drop down menu You can also change the Fitting Heuristics used during the reduction of Pointing and Focus observations see 8 5 1 3 2 4 2 HOW TO START ASTRID 25 Help Under the Help drop down menu you can bring up documentation for some but not all Applications 4 2 2 2 Toolbar The Toolbar is located just under the Drop down Menus near the top of the Astrid GUI The contents of the Toolbar change depending on which Application is being displayed in the Astrid GUI The Toolbar options are a subset of commonly used options from the Drop down Men
135. allow for the fact that focus measurement is done with respect to to focus tracking curve not last offset The Focus Rate is then chosen to give a 60sec scan time This is a trade off between completing the focus scan quickly and allowing any potential scan start anomalies to die away E At L through the focus rates and lengths are conservative limits set by subreflector hardware the absolute maximum would be 600mm min and 600mm F At and higher frequencies the peak length is rather larger to accommodate the beam separation in azimuth for these multi beam receivers location A Catalog source name or Location object It specifies the source upon which to do the scan hLength An Offset object It specifies the horizontal distance used for the Peak The default value is the recommended value for the receiver see Table 6 5 vLength An Offset object It specifies the vertical distance used for the Peak The default value is the recommended value for the receiver see Table 6 5 scanDuration A float It specifies the length of each scan in seconds The default value is the recom mended value for the receiver see Table 6 5 beamName A string It specifies the receiver beam to use for both scans beamName can be C 1 2 8 4 or any valid combination for the receiver you are using such as MR12 and MR34 The default value is the recommended value for the receiver If you configure for one beam and point
136. alue can be either positive or negative It should be noted that if any new attenuator setting is less than zero or exceeds the maximum value 31 for the IF Rack and 31 875 for the Converter Rack then the attenuator settings is made to be the appropriate limiting value Examples of the usage of ChangeAttenuation are ChangeAttenuation IFRack 1 0 ChangeAttenuation ConverterRack 0 5 6 2 6 Observing Script Objects Observing Script Objects are python objects that are used to contain multiple pieces of information within a single variable These are used with positions requiring a major and minor axis value along with an epoch times requiring the date and the time of day and for defining a horizon for the minimum elevation below which you would not want to observe 6 2 6 1 Location Object A Location object is used to represent a particular location on the sky Locations can be specified in the following coordinate modes J2000 B1950 RaDecOfDate HaDec ApparentRaDec Galactic AzEI and Encoder A Location is specified by two values the meanings of which are dependent on the coordinate mode chosen e g For J2000 the two values are time and degrees location Location J2000 16 30 00 47 23 00 Coordinates may be given in sexagesimal as a quoted string i e hh mm ss ss or as a floating point number in degrees For more information about Locatio
137. alue is the decimal hours since midnight An example of the use of GetUTC is while GetUTC lt 12 0 Track 0353 2234 None 600 which will repeatedly perform Track scans until the UTC time is past 12 0 hours 6 2 COMPONENTS OF AN OBSERVING SCRIPT 101 6 2 5 6 GetLST The GetLST function returns a float representing the current Local Sidereal Time at the time of execution The returned value is the decimal hours An example of the use of GetLST is while GetLST 13 5 Track 1153 1107 None 600 Track 1712 036 None 600 which will repeatedly observe the source 1153 1107 until the LST is past 13 5 hours when the source 1712 036 will be observed once 6 2 5 7 Now The Now function returns the current time as a UTC time object see 6 2 6 4 containing the UTC time and date An example of the usage of Now is while Now 2006 03 12 09 54 12 and Now None Track 1153 1107 None 600 which repeatedly performs Track scans of the source 11534 1107 until 09 54 12 UTC on 12 March 2006 Note that the while statement also checks that the returned value of Now is not None This is to ensure that Astrid does not get stuck in an infinite loop during validation when Now will always return a value of None 6 2 5 8 WaitFor The WaitFor time function pauses the scheduling block until the specified time is reached e g WaitFor 15 13 00 LST
138. an make travel plans and connections to Charlottesville whenever possible Transportation will then be available between the NRAO Charlottesville Headquarters office and Green Bank A GSA vehicle will usually be available at the NRAO Edgemont Road Office Building at Charlottesville for you to drive to Green Bank Plans to use the GSA vehicle should be arranged with Jessica Taylor in Green Bank 304 456 2227 email jtaylor nrao edu If you do not have your own transportation or cannot make connections through Charlottesville alternate arrangements may be made with Jessica Taylor 18 4 Housing The NRAO operates a residence hall where astronomers may stay while observing or reducing data after completion of their observations Single rooms 2 beds are available for 48 00 tax a day single occupancy or 30 00 tax per day per person double occupancy Students attending a degree conferring college or university and coming to Green Bank to use the telescope will pay single room rate 40 00 tax or 25 50 tax per day per person double occupancy In addition there are four one bedroom apartments with equipped kitchens at 72 00 tax per day Cribs high chairs and fold up beds are also available Costs of lodging in NRAO facilities can be waived on request in advance and on approval of the Site Director 18 5 Getting To Green Bank 18 5 1 Where is Green Bank A map showing the location of Green Bank relative to major nearby towns and cit
139. an type does allow the user to periodically move to a reference location on the sky please see RALongMap for a map that does not use a reference The starting point of the map is defined as hLength 2 vLength 2 Syntax RALongMap location hLength vLength referenceOffset referenceInterval scan Duration beamName unidirectional start stop The parameters for RALongMapWithReference are location A Catalog source name or Location object It specifies the center of the map hLength An Offset object It specifies the horizontal width of the map i e the extent in the longitude like direction vLength An Offset object It specifies the vertical height of the map i e the extent in the latitude like direction 6 2 COMPONENTS OF AN OBSERVING SCRIPT 83 vDelta An Offset object It specifies the distance between map rows Note that vDelta values must be positive referenceOffset An Offset object It specifies the position of the reference source on the sky relative to the Location specified by the first input parameter referenceInterval An integer It specifies when to do a reference scan in terms of map rows e g 4 means every fourth row scanDuration A float It specifies the length of each scan in seconds beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 2 3 A or any valid combination for the receiver you are using such as 12 Defaul
140. and beam 4 with 5 See Figure 8 3 At the Converter Rack one of the two beams is selected by appropriately setting the converter rack LO frequency Beams 2 4 5 and 6 are routed to Converter Rack A and beams 1 3 and 7 to Converter Rack B This constrains certain multi beam observing modes as is described in Chapter 9 120 CHAPTER 8 GBT IF SYSTEM Note that each GBT receiver has a maximum frequency offset between spectral windows set by band pass filters in the IF path For the due to the dual use of individual optical fibers there are strong constraints on the frequency separation of the individual spectral windows The maximum spectral window separation is 1 8 GHz and the maximum offset between the spectral window and the Doppler tracking frequency is 1 0 GHz See Appendix A for more details on the syntax for describing spectral windows Chapter 9 Mapping and the Data Reduction Pipeline GBT observers who are mapping spectral lines can take advantage of a data reduction pipeline to simplify the process of generating calibrated and gridded FITS images This chapter provides advice on how to prepare and optimize mapping observations used with the data reduction pipeline Offline use of the pipeline software itself is described in the Pipeline User s Guide The pipeline was developed in parallel with the 7 beam K band Focal Plane Array KFPA project to facilitate imaging the large datasets obtained with the KFPA The pip
141. antities to generate an ephemeris 6 2 COMPONENTS OF AN OBSERVING SCRIPT 95 After clicking Generate Ephemeris you should save the file to a directory in your area in Green Bank The ephemeris file will begin with a large amount of header information as shown below FKK K K K oko 2K 2K OK OK OK OK ok ok ok ok K K K 2K K 2K K I K FK K ok OO oe K K ok I K I ok K a FK ok oe FK FK ok I a I K K a ak aK ok ak K ak K ak ak ak ak ok ak ok ak ok ak ok JPL HORIZONS 103P Hartley 2 2012 May 09 13 53 04 Rec 900856 Soln date 2010 Oct 24_11 48 36 obs 2638 84 days FK5 J2000 0 helio ecliptic osc elements AU DAYS DEG period Julian yrs EPOCH 2455456 5 2010 Sep 17 0000000 CT Residual RMS 40404 EC 6951452964967095 QR 1 058690085281137 TP 2455497 756967203 OM 219 7626609177958 W 181 1954811299036 IN 13 61716956119923 A 3 472769398388862 353 716704933 ADIST 5 886848711496587 PER 6 471755792772 N 152296581 ANGMOME 023044608 DAN 5 88393 DDN 1 05878 L 40 924547 B 2814369 TP 2010 Oct 28 2569672 Physical amp non grav parameters KM SEC A1 A2 A3 AU d 2 DT days GVE n a RAD 800 Al 7 225261D 10 2 1 525012bE 9 A3 3 798639D 10 Disney Mi 14 6 VIO Ke fm o E PHCOF 030 COMET comments 1 soln ref JPL 183 data arc 2010 Aug 01 to 2010 Oct 24 2 k1 17 k2 5 phase coef 0 03 radar 1 delay 1 Dop I ll ll ge eknu sees 1
142. any valid combination for the receiver you are using such as MR12 and MR34 The default for each receiver is listed in Table 6 5 If you configure for one beam and focus with another using the beamName parameter you can have very very bad data Make sure that if you configure with the same beam with which you Focus In the following example a focus of the subreflector is performed from 200 to 200mm at 400mm min using beam 1 Focus 0137 3309 200 0 400 0 60 0 1 Or using the defaults Focus 01374 3309 Tip The Tip scan moves the beam on the sky from one elevation to another elevation while taking data and maintaining a constant azimuth Syntax Tip location endOffset scanDuration beamName startTime stopTime The parameters for Tip are location A Catalog source name or Location object It specifies the start location of the tip scan The Location must be in AzEl or encoder coordinates endOffset An Offset object It specifies the beam s final position for the scan relative to the location specified in the first parameter The Offset also must be in AzEl or encoder coordinates scanDuration A float It specifies the length of each scan in seconds beamName A string It specifies the receiver beam to use for the scan beamName can be C center 1 2 3 4 or any valid combination for the receiver you are using such as MR12 1 track halfway between beams 1 and
143. apping observations this means that the maps will start over from the beginning if there is a problem encountered while running a script since the same script will be restarted 5 The PI must provide very explicit and concise instructions for the operators to follow These must also include an example of what all the data should look like in the Astrid Data Display tab 6 The operators will not reduce any of the data in gbtidl or using any other data reduction package 7 The project will be charged for the observing time even if the data quality is not acceptable 227 228 APPENDIX H OPERATOR RUN OBSERVING GUIDELINES List of Acronyms Active Surface AS The surface panels on the GBT whose corner heights can be adjusted to form the best possible parabolic surface Astronomer s Integrated Desktop Astrid The software tool used for executing observations with the GBT 1 9 H7 1j 52 55 P9 TOT Caltech Continuum Backend CCB A wideband continuum backend designed for use with the GBT Ka band receiver Digital Continuum Receiver DCR A continuum backend designed for use with any of the GBT receivers Federal Aviation Administration FAA The U S Government agency that oversees and regulates the airline industry in the U S Finite Element Model FEM This is a model for how the GBT support structure changes shape due to gravitational forces at different elevation angles Field Effect Transistor FET A typ
144. appropriate values are stored in the config file and simply downloaded to the hardware when the manager is turned ON 10 3 3 IF Levels and Balancing VEGAS balancing is rather similar to the GBT Spectrometer balancing The IF system from the receiver to the IF rack is balaned in the same way The VEGAS balance API then adjusts the attenuators in the converter rack to balance the power level at the inputs to the VEGAS ADCs to be by default 20dBm For VEGAS modes higher than three digital filters are implemented in the FPGA The filtered output is requantized to 8 bits a digital gain adjustment is implemented in the FPGA to scale the digital filter output values so that there will be no overflow after requantization Both of these steps are performed when the Astrid Balance directive is issued A new keyword has been added to the Balance python dictionary see appendix G which can be used to change the target input level to VEGAS for example Balance VEGAS target level 17 will set the input target level to 17 dBm for both the ADC and requantizer balannce The IF system must be able to handle the large bandwidths all the way to VEGAS which then splits the signal into the more narrow 1 25 GHz bandwidths of the individual VEGAS banks This can be problematic as part of balancing the entire bandwidth is based on the signal received by a single VEGAS bank After the correct attenuation is set at the converter module
145. apter 11 for pulsar observing with GUPPI Chapter 12 for continuum observing with the CCB and Chapter for mapping with the Mustang bolometer array Additional information and special topics are covered in the Appendices New users should read Chapters and f in their entirety They should also read the remaining Chapters as needed CHAPTER 1 HOW TO USE THIS MANUAL Chapter 2 The GBT Observing Process 2 1 Overview Of The Green Bank Telescope The 100 meter Green Bank Telescope is intended to address a very broad range of astronomical problems at radio wavelengths and consequently has an unusual and unique design Unlike conventional telescopes that have feed legs projecting over the middle of the surface the GBT s aperture is unblocked so that incoming radiation meets the surface directly This increases the useful area of the telescope and reduces reflection and diffraction which ordinarily complicate a telescope s pattern of response to the sky To keep the aperture unblocked the design incorporates an off axis feed arm that cradles the dish and projects upward at one edge This requires that the figure of the telescope surface be asymmetrical To make a projected circular aperture 100 meters in diameter the dish is actually a 100 by 110 meter section of a conventional rotationally symmetric 208 meter figure beginning four meters outward from the vertex of the hypothetical parent structure see Figure The GBT s lack of circula
146. are the status can be Unknown or Not Connected If the status is Clear Info or Notice then there are no significant problems with the GBT If Warning then it is worth asking the Operator what the problem is but it may not affect observation quality If the status is Error then there is potentially something wrong that may need attention If the status is Fault or Fatal then something has definitely gone wrong with the observations 4 2 HOW TO START ASTRID 27 4 2 2 7 Queue Control The Halt Queue Control button located in the middle right of the GUI gives you some control over the execution of Scheduling Blocks If this button is not activated then Scheduling Blocks in the Run queue will continue to be executed in order If this button is activated it will finish the current Scheduling Block but will not allow the next Scheduling Block in the Run Queue to execute until the button is returned to its default off state 4 2 2 8 Observation Control The Observation Control area is located in the lower right of the GUL The Observation Control buttons gives the observer control of the during the execution of a Scheduling Block The Pause button when activated will stop the execution of the current Scheduling Block Observing Script when the next line of the Observing Script is encountered The Stop button will stop the current scan at the end of the next integration time This is a nice
147. ation by setting broadband 1 which is limited to using only 1 beam of the KFPA In this mode the system can process up to 7 5 GHz of bandwidth See Appendix B for details on configuring spectral windows Sections 6 2 1 2 and give examples of configuring the KFPA 121 122 CHAPTER 9 MAPPING AND THE DATA REDUCTION PIPELINE Table 9 1 Nominal beam offsets for each feed of the KFPA at orientation C arcseconds ORIENTATION 94 88 Beam X El Offset El Offset 1 0 00 0 00 2 0 00 94 88 3 82 16 47 44 4 82 16 47 44 5 0 00 94 88 6 82 16 47 44 7 82 16 47 44 ELEVATION TOP VIEW DOWEL He 47 44 47 44 POINTING COEFFICIENT SIGNS POS EL TOWARD TURRET CENTER 82 16 82 16 y Figure 9 1 Orientation of KFPA feeds on the GBT 9 2 KFPA Point and Focus For optimum telescope efficiency pointing and focus observations see Section 6 2 3 1 should be made at the beginning of an observing session and about once per hour after that Note that beam pairs 7 3 and 6 4 are at the same elevation on the sky and are appropriate for dual beam peak and focus observations 9 3 MAPPING PROCEDURES FOR THE GBT PIPELINE 123 9 3 Mapping Procedures for the GBT Pipeline The mapping pipeline works with spectral line data obtained with any of the standard GBT ma
148. ation A Catalog source name or Location object It specifies the source which is to be tracked endOffset An Offset object See for information on Offset objects It moves the beam to a new position during the scan which is specified relative to the location specified in the first parameter If no offset is desired use None for this parameter scanDuration A float This specifies the length of the scan in seconds beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 2 3 A or any valid combination for the receiver you are using such as MR12 and MR34 The default value for beamName is 1 startTime A time object This specifies when the scan begins If the start time is in the past then the scan starts as soon as possible with a message sent to the scan log If the start time plus the scan duration is in the past then the scan is skipped with a message to the observation log The value may be e A time object Note if startTime is more than ten minutes in the future then a message is sent to the observation log See for information on time objects e A Horizon object When a Horizon object is used the start time is implicitly computed e g Track 3C247 None 120 0 startTime Horizon If the source never rises then the scan is skipped and if the source never sets then the scan is started immediately In either case a message is sent to the o
149. axy cmb relative to Cosmic Microwave Background The default value is topo vdef This keyword specifies which mathematical equation i e definition is used to convert between frequency and velocity The keyword value is a string Allowed values are Optical Radio Relativistic V maa c 1 Vo 1 v2 y Vrelativistic 5 5 2 2 v The default value is Radio 64 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS iftarget This keyword specifies the target voltage level to use when balancing the Rack The keyword value is a float The nominal range of the Rack is 0 0 10 0 and the linear range is 0 1 5 0 Backend and Receiver Dependent Keywords Some configuration keywords depend on which backends and receivers are being used Some obser vations may require one of these keywords while for other observations none may be needed nchan This keyword is used to determine the number of spectral channels that VEGAS will provide It is a string Available values are low medium low medium medium high and high to select the 5 choices of spectral resolution for a given bandwidth see Table 10 1 This keyword does not have a default value dopplertrackfreq Rest frequency in MHz used to compute the velocity for Doppler tracking The default value of this keyword is the first restfreq
150. aytime observations are possible for extended Sources e Start the project with an AutoOOF unless observing extended sources during the day This sets the active surface including the thermal corrections as well as getting initial pointing and focus corrections 14 3 OBSERVING 187 Wheel Position Beam 1 Beam 2 defined wrt 1 Observing Sky Sky 1 Cold Cold Warm 2 Position2 1 4wave Sky circ 3 Position3 Sky Sky 4 Cold2 Warm Cold 5 Position5 Sky 1 4wave Circ Figure 14 2 Diagram showing the positions of the 4mm Calibration wheel The wheel is rotates above the cryostat and the location of the beams are separated by 180 degrees on the wheel In the Observing position both beams see the sky In the Cold1 position beam 1 sees the cold load and beam 2 sees the ambient load while for the Cold2 position beam 2 sees the cold load and beam 1 sees the ambient load The 1 4 wave plate can be placed over only one of the beams at a time e After configuration and balancing check the RF power levels in the IF rack to confirm that power is going through the channels and that the power levels are not saturated lt 10 Beam 1 uses channels 1 and 3 and beam 2 uses channels 5 and 7 To avoid possible saturation on the warm load the power levels on the sky need to be at 6 Although reasonable looking data may be detected downstream observers should avoid non linear calibration effects when the IF power saturates R
151. bmason ccbPub called ccbPeak turtle This scheduling block does a focus scan four peak scans and a symmetric nod for accurate photometry to monitor the telescope gain 12 1 3 Observing Modes amp Scheduling Blocks SBs Science projects with the CCB typically fall into two categories mapping and point source photometry The majority of CCB science is the latter since this is what by design it does best Template scheduling blocks for both are in users bmason ccbPub Observers and support scientists are strongly encouraged to use these template schedul ing blocks as the basis for their CCB observing scripts and make only the changes that are required Relatively innocuous changes can make the data difficult or impossible to calibrate with existing analysis software The basic template SBs are e ccb bsCycle turtle perform photometry on a list of sources e ccbRaLongMap turtle perform a standard RALongMap on a source see 6 2 3 4 e ccbMap turtle ccbMosaicMap turtle make maps using longer single scan custom raster maps Your staff friend will help tailor these to your project s needs should you choose this approach Point source photometry is accomplished with an On the fly variant of the symmetric NOD proce dure described in This procedure which we refer to as the OTF NOD alternately places the beam in each of the two beams of the Ka band receiver in a B1 B2 B2 B1 pattern This sequence can cels means an
152. bservation log See for information on Horizon objects stopTime A time object See for information on time objects This specifies when the scan completes If the stop time is in the past then the scan is skipped with a message to the observation log The value may also be e A Horizon Object When a Horizon object is used the stop time is implicitly computed e g a complete scheduling block for tracking VirgoA from rise until set and using a horizon of 20 degrees would be horizon Horizon 20 0 Track VirgoA None startTime horizon stopTime horizon If the source never sets then the scan stop time is set to 12 hours from the current time See 8 for information on Horizon objects fixedOffset An Offset object See 6 2 6 for information on Offset objects Track follows the sky location plus this fixed Offset The fixedOffset may be in a different coordinate mode than the location If an endOffset is also specified Track starts at the location plus the fixedOffset and moves by the endOffset during the scan ending at the location plus fixedOffset plus the endOffset The fixedOffset and endOffset must be both of the same coordinate mode but may be of a different mode than the location The fixedOffset parameter may be omitted 6 2 COMPONENTS OF AN OBSERVING SCRIPT 77 Scan timing must be specified by either a scanDuration a stopTime a startTime plus stopTime or a startTime plus scanDuration The followin
153. bserving Coldl Cold27 e dwellFractionList user specified ordered list of dwell fractions associated with the tablePosition List for use only with the auto mode By using auto mode with tablePositionList and dwellFrac tionList expert users can control the wheel in any order of positions and dwell fractions This input not needed for autocirc or manual modes is ignored in these modes if given Example usage of the CalSeq command e CalSeq auto 40 0 This command can be used for most observations which uses the default tablePositionList Observing Cold1 Cold2 e CalSeq auto 40 0 fixedOffset Offset J2000 00 00 00 00 02 00 This command can be used for bright objects where one wants a system temperature measurement on blank sky In this example the offset is 2 to the north If observing a large object one can increase the offset size to move off source for the blank sky measurement e CalSeq manual 10 0 tablePositionList Position2 Observing Coldl Cold2 This is an example command for calibration of VLBI observations with beam 1 circular polarization We can only observe the cold and ambient loads with linear polarization The calibration from linear to circular requires observations of the same sky with both linear and circular polarization Observing and Position2 respectively in this example 14 3 2 Pointing and Focus Blind pointing at
154. bserving Script can be executed Project Just as in the Edit Tab you use the drop down menu to select your Project ID If your project is not listed ask your GBT friend or the telescope Operator to add it to the database Session A session is a contiguous amount of time a block of time for which the project is scheduled to be on the telescope Each time a project begins observing for a new block of time it should have a new session number The session number is usually determined by Astrid and automatically entered However there are cases such as Astrid crashing where the session number could become incorrect You can type in the correct session number if needed 32 CHAPTER 4 INTRODUCTION TO ASTRID Note that a Session in Astrid is equivalent to an observing period in the lingo of the Dynamic Scheduling System DSS Session has a different meaning in the DSS Observer s Name This is a drop down list where you choose the observer s name Only the PI s on a project are guaranteed to have their name in this list If your name is not listed ask your GBT friend or the telescope operator to add it Operator s Name This is a drop down list from which you pick the current operator s name at the beginning of your observations 4 3 2 2 Submitting An Observing Script to the Run Queue In order to execute an Observing Script you must Step 1 Select the Observation Management Tab Step 2 Select the Run Tab
155. cal Almanac for the year 2006 Washington U S Government Printing Office USGPO 2006 U S Naval Observatory USNO Royal Greenwich Observatory RGO pointing cat Condon s master pointing catalog for the https safe nrao edu wiki bin view GB PTCS PointingFocusCatalog Iband pointing cat cband pointing cat pointing cat kuband pointing cat kband pointing cat kaband_pointing cat qband_pointing cat wband pointing cat mustang pointing Extracted from pointing catalog for 21 cm band 1 4GHz Extracted from pointing catalog for the 6 cm band 6GHz Extracted from pointing catalog for the 3 5 cm band 9GHz Extracted from pointing catalog for the 2 cm band 14GHz Extracted from pointing catalog for the 1 5 cm band 20GHz Extracted from pointing catalog for the 9 mm band 32GHz Extracted from pointing catalog for the 7 mm band 43GHz Extracted from pointing catalog for the 3 5mm band 86GHz Extracted from pointing catalog for the 3 3mm band 90GHz HLstrong cat pulsars all cat pulsars all GBT cat pulsars_brightest_GBT cat pulsars bright MSPs GBT cat Galaxies with strong HI lines extract from Rich Fisher s database http www gb nrao edu rfisher GalaxySurvey galaxy survey html All 1533 pulsars in the AT NF database as of 26 Aug 2005 All 1054 pulsars visible from Green Bank The brightest pulsars visible from Green Bank Bright millisecond pulsars visible fro
156. cal plane array receiver covering 18 26 5 GHz 163 Ku band A region of the electromagnetic spectrum from 12 18 GHz L band A region of the electromagnetic spectrum covering 1 2 GHz MUSTANG The 80 100GHz bolometer receiver MUltiplexed SQUID TES Array at Ninety GHz 112 PF1 The first of two prime focus receivers for the GBT This receiver has four different bands 290 395 385 520 510 690 and 680 920 MHz PF2 The second of two prime focus receivers for the GBT This receiver covers 901 1230 MHz 59 112 PROCNAME A GO FITS file keyword that contains the name of the Scan Type used in Astrid to obtain the data PROCSEQN A GO FITS file keyword that contains the current number of scans done of the total scans given by PROCSIZE in a given Scan Type PROCSIZE A GO FITS file keyword that contains the number of scans that are to be run as part of the Scan Type given by PROCNAME Q band A region of the electromagnetic spectrum from 40 50 GHz S band A region of the electromagnetic spectrum covering 2 4 GHz Ow The two dimensional standard deviation of the GBT pointing error resulting from the wind Spectral Processor A spectral line and pulsar backend Usually used for spectral line observations at low frequencies or when strong RFI may be present Also used to observe the brightest pulsars Glossary 235 The opacity of the atmosphere 197 Tree The blackbody equivalent temperature flux that the GBT receiver
157. ceivers lack attenuators and do not need to be balanced If the argument to Balance is blank then all devices for the current state of the IF system will be balanced Without any arguments the Balance command uses the last executed configuration to decide what hardware will be balanced Strategies for balancing the hardware in the are discussed in 7 1 An simple example of the use of Balance is Configure myconfiguration Balance For more details about the Balance command refer to Section 7 1 and Appendix 100 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS 6 2 5 3 Break The Break function inserts a breakpoint into your Observing Script and gives the observer the choice of continuing or terminating the Observing Script When a breakpoint is encountered during execution your Observing Script is paused and a pop up window is created The Observing Script remains paused for a set amount of time or until you acknowledge the pop up window and tell Astrid to continue running your script The Break function can take two optional arguments a message string and a timeout length Why have a timeout If an observer walks away from the control room during his or her observing session e g to go to lunch or the bathroom and a breakpoint is reached it would be counterproductive to pause the observation indefinitely This will help to save valuable telescope time 6 The full syntax for the Break fu
158. ckend VEGAS We wish the cycle time to go through a full switching cycle to be 1 second swper 1 0 We want VEGAS to record data every 30 seconds tint 30 We wish to Doppler track the spectral line with rest frequency 1420 405 MHz dopplertrack freq 1420 405 in the commonly used Local Standard of Rest velocity frame vframe Isrk vdef Radio We would like to use the low power noise diode noisecal lo and wish to take the data using circular polarization pol Circular We wish to configure the 7 lines to be observed with different bandwidths deltafreq polarization and integration time For example the restfreq 1420 405 will be observed with bandwidth 15 625 MHz and spectral resolution 0 24 KHz The deltafreq for this line is set to 0 and cross product will be recorded to the FITS file restfreq 1420 405 bandwidth 15 625 res 0 24 deltafreq 0 vpol cross 6 2 2 1 Executing A Configuration Although one can put any number of configuration definitions into an observing script the standard practice is to put all the configuration definitions into a separate file that is then included in the Observing Script This strategy a keeps the Observing Scripts simple and without clutter and b allows changes to be made to the configuration without having to validate and re save the Observing Scripts 60 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS With the co
159. contributes to the detected signal Tac The blackbody equivalent temperature flux from the astronomical source i11 Tsys The blackbody equivalent temperature flux that the GBT sees if there is no astronomical signal detected VEGAS VErsatile GBT Astronomical Spectrometer The new spectral line backend 6 Voptical The velocity of a source using the optical approximation of the velocity frequency relationship Vradio The velocity of a source using the radio approximation of the velocity frequency relationship Vrelativistic The velocity of a source using the relativistic definition of the velocity frequency relationship W band A region of the electromagnetic spectrum covering 75 111 GHz X band A region of the electromagnetic spectrum covering 8 12 GHz
160. controlled individually to allow for differential or total power calibration Unlike other GBT backends the noise diodes are either on or off for an entire integration there is no concept of phase within an integration The minimum practical integration period is 5 milliseconds integration periods longer then 0 1 seconds are not recommended The maximum practical beam switching rate is about 4 kHz limited by the needed 250 micro second beam switch blanking time Switching slower than 1kHz is not recommended 2 1 OVERVIEW OF THE GREEN BANK TELESCOPE 7 2 1 4 3 VEGAS The VErsatile GBT Astronomical Spectrometer VEGAS is the new spectral line backend for the GBT It consists of eight independent spectrometers that can be configured in any one of 19 modes and can be used with any receiver except Mustang It provides up to 64 spectral windows as well as wide bandwidths 1000 1500 MHz Chapter 10 for detailed information on VEGAS 2 1 4 4 GUPPI The Green Bank Ultimate Pulsar Processing Instrument GUPPI has one hardware mode and many software modes GUPPI can be used with any receiver with the exception of MUSTANG Only one polarization would be available for the Ka band receiver GUPPI uses 8 bit sampling to dramatically improve upon the dynamic range and RFI resistance of the SP Currently GUPPI can use bandwidths of 100 200 and 800 MHz with 2 polarizations and full stokes parameters The minimum integration time is 40 96u s using 2048 c
161. cy offsets That is the frequency offsets are equal to 0 0 8 5 3 5 1 5 4 5 7 5 8 5 22 5 deltaf scanDuration A float It specifies the length of the subscans in seconds It must be evenly divisible by 8 seconds Each subscan each frequency will integrate for 1 8 of the Scan Duration beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 2 3 A or any valid combination for the receiver you are using such as MR12 and MR34 The default value for beamName is 1 F 2 SPECIALTY SCAN TYPES SUBMITTED BY OBSERVERS 223 The following example generates an LSFS observation of 12584 6126 LSFS 1258 6126 0 0244 80 F 2 2 Spider Spider executes the specified number of slices of duration scanDuration through the specified location Each slice is of length 2 startOffset The argument startOffset also specifies the angle of the initial slice The user may specify unidirectional or bidirectional subscans of length calDuration and when to run calibration subscans relative to each slice i e at begin end or both Syntax Spider location startOffset scanDuration slices beamName unidirectional cals calDu ration The parameters for Spider are location A Catalog source name or Location object It specifies the source which is to be tracked startOffset An Offset object It specifies the 1 2 length of the subscans and the angle
162. d The ALMA Calibrator Source Catalogue has an extensive record of the flux density histories for many of the bright 3mm point sources https almascience eso org sc By using ALMA flux density values as a function of time 10 absolute calibration uncertainties can be obtained for W band data The standard GBTIDL scripts getps getnod getfs do not work since these assume a noise diode for calibration W band scripts for the reduction of spectral line data can be found at home astro util projects 4mm PRO For continuum DCR reduction contact your support scientist Users can use the calseq pro within GBTIDL to derive the gains for each of the channels After deriving the gains users can and reduce the spectra line data for example using wonoff gain pro The formulae for calibrating data are given below The observed antenna temperature is Ta Tsys Von Vorr Vorr 14 1 where Von and Vorr are the observed voltages of the ON and OFF scans The system temperature is given by 9 Vorr 14 2 and the gain g is 9 Lame Teold Vamb Veota 14 3 where Tamb and are the temperatures of the ambient and cold loads and Vamp and Veola are the observed voltages of the ambient and cold load scans The ambient load is given on the receiver CLEO page and within the receiver FITS files The cold load is measured in the lab Table 18 2 The main beam temperature Tm is related to the observed antenna temperat
163. d gradients in the atmospheric or receiver emission with time Plotting the beamswitched data from this sequence produces a sawtooth pattern shown in Figure this is discussed more in 12 1 5 Each NOD is 70 seconds long 10 seconds in each phase with a 10 second slew between beams and an initial 10 second acquire time Note OTF NOD is not one of the standard scan types it is implemented in the scripts mentioned here e g ccbObsCycle turtle 160 CHAPTER 12 THE CALTECH CONTINUUM BACKEND CCB Beamswitched power Beam 1 Beam 2 Figure 12 1 Data from a CCB beamswitched OTF NOD showing data and model versus time through one B1 B2 B2 B1 scan The white line is the CCB beamswitched data and the green line is the fit for source amplitude using the known source and telescope as a function of time positions 12 1 4 Calibration If at all possible be sure to do a peak and focus and perform photometry an OTF NOD as implemented in ccbObsCycle turtle or ccbPeak turtle on one of the following three primary flux calibrators 3c48 3c147 or 3c286 This will allow your data to be accurately calibrated our calibration scale is ultimately referenced to the WMAP 30 GHz measurements of the planets If this is not possible the calibration can be transferred from another telescope period observing session within a few days of the session in question 12 1 5 Online Data Analysis It is important to assess data quality during your
164. d then almost imme diately turn right onto Hershberger Road Go about 1 2 mile and then take I 581 north to I 81 north Go two exits on I 81 north to US 220 the Daleville Troutville exit Take US 200 north toward and through Fincastle until you reach I 64 Take I 64 west to White Sulpher Springs WV Take the first White Sulpher Springs exit and turn right After about 1 2 mile turn right onto route 92 north and this will take you to Green Bank 18 5 3 Once You Are in Green Bank The entrance to the observatory is about one half mile north of downtown Green Bank on the west side of route 92 28 see Figure 18 2 Look for the Jansky and Reber antennas They are located on either side of the entrance To pick up your keys you will need to come to the Jansky Lab The Jansky lab is the second building on the left as you enter the site Go in the atrium main entrance If after working hours use the 18 5 GETTING TO GREEN BANK 207 ym Figure 18 2 NRAO Green Bank site map telephone on the left to call the GBT operator at 2341 The operator will then buzz you in If during normal working hours just walk in The room packets and keys will be found near the begining of the hallway on your right as you enter the Jansky Lab The residence hall is the first building on the right as one enters the observatory Adequate parking is provided on the west side of the residence hall Enter the residence hall through the doubl
165. dated in the M amp C system The expected Full Width at Half the Maximum of the Gaussian fitted to the observed pointing data as the GBT slews across the source should be 740 vag arc seconds where vay is the observing frequency in GHz For a focus scan the resulting data should approximate Gaussian with a FWHM of 3 6mm where Amm is the observing wavelength in millimeters The default behavior is to asssume that a pointing fit is bad if the differ from the expected value by more than 30 or if the pointing correction is more than twice the in magnitude The default for a bad focus scan is if the FWHM is more than 3096 from the expected value uses the Automatically accept good fits automatically reject bad fits criteria as the default The user may change fitting acceptance criteria by Step 1 Select the Data Display Step 2 Select the Pointing Tab or the Focus Tab see note below Step 3 Click on the Tools pull down menu Step 4 Select Options Step 5 Select the new mode in the pop up window see Figure 5 3 40 CHAPTER 5 NEAR REAL TIME DATA AND STATUS DISPLAYS The options dialog is available only for the Pointing and Focus data displays Please note that the values are set independently for the pointing data reduction and the focus data reduction Therefore the Pointing and Focus can have different option values recognizes the following fitting acceptance criteria only when Astrid is in one of its on line modes D
166. der the File drop down menu you will find the New Window option Under the New Window side menu option you will be able to launch Applications within the GUI or in an independent GUI The Close Window option will allow you to close the currently displayed Application in the 24 CHAPTER 4 INTRODUCTION TO ASTRID Astrid ONLIE ioj xi Fie Edit View Tools Hep WX det lt gt i ObservationManagement 1 DataDisplay 1 Observation Statz Eon Aun idle Project 24 JAPI E 25 Now we actually configure Iband ee 26 Comment Configuring the system for L band Scheduling Blodks 27 Contigure banc GBT Status KaPtgDirect claar 7 KaScal 29 thats it for basic configuration KaTios 30 Comment Basic initialzaton completed 31 pom 92 get my list of sources Queue kbancpeakcatald 99 exectile jsecs mmellortrurkfregressiontests scrp s scurces py Halt Queue 9 F kbang gman L band Nmake sure the Antenna is in the ScanCoordiantor Ibandfocu SetValues ScanCoodinator subsystemSelect Antenna 1 Observation Control Ibandp Pause Nyet default catalog 1 i Catalog Stop Nicole s Test Ser Abort Onoff use the source 1800 7828 for regression tests since its good for k and x bands interactive 42 ri 2 peak pics test pulsar sb FL 3 Miri ou are currently editing lbandpe
167. detectors and DCR Figure 8 2 A simplified flow chart of the 8 1 From the Receiver to the IF Rack The frequency that is observed is given by Fsky Within the receiver the detected signal at Fsky is mixed with the LO1 signal The LO1 frequency is derived from a synthesizer and can vary in time when Doppler tracking the velocity of a spectral line The result of the mixing of Fay and LO1 is the frequency IF 1 The allowed IF 1 center frequencies are 1080 3000 and 6000 MHz Filters limit the bandwidth in the receivers both before and after the LO1 mix There are also filters in the IF Rack that limit the bandwidth The resulting allowed bandwidths are 20 80 320 1280 MHz and All Pass i e no filtering other than the response of the receiver 8 2 FROM THE CONVERTER RACK TO THE BACKEND 119 In the IF Rack each signal is split into two single beam receivers only copies of the original signal Each signal in Rack is detected and then sent to the as used during pointing and focus observations Each signal is also sent as an analog signal over optical fiber to the Jansky Lab to the Converter Rack 8 2 From the Converter Rack to the Back end When the signal reaches the Converter Rack it is split into four separate copies This allows up to eight different copies of the received signal for single beam receivers and four copies of each received signal for dual beam receivers In the Converter Rack the signal is mixed with
168. ditionally for modes 4 29 the signal is decimated after being read by the ADCs and requires an additional scaling to be included into Equation 10 2 Table 10 3 lists for the various modes The exact formula for these modes is still being worked out and will be included as soon as possible These spurs are relatively stable Vspurs will remain constant for a given mode and the magnitude of the spurs is relatively constant These features are also quite small by most standards Spurious Free Dynamic Range no more than 60dBc but nevertheless can be problematic when looking for faint 1The 33 lt i lt 64 spurs alias back to the 0 lt i lt 32 spurs when creating the power spectrum 10 8 KNOWN BUGS AND FEATURES 143 6 T T T T T T T T T T T T 10 Counts 41 6 41 8 42 0 AF 7 42 4 GHz Figure 10 13 Data from Figure 10 12 after the high pass filter in black with the vertical red lines denoting the locations of the spurs as dictated by Equation Table 10 3 vy for each VEGAS mode modes 1 2 750 3 540 4 6 750 7 9 400 10 29 TBD narrow features The stability of these features allows them to be removed by standard data practices such as position and or frequency switching but they are an added noise source
169. e off M1 or M5 xfer This expert keyword sets the beam switch for the Ku band and receivers The keyword is a string Allowed values are ext thru or cross The default values are ext when swtype bsw and thru otherwise polswitch This expert keyword sets the polarization switch for the and receivers The keyword value is a string Allowed values are ext thru and cross The default value is ext if swtype psw and thru otherwise ifbw This expert keyword sets the minimum IF bandwidth to be used in filters within the receiver and in the IF Rack The keyword value is float with units of MHz ifOfreq This expert keyword is used to set the center frequency of the after the mixing the signal with the first Local Oscillator LO The keyword value is a float with units of MHz lolbfreq This expert keyword is used to set the frequency of the synthesizer used for the alternative First LO LO1 LO1B This keyword is only to be used with the receiver The keyword value is a float with units of MHz lo2freq This expert keyword is used to set the frequency values of the eight Second LO LO2 synthe sizers within the Converter Rack The keyword values are a comma separated list of floats with units of MHz There should be nwin entries for this keyword value if8freq This expert keyword is used to set the IF input frequency of the backend The keyword value i
170. e Specifying a calibrator bypasses the search process Please note that NVSS source names are used in the pointing catalog If the name is not located in the pointing catalog then all the user specified catalogs previously defined in the scheduling block are searched If the name is not in the pointing catalog or in the user defined catalog s then the procedure fails location A Catalog source name or Location object see Appendix D It specifies the center of the search radius The default is the antenna s current beam location on the sky frequency A float It specifies the observing frequency in MHz The default is the rest frequency used by the standard continuum configurations or the current configuration value if configure is False see Table 6 5 flux A float It specifies the minimum acceptable calibration flux in Jy at the observing frequency The default is 20 times the continuum point source sensitivity radius A float The routine selects the closest calibrator within the radius in degrees having the minimum acceptable flux The default radius is 10 degrees If no calibrator is found within the radius the search is continued out to 180 degrees and if a qualified calibrator is found the user is given the option of using it default aborting the scan or continuing the scheduling block without running this procedure balance A Boolean Controls whether after slewing to the calibrator the routine balances the power along the
171. e minutes Jg 150 8 100 m 50 0 0 50 gt 100 v 150 200150100 50 0 50 100 20 15 100 50 0 50 100 206156100 50 0 50 100 Cross Elev Offset arcsec Figure 5 9 A plot of raw OOF data on a source which is too faint 5 1 5 Continuum Data Display Continuum data taken with the that are not part of pointing and focus scans will show up in plots under the Continuum Tab see Figure 5 10 This will show the uncalibrated continuum data as a function of time only 5 1 6 Spectral Data Display The Spectral Line Display was a tool originally designed for browsing the previous GBT Spectrometer spectral line data Although this tool can provide limited VEGAS information there is a separate more flexible web based display intended for VEGAS See Chapter 10 for more details When you are offline one integration at a time can be selected while in online mode the most recent integration is automatically plotted See Figure for a screen capture of the spectral line data display The spectra displayed are raw data and no calibration has been applied to them All user interaction for this plugin occurs in the right hand side options panel The check boxes allow selection of spectra to plot via astronomical variables Beams Polarizations Numbers and Phases For offline usage the desired integration can be selected either using the up down arrows or by typing in a value in the edit box For online usage the latest in
172. e compared to uniformly distributed integration The daisy scan pattern is supported by ASTRID directly and can be invoked as follows where e daisyRadius is the radius of the circular area to be covered in arcminutes e daisyRadialPeriod is the period of radial oscillations in seconds not to be less than 15 sec x daisyRadius 1 5 arcmin for radii gt 1 5 and in no case under 15 seconds e scanDuration is the scan duration in seconds Approximately 22 radial periods are required to completely cover a circular area with the default parameters Also see notes in section 13 6 7 e beamName must be C for MUSTANG since individual beam offsets are not defined in the antenna database An example trajectory is shown in Figure For photometry of point sources you want the array at some point to be completely off source r 0 8 Typical radii are 1 to 5 To cover rectangular areas more uniformly there is a custom Box scan procedure invoked as follows where e 0 and y0 specify the box width and height in arcmin e taux and tauy specify the periods of motion in either direction in seconds e scanDuration specifies the scan duration in seconds e dx and dy specify dither offsets for the trajectory in arcminutes In practice a 2 3 beam 6 triangular dither serves well 13 3 OBSERVING WITH MUSTANG 169 Figure 13 1 Full 22 cycle daisy scan trajectory with a radius r 1 5 boxtraj executes a truncat
173. e corrections show up instantanly within the cleo status window but do not take effect until the start of the next scan At high frequency it is not uncommon for fits to fail due to the Heuristics criteria even though the fits can be adequate In these cases the derived solutions within the Pointing or Focus data windows can be entered manually with this tab Also users can derive solutions via offline processing e g using different processing parameters Sometimes at the highest frequencies e g the w band 68 92 GHz Receiver the fits do not always represent the data well In these cases users can derive approximate offsets by moving the cursor to the position of the desired solution within the pointing or focus data window The x position value of the cursor is shown in the lower left of the window represents the delta offset dAz2 AEP Offset for Az El and focus corrections respectively For the pointing solutions the NewAz2 OldAz2 dAz2 and NewEl OldEl dEl The Az2 term includes a cos El correction term also called in the gbtstatus window within astrid The pointing model also includes Az1 correction which is independent of El but this is not currently used For the focus corrections the New LFC Offset Old DFC If in doubt on the proper pointing or focus corrections users can retake the observations 5 1 4 OOF Data Display OOF Out Of Focus holography is
174. e error messages notices and warnings from the Validation in this area Before an Observing Script can be run within Astrid it first must pass Validation To Validate a script without saving it you can just hit the Validate button An Observing Script automatically undergoes a validation check when you hit the Save to Database button in the editor Any messages etc from the validation will appear in the Validation Output test area You can export these messages to a file on disk by hitting the Export button in the validation area The state of an Observing Script s validation is shown by the stop light If the script has never been validated or has been changed since the last validation the stop light will have the yellow light on If the Observing Script fails validation the stop light will turn red while it will turn green if the Observing Script passes validation Note that for loops with many repeats can take an extended amount of time to validate since the Validator will go through each step in the loop Also be careful of infinite loops in the validation process Use of time functions such as Now see Chapter 6 always return None in the validation 4 3 2 The Run Tab The Run Tab is shown in Figure In the Run Tab you will queue up Observing Scripts to perform the various observations that you desire to make The Run Tab has five components Across the top of the Run Tab you enter information that will be put int
175. e full sequence of 5 will run in about 10 minutes with the chosen radial period of 25 seconds parfulldaisy script to execute 22 radial cycles chopped into 5 scans of a daisy scan which gives full coverage mySrc 1256 0547 CATALOG none needed for planets standard pointing source catalog home astro util pointing pcals4 0 pointing cat Catalog Configure users bmason mustangPub sb mustang conf TE IT TT TE ITT FRE A TT Daisy Params daisyScanDur 100 daisyRad 2 8 daisy RadPd 25 Coord Sys in which to execute trajectory ji eg J2000 Encoder 8 J2000 don t change below here embedded in Daisy astrid routine periodRat 3 14159 Slew mySrc Derived Parameters chop the full daisy 22 cycles into 5 individual scans daisyScanDur daisyRadPd 22 0 5 0 nradosc daisyScanDur daisyRadPd rotphasestep 2 3 14159265 nradosc periodRat 182 CHAPTER 13 MUSTANG myphases 0 rotphasestep rotphasestep 2 rotphasestep 3 rotphasestep 4 for myphase in myphases Daisy mySrc daisyRad daisyRadPd 0 myphase daisyScanDur beamName C cos_v True coord Mode coordSys 0 Notes on Daisy Scans The way the daisy scan is set up it takes 22 radial periods to more or less complete one full daisy The radial periods are typically
176. e g during a Doppler track These data are blanked in the true VEGAS spectral data acquisition but may cause drop outs in the VEGASDM samples Chapter 11 Pulsar Observing with GUPPI The Green Bank Ultimate Pulsar Processing Instrument GUPPI is an FPGA GPU backend that offers many advantages over previous pulsar backends GUPPI uses 8 bit sampling to dramatically improve upon the dynamic range and RFI resistance of the Spectral Processor GUPPI can observe in either incoherent or coherent dedispersion modes over bandwidths of 100 200 or 800 MHz with 64 128 256 512 1024 2048 or 4096 spectral channels Three pulsar observing modes are available with either dedispersion mode search on line folding and cal a specialized on line folding mode Integration time is highly configurable subject to the maximum data rate of 200 MB s Typically all four Stoke s parameters are recorded but the option to only record total intensity Stoke s I is available in incoherent search mode GUPPI can be used with any receiver with the exception of MUSTANG only one polarization is available when using the Ka band receiver GUPPI is controlled by a machine called beef which also mounts two disks used to record incoherent mode data In coherent modes the total bandwidth is divided into eight parts with each part being sent to an HPC equipped with an nVidia GPU that performs the coherent dedispersion These data are then combined in the fir
177. e glass doors on the west side of the building The observer s lounge is located on the second floor of the residence hall directly above the entrance 208 CHAPTER 18 PLANNING YOUR OBSERVATIONS AND TRAVEL Chapter 19 After Your Observations 19 1 Taking your data home There are several methods that you could use for taking you data home with you We have the capabilities of writing ExaByte Dat Mammouth and DLT tapes We can also write your data onto CDs or DVDs Please contact your scientific support person to help you decide which method will be best for you NOTE When using the scp utility to copy your data to another machine please limit your band width to 2000 Kbit s For example 19 2 Installing GBTIDL Most spectral line observers will use GBTIDL to reduce their data If you have an idl license at your home institution then you can obtain a copy of GBTIDL from http gbtidl nrao edu Instructions for installation can also be found at the above web page 19 3 Keep Your Contact Person Informed Don t hesitate to ask your scientific contact person if you are having trouble reducing your data or if you have questions about your data It does not matter how long its has been since you observed your contact person will be more than happy to help you 19 4 Press Releases and News worthy Items News worthy items should be discussed with the press officer The press officer can help write an NR AO pre
178. e of amplifier used in the receivers Focus Rotation Mount FRM A mount that holds the Prime Focus Receivers which allows the receivers to be moved and rotated relative to the focal point The FRM has three degrees of freedom Z axis radial focus Y axis translation in the direction of the dish plane of symmetry and rotation Full Width at Half the Maximum FWHM Used as a measure for the width of a Gaussian Green Bank Telescope GBT An off axis 100 meter single dish telescope Erin po oe BSE 55 56 5 72 ES 9S 99 03 TT 172 TAHT 193 GBT IDL Data Reduction Package GBTIDL Data reduction package written in for analyzing GBT data GBT Fits Monitor GFM The software program that provides real time looks at GBT data 37141 229 230 List of Acronyms GBT Observing GO B31 09 Intermediate Frequency IF A frequency to which the Radio Frequency is shifted as an intermediate step before detection in the backend Obtained from mixing the RF signal with an LO signal 6 109 Intermediate Frequency paths IF path The actaul signal path between the reciever and the backend through the IF system Intermediate Frequency system IF A general name for all the electronics between the receiver and the backend These electronics typically operate using an Intermediate Frequency IF 9 213 Local Oscillator LO A generator of a stable constant frequency radio signal used as a reference f
179. e sure to save the scheduling block first It is highly recommended that this be done using a short scan in cal mode These data will be written to disk but you should only use the scans that are properly scaled for your actual science so make a note of which scan is which Once you have determined an appropriate guppi scale value be sure to update any other configurations accordingly DO NOT leave guppi_monitor running during your observations as it uses a lot of resources DO re run it from time to time during your session to monitor the RFI environment and close the program once you are done In practice appropriate guppi scale parameters have already been determined for most common configurations and it is a good idea to re use these values Contact your project friend for advice on which values to use This will reduce the guppi monitor step to a sanity check check of the RFI environment and reduce overhead time 11 3 BALANCING AND CHECKING LEVELS 149 Figure 11 1 The guppi adc hist screen The two histograms one for each polarization channel should be of roughly the same width and amplitude Both should be roughly Gaussian in shape and have FWHMs of about 30 150 CHAPTER 11 PULSAR OBSERVING WITH GUPPI Figure 1 Figure 11 2 The guppi monitor screen In this example the bandpass at 350 MHz is shown The red line shows the average and the blue lines show the maximum and minimum over the las
180. e the pulsar or cal before dumping a set of profiles to disk It must be shorter than the scan duration that you set via the Track command guppi fold bins GUPPILspecific keyword Number of bins in profile guppi fold parfile GUPPlI specific keyword Pulsar ephemeris parameter file make sure that it exists guppi datadisk GUPPlI specific keyword This is the top level directory ie RAID array datal or data2 where your data will be stored It will go in a subdirectory called guppi datadisk observername projectID date Since the data will be owned by the monctrl computer account you will not be able to remove it that means Scott Ransom will bug you mercilessly until you process your data Expert Keywords These keywords should only be used by very experienced observers who have expert knowledge of how a given backend works or in how the works spect numbanks This is an optional expert keyword that can be used to set the number of banks that the spectrometer uses In most cases there is only one choice and the config tool chooses the default There are a few cases in which one may choose an alternate number of banks The keyword value is a string and can be None 1 2 or 4 vlbi phasecal This expert keyword turns the Very Long Baseline Interferometer VLBI phase cals on or off The phase cals can can run at 1 MHz M1 or 5 MHz M5 The keyword value is a string Allowed values ar
181. e validation and saving of the Observing Scripts In the following sections we discuss each of these components 6 2 1 Configuration of the GBT IF System 6 2 1 1 Overview The routing of signals through the system is controlled by many electronic switches which eliminate the need to physically change cables by hand The GBT s electronically configurable IF allows many and 6 2 COMPONENTS OF AN OBSERVING SCRIPT 53 more complicated paths for the signals to co exist at all times Experience has shown us that manual configuration of the is not practical due to setup times which typically lasted 30 minutes to 1 hour We have thus developed a software tool which will configure the based on the values of about one dozen input parameters This suite of software can typically configure the in under one minute The basic syntax for a configuration definition is 25 25 0 myconfiguration This is a comment and is ignored by the software primarykeywordl your primarykeyword value primarykeyword2 your primarykeyword value primarykeywordN 92 your primarykeyword value 6 2 1 2 Example Configurations The best way to learn about how to define and perform configurations is through examples We will discuss how to use the example configuration definition shown below in an Observing Script in 6 2 2 1 All of the keywords available for use in a configuration definition will be discussed in 8 6 2 2 2 Continuum Observations
182. econds to start a RALongMap mapping scan So observers scheduling scans much shorter than 1 minute will lose a large fraction of their observing time to overheads Using Daisy pattern scans are more efficient for scheduling small maps as a region can be mapped in a single scan However there is an additional delay in starting a Daisy procedure as the system computes the antenna trajectories As a rule of thumb maps larger than about 10 in size should use the RALongMap or DecLatMap procedures while smaller maps should use Daisy scans For practical reasons it is often best to keep the scan length under about 15 minutes 124 CHAPTER 9 MAPPING AND THE DATA REDUCTION PIPELINE 9 6 Advice on Testing the Spectral Config uration It is good practice for the observer to schedule a short observation towards a strong spectral line source at the beginning of each observing session The observer should process and check the spectra before proceeding with the mapping scans to confirm the spectral configuration It is also important to check the system temperatures for each of the beams Poor configuration choices for the backend will sometimes be detected as anomalous system temperatures 9 7 Optimal Observing Configuration for the Mapping Pipeline The following sample Astrid script demonstrates a KFPA observing sequence that can use the pipeline We assume that the telescope has been configured prior to running this script Identify
183. ed sawtooth waveform in each direction RA and Dec typically with specifi cable periods taux and tauy Combinations of taux tauy x0 y0 scanDuration which give approximately uniform coverage have been determined by experimenting with simulations Some common ones which also comply with GBT motion limitations are 2 x 2 to 3 x 3 square patterns are well covered by taux 10 sec tauy 8 sec and a 160 second total scan duration e 5 x5 to 7 x 7 square patterns are well covered by taux 9 tauy 8 and a total scan duration of 290 seconds An example box scan trajectory is shown in Figure If the area to be covered is substantially larger than any of these regions and not suitable to be covered by tiling your staff friend can help find suitable parameters 13 3 2 Sensitivity When mapping a 3 x 3 region uniformly i e with a box scan approach MUSTANG typically achieves a map noise of 0 4mJy beam RMS in one hour of integration time This RMS descreases as Vt for many hours under good conditions and for a fixed integration time increases as the area covered for larger areas Gains cannot be made by covering smaller areas uniformly due to practical limitations associated with the telescope motion and detector noise characteristics However for photometry of point or compact sources the daisy scan will deliver a factor of 1 9 improvement in RMS for a fixed integration time 0 2mJy beam RMS in one hour integration
184. ee Fig Each bank within VEGAS can be configured with a different spectral resolution bandwidth and number of spectral windows However the integration time switching period and the frequency switch must be the same for all banks The resolution and bandwidth for all spectral windows from a single VEGAS bank must be identical but the center frequencies may be set independently within limits The available VEGAS modes for each bank are given in 10 1 Although the individual spectrometers could be arranged to cover 10 GHz of total bandwidth the maximum bandwidth is typically limited to 4 6 GHz by filters in the GBT IF system see your project friend for more information All spectrometers have the same switching signal i e same switching period same frequency switch which is controlled by spectrometer bank A Each spectrometer can be configured in one of 29 modes see Table 10 1 Modes 1 19 provide a single spectral window per spectrometer while Modes 20 29 provide up to eight spectral windows per spectrometer In the latter modes the spectral windows for a single spectrometer must be placed within the bandwidth processed by that spectrometer 1500 MHz with a useable bandwidth of 1250 MHz for modes 20 24 and 1000 MHz with a useable bandwidth of 800 MHz for modes 25 29 Each mode provides the full polarization products e g XX YY XY YX necessary for observations of polarized emission without requiring a reduction in the numb
185. efinition for multiple spectral line observations using frequency switching 9999 vegas fs aconfig receiver Rcevr1 2 beam UBI 6 2 COMPONENTS OF AN OBSERVING SCRIPT 59 obstype Spectroscopy backend VEGAS swmode 5 swtype fw swper swfreq ze tint 10 0 vlow 00 vhigh zx vframe Else vdef Radio noisecal lo pol Linear dopplertrackfreq 1420 405 bandwidth 15 625 restfreq restfreq 1420 405 bandwidth 15 625 res 0 24 pol s cross s 1 restfreq 1612 231 bandwidth 15 625 res 1 9 deltafreq 0 restfreq 1665 402 bandwidth 15 625 res 0 24 ales eross IS restfreq 1667 359 bandwidth 15 625 res 0 24 deltafreq 0 vpol cross restfreq 1720 530 bandwidth 15 625 res 1 9 deltafreq 0 restfreq 1350 414 bandwidth 23 44 res 0 7 deltafreq 0 tint 1 0 restfreq 1532 557 bandwidth 100 res 1 5 deltafreq 0 3929 39 The configuration definition to be considered has the name vegas_fs_aconfig and can be used for spectral line observations obstype Spectroscopy using position switching swmode tp swtype none For these observations we wish to use the single beam L band 1 to 2 GHz receiver receiver Revr1_2 beam B1 and the VEGAS as the backend ba
186. elect the Heuristics tab in the pop up window Step 6 Select the new Heuristics mode in the pop up window see Figure 5 4 GFM uses standard Heuristics as the default upon initialization The options dialog is available only for the Pointing and Focus data displays Please note that the values are set independently for the pointing data reduction and the focus data reduction Therefore the Pointing and Focus can have different option values 5 1 THE ASTRID DATA DISPLAY TAB 41 allows the observer to switch between standard relaxed and user defined heuristics The standard and relaxed heuristic values are predefined and cannot be changed by the user Under normal observing conditions the observer should expect to use the standard values Under marginal weather conditions and or high frequency observations relaxed heuristics may be appropriate The user defined heuristic values should only be used by experts If you wish to use user defined heuristics then you should contact your support scientist X Pointing Options Fitting Acceptance Criteria Heuristics Data Processing Send Corrections Standard Relaxed UserDefined 2 ok cancel Figure 5 4 The pop up menu to change the pointing and focus fitting heuristics The standard heuristics expect that the fitted Gaussians have aJF WHM within 30 of the expected value
187. eline can also calibrate and map data taken with other receivers when they are used with standard observing modes Most observers will use the KFPA with the VEGAS backend but mapping can also be accomplished with the spectrometer 9 1 KFPA Beam Selection and Configura tion Figure 9 1 shows the orientation of the KFPA feeds on the sky The nominal beam offsets for each feed are listed in Table Observers can use all 7 KFPA beams for mapping or select a subset of them To maximize versatility and observing efficiency most observers will want to use the full set of 7 beams and pair the observations with the VEGAS backend Certain types of observations though may benefit from using fewer beams Figure 8 3 shows the IF path for the KFPA Note the simple IF down conversion sequence for beams 1 through 4 which can be used simultaneously in 4 beam observing modes Only beam combinations that route equal numbers of beams to Converter Rack Modules A and B are allowed The KFPA can be configured to observe multiple spectral windows simultaneously However there are constraints on the frequency separation of individual spectral windows The maximum frequency separation for a multi beam configuration is 1 8 GHz and the maximum offset between the tuning of each spectral window and the doppler tracking frequency is 1 0 GHz Up to seven beams can be used in these narrowband modes There is also a broadband mode achieved in the Astrid configur
188. emth System Temperature From All Sources Except Receiver Ui 0 10 20 30 40 50 Frequency GHz Aw Mass 12 10 d 8 a a 6 4 2 0 10 20 30 40 50 60 70 80 90 Elevation Figure 16 3 The top panel shows opacities under three typical weather conditions The black blue and red curves represent the opacity under the best 25 50 and 75 percentile weather conditions The average opacity over the winter months is best described by the 50 percentile graph The middle panel is an estimate of the contribution to the system temperature at the zenith from the atmosphere spillover and cosmic microwave background The bottom panel shows the number of air masses the astronomical signal must pass through as a function of elevation 16 4 GBT WEATHER RESTRICTIONS 199 Representative Total Zenith System Temperatures For Typical Winter Weather Conditions 150 25 Percentile 50 Percentile 2 75 Percentile o zy a e m 8 s it t 100 B E p j Ki y z 5 s iH E Ve T d C37 s 1 A i wy M u 3 4 VN 50 8 3 57 7 M CA o Sn RAY 0 1 1 1 1 L L L 0 10 20 30 40 50 Frequency Figure 16 4 The zenith system temperatures for typical weather conditions During the cold months high frequency observers can expect to be observing with opacities that are at or below the a
189. en Bank network Position Switched Observations where we repeatedly observe the same source E first we load the configuration file execfile home astro util projects 6D01 configurations py E now we load the catalog file Catalog home astro util projects 6D01 sources cat ji now we configure the IF system for frequency switch HI observations Configure vegas_ps_config E now we balance the IF system Balance 100 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS now we use a Break so that we can check the IF system Break Check the Balance of the IF system specify which source we wish to observe srcs Objectl specify how far away from the source the off position should be offset two minutes of time in Right Ascension myoff Offset J2000 00 02 00 0 0 specify how many times to observe the source numobs 20 observe 4 gt on source for 2 minutes and off source for 2 minutes and then repeat for i in range numobs OnOff srcs myoff 120 6 2 7 3 Position Switched Observations of Several Sources and Using the Horizon Object In this example we perform position switched observations of three sources We observe the first source until the second source rises above 20 degrees elevation Then we observe the second source until it goes below 20 degrees elevation at which poi
190. eq is a list and input with the dictionary syntax beam 1 2 nwin 2 restfreq 23706 3 24139 417 deltafreq 0 specifies the same KFPA configuration as does the new syntax restfreq 23706 3 1 2 24139 417 1 2 DopplerTrackFreq 24000 deltafreq 23706 3 0 24139 417 0 nwin 2 beam 1 2 Example 4 8 different rest frequencies specified restfreq 23706 3 1 24139 417 2 24139 417 3 24706 3 4 24149 417 5 24122 417 6 23899 7 24876 1 1 DopplerTrackFreq 24876 Example 5 a configuration that specifies delta frequencies beam all restfreq 24000 1 2 3 4 23400 5 6 7 25500 1 DopplerTrackFreq 24876 deltafreq 24000 0 23400 500 25500 O Appendix C Usage of vlow and vhigh The configuration keywords vlow and vhigh give the range of velocities of all sources to be observed This information is used to set various filters in the system so as to admit the required range of frequencies Setting the velocity for each specific source is done later in the observing block For galactic sources where the range of velocities is rather small it is usually best to set both vlow and vhigh to zero When strong RF is present is it best not to use vlow and vhigh The use of vlow and vhigh can cause the GBT IF system to have a larger IF bandwidth than is necessary for a single source This can let parts of the IF system be unnecessarily affected by The obser
191. er Monitor button VEGAS Data Monitor The VEGAS Data Monitor VEGASDM provides a real time display of the current total power level as measured by the VEGAS ADCs as well as a histogram of the distribution of ADC counts VEGASDM may be launched by source home gbt gbt bash or csh 4 VEGASDM or by clicking on the VEGAS CLEO screen VEGAS Power Monitor button The VEGASDM display will appear as in Figure VEGASDM has nine tabs one for each Bank and one overview tab If a Bank is active the tab label will be green otherwise it will be red Each Bank tab shows whether the Bank is in the running state and what mode it is in The upper plot shows the total power from each polarization as a function of time while the lower two plots show the distribution of ADC counts for each polarization If VEGAS 10 8 GENERAL OPERATION 133 Vegas Data Display Mozilla Firefox OA G File Edit View History Bookmarks Tools Help 2 Vegas Data Display v E Google Lb gb nrao edu vegasdisplay VEGAS Data Display Running Project id TGBT14A 912 46 Scan 4 Int 43 Reset Crosshairs Column 1 Row 0 Spec A Band 0 E F G H 0 A B 1 11 1 0 10 1 0 9 9 815 9 82 9 625 Figure 10 6 The VEGAS real time data display 6 90Z Most Visitedv Mj NRAO Green Bank 5 GjOutlook Web App CICADA W NRAO
192. er of channels or sampling speed VEGAS can also record only a single polarization for single polarization receivers 125 126 CHAPTER 10 VEGAS a b Maximum of 8 sub bands BankA BankA BankB BankB Bank pal BankE BankE Bol BankF BankF Bank G Bank G 23 44 MHz Bank Bank ai at g Frequency Frequency fobs lt 10GHz Observing bandwidth 125 GHz Observing bandwidth Figure 10 1 Examples of two basic VEGAS setups Since each spectrometer can be configured indepen dently these setups can be mixed and matched with the restriction that all spectrometers will have the same switching signal In both setups each spectrometer processes signals from two polarizations a Wide band single beam dual polarization observations The 8 spectrometers can be tuned to different frequencies covering a bandwidth of up to 10 GHz although the GBT IF system typically limits this to 4 6 GHz depending the receiver In this case each spectrometer produces a single spectral window b Narrow band multiple beam dual polarization mode Each spectrometer can provide a maximum of 8 spectral windows within the bandwidth processed by the spectrometer 1500 MHz with a useable bandwidth of 1250 MHz for modes 20 24 and 1000 MHz with a useable bandwidth of 800 MH
193. es from WMAP5 and accurate positions from the VLBA calibrator surveys through VCS6 e PTCS PN 72 introduces PCALS4 5 with high frequency flux densities updated by WMAPT the Planck Early Release Compact Source Catalog and the Australia Telescope AT20G survey 90 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS e PCALS 4 7 adds new 30 44 70 and 100 GHz flux densities from the final Planck Catalogue of Compact Sources Planck Collaboration 2013 arXiv 1303 5088 and 20 GHz fluxes from Righini S Carretti E Ricci R et al 2012 MNRAS 426 2107 A 20 GHz bright sample for delta 72 deg I Catalogue There is no PTCS PN describing this release Table 6 6 The following Catalogs are present as of November 2013 The flux densities of pointing calibrators vary by up to a factor of two on time scales of years at frequencies higher than 8 GHz so the pointing calibrators will never be good flux calibrators The main reason for updating their flux densities is to make sure the observer gets a strong enough pointing calibrator For genuine flux density calibration we recommend observers use the latest flux densities of 3C 48 3C 138 3C 147 3C 286 and 295 listed in the VLA calibrator manual at http www vla nrao edu astro calib manual baars html Catalog Description fluxcal cat Calibrators with well determined flux densities U S Government Printing Office Usgpo 2006 The Astronomi
194. es are case insensitive The following example will be used to describe some of the Catalog Header Keywords 6 2 COMPONENTS OF AN OBSERVING SCRIPT 87 FORMAT This tells the type of catalog and must be the first line in any catalog Possible val ues are spherical ephemeris nntle and conic For the SPHERICAL format the first line would contain FORMAT SPHERICAL This is the default format hence the FOR MAT SPHERICAL may be omitted HEAD This gives the header for tabular data and consists of a list of any keywords This should appear as the last line in the header before lines giving information about the sources in the catalog You can also create your own header keyword such as the type column in the above example The default header is HEAD NAME RA DEC VELOCITY In the above example we have added more entries than the default We have also created a new keyword named type NAME The source name is any string up to 32 characters long The name as given in the catalog does not have to be surrounded by quotes unless it contains embedded blanks or hashes In the above example we needed to use quotes around Src A because of the space in the name COORDMODE The default is J2000 Possible values are J2000 B1950 JMEAN mean coordi nate of date given by EQUINOX GAPPT geocentric apparent coordinates of date GALACTIC HADEC AZEL ENCODER In the above example we put the COORDMOD
195. es are taking data This usually indicates that the data acquisition software has crashed on that node You may also see a status of Unk for unknown which usually means that the GPU node itself crashed In both cases ask the operator to contact the on duty support scientist In coherent fold or cal mode you can check data using a web browser by navigating to www gb nrao edu guppi This page shows a summary of the most recent output file written to disk on each GPU node and updates automatically It can be accessed from anywhere If it doesn t appear 11 5 MONITORING GUPPI DURING AN OBSERVATION 3 Session Edit View Bookmarks Settings Help Current GUPPI status TELESCOP PROJID NRCVR OBSFREQ TRK_MODE RA DEC BMIN NLEN JAS END PKTFMT OBSBW OBSNCHAN POL TYPE NBITS NBITSADC CAL MODE STT IMJL STT_OFFS DROPT OT CURBLOCK CAL FREQ CAL PHS Current data block info PKTIDX Last update Thu Aug 28 15 49 52 274 188 Shell i Shell No 2 to SIDES Figure 11 3 The GUPPI Status Display screen 154 CHAPTER 11 PULSAR OBSERVING WITH GUPPI to be updating as expected the auto plotting routine may have crashed You can check data directly by ssh ing into the GPU nodes e g ssh gpu1 and navigating to data gpu partial gpu 1 9 where gpu 1 9 refers to the GPU node of interest Note that though there are nine GPU nodes only eight are used at a given time one is a spare 11 6 Proc
196. es the period in seconds over which the full switching cycle occurs The value is a float Default values are 0 2 for obstype continuum 0 04 for obstype pulsar and 1 0 for any other value for the obstype keyword See the GBT Propser s Guide for recommended minimum switching periods for different modes swfreq This keyword defines the frequency offsets used in frequency switching swtype fsw The value consists of two comma separated floats which are the pair of frequencies in MHz Default values are swfreq 0 25 Bandwidth 0 25 Bandwidth for swtype fsw and swfreq 0 0 other wise tint This keyword specifies the backend s integration dump time The value is a float with units of sec onds Default values are 10 0 for obstype continuum tint swper for obstype spectroscopy and 30 0 of any other value for the obstype keyword See the GBT Proposer s Guide for recom mended integration times beam This keyword specifies which beams are to be used for observations with multi beam receivers The keyword value is a string Possible values are B1 B2 B3 B4 B12 both beams 1 and 2 B34 both beams 3 and 4 This has a different meaning from the beamName in the observing scans This beam indicates which signals from the receiver are to be recorded e g B12 means to record data from both feeds 1 and 2 The default value is B1 nwin This keyword specifies the number o
197. escales are problems in this data Figure 12 3 OTF NOD data on a bright source under marginal conditions The differences between the data and the model are clearly larger in this case 12 1 OBSERVING WITH THE CCB 163 Indexscans si analagous to filling Readccbotfnod si 12 q read scan 12 into variable q Fitccbotfnod q fit the nod Figure 12 4 CCB OTF NOD measurement of a weak mJy level source under good conditions The IDL commands used to obtain this plot are shown inset Indexscans si Readccbotfnod si 12 q Fitccbotfnod q binw 0 5 bin into 0 5 sec integs before fit Figure 12 5 The same weak source data this time with the individual integrations binned into 0 5 second bins using fitccbotfnod s binwidth optional argument in seconds so the thermal noise scatter doesn t dominate the automatically chosen y axis scale This better shows any gradients or low level fluctutions in the beamswitched data due for instance to imperfect photometric conditions In this data they are not significant 164 CHAPTER 12 THE CALTECH CONTINUUM BACKEND CCB This will be a beamswitched map The beamswitching can be removed by an deconvolution algorithm also implemented in the code Your GBT friend will help you with this if needed 12 2 Performance Recent tests under excellent conditions show a sensitivity of 150 uJy RMS for the most sensitive single channel 34 GHz or 100 RMS for all channels c
198. essary You will also need to let the operator know what computer you will be using during your observations At this time you will begin to open a Virtual Network Computer session that you will use for the remote observations Starting this early will allow for any problems encoun tered while preparing to observe remotely to be solved before the observations are to begin You can find information about remote observing policies at https safe nrao edu wiki bin view GB Observing GbtObservingPolicies and you can find information about opening a session at http www gb nrao edu gbt remoteobserving shtml Step 10 The operator on duty will handle several tasks for you at the beginning of your observations They will put you in the gateway give you security access so that you can control the They will also get the correct receiver into the focus position of the GBT get the antenna motor drives ready for movement place the correct pointing models into the system and set the GBT s active surface AS into the proper state The operator is there to take care of all safety issues concerning the Step 11 Now you are ready to observe You will use the Astronomer s Integrated Desktop Astrid see Chapter to perform your observations by submitting an Observing Script see Chapter 6 The steps you will take in observing are generally A Configure the receiver Intermediate Frequency system IF and backend to the desired sta
199. essing Your Data Data are recorded in the PSRFITS standard which can be processed by all common pulsar data analysis packages e g PRESTO SIGPROC PSRCHIVH and DSPSR Incoherent mode data are written to data 12 username projectID date where data 12 refers to either datai or data2 whichever you specified with guppi datadisk username is your NRAO user name project ID is the GBT project ID as it appears in astrid e g AGBT14A 507 and date is the UTC date in YYYYMMDD format Each data disk has a capacity of 7 5 TB but in practice we usually are only able to keep 3 TB free on each disk Please make arrangements to move large volumes of data off of beef as quickly as possible after your observing session It can be extremely problematic if the disks get too full You can expect to be bugged relentlessly if data are not moved off of the beef disks in a timely manner Please contact your project friend if you need help managing your data Coherent mode data are written to each GPU node and need to be combined to recover the full bandwidth For fold and cal mode data you can do this yourself using the executable scripts home gpu bin get data or home gpu bin combine_psrfits These should be run in home scratch area while you are logged in to beef or in your user area on datai or data2 But note that you must be logged in to beef These scripts will rsync the data off of each GPU node and put them in temporary sub direc
200. eters properly reflect the needs of the project The project Friend assigned by NRAO can also offer advice on optimizing session parameters where appropriate In some cases a session s target position may be representative of a group of objects clustered on the sky As the project progresses and some of these targets are observed this representative position may need to be updated In this case the PI should send an email request to the DSS helpdesk The DSS can automatically update the sky coordinates of common fast moving solar system objects including comets The position is updated each day prior to scheduling On the project page under Project Sessions an asterisk next to the coordinates indicates that the position for that session is automatically updated in this manner Many observers find it helpful to use a sky plotting tool to help plan their observations and keep track of target locations on the sky The cleo scheduler tool which runs on Linux systems in Green Bank and can be run remotely through is one such tool that allows a GBT user to plot target locations on the sky for any date and time This application can read target coordinates from a standard astrid catalog file Observers will find this tool handy for identifying the time of day a project may get scheduled as well as helping to plan observations in detail after they are scheduled To run the program type unix cleo scheduler 3 5 Contact Information and Projec
201. f frequency windows that will be observed The value for this keyword is an integer from 1 through 64 The maximum value for nwin is backend and receiver dependent see 2 1 4 The number of values given for the restfreq keyword must be the same as nwin There is no default value for VEGAS configurations the default value is 1 for all other configurations deltafreq This keyword specifies offsets in MHz for each spectral window so that the restfreq is not centered in the middle of the spectral window The values for this keyword are either a single offset or a comma separated list of floats The default value is 0 0 See Appendix B for more details on the use of deltafreq vlow and vhigh These keywords specify the minimum and maximum velocity to be observed from a group of sources The value is a float and is in km s for velocities The default value is 0 0 See Appendix C for more details on the use of vlow and vhigh The use of vlow and vhigh is not recommended for frequencies where there can be large amounts of Radio Frequency Interference EFI vframe This keyword specifies the velocity frame the inertial reference frame The keyword value is a string Allowed values are topo topocentric i e Earth s surface bary Barycenter of solar system Isrk Local Standard of Rest kinematical definition i e normal LSR definition lsrd Local Standard of Rest dynamical definition rarely used galac center of gal
202. ff 120 now observe srcC five times numobs 5 for i in range numobs OnOff srcC myoff 120 To print the rise and set times in the above example you would just need to add print the rise and set times to the log using Comment risesetstring 20 deg elev rise s and set 96s 96 riseSrcB setSrcB Comment risesetstring to the script 6 2 7 4 Frequency Switched On The Fly Mapping In this example we perform frequency switched observations of the HI 21 cm line to map a 5 by 5 degree region of the sky We use pixels that are arc minutes in size and have an integration time of 2 seconds per pixel We do not observe the whole map in this example This example is available as home astro util projects 6D01 example four py Frequency Switched Observations where we loop through a list of sources E first we load the configuration file execfile home astro util projects 6D01 configurations py E now we load the catalog file Catalog home astro util projects 6D01 sources cat now we configure the GBI IF system for freq switched HI observations Configure vegas_fs_config i now we balance the IF system Balance i now we use a Break so that we can check the IF system Break Check the Balance of the IF system Us now we set the parameters for the map which source srcs Object2 108 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERV
203. flexibility e Location in the National Radio Quiet Zone Comparatively low environment See Fig e Dynamic Scheduling matching the optimum weather conditions to science programs 2 1 2 National Radio Quiet Zone The National Radio Quite Zone was established by the Federal Communications Commission FCC and by the Interdepartmental Radio Advisory Committee IRAC on November 19 1958 to minimize possible harmful interference to the National Radio Astronomy Observatory in Green Bank WV and the radio receiving facilities for the United States Navy in Sugar Grove WV The NRQZ is bounded by NAD83 meridians of longitude at 78d 29m 59 05 W and 80d 29m 59 25 W and latitudes of 37d 30m 0 4s N and 39d 15m 0 4s N and encloses a land area of approximately 13 000 square miles near the state border between Virginia and West Virginia More information on the NRQZ can be obtained at http www gb nrao edu nrqz nrqz html 2 1 3 Front Ends The GBT receivers cover several frequency bands from 0 290 50 GHz and 80 100 GHz Tables and list the properties of the Prime Focus receivers and the Gregorian Focus receivers System temperatures are derived from lab measurements or from expected receiver performance given reasonable assumptions about spillover and atmospheric contributions The Proposer s Guide http www gb nrao edu gbtprops man GBTpg GB Tpg tf html vides more information on the receivers pro Table 2 1 Propertie
204. for one bank the system can potentially require amplification for other portions of the bandpass This can cause the system gain to transition to the non linear regime where changes in the input signal do not linearly change the recorded output We have found that using when using a 3 5 GHz bandwidth the system was able to properly configure across all frequencies We were not able to sufficiently test using larger than 3 5 GHz of total observed bandwidth across the system It is recommended that users hoping to push the bandwidth limit should watch the attenuation levels in the converter module and if necessary discuss the optimum settings with their support scientist 10 3 4 Monitoring VEGAS observations The GFM tab in Astrid is not capable of displaying VEGAS observations in real time it will display passbands at the end of a scan and may be used in offline mode Rather there are four monitoring tools that are useful with VEGAS e the VEGAS Data Display vegasdisplay gb nrao edu e the VEGAS CLEO screen 132 CHAPTER 10 VEGAS e the VEGAS Data Monitor VEGASDM e the VEGAS shared memory display vegas_status The first three items are generally useful while observing with VEGAS while the last one is for more specialized problem diagnosis Each tool is described in more detail below The VEGAS Data Display The VEGAS real time data display may be accessed by pointing a web browser to http vegasdisplay gb nrao edu note this
205. frequency projects can be considered as well There is no intention to implement service observing by GBT scientific staff Green Bank scientific staff will not be on hand to check operator run projects Getting a project approved as an operator run backup requires consent from the GBT Friend and the GBT DSS staff To identify your project as a backup project of either sort inform your GBT Friend 3 11 Session Types There are four types of sessions defined for astronomy projects open windowed elective and fixed Open sessions have no major constraints on when they can be scheduled beyond the functional require ments that an observer is available the source is above the horizon and the weather is suitable Most sessions fall into this category and provide the most flexibility in the DSS At the other extreme are fixed sessions that have no flexibility and are prescheduled at a particular date time that is their telescope periods have already been defined The other two types are windowed and elective sessions which have some constraints but are not fixed on the schedule T he most common examples are monitoring and VLBI sessions where the science demands that an object must be observed at defined intervals or times Windowed sessions are defined by a cadence that may be either periodic or irregular For example an observer may require observing a target once per month for five months with each observation having a tolerance of pl
206. g example tracks 3C48 for 60 seconds using the center beam Track 3C48 None 60 0 The following example tracks a position offset by one degree in elevation from 3C48 Track 3C48 None 60 0 fixedOffset Offset AzEI 0 0 1 0 The following example scans across the source from 1 to 1 degree in azimuth Track 3C48 endOffset Offset AzEl 2 0 0 0 60 0 fixedOffset Offset AzEI 1 0 0 0 OnOff The OnOff scan type performs two scans The first scan is on source and the second scan is at an offset from the source location used in the first scan Syntax OnOff location referenceOffset scanDuration beamName The parameters of OnOff are location A Catalog source name or Location object It specifies the source upon which to do the On scan referenceOffset An Offset object It specifies the location of the Off scan relative to the location specified by the first parameter scanDuration A float It specifies the length of each scan in seconds beamName A string It specifies the receiver beam to use for both scans beamName can be C 1 2 8 4 or any valid combination for the receiver you are using such as MR12 and MR34 The default value for beamName is 1 The following example does an OnOff scan with reference offsets of 1 degree of arc in Right Ascension and 1 degree of arc in Declination and a 60 second scan duration using beam 1
207. ge net http dspsr sourceforge net 11 8 WARNINGS 155 e The GBT noise diodes are stable over short to medium time scales and a number of continuum flux calibration scans are available for common observing set ups this is especially true of 820 MHz and L band NANOGrav set ups because NANOGrav observes flux calibrators at least once a month If you re project requires flux calibration consider contacting your project friend to see if appropriate calibration data already exist e Before writing scheduling blocks from scratch ask your project friend if there are any already available from other projects that might suit your needs This minimizes the possibility of an incorrect set up or scheduling block 11 8 Warnings e Do not run any commands from the GUPPI prompt e Do not run guppi set params from the command line at all This is all handled by configuring in Astrid now 11 9 More Information There are several other example configurations which you can copy load into Astrid or simply browse in users sransom astrid They are e users sransom astrid GUPPI astrid example py The well documented S band search mode ex ample from above users sransom astrid GUPPL_astrid_820MHz_cal py A 200 MHz BW cal scan using the PF1 receiver at 820 MHz users sransom astrid GUPPI astrid 820MHz fold py A 200 MHz BW fold scan of a bright MSP using the PF1 receiver at 820 MHz users sransom astrid GUPPI astrid
208. h 6 2 COMPONENTS OF AN OBSERVING SCRIPT 75 e Ka band with CCB preferred If the Ka band is the current receiver Rcvr26 40 then AutoOOF will automatically configure the CCB and will use the second highest frequency channel 34 25 GHz because it provides significantly better receiver temperature than the highest frequency band Use the same commands as for Q band above e Ka band with DCR backup In case the preferred backend CCB is not functional the DCR can be used instead In order to do this you must configure the DCR prior to calling AutoOOF As an example we provide a DCR configuration used by GB PTCS execfile home groups ptcs obs turtle configs py Configure kaband AutoOOF source 2253 1608 configure False e AutoOOF with MUSTANG Here is an example of setting up and running AutoOOF with Rcvr PAR a k a MUSTANG One must set up and tune up the MUSTANG system first refer to Chapter 13 Configure users bmason mustangPub sb mustangfull conf mySre 71159 2914 Catalog Slew mySrc AutoOOF source mySrc More information on n AutoOOF can be found at 76 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS 6 2 3 3 Observing Scans Track The Track scan type follows a sky location while taking data Syntax Track location endOffset scanDuration beamName startTime stopTime fixedOffset The parameters for Track are loc
209. hannels and an 800 MHz bandwidth See the introduction to GUPPI in Chapter 11 2 1 4 5 MUSTANG See the introduction to MUSTANG in Chapter 2 1 4 6 VLBI The supports observations with a Mark5 VLBA recorder This recorder can also be used in a single dish mode to make high time resolution observations For more information consult the web page http www gb nrao edu fghigo gbtdoc vlbinfo html 2 1 4 7 Radar Planetary radar observations are supported by a portable fast sampler sampling at 2 4 bits at rates up to 20 MHz This backend is used and maintained by groups at Arecibo Cornell and CalTech Those interested in planetary radar should consult people in those groups As an introduction refer to the web page https safe nrao edu wiki bin view GB Observing RadarObserverAdvice 2 1 5 Polarization Measurements Measurement of Polarization and Stokes parameters is possible using VEGAS and GUPPI This is an expert user mode users should contact their GBT support person or the GBT helpdesk For an intro duction to polarization observations see A Heuristic Introduction to Radioastronomical Polarization by C Heiles ASP Conference Series Vol 278 2002 8 CHAPTER 2 THE GBT OBSERVING PROCESS 2 2 Computing Facilities Workstations are available for visitors in Room 105 in the Jansky Lab Most are Unix stations and there is also a Windows machine Laptop connections are provided there and in several loca
210. have a speaker phone however e When your observing time starts and the operator gives you permission you should use Astrid to load your configuration and start observing 17 2 VNC Setup Instructions Instructions for opening a VNC session for remote observing can be found at http www gb nrao edu gbt remoteobserving shtml Chapter 18 Planning Your Observations And Travel 18 1 Preparing for Your Observations After your proposal has been accepted you will be notified of how much observing time you will receive on the GBT You will also be notified of who your scientific contact person friend will be You should contact your scientific support person well in advance of your observations to help you develop observing strategies and your observing scripts We require that new observers or experienced observers doing new projects outside their pre vious realm of experience come to Green Bank for their initial observations Advisers are also re quired to accompany their students for their first trip to Green Bank All policies can be found at https safe nrao edu wiki bin view GB Observing GbtObservingPolicies You can use the online reservation system at https bos nrao edu reservations or contact Jessica Taylor at 304 456 2227 or email jtaylor nrao edu to reserve rooms in the Green Bank Residence Hall Contact your GBT friend well in advance of the observations to determine the optimum dates for your visit and ens
211. he results appear stable but we recommend performing a check at least once every sixty minutes in any event 7 5 Calibration Strategies For best flux density calibration of spectra it is recommended that you should observe continuum flux density calibration sources at least once during an observing session To do this do a Peak Focus on the calibrator followed by an observation in the same spectral line setup used for the program sources This will give the relation of flux density to antenna temperature as a function of frequency that can be applied to the program spectra Of course there may be other outstanding reasons to perform calibration observations more often If you have concerns over how often you should observe a calibrator you should get into contact with your support person 7 6 Balancing The Converter Rack When using pulsar or Radar backends it may be necessary to set attenuation levels in the Converter Rack This currently does not happen automatically This can be accomplished in one of two ways The first is to specify the target power level in volts of the Converter Rack modules This is accomplished using the BalConvRack function Here is an example of how you would use this function in an Observing Script make the function available execfile users tminter astrid BalConvRack py E to use BalConvRack module list target values E 2 module list is an array with a list of converter module number
212. he surface or a new AutoOOF may be necessary e Daytime During the daytime this is a difficult question to answer as it depends on how much the pose of the telescope is changing with respect to the Sun cloud cover changes etc The answer can be anything from 1 4 hours In practice we suggest running an AutoPeak every 30 40 minutes and watching for the reappearance of a sidelobe on the elevation scans When the sidelobe becomes significant it is probably a good time for another AutoOOF AutoOOF Scheduling blocks The scheduling block to execute AutoOOF is quite simple The command normally does not require any arguments although specifying the source is prudent We recommend choosing a source with a flux density of at least 3 4 Jy You may specify a flux density cutoff using the flux argument e Q band with DCR If Q band is the current receiver Rcvr40 52 then AutoOOF will automatically configure the DCR to use the widest continuum filter 1280 MHz So you may simply issue AutoOOF source 2253 1608 Break Examine solutions and send them to active surface The default polarization is R If you want to select the L channel then specify an additional argument channel 0 If you don t know the name of a bright nearby calibrator you may alterna tively specify a flux density cutoff AutoOOF flux 3 0 but beware that the flux density database is not kept current and this option has not been tested muc
213. heduling Blocks a list of Observing Scripts if any that have been previously saved into the Astrid database All of the saved Observing Scripts for a given project will show up in the Scheduling Blocks section of the Edit Tab If an Observing Script has been Validated i e it is syntactically correct then it will appear in bold face type This means that it can be executed If the script has been saved but is syntactically incorrect it will appear in lighter faced type 4 3 1 2 Editor You can use the Editor to create or modify an Observing Script within Standard Windows functions like Ctrl X to delete selected text Ctrl C to copy selected text and Crtl V to paste selected text can be used in the editor The editor lists the line number on the left hand side of the editor and uses color coding for the type of lines within the Observing Script Green characters are for commented characters black is for variables and standard python commands syntax purple magenta is for strings and dark blue is for function names The contents of loops if statements etc that are normally indented in python are also indicated on the left hand side of the editor The start of a loop for example is indicated by the symbol and the contents of the loop are within a black line that connects to the O symbol The editor also has four operational buttons These are Save to Database This button will check the validation of the current Observing
214. ibes all the plotting functionality available in There is also a plotting Tutorial that illustrates the plotting capabilities by example which is available at http deap sourceforge net tutorial index html 5 2 THE CLEO UTILITIES 49 5 2 The CLEO Utilities The CLEO Control Library for Engineers and Operators system provides a large number of utilities for monitoring and controlling the GBT hardware systems Some of these are quite useful for observers although most are intended for expert users and GBT staff Here described are just a few CLEO utilities that are very useful for observers To start CLEO log in to any Linux workstation in Greenbank open a terminal window and type cleo A CleoLauncher window will appear Click on the Launch menu to get a list of programs that can be run Documentation is available on the following web pages but is somewhat out of date so its best to consult your GBT friend for details Useful help messages pop up when you hover the mouse over any CLEO widget for a few seconds http www gb nrao edu rmaddale GBT CLEO Manual index html and http www gb nrao edu rmaddale GBT CLEOManual tableofcontents html 5 2 1 Talk and Draw Launch Utilities Tools TalkandDraw Talk and Draw brings up a window for communication with the GBT Telescope Operator Any thing you type in the window will be seen by the Operator and he can type replies which will show up in your window A
215. ies is shown in Figure Simplified directions are also shown in Figure Green Bank is located in Pocahontas County WV very close to the Virginia border and at about the mid point of the full extent of the Virginia West Virginia border 18 5 2 Directions to Green Bank The following are directions to Green Bank from airports in Pittsburgh Pa Washington DC Char lottesville Va and Roanoke Va The duration of the drive from either Pittsburgh or Washington is four to five hours The duration of the drive from Charlottesville and Roanoke is about 2 1 2 hours Beware of GPS GPS systems Mapquest and other such automated route finding systems are notoriously unreliable within 50 miles of the Observatory Some roads that are recommended by these systems are passable only with 4 wheel drive vehicles Do not turn onto unpaved roads To Co lu 18 5 GETTING TO GREEN BANK 70 Wheeling Pittsburgh 79 Washington 205 Directions to the National Radio Astronomy Observatory Green Bank West Virginia From Charleston WV Via l 64 East exit at White Sulphur Springs Exit 175 and take Rt 92 North to Green Bank From Roanoke VA Via l 64 West exit at White Sulphur Springs Exit 181 and take Rt 92 North to Green Bank From Pittsburgh Via 1 79 South exit at Weston Buckhannon Exit 99 and travel US 33 East to Elkins then take Rt 92 South to Green Bank From Washington DC Via l 66 West to l 8
216. iew GB Gbt4mmRx e 4mm Status and Commissioning Wiki which provides latest info on performance and notes for users https safe nrao edu wiki bin view GB Gbt4mmRxCommissioning 192 CHAPTER 14 THE 4MM 68 92 GHZ RECEIVER Chapter 15 Radio Frequency Interference Radio Frequency Interference can be a significant problem for some observations The most up to date information on the environment at the can be found at http www gb nrao edu IPG Useful resources referenced from the above web page include a list of known sources of RFT https safe nrao edu wiki bin view GB Projects RFIReportsTable and plots of RFI monitoring data http www gb nrao edu IPG rfiarchivepage html Every observer should check for known around their observing frequencies If you suspect that this could have a significant impact on your observations you should contact your scientific support person to decide on an appropriate course of action Mitigation of known RFI signals In some cases it is possible to turn off a known RFI source For example there is an amateur transpon der at about 432 MHz which we can request to be shut down If there are known RFI signals the user should discuss them with the scientific support person Given enough advance warning days to weeks we may be able to have them shut down during the observing 193 194 CHAPTER 15 RADIO FREQUENCY INTERFERENCE Chapter 16 How weather can affect your
217. ificantly out of focus Syntax AutoPeakFocus source location frequency flux radius balance configure beamName gold The parameters to AutoPeakFocus are 6 2 COMPONENTS OF AN OBSERVING SCRIPT 67 Table 6 4 The most commonly used Scan Types available for the Observing Type Scan Type Description Continuum AutoPeakFocus Selects and observes a nearby calibration source and updates the pointing and focus corrections Continuum AutoPeak Selects and observes a nearby calibration source and updates the pointing corrections Continuum AutoFocus Selects and observes a nearby calibration source and updates the focus correction Continuum AutoOOF Selects and observes a nearby calibration source with different focus settings to create an out of focus holography map to update the surface Continuum Peak Performs a pointing observation Continuum Focus Performs a focus observation Continuum Tip Performs an observation to derive vs elevation Continuum Line Slew Slews the telescope to the specified source or Location Pulsar Continuum Line Track Follows a single position or moves with a constant Pulsar velocity while taking data Continuum Line OnOff Observe a source and then a reference position Continuum Line OffOn Observe a reference position and then the source Continuum Line OnOffSameHA Observe a source and then a reference position usi
218. ill not be called on to observe during times they have blacked out on their DSS calendar Operator run projects contain observing scripts that may be run by the GBT operator without need for direction from project team members The observational strategy must be simple Operator run projects are characterized by e Minimal calibration requirements e g a single pointing focus calibration at the beginning of the run If the observation requires more calibration than a single pointing focus or simple repetition of a pointing focus script at regular intervals then it will not qualify as an operator run candidate e Minimal changes in observing mode e Use of only one receiver e No scientist intervention required An operator can be expected to determine if a point focus measurement is reliable but cannot be asked to judge the quality of astronomical data The operator also cannot be asked to judge which source would be best to observe at any given time If there is any doubt whether an observation will produce reliable blind results then this project is not suitable as an operator run candidate e Clearly written instructions for the telescope operator describing the observing procedure including which scripts to run These instructions can be stored in the Project Notes on the DSS web page 18 CHAPTER 3 INTRODUCTION TO THE DYNAMIC SCHEDULING SYSTEM These requirements bias operator run projects to low frequency observations but high
219. ill typically use only certain values for some Astrid configtool keywords These are described below obstype will always be Pulsar backend will always be GUPPI bandwidth can be either 100 200 or 800 ifbw will be 80 for 100 MHz bandwidth modes and 0 for 200 or 800 MHz bandwidth modes tint is very flexible Under the hood it is controlled by the hardware accumulation length so that tint acc len x Nchan BW acc_len can take on values from 4 down to two in some special cases up to 1024 Most observers will want to keep their integration times fast enough to resolve fast MSPs while keeping data rate 200 MB s swmode will either be tp for calibration scans or tp nocal for pulsar scans noisecal should be lo for calibration scans this uses the low power noise diodes and off for pulsar scans The Astrid configtool also supports a number of GUPPI specific keywords some of which are only actively used in certain observing modes These keywords and their allowed values are described below guppi obsmode controls both the dedispersion and observing mode All data are written in PSRFITS format Allowed values are search Incoherent search mode i e spectra are rapidly written to disk fold Incoherent fold mode i e spectra are are folded on line using a pulsar ephemeris with sub integrations written to disk at a rate controlled by the guppi fold dumptime keyword Note incoherent fold mode is effectively deprecated in
220. in the range of 15 30 seconds depending on the radius being used so 22 20 sec 440 sec a fairly long time Such a long trajectory being sent to the antenna manager due to intrinsic inefficiencies in GRAIL s array handling mechanism really slows things down the overhead at scan start can easily exceed 1 minute Therefore one should typically keep individual scans which have nontrivial trajectories to 5 minutes or less parfulldaisy is a SB that does 22 radial periods broken up into 5 individual invocations of the Daisy procedure There is an optional phase argument to the daisy that lets you do this so that scan 2 starts where scan 1 left off See above example 13 6 8 boxmap covers a rectangular region with a sawtooth scan pattern in each direction To limit the accel erations at the turnaround points only the first few terms in the fourier series are retained This SB executes the map three times each requiring five minutes with a triangle patterened 6 dither between the three helping to smooth out small variations in the coverage The coordinate system choice Encoder here denotes the coordinate system used for the trajectory offset not for the central point inthe map which is defined by the source catalog Therefore this SB as written will map a rectangular region around a given point on the sky with the rectangle rotating with parallactic angle mySrc rxjl347 CATALOGS none needed for pla
221. ingle integration lEmerson Klein Haslam 1979 A amp A 76 92 Chapter 13 MUSTANG NOTE this chapter describes the use of MUSTANG not of its successor MUSTANG 1 5 which will be installed on the GBT for commissioning and shared risk science in early 2014 The use of MUSTANG 1 5 will be documented after commissioning is complete MUSTANG MUltiplexed SQUID TES Array at Ninety GHz the GBT s first 3mm instrument comprises a nearly fully sampled array of 64 Transition edge Superconducting TES bolometers which provide a 9 beam on the sky and instantaneously measure a 40 x 40 field of view It was built at the University of Pennsylvania by PI Mark Devlin s group in collaboration with NIST NASA NRAO and Cardiff University It is now a facility instrument on the GBT This chapter of the Observing Guide describes how to observe with MUSTANG on the GBT 13 1 Conditions Affecting MUSTANG Ob servations This section outlines the factors which can affect the efficiency and success of MUSTANG observations 13 1 1 Weather amp Solar Illumination Observations at 90 GHz are affected by clouds and water vapor which attenuate the astronomical signal and contribute spurious emission As a rule of thumb data obtained with zenith 90 GHz sky brightnesses at zenith under 35 K provide good data and data obtained with 90 GHz sky brightnesses under 50 K provide usable data for some of the easier types of projects compact or bright
222. kends are balanced so that they should be in their linear regimes see 6 2 5 Finally the desired observations are performed using one of the pre defined scans from 51 52 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS 6 1 What Are Scheduling Blocks and Ob serving Scripts At the we use Scheduling Blocks to perform astronomical observations A Scheduling Block is defined by metadata the header information provided in the Astrid Run Tab and an Observing Script The Observing Script is a list of commands that are executed in order to acquire observational data The Observing Script can contain information for configuring the telescope balancing the IF and other commands to tweak the telescope system observing directives along with the commands scan types to collect observational data An Observing Script is only part of a Scheduling Block The Observing Script does not include the observing metadata such as observer name etc and it does not include constraints on when the Scheduling Block should be executed such as weather required or the sequence in which Scheduling Blocks must be run Astrid interprets Observing Scripts via Python Thus Observing Scripts should follow Python syntax rules such as indentation for loops and can also contain or make use of any Python commands 6 1 1 Making An Observing Script Observing Scripts must be created well prior to your telescope time We suggest
223. l M amp C overhead per map plus 1 minute for processing for a total of 19 minutes The processing is launched automatically upon completion of the third map and the result is displayed in the OOF plug in tab of Astrid Because this is a new observing mode it is incumbent upon the user to examine the solutions and click the button in the Astrid DataDisplay tab to send the selected solution to the active surface It is recommended that when sending the solutions you use the yellow button in the OOF display tab labeled Send Selected Solution with Point and Focus Corrections new recommended method By using this method it is no longer necessary to follow AutoOOF with another AutoPeakFocus If you plan to run AutoOOF as the first thing during your observing slot we recommend running an AutoPeakFocus before the AutoOOF Subsequent runs of AutoOOF will not need a pre point focus as small errors in these values do not harm the results How long does the solution remain valid e Nighttime If the corrections are measured at least an hour after sunset then they should last for the next few hours as the backup structure cools off This can take many hours if it was a sunny day At frequencies below 90 GHz the corrections can be turned off sometime between midnight and 3AM If a sidelobe begins to appear on a bright pointing source during this timeframe then the previous AutoOOF is no longer valid Turning off the corrections may improve t
224. ld be trained on site by GBT staff not off site by others Training and certification received prior to the DSS test period are still valid Experienced observers when using instruments or observing modes unfamiliar to them should plan to visit Green Bank if they require assistance See Chapter 17 for more about remote observing Additional information is available at http www gb nrao edu gbt remoteobserving shtml Contact your project friend or the DSS helpdesk helpdesk dss gb nrao edu if you believe the DSS does not have you listed properly as a qualified remote observer 3 9 THE DAILY SCHEDULE 17 3 9 The Daily Schedule Each day between about 5 00 and 10 00 AM ET the telescope schedule is fixed for the 24 hour period beginning 8 00 AM ET the next day For example by 10 00 AM Monday the observing schedule is fixed for the period 8 00 AM Tuesday through 8 00 AM Wednesday Each morning this daily schedule is published and can be viewed on the DSS web site by anyone Those with projects on the 24 hour fixed schedule will be notified by email Observers must ensure that their blackout dates and session enabled flags are up to date each day by about 5 00 AM ET Changes made after this time may not be reflected in the upcoming day s schedule It is possible that weather conditions may change after a schedule is published compromising the observing efficiency for some scheduled telescope periods The observer or GBT staff may
225. ller prints a summary in home sdfits lt project gt lt project gt log indicating 10 3 GENERAL OPERATION 137 what scans were filled had problems and were skipped and if any data was skipped because the data rate was too fast The decision on whether to fill or not is made independently for each bank For cases where the integration time is close to the limit it s possible that some banks might be filled while others are not filled for the same scan if the number of subbands or the number of polarizations vary across the banks The summary log file will indicate when this happens If observers are concerned about the interpolation across the center channel they can turn that off in sdfits by using the nointerp option At the time of writing December 2014 online sdfits development is focused on using the VEGAS and other data streams to fill the live data as the scan is in progress Once complete this should eliminate many if not all of the current filler performance concerns Filling Offline You may wish to re fill your data offline In this case you make use the SDFITS filler program in the standard manner Note however that the actual VEGAS data is stored to a high speed lustre file system At the time of writing December 2014 this file system is only mounted on a small number of high performance machines planck fourier and newton and explictly is not mounted on the observing machines If you try to fill da
226. llow a link to the NRAO support center e Set the default time zone via the Preferences link e Access DSS documentation e Establish an iCalendar subscription Instructions for using iCalendar are available by hovering the mouse cursor over the iCal icon on the DSS Home Page By selecting a project ID observers are presented with the project page where they can e See a project calendar e Inspect session parameters e Enable or disable individual sessions e Specify observers from the project team and set the order they should be contacted by GBT operations e See a list of blackout dates for all observers on the project e See a list of completed telescope periods e Store and share project notes The project calendar gives observers an idea when their project is eligible for scheduling Regardless of the weather there will be times when a project is not eligible for scheduling for example because of no receiver availability observer blackouts fixed telescope maintenance periods and other fixed projects appearing on the GBT schedule Times not eligible for scheduling will be grayed out on the project calendar The project calendar helps with planning in a number of ways However it is important to under stand that a session s eligibility is based on ever changing constraints and can change from not eligible to eligible at any time Therefore if observers wish to take a break from observing based on the calendar outlook they should
227. lt 0 15 per airmass in useful observing conditions which attenuates the astronomical signal at low elevations the MUSTANG cryogenics which do not operate effectively below 19 degrees elevation microphonics from other receivers which couple more strongly at lower elevations and the antenna primary surface which shows a constant 90 GHz gain between 20 and 80 degrees elevation but can drop off sharply outside of this range Putting these considerations together and summarizing e elevations below 20 degrees not recommended due to reduced telescope gain and severely degraded MUSTANG cryogenic performance e 20 30 degrees elevation usable performance for observations of bright sources Receiver noise can be several times higher due to microphonics and the astronomical signal will be attenuated by a factor of 2 to 3 more than at zenith e 30 80 degrees elevation good performance Within this range the optimal performance is seen between 50 and 65 degrees elevation e above 80 degrees elevation not recommended Photometric performance in this range is not consistent probably due to degradation of the primary surface model Above 85 degrees the antenna often fails to execute MUSTANG scan trajectories due to the rapid slew rates in azimuth that are required for an Alt Az telescope such as the GBT to track close to the zenith 13 1 3 Receiver Cryogenic State The receiver should be cold and stable before observations begin Whether or not
228. luxcal Daisy location 3C123 map radius 5 radial_osc_period 60 radial_phase 0 rotation_phase 0 scanDuration 1200 6 2 4 Catalogs The Source Catalog system in Astrid provides a convenient way for the user to specify a list of sources to be observed as well as a way to refer to standard catalogs of objects At a minimum for each source there must be a name and a location Ra Dec or Glat Glon etc Other parameters may be set such as radial velocity An example of a simple Catalog is There are three formats of catalogs SPHERICAL A fixed position in one of our standard coordinate systems e g RA DEC AZ EL GLON GLAT etc EPHEMERIS A table of positions for moving sources comets asteroids satellites etc NNTLE NASA NORAD Two Line Element TLE sets for earth satellites The CONIC format is no longer supported In addition major solar system bodies may be referred to by name Sun Moon Mercury Venus Mars Jupiter Saturn Uranus Neptune Pluto These names case insensitive They may be given to any Scan Type function Track RALongMap etc No catalog needs to be invoked for the system to understand planet names and Pluto To use the catalog system the user invokes the Catalog command in her Observing Script and passes the name of the desired object to any of the scan functions All sources named in all the catalogs that
229. m 3 beamName 6 refBeam 4 for the gold A Boolean If True then only Gold standard sources i e sources suitable for pointing at high frequencies will be used by AutoPeakFocus This parameter is ignored if the source parameter is specified The sequence of events done by AutoPeakFocus in full automatic mode i e with no arguments are Step 1 Get recommended beam antenna subreflector motions and duration for peak and focus scans Step 2 Get current receiver from the system Step 3 Get current antenna beam location from the control system 6 2 COMPONENTS OF AN OBSERVING SCRIPT 69 Step 4 Configure for continuum observations with the current receiver Step 5 Run a balance see 6 2 5 2 to obtain accurate system temperature readings from the Step 6 Select a source using computed minimum flux observing frequency location and search radius Step 7 If no pointing source is found within the specified radius then provide the observer the option to use a more distant source default and if none found either aborting second default or continuing the scheduling block Step 8 Slew to source Step 9 Run a balance to set scan power levels Step 10 Run a scan using Peak Step 11 Run a scan using Focus Setting optional arguments will cause the scan to skip some steps These examples demonstrate the expected use of AutoPeakFocus AutoPeakFocus use all default values AutoPeakFocus
230. m Green Bank 6 2 4 5 Catalog Functions Two useful catalog functions are available c keys Acts like a python function that returns a list of all the source names in the Catalog loaded into the variable i e via c Catalog mycatalog c sourcename keyword Returns the value of the keyword for the named source in the Catalog loaded into the variable This function can be used to pass information in the Catalog on to the Observing Script e g specifying different map sizes for different sources directions The c keys function can be used so that the Observing Script will automatically loop through all the sources in a Catalog Here is an example of how to do this 6 2 COMPONENTS OF AN OBSERVING SCRIPT 91 Catalog home astro util astridcats HI strong cat sourcenames c keys for s in sourcenames Nod s 120 The c sourcename keyword function can be used to get information out of the keyword column of the Catalog for use within the Observing Script In the following example we get the source s Declinations and only observe those sources above 20 Declination note that the coordinates are always returned in degrees c Catalog home astro util astridcats lband pointing cat sourcenames c keys for s in sourcenames print c s dec if c s dec gt 20 Nod s 120 The c sourcename keyword function can also be u
231. m successful observations with the Green Bank Telescope GBT In Chapter 2 we briefly outline the features of the and the general observing process In Chapters 5 we provide an introduction to the Astronomer s Integrated Desktop Astrid the observing interface In Chapter 6 we provide example observing scripts that can be used in We also provide detailed descriptions of the contents of observing scripts In Chapter 7 we provide information on the strategies that should be used and advanced techniques for observing with the In Chapter 8 we provide a short overview of the Intermediate Frequency system IF In Chapter 9 the observing steps required for mapping and effective use of the data reduction pipeline are outlined In Chapter 15 we provide the locations of where to find more information about Radio Frequency Interference RFI in Chapter 3 you are introduced to the Dynamic Scheduling System and in Chapter is a discussion of the effect of weather conditions on observing In Chapter 17 there is advice on remote observing In Chapter 18 we provide information on what happens before your observations and directions on getting to Green Bank In Chapter we provide information on how to take your data home with you and where to obtain the GBT Data Reduction Package GBTIDL Later chapters give basics of observing with various specific instruments Chapter for spec tral line observing with VEGAS Ch
232. m the Washington National Airport take US 1 Va 110 US 50 to Interstate 66 ask at airport for exact details Take I 66 west to I 81 From here there are two alternative routes to Green Bank a Follow I 81 south to the exit for route 55 near Strasburg VA Go west on 55 to Moorefield WV Turn south on US 220 55 and drive to Petersburg WV Go south on route 28 55 to Seneca Rocks Continue south on 28 through Judy Gap to Bartow Follow route 92 28 south to Green Bank b Follow I 81 south to Harrisonburg VA Go west on US 33 through Franklin WV to Judy Gap Turn south on route 28 and drive to Bartow WV Follow route 92 28 south to Green Bank Route a is the preferred route Most of route 55 in WV has been upgraded to a new 4 lane highway and this is where you cross most of the mountains in getting to Green Bank Charlottesville to Green Bank From the Charlottesville Albemarle Airport go east straight on Airport Road to US 29 Take 29 south to US 250 and follow 250 west to Interstate 64 Go west on I 64 to Interstate 81 near Staunton VA After traveling north on I 81 for about two miles take the Woodrow Wilson Parkway exit Go west on the parkway to US 250 and follow 250 west to Monterey VA In Monterey turn south on US 220 and shortly thereafter veer west on route 84 to go to Frost WV Follow route 92 28 north to Green Bank Roanoke to Green Bank From the Roanoke Airport go left south on Valley View Drive Airport road an
233. n Annotation CALTAG SetValues ScanCoordinator source nothing Configure users bmason mustangPub sb caloff conf 13 6 4 This SB runs a sequence of five maps at a range of subreflector focus settings about the nominal focus The nominal focus is in the script as the variable nomFocus you should set it to the current best determined focus setting and remember that the script will leave it at that value upon completion Each map takes 45 seconds the total SB should run in about 5 minutes jii some good sources are 1642 3948 2253 1608 09274 3902 03194 4130 03594 5057 1955 5131 1256 0547 0854 2006 mySrc 14154 1320 HAHH CATALOGS none needed for planets Catalog Configure users bmason mustangPub sb mustang conf T T T T T start stop and increment for focus in mm ji current nominal LFC nomFocus 0 LFC deltas to try around this dfocus 10 3 0 3 10 focus is left at nomFocus LESTIE CTI LETT ORT TT LORE IO OE Daisy Params daisyScanDur 45 0 daisyRad 1 5 daisyRadPd 15 0 13 6 EXAMPLE ASTRID SCRIPTS 179 TTT TTT Do not modify below here from time import sleep Slew mySrc Configure users bmason mustangPub sb mustang conf relock MUX execfile users bmason mustangPub
234. n 78 i Focus list Focus v Full Screen Allowed Values 13 4 5 80 81 82 EGR A No v Yes 22 Append Data Show Current Hap Show Coverage polices Path Yusers bnason Shou calibration hap 0 TE To w Disk 4 Henory Hives Beet Forus Show Tine Stream Select Nap Fron Hemos From Disk Fit nap Du Hapet Fion Hense Eee Henne 9 Save FITS image Export Image Clas Error Clear Data Show Help Elev az LPC el LPC LFC Y arcn s cal fo BEPRPPEBESZE iino s ios ti bto eeessesseo fsfo folo folo olo talo Figure 13 4 Specifying scans to image in the MUSTANG IDL GUI The top shows the gain in nominal counts per Jansky and the bottom shows the column row mask denoting optically responsive detectors with 1 and optically non responsive detectors or those flagged by automated criteria by 0 The pixel gains serve the purpose of flat fielding the detectors but the flux density scale is fiducial only and celestial calibration is still essential The routine summarizes its findings in the above form organized by logical row and column i e electrical labels for each detector rather than array face geometry In this case all of column zero is non responsive and only four columns are shown due to space limitations Row 8 zero indexed is always non responsive since this is by design each column s dark SQUID not connected to
235. n Center Freq MHz 3000 000 Sw Period sec 1 Frequency State switching 2 002 Wind Vel m s 2 464 IF1 0 103 CM1 0 049 1 0 259 ACS J9 0 1109 backendIF 1419622228 0 103 CM5 0 054 CF5 0 239 ACS J13 0 13313 backendIF 1419622228 IF1 0 103 DCR A_1 0 430 TSys1 6 075 backendlF 1419622228 H 0 103 DCR A 3 0 430 5 53 6 053 backendIF 1419622228 eee ObservationManagement Log 1 DataDisplay Log 1 GbtStatus Log 1 Command Console Figure 4 8 The Astrid Gbt Status Tab showing the bottom portion of the status To see the rest of the status screen you will need to use the scroll bar Source The source name Source Vel The source velocity km s Observer The observer name as recorded in the FITS file Last Update The local time when the database was last updated Operator This field is currently not working UTC Time The UTC time of the last update UTC Date The UTC date of the last update Project ID The data directory of the FITS files LST The LST of the last update MJD The Modified Julian Date MJD Status The status of the GBT The GBT status is either e Not Connected e Unknown Clear e Info e Warning e Error 4 5 THE GBTSTATUS TAB 35 e Fault e Fatal If the M amp C system is not communicating properly with the hardware the status can be Unknown or Not Connected If the status is
236. n and 5 degrees in Declination See Appendix E for more information on angle formats and units in defining an Offset object 6 2 6 3 Horizon Object Observing Scripts allow an observer to specify a definition of the horizon The user defined horizon can be used to begin an observation when an object rises and or end the observation when it sets relative to the specified elevation of the horizon The Horizon object may be used to obtain the initial time that a given source is above the specified horizon including an approximate atmospheric refraction correction The horizon object is created via myhorizon Horizon 10 0 In this example a horizon that is at 10 degrees elevation is created If no argument is given to Horizon it will assume a default of elevation of 5 25 degrees the nominal horizon limit Any Horizon object may be substituted as a start or stop time in scan types such as Track The rise and set times for any sky location in spherical coordinates may be obtained as a UTC time and date see 8 6 2 6 4 horizon GetRise source will return the nearest rise time and horizon GetSet source will return the next set time of the source For example to display the rise time of 0616 1041 the previous rise time if the source is above the horizon or the next rise time if the source is below the horizon print Horizon GetRise 0616 1041 For northern circumpolar sources which never set horizon GetRise s
237. n into circular polarization using a 1 4 wave plate in front of one of the beams for VLBI observations The two beams are separation by 286 in the cross elevation direction on the sky i e along azimuth In this chapter we present information for carrying out W band observations We concentrate on items specific to W band and assume the user is familiar with the other chapters of the observing guide Contact your support astronomer if you have questions 14 2 Configuration The 4mm Receiver uses the standard config tool software that automatically configures the GBT IF system based on user input e g frequency and bandwidth Example w band configuration files are given in home astro util projects 4mm The 4mm system is broken into into four separate bands e FL1 67 74 GHz e FL2 73 80 GHz e FL3 79 86 GHz e FL4 85 93 GHz You can only use one of these bands at a time i e you cannot simultaneously observe lines in more than one band The millimeter down converter filters of the system limits the instantaneous bandwidth to 4 GHz for 73 93 GHz filters FL2 FL3 FL4 while up to 6 GHz of total bandwidth is available for 67 74 GHz filter FL1 The configuration items specific to the 4mm receiver are the following 185 186 CHAPTER 14 THE 4MM 68 92 GHZ RECEIVER 300 250 iciency 200 150 100 System Temperature K Telescope Eff 50 F aT June 2012 o December 2012 65 70 79 80 85 90
238. n mustangshutdown to leave the receiver in a quiescent state 168 CHAPTER 13 MUSTANG 13 3 Observing with MUSTANG 13 3 1 Mapping Strategies All MUSTANG data are collected with variants of an on the fly OTF mapping strategy in which the antenna is slewed to cover a given region of interest while data are recorded Two main scan strategies have been developed a box or billiard ball scan which covers a rectangular region with approximately uniform coverage and a daisy or spirograph scan pattern which covers a circular area with a more center weighted distribution of integration time on the sky Under normal circumstances we do not recommend the standard ASTRID observing procedures RALONGMAP or DECLATMAP which perform discrete linear raster scans over a given region because these tend to excite vibrations of the GBT feedarm which in turn give rise to unacceptable pointing errors at 90 GHz Due to the desirability of covering a given point of interest on the sky with many detectors and due to the effects of fluctuations in detector gain and sky noise we do not recommend staring at a single point either even for point source photometry projects Under these circumstances the center weighted coverage of the daisy scan is appropriate For the identical total integration times and areas covered the daisy pattern gives a factor of 3 6 more integration time on the central field of view or a reduction of 1 9 in RMS nois
239. n using some VEGAS specific tools 8 10 3 4 130 CHAPTER 10 VEGAS e Fill your data either replying on the on line filler or by running SDFITS manually 5 10 3 5 e Process your data using GBTIDL 5 10 3 6 10 3 1 New Updated Configuration Keywords Most of the keywords defined in 6 2 2 2 applicable for VEGAS New keywords defined for VEGAS and additional values accepted by existing keywords are described below restfreq restfreq may now be a dictionary which allows the specification of configuration values to over ride the corresponding values in the configuration block See Section 6 2 2 2 for more details nwin This keyword has the same meaning as specified in It specifies the number of frequency windows that will be observed The value for this keyword is an integer from 1 through 64 The maximum value for nwin is backend and receiver dependent see 2 1 4 The number of values given for the restfreq keyword must be the same as nwin bandwidth This keyword has the same meaning as specified in 6 2 2 2 It gives the bandwidth in MHz to be used by the specified backend The value of the keyword should be a float It accepts values for bandwidth specified in Table nchan This keyword has the same meaning as specified in 6 2 2 2 It is used to determine the number of spectral channels Values may be specified as low medium low medium medium high and high or may be given as integer values corresponding to
240. nDuration The parameters for Nod are location A Catalog source name or Location object It specifies the source upon which to do the Nod beamNamel A string It specifies the receiver beam to use for the first scan beamNamel can be 1 2 or any valid combination for the receiver you are using such as MR12 and beamName2 A string It specifies the receiver beam to use for the second scan beamName2 can be I 2 or any valid combination for the receiver you are using such as MR12 and MR34 scanDuration A float It specifies the length of each scan in seconds The following example does a Nod between beams 1 and 2 with a 60 second scan duration Nod 1011 2610 1 2 60 0 6 2 COMPONENTS OF AN OBSERVING SCRIPT 79 SubBeamNod For two beam receivers SubBeamNod causes the subreflector to tilt about its axis between the two feeds at the given periodicity The primary mirror is centered on the midpoint between the two beams The beam selections are extracted from the scan s beamName i e MR12 or MR34 The first beam 1 or 3 performs the first integration The periodicity is specified in seconds float per nod half cycle A nod is limited to a minimum of 4 4 seconds Syntax SubBeamNod location scanDuration beamName nodLength nodUnit The parameters for SubBeamNod are location A Catalog source name or Location object It
241. nction is Break message timeout where message is a string that is displayed in the pop up dialog with a default of Observation paused and timeout is a float that determines how long the system waits in seconds to get user input before continuing the Observing Script The default for timeout is 300 seconds or 5 minutes If you wish for the timeout to last forever then use None i e Break Wait Forever None or Break timeout None Here are examples of the use of Break Break This will time out in 5 minutes the default Break This will time out after 10 minutes 600 Break This will never time out None 6 2 5 4 Comment The Comment function allows you to add a comment into the Astrid observing process which will be echoed to the observation log during the observation The syntax is Comment Text to display during the observation What s the difference between this and just writing comments with the pound sign in your Observing Script When you use the pound sign to write your comments they will not appear in the observation log when your Observing Block is run Using the Comment function directs your comment to the output in the observation log Here is an example of the use of Comment now slew to the source Comment Now slewing to 286 Slew 3C286 6 2 5 5 GetUTC The GetUTC function returns a float representing the current time in UTC The returned v
242. nd Foci amp 22 eea a eee EG GG S Ws 122 Boia te As APA As Seo T 123 Edd dae tees MESSE EAST ees 123 TT 123 he a fu eM E 124 9 7 Optimal Observing Configuration for the Mapping Pipeline 124 10 VEGAS 125 T DUCTU 125 TTL TTL 128 LAD oe UULTUS 129 130 10 3 2 VEGAS ADC MMCM OGP and INL Calibration 130 10 3 3 IF Levels and 131 X TE Soe a ee ee SE hh 131 beh RRS Googe Pig eae a eee aa eG ae Sk A 132 dde d 132 pe bbe TT 132 e dob E ECRO eee ee bh new ob phe we mon ens 134 10 3 5 The Online Filler and Filling VEGAS data using SDFITS 135 epee Rhee Oe Ge Goes Lage be yaaa eae Ge 135 Lyase 4 Gee ed ee eee 4 ee ee 137 10 3 6 Processing VEGAS data using 137 10 4 Blanking art 0 4 oa oo ba doe amp FO a ARE OARS eae OWS Ped dodo Me dos 138 10 5 Baseline Performance 139 e a 140 10 7 Instrumental Features and their Cure 140 OUS bh RO eco a ela ale wierd T a a p A Ad 141 td eth Oa a a ave bee oe Ie RA ee aaa oe 141 wh Gp a Ge BE no GB Ge 143 EEEE TESST 143 144 i PRESS 144 11 Pulsar Observing
243. nd puts the instrument out of use for that time it is possible to observe without provided new biases are obtained support staff can help with this If the He3 has run out it must be recondensed e The MUSTANG IDL pipeline has an automatic binary cache mechanism which greatly speeds up processing of a given scan after the first time it has been read Unfortunately if the first reading of a scan was messed up for some transient reason the binary cached version can get messed up If the data are strange or repeatedly unprocessable try including the forceread or focewrite options in analysis routines such as multimakemap or best focus e Data Latencies Crash IDL as previously noted it sometimes takes 10s of seconds for the data files to be complete and visible on disk to IDL Trying to read the latest scan too soon can result in IDL crashing In this case restart the IDL gui reselect your project or click online if you are observing which will automatically select the most recent telescope period with data reselect the cal scan and proceed 13 6 EXAMPLE ASTRID SCRIPTS 177 13 6 Example ASTRID Scripts The following sub sections present some template ASTRID scheduling blocks SB s Templates are also kept in ASCII format in users bmason mustangPub sb Note the SBs in this document are for the sake of example only use the template SBs in the above UNIX file path to get the latest version 13 6 1 mustanginit Configure
244. nets standard pointing source catalog home astro util pointing pcals4 0 pointing cat Catalog Box Trajectory Parameters 4 box width and height in arcmin x0 5 0 0 5 0 number of times to repeat the map nrepeat 3 dithering offsets THE LENGTH OF THIS ARRAY MUST BE THE SAME AS NREPEAT 3 to not dither set them all to zero 13 6 EXAMPLE ASTRID SCRIPTS 183 dx 0 0 0 07 0 07 dy 0 1 0 07 0 07 period for h and v oscillation sec taux 9 tauy 8 duration sec scandur 290 this SB will therefore run for 290 x nrepeat seconds plus overhead phase of scan in seconds default 0 tstart 0 NOTES 3 x3 or 2 x2 covered well by taux 10sec tauy 8sec 160 sec scan 5 x5 or 7 x7 covered well by taux 9 tauy 8 290sec TET LUT LAT T CST UT Coord Sys in which to execute trajectory jii eg J2000 Encoder coordSys Encoder do not change from here down Slew mySrc Configure users bmason mustangPub sb mustang conf DefineScan boxtraj users bmason gbt dev scanning ptcsTraj boxtraj py for i in range nrepeat boxtraj mySrc dx dx i dy dy i phix tstart phiy tstart x0 x0 yO y0 taux taux tauy tauy scanDuration scandur calc_dt 0 25 coordMode coordSys 13 6 9 mustangshutdown Set Values Revr_PAR cryoCycleType Custom Set Values Revr
245. nfiguration definitions defined in a separate file from the Observing Script you need to use the python execfile function to bring the configuration definitions into the Observing Script Note that you do not want to use the python import command to do this because it will not reread the file and will miss any changes that you may have made We have placed all four example configurations in 6 2 1 2 within a single configuration file with the name home astro util projects 6D01 configurations py An Observing Script for continuum observations would look like observing script to make a continuum map of 3 286 load the source catalog Catalog home astro util astridcats fluxcal cat load the configuration definitions execfile home astro util projects 6D01 configurations py perform the configuration Configure continuumconfig slew the telescope to 3C286 Slew gt 30286 Make an on the fly map with 6 rows each 120 long using a spacing of 6 and scan rate of 720 min RALongMap 3 C286 Offset J2000 2 0 cosv True Offset J2000 0 5 cosv True Offset J2000 0 1 cosv True 10 0 The configurations are a all contained in one external file and b brought into the Observing Script using the execfile command The desired configuration is then executed using the name of the config uration definition as an argument to the Configure
246. ng the same Hour Angle as the source observations Continuum Line Nod Observe a source with one beam and then with the other beam for a dual beam receiver Continuum Line DecLatMapWithReference Make an on the fly raster map by moving along the minor axis of the coordinate system and making periodic reference observations Continuum Line DecLatMap Make an on the fly raster map by moving along the minor axis of the coordinate system Continuum Line Pulsar PointMap WithReference Make a map using individual pointings with periodic reference observations Continuum Line Pulsar PointMap Make a map using individual pointings Continuum Line RALongMapWithReference Make an on the fly raster map by moving along the major axis of the coordinate system and making periodic reference observations Continuum Line RALongMap Make an on the fly raster map by moving along the major axis of the coordinate system Continuum Line BalanceOnOff Move to the source and then a reference position and then balance the IF system to the mid point of the two power levels Continuum Line SubBeamNod Moves the subreflector alternately between two beams of the receiver 68 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS source A string It specifies the name of a particular source in the pointing catalog or in a user defined Catalog The default is Non
247. ns see Appendix D Also see Appendix E for angle formats and units 6 2 6 2 Offset Object An Offset is a displacement from the position of a source or from the center position of a map Offsets can be specified in the following coordinates J2000 B1950 RaDecOfDate HaDec Apparen tRaDec Galactic AzEI and Encoder An Offset is specified by two values generically called h and v with h being the value of the offset for the major axis and v being the offset value for the minor axis For example h refers to Right Ascension and v refers to Declination in J2000 coordinates Values can be entered in sexegesimal notation in quotes or decimal degrees Also the user can specify whether the cos v correction should be taken into account for the Offset The correction is applied when cosv 6 2 COMPONENTS OF AN OBSERVING SCRIPT 103 True i e h cos v is the offset value used in the direction of h False means that the correction is not applied The default value for cosv is True Offsets may be added together and may also be added to Locations if their coordinate modes are the same See Appendix D and Appendix E for more information about Locations and Offsets Here is an example of how to specify an Offset myoffset Offset J2000 00 30 00 05 00 00 False This offset is defined in J2000 coordinates The offset is 30 minutes in Right Ascensio
248. nt we observe a third source This example is available as home astro util projects 6D01 example three py from any computer within the Green Bank network Position Switched Observations where we observe the first source until the second source rises and then we observe a third source after the second source sets first we load the configuration file and the catalog file execfile home astro util projects 6D01 configurations py Catalog home astro util projects 6D01 sources cat now we configure the GBT IF system for frequency switch HI observations Configure vegas_ps_config now we balance the IF system and use a Break to check the IF system Balance Break Check the Balance of the IF system specify that the off position should be offset 2 min of time in RA myoff Offset J2000 00 02 00 0 0 define the horizon to use 20 degrees elevation in this case h Horizon 20 0 define which sources to observe srcA Object4 srcB Object3 srcC Objectl 6 2 COMPONENTS OF AN OBSERVING SCRIPT 107 now get rise and set times of srcB riseSrcB h GetRise srcB setSrcB h GetSet srcB observe srcA until srcB has risen above 20 deg elevation while Now lt riseSrcB and Now None OnOff srcA myoff 120 now observe srcB until it sets while Now lt setSrcB and Now None OnOff srcB myo
249. ntLocation returns a Location object see 5 containing the coordinates of the currently selected receiver beam s position on the sky as selected in the most recent scan type e g location GetCurrentLocation J2000 The position is read from the antenna at the time the directive is executed in the Observing Script The returned location may be used in conditional statements or as an argument for scan types F 1 5 SetSourceVelocity The SetSourceVelocity function sets the source velocity directly in units of km s The syntax is SetSourceVelocity 10 5 Note that if you include the velocities in your Catalog then you do not need to use this function This function is mainly used in pulsar observations F 2 Specialty Scan Types Submitted By Ob servers 2 1 LSFS This scan type performs a Least Squares Frequency Switch where a single scan is broken into 8 equal parts such that each subscan has a difference frequency as described above LSFS only works with the Spectrometer as the backend If you wish to use Least Squares Frequency Switching you should read GALFA Technical Memo 2005 1 by Carl Heiles Syntax LSFS location deltaf scanDuration beamName The parameters to LSFS are location A Catalog source name or Location object It specifies the source which is to be tracked deltaf A float It specifies the change in frequency in MHz which sets the multiplicative factor for the frequen
250. ny number of users can open Talk and Draw windows at the same time Everyone running Talk and Draw can send messages which will be seen by everyone else This is a great conve nience when doing remote observing One can also use it for communicating with other members of an observing team who are in remote locations 5 2 2 Scheduler and Skyview Launch Utilities Tools gt Scheduler amp Skyview This displays a plot of the sky in Az El coordinates as viewed from Green Bank One can import a catalog of source positions to be displayed or display one of the lists of standard calibration sources By default it displays solar system objects For example to display the x band pointing sources start with the Catalog button Catalog Add Select DeSelectCatalogs zband pointing OK If one selects Schedule button at upper right one may enter a date and time and display the sky for that time It shows the corresponding LST and moving the cursor on the plot displays the RA DEC and Az EL under the cursor This is very useful for planning observations There is also a Real Time option in which the location of objects and the direction the GBT is pointed are displayed for the current time 5 2 3 Status Launch Status This displays the status of many GBT systems all on one screen While very useful it is not recommended for use remotely because it is a heavy user of computing resources For remote observing it i
251. o not apply corrections Local pointing focus corrections are never applied even when the fit is good e Automatically accept good fits automatically reject bad fits This is the default for Automatically accept good fits interactively accept bad fits Interactively accept good and bad fits Accept all automatically A very dangerous mode that should only be used by experts Pointing Options Fitting Acceptance Criteria Heuristics Data Processing Send Corrections Do not apply corrections amp Automatically accept good fits automatically reject bad fits Automatically accept good fits interactively accept bad fits Interactively accept good and bad fits Accept all automatically 2 ok Cancel Figure 5 3 The pop up menu to change the pointing and focus fitting acceptance criteria 5 1 3 2 Heuristics Options Heuristics is a generic term used at the GBT to quantify the goodness of fit of the pointing and focus data reduction solutions Based on the known properties of the parts of the solution such as the beam width in pointing data should have certain values within measurement errors The Heuristics define how large these errors can be The user may change the Heuristics by Step 1 Select the Data Display Step 2 Selecd the Pointing Tab or the Focus Tab see note below Step 3 Click on the Tools pull down menu Step 4 Select options Step 5 S
252. o the headers associated with the observations On the left is a list of Observing Scripts that you can execute On the right are the Run Queue which holds Scheduling Blocks that are to be executed in the future and the Session History which shows which Scheduling Blocks Observing Scripts have previously been executed At the bottom is the observing log 43 THE OBSERVING MANAGEMENT TAB 2006 12 05 16 35 49 2006 12 05 16 24 33 2006 12 05 18 41 14 2006 12 05 19 37 45 2006 12 05 20 00 36 Observing Scripts A 26 1208169426 2006 12 08 19 43 37 Saved in Astrid 2006 12 12 162955 Database 2b 2006 12 12 16 3039 B 2006 12 15 16 28 01 2006 12 15 16 28 10 2007 01 23 12 39 08 oointina check 2006 12 05 16 30 27 Observation Log Optians Z Comeners C Trace C Sounds 14 04 25 source 39 INTENSITY 1 0 location J2000 18 52 47 80 00 35 47 00 velocity 105 9 14 04 26 Track Suhscan 1 of 1 2007 01 23 132227 jan23 b 2007 jan23 a 2007 peakspeal peakcal Run Queue 14 04 42 Notice This subscan wil be numbered as scan 15 in your data reduction package ObsevaronManagemerr Log 1 DataDisplay Log 1 GbeStatus Log 1 Command Console 31 Observabon Corarol Figure 4 6 The Observation Management Run Tab 4 3 2 1 Header Information Area The meta data consists of the project the session the observer s name and the operator s name All fields must have entries before an O
253. o use frequency switching to optimize the time on source Again refer to your friend of the project for suggestions on the type of observing procedure best suited for your observations 98 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS 6 2 4 7 NNTLE tracking earth satellites NNTLE stands for NASA NORAD Two Line Elements This refers to a standard NASA format for orbital elements for Earth satellites see e g http ghrc msfc nasa gov orbit tleformat html or http www amsat org amsat keps formats html The first non comment line of the Catalog must contain FORMAT NNTLE If the FILE keyword is used then one should only give the name of the object in the Catalog as the elements of the orbit are retrieved from the file or URL Note that the full path name of the file must be given and the file must have world read permission The remainder of the non comment lines contain the names for one or more satellites and their orbital elements in the NASA NORAD Two Line Element format An example of a valid file is as follows data taken from the AMSAT URL listed above Richard s sample nntle catalog FORMAT NNTLE USERADVEL 1 optional keyword OSCAR10 1 14129U 88230 56274695 0 00000042 10000 3 0 3478 2 14129 27 2218 308 9614 6028281 329 3891 6 4794 2 05877164 10960 GPS 0008 1 14189U 88230 24001475 0 00000013 0 5423 2 14189 63 0801 108 8864 0128028 212 9347 146 3600 2 00555575 37348
254. object For UTC times the sexegesimal representation may include a UTC suffix Note that mxDate Time objects are always UTC LST time may only be used with relative times and the sexegesimal representation must include a LST suffix Time Objects can have slightly varying formats and can be created in a few different ways Some examples are 2006 03 22 15 34 10 Absolute time in UTC represented by a string DateTime TimeDelta 12 0 0 Relative time in UTC as a mxDateTime object 2006 03 22 15 34 10 UTC Absolute time in UTC represented by a string 22 15 48 LST Relative time in LST as a string DateTime DateTime 2006 1 21 3 45 0 Absolute time in UTC as a mxDateTime object In this example we will continue to do one minute observations of srcA until Feb 12 2007 at 13 15 UTC when we will then do a ten minute observations of srcB from mx import DateTime emptyline switchTime DateTime DateTime 2007 2 12 13 15 0 Feb 12 2007 13 15 UTC emptyline while Now lt switchTime and Now None Track srcA None 60 emptyline Track srcB None 600 6 2 7 Example Observing Scripts For the following observing script examples we will use the configuration examples from 6 2 2 1 We will use a Catalog that is as follows The configuration file will be in home astro util projects 6D01 configurations py and the Catalog file will be in home astro util projects 6D01 sources cat these files
255. observers interested in using this class should contact their GBT support person 6 2 3 4 Mapping Scans DecLatMapWithReference A Declination Latitude map with reference observations or DecLatMapWithReference performs a raster scan centered on a specific location on the sky while periodically moving to a reference location Scanning is done in the declination latitude or elevation coordinate depending on the desired coordinate mode This procedure allows the user to periodically move to a reference position on the sky please see DecLatMap if no reference is required The starting point of the map is defined as hLength 2 vLength 2 Syntax DecLatMapWithReference location hLength vLength hDelta referenceOffset referen ceInterval scanDuration beamName unidirectional start stop The parameters to DecLatMapWithReference are location A Catalog source name or Location object It specifies the center of the map hLength An Offset object It specifies the horizontal width of the map i e the extent in the longitude like coordinate vLength An Offset object It specifies the vertical height of the map i e the extent in the latitude like coordinate hDelta An Offset object It specifies the distance between columns in the map Note that hDelta values must be positive referenceOffset An Offset object It specifies the position of the reference source on the sky relative to the Location specified by the first in
256. observing session There are a set of custom IDL routines for analyzing CCB data if you use the observing procedures and config files described here your data should be readily calibratable and analyzable by them To use the IDL code start IDL by typing from the GB UNIX command line users bmason ccbPub ccbidl Here is an example data reduction session that provides a quick look at your data set up global variables don t write files or plots to disk proj AGBT06A_049_09 setccbpipeopts gbtproj proj ccbwritefiles 0 gbtdatapath home archive science data tape 0016 to use postprocessing scripts set ccbwritefiles 1 a good color table for the plots 12 1 OBSERVING WITH THE CCB 161 loadct 12 create an array indexing scan numbers to file name indexscans 51 summarize the project summarizeproject read nod observation from scan 12 readccbotfnod si 12 q fit the data binning integrations to 0 5sec bins fitccbotfnod q qfit bin 0 5 the resulting plot shows the differenced data white and the fit to the data green for each of 16 CCB ports the first 8 are blank look at the next nod that just came in this time calibrate to antenna temperature before plotting First you need to derive a calibration which requires a scan with both cals firing independently dogain tells the code to solve for the calibration the results are stored in
257. ocusDaisies and analyzing the data you can send the pointing in arcminutes and focus corrections in millimeters either by telling them to the operator or by editing and running the example applyptg SB Every half hour you should check the focus and beam shape by obtaining a single quick map SB quickdaisy of a calibrator source monitoring the beam size pointing and relative source amplitude over time At this time another calandblank should also be done If the beam size increases by more 13 3 OBSERVING WITH MUSTANG 171 Name R A J2000 Dec J2000 Notes Uranus Oh Od In ASTRID Neptune 22h 12d In ASTRID Mars 13h 24h 10d In ASTRID extended Saturn 12h Od In ASTRID extended Ceres 17h 22h 20d Use custom ephemeris W3 OH 02 27 03 8 61 52 24 8 extended Mwc349 20 32 45 6 40 39 37 CRL2688 21 02 18 8 36 41 37 8 slightly extended Table 13 1 A list of secondary flux calibrators suitable for use with MUSTANG Coordinate ranges are for the 2010 2011 observing season than 10 or the source amplitude decreases systematically by 15 or more then it is likely that the thermal corrections to the GBT primary and or the subreflector focus corrections need updating and it is time to do another AUTOOOF note beam size and source amplitude degradation may also be caused by poor weather While the AUTOOOF procedure will update the telescope pointing corrections as well it is
258. of 12 2 CCB data from an OTF NOD observation of a bright source showing data and model 182 12 3 OTF NOD data on a bright source under marginal conditions The differences be tween the data and the model are clearly larger in this 162 12 4 CCB OTF NOD measurement of a weak mJy level source under good conditions The IDL commands used to obtain this plot are shown 163 12 5 The same weak source data this time with the individual integrations binned into 0 5 sec ond bins using fitccbotfnod s binwidth optional argument in seconds so the thermal any gradients or low level fluctutions in the beamswitched data due for instance to imperfect photometric conditions In this data they are not significant 13 1 Full 22 cycle daisy scan trajectory with a radius r 1 5 13 2 4 box scan trajectory 2 Rss 170 13 3 Selecting the CAL scan in the MUSTANG IDL GUL sns 173 13 4 Specifying scans to image in the MUSTANG IDL GUL leen 174 13 5 Specifying the coordinate system for the maps in MUSTANG IDL GUL 175 13 6 Summary plot produced by best focus showing an optimum value for LFC Y of about VETTER T ena Oe Ut aaa pu fe ce a ee ag ee 176 eus o mS a b b degere 186 Deepa e dede dos be ba 4 Ph ded qo eee ADS Sl te E E SP Pob AAD ESE 187 hee ge oe A ch cP ea ae ee
259. of 1 37 Blank Track 1 of 1 38 0423 0120 RALongMap 1 39 0423 0120 RALongMap 2 40 0423 0120 RALongMap 1 41 0423 0120 RALongMap 4 42 0423 0120 RALongMap 43 cal Track 1 of 1 44 Blank Track 1 of 1 45 0423 0120 RALongMap 7 46 0423 0120 RALongMap 7 47 0423 0120 RALongMap 4 48 0423 0120 RALongMap BE I I I O z5 0 23 0 02 7 14 mm 26 0 23 0 02 7 35 mm Queue Control raw data fitted beam map 7 Show Fixed Scale Image Show Solutions with Focus Removed Observation Control Auto OOF Processing Status Project Name 100120 Number n Send Selected Solution with Point and Foc Corrections new recommended method Send Selected Solution with no Point or Focus Correction original method Zero and Tum Off Thermal Zernike Solutid 38250000384 000000 Hz polarization instead for data processing o Cannot find beam 1 with XL polarization at 38250000384 000000 Hz in the backend FITS file Using default selection beam 1 with R at 38250000384 000000 Hz polarization instead for data processing ObservationManagement Log 1 DataDisplay Log 1 GbtStatus Log 1 Command Console L E Figure 5 7 The Data Display Tab showing OOF data 44 CHAPTER 5 NEAR REAL TIME DATA AND STATUS DISPLAYS Solutions must be manually
260. of the KFPA can be routed to the VEGAS spectrometers The routing can be to 1 2 3 4 5 6 7 or 8 different VEGAS spectrometers This routing is not applicable to a single beam of a dual beam receiver LES lt lt e Figure 10 3 A graphic demonstration of how dual beam receivers including two beams of the can be routed to the VEGAS spectrometers Each beam can be routed to 1 2 3 or 4 different VEGAS spectrometers 10 3 GENERAL OPERATION 129 Figure 10 4 A graphic demonstration of how four beam mode can be routed to the VEGAS spectrometers Each beam can be routed to 1 or 2 different VEGAS spectrometers N AA X 8 9 5 AAAA tn Figure 10 5 A graphic demonstration of how all seven beams of can be routed to the VEGAS spectrometers The routing of a second spectral window from beam 1 to spectrometer eight 7 1 mode of the KFPA is optional 10 3 General Operation VEGAS operation is quite straightforward and is extremely similar to observing with the old GBT Spectrometer In brief e Command VEGAS through Astrid define a configuration in Astrid perhaps using some VEGAS specific keywords configure the system as normal using the Configure directive balance the system as normal using the Balance directive execute a scan as normal to acquire data e monitor your observatio
261. om the execution of Observing Scripts The observing log can be saved to a disk file by hitting the Export button that is just above the top right corner of the log display area 4 4 THE DATA DISPLAY TAB 33 4 4 Data Display Tab The Data Display Tab provides a real time display of your data The Data Display Tab will be discussed in Chapter 5 4 5 The GbtStatus Tab The GbtStatus Tab displays various specific parameters sampled values and computed values Special care was taken to promote its use for remote observing Examples of how the Status Display appears in are shown in Figures 4 7 and v Astrid ONLINE MONITOR ONLY Ox File Edit View Tools Help ObservationManagement 1 DataDisplay 1 GbtStatus 1 Observation State Observer Peter Martin Last Update 2007 01 22 13 32 24 Project ID AGBTO7A 104 03 UTC Date 2007 01 22 GBT State Status Notice UTC Time 18 32 24 LST 21 19 57 MJD 54122 7725051 dius Az commanded deg 363 406 Elcommanded deg 40 151 actual deg 363 4064 El actual deg 40 1504 Az error arcsec 0 308 El error arcsec 0 012 Queue Control Coordinate Mode Galactic Antenna State Guiding Major Coord 123 116 Minor Coord 23 942 Major Cmd Coord 123 112 Minor Cmd Coord 23 942 LPCs Az XEV El 0 000 11 512 9 727 LFCs XYZ mm 0 00 25 61 0 00 DC 2 0 000 0 000 0 000 LFCs XYZ deg 0 00 0 00 0 00
262. ombined together These are the RMS of fully calibrated 70 second OTF NODs on a very weak source Typical reasonable weather conditions are a factor of two worse Improvements to the receiver made since these data were acquired may result in better sensitivity for the 2010 2011 season 12 3 Differences Between the CCB Ka Sys tem and other GBT Systems There are a few differences between the CCB Ka system and other GBT receiver backend systems which users familiar with the GBT will want to bear in mind e Because it is a direct detection system the GBT IF system does not enter into observing The Ka CCB gains are engineered to be stable 10 20 over months so no variable attenuators are in the signal chain Consequently there is no Balance step e To optimize the RF balance for spectral baseline and continuum stability the OMT s have been removed from the Ka band receiver It is therefore sensitive to one linear polarization per feed The two feeds are sensitive to orthogonal linear polarizations X and Y e Feed orientation is 45 from the Elevation cross Elevation axes All other receivers have feed separations that are parallel to the Elevation cross Elevation axes except for the There are two cal diodes one for each feed and they are separately controlled 1 it is possible to turn one on and not the other Cals are ON or OFF for an entire integration they are not pulsed ON and OFF within a s
263. oming out of the Analog Filter Rack after all filters have been applied used with 1 6 GHz Samplers ACS Port The displayed is the number corresponding to the port of the Spectrometer in use The value displayed is the duty cycle in db This value is relative to the optimum power level for best performance it should be between 3 and 3 db SPP Port The displayed is the number corresponding to the port of the in use The value displayed is the power level in db Radar Port The displayed is the number corresponding to the port of the Radar in use DCR Port The displayed is the bank and number corresponding to the port of the in use The value displayed is the total power in raw counts backendIF The value displayed is the frequency of the Doppler track rest frequency as seen by the backend in GHz TSYS The displayed is the number corresponding port in use The value displayed is the system temperature as reported by the should be considered a loose approximation 12 represented in db is given by 10logz 211 212 APPENDIX A THE GBTSTATUS IF PATH NOMENCLATURE Appendix B Introduction to Spectral Windows Several simultaneous frequency bands may be specified by the configuration keyword nwin number of spectral windows see 5 2 2 2 and a list of rest frequencies and offsets keywords restfreq deltafreq Each spectral window includes both polarizations i e if you specify one window you get two IFs
264. omment GBT pointing scan stations gbt_vlba peak 1 source J0920 4441 dwell 08 00 vlamode VA norecord nopeak It is important to specify only the stations gbt_vlba when putting in PEAK 1 Otherwise it may do a reference pointing for the whole and if the selected pointing source is under about 5 Jy for the VLBA it could produce bad results VLBI observers should see http www gb nrao edu fghigo gbtdoc vlbinfo html for more details Chapter 8 GBT IF System In this chapter we provide a general outline of the GBT IF Figures 8 1 and give a simplified overview of the path and will guide our discussion We will not cover the MUSTANG Ka band receiver IF paths Note that during each frequency mix each polarization pair is mixed with a signal from the same synthesizer All synthesizers are locked to our H maser frequency standard GBT Electronics Schernatic GBT Receive Room VIF Analog Filter Rack GBT Spectrometer Analog Fiber Hobaraphy PF or Gregorian GBT Equipment Room Figure 8 1 A simplified flow diagram of the routing 117 118 CHAPTER 8 GBT IF SYSTEM Simplified GBT LO IF system Fsky Filters GHz Receiver Filter Bank allpass 3GHz 20 MHz 80 320 1280 0 15 0 55 LO1 Fsky IF1 5 IF3 LO3 LO2 IF1 Fsky 11GHz a 1280 LO2 IF1 103 IF3 LO1 Fsky IF1 Fsky 11 GHz To Square law
265. on pol linear If you are unsure as to what is meant by these keywords then you should see 6 2 2 2 Spectral Line Frequency Switching Observations configuration definition for spectral line observations using frequency switching vegas fs config receiver Revrl_2 beam B1 obstype Spectroscopy backend VEGAS nwin 1 restfreq 1420 bandwidth 23 44 swmode sp swtype fsw swper 1 0 swfreq 0 2 5 3 vframe lsrk vdef Radio nchan medium high vegas subband 1 noisecal lo pol Linear 2235 25 The configuration definition will be named vegas_fs_config and can be used for spectral line obser vations obstype Spectroscopy using frequency switching swmode sp swtype fsw For these ob servations we wish to use the single beam L band 1 to 2 GHz receiver receiver Revr1_2 beam B1 and as the backend detector without cross polarization products backend VEGAS We wish to take data with a single band nwin 1 which has 23 44 MHz bandwidth bandwidth 23 44 centered on 1420 MHz restfreq 1420 with 262144 number of spectral channels see Table 10 1 nchan medium high vegas subband 1 We wish the cycle time to go through a full switching cycle of 1 sec swper 1 0 while we wish the frequency switching states to be centered on the line and then shifted by 2 5 MHz swfreq
266. on is not as complete as one might like Please refer to the MUSTANG chapter Chapter 13 section 13 3 1 and section 13 6 or consult your GBT friend The parameters to Daisy are location A Catalog source name or Location object It specifies the center of the map map radius A float which specifies the radius of the map s daisy petals in arc minutes This param eter is equivalent to a in Figure radial osc period A float which specifies the period of the radial oscillation in seconds radial phase A float which specifies the radial phase in radians rotation phase A float which specifies the rotational phase in radians scanDuration A float It specifies the length of the scan in seconds beamName A string It specifies the receiver beam to use for both scans beamName can be C 1 2 8 4 or any valid combination for the receiver you are using such as MR12 and MR34 The default value for beamName is 1 cos v A Boolean It specifies whether secant minor corrections should be used for the major axis of the coordinate system The default is True coordMode A string It specifies the coordinate mode for the radius that generate the map The default is AzEI calc_dt A float It specifies time sampling and should be between 0 1 and 0 5 The default is 0 1 This example produces a three leaf map about 3C123 6 2 COMPONENTS OF AN OBSERVING SCRIPT 85 Catalog f
267. ool but it is possible on occasion that by running it they might be able to give support scientists engineers some useful information in the case of problems 10 8 GENERAL OPERATION 135 X VEGAS Bank Data Monitor BankAMgr BankBMgr BankCMgr BankDMgr BankEMgr BankFMgr BankGMgr BankHMgr All measpwr State Ready Mode 12 Sampler Input Samplers v measpwr vj1 vj2 0 100 150 measpwr options Time seconds adcpwr1 J1 adcpwr2 J2 1 000 1 000 Figure 10 8 The VEGAS Data Monitor screen 10 3 5 The Online Filler and Filling VEGAS data using SDFITS Similar to the Spectrometer VEGAS writes Engineering FITS files Once a scan is over the Filler reads these files combines the data with metadata from the Antenna and other FITS files and produces a single dish SDFITS file This can be done automatically by the on line filler or manually by the Observer Due to the significantly higher data rate and some other features of VEGAS the filling process is slightly different than was the case for the Spectrometer The Online Filler The online filler will make every attempt to fill the SDFITS file automatically In this case a file will be produced in home sdfits lt project gt and GBTIDL can connect to it automatically using the online or offline lt project gt commands There are some caveats however 136 CHAPTER 10 VEGAS
268. or determining which radio frequency to observe First LO LO1 The first LO in the GBT IF system This LO is used to convert the RF signal detected by the receiver into the IF sent through the electronics to the backend This is also the LO used for Doppler tracking 117 Third LO LO3 The third LO in the GBT IF system which operates at a fixed frequency of 10 5 MHz 211 Second LO LO2 The second LO in the GBT IF system This is actually a set of eight different LOs that can be used to observe up to eight different spectral windows at the same time Local Pointing Correction LPC Corrections for the general telescope pointing model that are measured by the observer Monitor and Control M amp C The group of software programs which control the hardware devices which comprise the GBT 25 26 55 38 39 68 221 Modified Julian Date MJD 84 North American Datum of 1983 NAD83 An earth centered model for the Earth s surface based on the Geodetic Reference System of 1980 The size and shape of the earth was determined through measurements made by satellites and other sophisticated electronic equipment the measurements accurately represent the earth to within two meters 4 National Radio Astronomy Observatory NRAO The organization that operates the GBT VLA VLBA and the North American part of ALMA E BHEO 203 209 List of Acronyms 231 National Radio Quite Zone NRQZ An area around the GBT setup by the
269. or the pointing data reduction and the focus data reduction Therefore the Pointing and Focus can have different option values 5 1 3 4 Send Corrections A Pointing Options Fitting Acceptance Criteria Heuristics Data Processing Send Corrections Corrections Az2 arcmin El arcmin 9 ok Cancel Figure 5 6 The pop up menu to manually send pointing corrections to the telescope For most observations the GFM processing produces good fits and the solutions are automatically sent to the telescope using the default settings However at the high frequency especially w band fits may fail and the user may want to manually send the corrections to the telescope The user may tell the operator to enter a solution or they can send the corrections themselves using the Send Corrections tab This can be done by Step 1 Select the Data Display Step 2 Selecd the Pointing Tab or the Focus Tab Step 3 Click on the Tools pull down menu Step 4 Select Options Step 5 Select the Send Corrections Tab in the pop up window if not visible use arrow button on the right the Send Corrections tab is farthest to the right Step 6 Enter the corrections in the text box and click Send to send the solutions to the telescope see Figure 5 6 5 1 THE ASTRID DATA DISPLAY TAB 43 Users can send both the pointing and focus solutions to the telescope using this method Th
270. ou can see the current LFCY in the ASTRID GbgStatus tab in the entry labeled LFC XYZ mm it is the second number of the three 13 5 Troubleshooting GBT 90 GHz observing requires diligence on the part of the observer Following are some problems that can come up their symptoms and first actions to take in response e GBT out of focus the beam gets larger and the peak gain lower than it had been before Check and reset the telescope focus 176 CHAPTER 13 MUSTANG Peak max 5 LFC mrn FWHM 3 97mm LFC mrn Figure 13 6 Summary plot produced by best focus showing an optimum value for LFC_Y of about 3 7 mm e GBT primary deforms due to changing structure temperatures after optimizing the focus the in focus beam is still larger or lower gain than before Rerun AutoOOF e Detectors reach the edge of their dynamic range DAC values in mustang monitor reach 0 or 16384 run calandblank which relocks the detectors mid scale or relock manually in the MUSTANG CLEO screen column control tab e A greatly diminished cal or source response or greatly diminished number of live detectors can occur if the He4 runs out and the detectors warm up a little With Helium 3 and Helium 4 both the Array GO detector array temperature should read about 300 mK when detector biases have been applied for a few minutes with only Helium 3 it will read about 340 mK with biases Recondensing the He4 requires 1 5 hours a
271. ou should also not try to make a map with the current scan wait about 1 minute after the completion of a scan to try and map it We tried to make the IDL code as robust as possible but this will sometimes crash the code In this event restart the IDL gui re enter the proejct or click online and re select the cal scan you dsire The relative pixel gains are calibrated by flashing an internal cal lamp on and off done by the calandblank SB The data from a CAL scan are analyzed by selecting the desired scan in the drop down box in the GUI see Figure 13 3 Partial example output is as follows docalib calscan 1 gain mygain crmask mycrmask GAINS 1 18084e 12 0 0 00000 1 18084e 12 0 0 0 0 0 0 00000 00000 00000 00000 00000 00000 0688694 93 2362 0 320343 77 4885 81 9272 82 3489 57 1215 59 1193 0 000713527 CRMASK and total 0 0 0 0 00000 00000 00000 00000 0 00000 1 00000 0 00000 1 00000 155 829 83 6297 101 007 141 224 79 5458 92 1591 73 7274 73 8523 0 0108514 49 0000 1 00000 1 00000 1 00000 1 00000 200 706 148 163 298 489 184 050 107 280 0 0603582 148 184 313 731 0 0494373 1 00000 1 00000 1 00000 1 00000 174 CHAPTER 13 MUSTANG Basic Options Advanced Options DISPLAY OPTIONS Browse Projects Vhome gbtdata AGBTOBC_026_06 Update Scan List Change Color Calibratio
272. ou will be able to see near real time data from the GBT Work offline In offline mode you can edit and syntactically validate your Observing Scripts You can also use the data display part of to look at previously obtained data Once you see the screen shown in Figure 4 3 you have successfully started Astrid Edie Too Hep BKURdD ObsesvvionManagemere 1 DataDisplay 1 1 Edi Rin Qesenanco State Project Editor Validation iv State Scheduling Blocks GBT Status Queue Corot Observation Cortot Imper fram File Export to Fle Export Observation Log Options Comment C Trace Export Log f T T ObsesvasionManagemere Lo DataiNsplay Log 1 GatStans Log 1 Command Consola L zi Figure 4 3 The initial screen upon startup 4 2 2 Astrid GUI Composition The Astrid GUI layout consists of drop down menus a toolbar application component tabs an observa tional status section a queue control section an observation control section the application component and a log window These are shown in Figure 4 2 2 1 Drop down Menus In the top left hand side of the GUI you will find the drop down menus The contents of the drop down menus change according to which Application is currently being displayed on the GUI We will not discuss all of the options under the drop down menus in this document but we will provide some highlights File Un
273. ource returns the current time and horizon GetSet source returns None For southern circumpolar sources which never rise hori zon GetRise source returns None and horizon GetSet source returns the current time Note that Horizon only works for objects defined in catalogs with spherical coordinates Horizon will not work with planets and ephemeris tables 6 2 6 4 Time Object The Time Object is primarily used for defining scan start or stop times The time may be represented as either a sexegesimal string or in a python mxDateTime object You can learn more about mxDateTime at http www egenix com files python mxDateTime html The Time Object can be expressed in either UTC or LST The time can be either absolute or relative An absolute or dated time specifies both the time of day and the date An absolute time may be represented by either a sexegesimal string i e yyyy mm dd hh mm ss or by a DateTime object Relative or dateless times are specified by the time of day for today WaitFor will treat a dateless 5 Note one must access the python DateTime module directly from an observation script to generate time objects i e using mx import DateTime 104 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS time that is more than 10 minutes in the past as being in the future i e the next day Relative times may be represented by either a sexegesimal string i e hh mm ss or a DateTimeDelta
274. ox change taking about 4 hours and done only during scheduled maintenance days The 0 29 0 92 GHz receiver is divided into 4 frequency bands within the same receiver box The receivers are cooled Field Effect Transistor FET amplifiers The feeds for the lower three bands are short backfire dipoles and the feed for the fourth 680 920MHz is a corrugated feed horn with an 6 CHAPTER 2 THE GBT OBSERVING PROCESS Ortho Mode Transducer OMT polarization splitter A feed change required to switch between bands takes 4 hours The 0 920 1 23 GHz receiver uses a cooled and a corrugated feed horn with the 2 1 3 2 Gregorian focus receivers The Gregorian receivers are mounted in a rotating turret in a receiver room located at the Gregorian Focus of the telescope The turret has 8 portals for receiver boxes Up to 8 receivers can be kept cold and active at all times The Gregorian subreflector can be used for slow chopping with a minimum 4 5 second half cycle Changing between any two Gregorian receivers that are installed in the turret takes about one to 1 5 minutes 2 1 3 3 The MUSTANG Receiver MUSTANG MUltiplexed SQUID TES Array at Ninety GHz is a multi pixel bolometer array observing at 80 100 GHz mounted at the Gregorian focus It is both a receiver and the associated back end and is described in Chapter 13 The MUSTANG receiver must be used at elevations above 30 degrees due to the design of the cryogenics 2 1 4 Backends
275. path The keyword value is a string with allowed values of In or Out The default value is In vegas vpol Keyword to specify which spectral product to record in the FITS file It assumes values 1 self2 self and cross They value selfl corresponds to the spectrum of signal connected to port A of the vegas and self2 corresponds to that connected to port B Default value is self vegas subband Keyword used by config tool to select between 23 44 MHz VEGAS modes with single and multiple spectral windows see Table 10 1 It assumes values 1 or 8 Default value is 8 guppi obsmode GUPPI specific keyword see Chapter 11 Obsmode can be search fold or cal guppi numchan GUPPl specific keyword Numchan can be a power of two from 64 to 4096 guppi polnmode GUPPIspecific keyword Polnmode is full_stokes or total intensity guppi scale GUPPL specific keyword see Chapter 11 for details l There are expert values of on mcb on ext lo mcb hi mcb lo ext and hi ext whose use is beyond the scope of this document Please contact a support person about the use of these values 6 2 COMPONENTS OF AN OBSERVING SCRIPT 65 guppi outbits GUPPILspecific keyword Currently only outbits 8 is available guppi fold dumptime keyword Fold specific parameters are not needed for cal or search For fold or cal observations this is how much we will integrat
276. ple Spectral Lines KFPA Observations configuration definition for spectral line observations with KFPA vegas_kfpa_config receiver RevrArray18_26 beam alll obstype Spectroscopy backend VEGAS restfreq 24000 1 2 3 4 23400 5 6 7 25500 DopplerTrackFreq 25500 deltafreq 24000 0 23400 0 25500 0 bandwidth 187 5 swmode swtype swper 1 0 tint 30 vlow 0 vhigh 0 vframe vdef Radio noisecal lo pol Circular nchan low vegas vpol cross 2229 39 27 72 0 6 2 COMPONENTS OF AN OBSERVING SCRIPT 57 The configuration has the name vegas_kfpa_config and can be used for spectral line observations obstype Spectroscopy using cal switching observations swmode tp swtype none with the multi beam 18 to 26 5 GHz all beams receiver receiver RevrArray18_26 beam all and VEGAS as the backend with cross polarization products backend VEGAS vegas vpol cross We request that beams 1 2 3 and 4 have a rest frequency of 24000 that beams 5 6 7 have a rest frequency of 23400 and the second beam 1 IF band has a rest frequency of 25000 All delta frequencies are set to 0 for this observation The bandwidth used is 187 5 MHz bandwidth bandwidth 187 5 with the lowest value for the number of spectral channels 32768 nchan low We wish the cycle time to go through a full total power
277. pping pro cedures including RALongMap and DecLatMap With a procedure such as RALongMapWithReference the pipeline will correctly interpret the associated calibration scans The observer can use either frequency switching or position switching observing schemes For position switched maps the user should observe separate reference scans using the Track procedure before and or after each mapping block These enable calibration of the receiver and sky contributions to the observations For frequency switched ob servations the reference spectra are obtained simultaneously with the signal spectra and no additional calibration observations are required The mapping pipeline was developed initially to support calibration and imaging for the KFPA but it can be applied to data taken with any of the receivers that use standard position switched or frequency switched observing modes When using standard mapping procedures astrid sets scan header parameters that the pipeline uses to identify mapping scans and reference scans The observer can also specify reference scans by hand when running the pipeline see the Pipeline User s Guide 9 4 Calibration The KFPA receiver has variable noise diodes that can change so it is important that users calibrate their data for every session The diodes have effective temperatures that can drift slowly over time change after a thermal cycle of the cyrostat and sometimes their properties can suddenly change by
278. produce vibrations that contaminate the MUSTANG data Thus users of MUSTANG can request that the operator turn off the feed blower at the start of their observing session One hour before the end of a MUSTANG observing session the operator will decide whether or not the blower needs to be turned back on in order to ensure the feeds for all receivers are in good shape for the next observer The operators use the criteria that the blowers will be turned back on for the last hour if either 1 the dew point is within 5 Fahrenheit of the air temperature or 2 the air temperature went from above to below freezing anytime during the MUSTANG run Chapter 17 Remote Observing With The GBT 17 1 Remote Observing Guidelines for Ap proved Projects Permission to observe remotely must be explicitly granted by the Head of Science Operations at the moment that s Toney Minter at least two weeks prior to the observing run Permission will be granted based on the appropriateness of the project and the demonstrated experience of the observer Guidelines for approved remote observing projects are as follows or observers Wess for information on observing policies and re and M T WWW E nrao m m mote observing e Consult with the staff support astronomer at least two weeks prior to observing time e Provide the staff support astronomer with your telephone contact numbers work home and cell and agree in advance
279. put parameter i e the center of the map referenceInterval An integer It specifies when to do a reference scan in terms of map columns e g 4 means every fourth column A reference scan is always done before doing column number 1 scanDuration A float It specifies the length of each scan in seconds beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 2 3 4 or any valid combination for the receiver you are using such as 12 Default is 1 unidirectional A Boolean It specifies whether the map is unidirectional True or boustrophedo nically False Default is False start An integer It specifies the starting column for the map The default value for start is 1 start and stop are useful for doing a portion of a map or restarting a partially observed map stop An integer It specifies the stopping column for the map The default value for stop is None which means go to the end from the Greek meaning as the ox plows i e back and forth 6 2 COMPONENTS OF AN OBSERVING SCRIPT 81 This example produces a boustrophedonic bidirectional or back and forth map with 21 columns each 12 arc minutes long along a great circle of Declination using a spacing of 0 24 arc minutes using beam 1 This map goes to a reference point 2 degrees north and 3 degrees east of the map center every 3 columns DecLat Map WithReference ORIONKL
280. quency in a catalog only changes the values in the First LO LO1 manager If either value is changed by a large amount the receiver selection or bandpass filters or the frequency spacing between spectral windows may change Thus one should re configure the for a large change in velocity or frequency The user should be wary of how much the velocity or rest frequency can change for a particular configuration Finally we show an example Catalog with user defined keywords The user may make up arbitrary keywords or equivalently column headings These are available within an Observing Script but are otherwise ignored 6 2 4 4 Standard Catalogs Several standard catalogs are available for use within the Green Bank computing system They are all ASCII files in the directory home astro util astridcats and are listed in Table Note that for convenience these standard catalogs may be referred to within Astrid simply by name without the cat extension e g c Catalog kaband_pointing Since 2006 the GBT pointing catalog has been updated several times to include better positions and more recent flux densities These changes are described in the PTCS project notes posted at https safe nrao edu wiki bin view GB PTCS ProjectNotes e PTCS PN 58 introduces PCALS4 1 and gold standard pointing calibrators for use at higher frequencies e PTCS PN 66 introduces PCALS4 4 a catalog upgrade incorporating high frequency flux densiti
281. r greater than what was seen before the surface correction was sent If the data pass these sanity checks you are ready to proceed to your science observing Otherwise repeat the focus and or primary surface measurement The AUTOO0F procedure also determines and applies subreflector focus and pointing corrections Note once the processing is complete it is the first Send Solutions button marked new recommended method that you want to push to send the surace pointing and focus corrections to the telescope If you push the second old original button the focus offset will not be sent which may result in irretrievable degradation of the quality of your data You can also manually check the focus with a more fully sampled series of maps typically five collected at a range of focus positions The parFocusDaisies example scheduling block implements such a measurement which can be analyzed as described in 8 13 4 We recommend you only take this approach if you have reason to doubt the corrections derived by AutoOOF for instance the peak source intensity obtained after applying the focus and pointing solutions from AutoOOF is lower than the peak source intensity before Note parFocusDaisies centers the focus scans on the focus correction value LFCY set by the variable nomfocus and leaves it at this value at the end Do not forget to set nomfocus to the current local focus Y correction LFCY before running it After running parF
282. r symmetry greatly increases the complexity of its design and construction 208 m parent virtual parabola b id x a lt a P 4 TE GBT 100 x 110 m Parabola Section Figure 2 1 Left The parent parabola for the Right The off axis optics of the To maintain precise surface figures and pointing accuracy at high frequencies the telescope is equipped with a complex Active Surface AS At higher frequencies gravity distorts the surface fig ure of the telescope to unacceptable levels Temperature variations and wind can also deform the figure of the dish To compensate for these distortions the surface of the GBT is active i e it is made up of 2008 independent panels and each of these panels are mounted on actuators at the corners which can raise and lower the panels to adjust the shape of the dish s surface 3 4 CHAPTER 2 THE GBT OBSERVING PROCESS 2 1 1 Main Features of the GBT e Fully steerable antenna 5 to 90 elevation range 47 to 90 declination 85 coverage of the celestial sphere But note that observing near the zenith elevation gt about 86 may fail due to the high azimuth rates required e Unblocked aperture reduces sidelobes Radio Frequency Interference RFI and spectral standing waves e Active surface compensates for gravitational and thermal distortions e Frequency coverage of 100 MHz to 100 GHz 3 orders of magnitude of frequency coverage for maximum scientific
283. r to Chapter for discussion of how weather affects the GBT The effect of wind is somewhat less on MUSTANG observations than for traditional targetted single beam photometric observations since the sky is densely sampled and all observations are conducted on the fly one needs only to know where the beams were pointed at a given time rather than to keep the telescope pointed accurately at a given spot A quadrant detector on the GBT helps to increase the accuracy of this reconstruction on the GBT and the data from it is automatically used by analysis algorithms A good rule is to only use data from scans with mean winds under 10 mph and peak winds under 12 mph There are three GB weather stations and to be conservative use the maximum of the readings of the operable weather stations at a given time The data reduction tools described in 13 4 provide this information on a scan by scan basis during or after the observations Conditions can also be monitored in the GBTSTATUS tab of astrid and in various CLEO screens principally the weather and status screens The Dynamic Scheduling System DSS will schedule MUSTANG proposals when the forecasted winds are lt 10mph opacities are reasonable lt 0 25 and cloud cover is sufficiently low 13 1 2 Source Elevation Several considerations constrain the range of elevations at which useful MUSTANG observations can be conducted the atmospheric opacity typically 0 07 lt
284. rators Your scientific contact person can help you if you wish to use Get Value F 1 2 SetValues The SetValues function can be used to directly set any of the parameters within the Monitor and Control system As a result it is used to support complex configurations and expert observations Please note that SetValues does not issue a prepare on the M amp C Manager containing the parameter If you wish to do a prepare you can also use Set Values to do that as well A complicated example which assumes that you have defined values for lfYs and other variables is the following lfcValues gt local_focus_correction Y 1fYs local focus correction Z lfZs local focus correction Xt lfXsTilt local focus correction Zt lfZsTilt localPointing ffsets az ffset2 lpcAz2 SetValues Antenna 1fcValues SetValues Antenna state prepare Your scientific contact person can help you if you wish to use Set Values 221 222 APPENDIX F ADVANCED UTILITY FUNCTIONS F 1 3 DefineScan If you have written your own scan type using the Python language the DefineScan directive is used to load your new scan type into the current observing script Once loaded it can be referred to by name just like any other scan type The syntax is DefineScan ScanName path to my NewScan py and the new scan must be written in Python F 1 4 GetCurrentLocation Given a coordinate mode GetCurre
285. remotely You should arrive in Green Bank at least one business day before your observations This will allow you to meet with the contact scientist and also with the scientific staff person who will be on call during your observations these might be different people Step 8 Unless you are running a project which must be fixed to a certain date and time your observa tions will be dynamically scheduled See Chapter 3 for details on how dynamical scheduling is done with the Vhen your project is scheduled you will receive an e mail notification indicating the exact time the observing session will start Notifications go to the project PI and all others designated as observers on the project Thus you should have prepared your scripts and be ready to observe with 24 36 hours notice If there are periods of time or dates when you cannot observe you should indicate these as blackout dates in the DSS web page https dss gb nrao edu Step 9 If you are present in Green Bank go to the control room shortly before your observations begin You can log into one of the computers and bring up any programs that you need so that you are prepared when your observation time begins If you are observing remotely you should contact the operator 304 456 2341 or 304 456 2346 about 30 minutes before your observations You should give the operator your contact information phone numbers emails so that they can contact you during the observations if nec
286. rformance 5 rms flux errors from pointing alone Receiver Frequency wind limit Performance Observing GHz m s mph Level Strategy 0 340 43 3 96 9 Good A 0 415 39 6 88 6 Good A 0 680 30 6 68 5 Good A 0 770 28 9 64 6 Good A 0 970 26 0 58 2 Good A 1 4 21 4 47 9 Good A 2 0 18 0 40 3 Usable A 5 0 11 4 25 5 Usable B 5 0 9 5 21 3 Good B 10 0 8 5 19 0 Usable B 10 0 7 0 15 7 Good 15 0 6 7 15 0 Usable 15 0 5 5 12 3 Good 25 0 4 8 10 7 Usable 25 0 3 7 8 3 Good D 32 0 4 0 8 9 Usable 32 0 2 6 5 8 Good D 45 0 2 6 5 8 Usable D 45 0 2 2 4 9 Good D 90 0 4 5 10 Usable D Strategy A Appropriate for Prime Focus L band and S band observing The antenna should deliver good pointing and focus performance under all allowed wind conditions and in the presence of any thermal gradients We always recommend at least one peak for all receivers and one focus except when using the Prime Focus Recievers at the start of a new observing program if only to ensure that the antenna has not been left misconfigured e g well out of focus because the previous observer was performing out of focus beam maps After this initial check the blind pointing focus performance of the antenna should provide sufficient accuracy Strategy B Appropriate for or usable performance at X band Ensure that the wind speeds do not exceed the limits listed in Table Extreme thermal gradients typically only
287. roubleshooting 4 k SR SCR Ree ORC UU Po db Sad s 175 PEGEMHs ESS PEPER EAL edo EP RSS 177 13 0 1 3n stanglbidt A Se eG a at ee cce a A UR 177 ee eee ee 177 13 6 3 calandblank 44 4 09 a PEELS SSO EE SE ee ww VE DSS 177 13 6 4 parFocusDaisies s s sona 2s 178 13 6 5 ApDlyptg 9 gy dea aid Re a eee OO Reb de er s A 179 13 6 6 quickdaisy A ee RAS eee d 180 13 6 1 4 s s aoo ee RR eos a ars a UR 181 TV 182 13 6 8 o c e s yadi aka 244d ee Po 9 moe s 182 13 6 9 mustangshutdown 183 14 The 4mm 68 92 GHz Receiver 185 oA he eA we we iat neers area Ae AK 185 Gob cB Bette eee eee ed 4 3 do E ELAS eee Re 185 14 3 Obserying 4 cx 40 9 9 ee Se Rh E XOEUR eR 91913 Reo a 186 4 3 1 CalSeg 2 23 eee kale oe eR em RU up be oR 187 stadteavivedcddadges cad S464 44 ean e wes 188 14 3 3 AutoOOF Thermal Corrections oaoa e a 189 aR E Gi a ee ate te e aS GS AE Se 189 a 9 o4 aq E Pububud od som por Ro xo 9o x 4 191 193 195 16 1 Lime ot Day 42 46 km m cem eot es Gh 9 Ogre BE 195 10 2 Wands amp P 2a 590 09 ow mo REOR RB ede dee eth bite ee ded xu etg 195 CPC e
288. rs as AutoPeakFocus However the receiver parameter is limited to Rcvr26 40 Revr40_52 Revr68 92 and i e MUSTANG When using the an additional parameter nseq can specify the number of OTF maps to be made with Au toOOF This must be either 3 or 5 The intent of the AutoOOF scan is to automatically run an Out of Focus holography scan for the current location on the sky and with the current receiver therefore it should not require any user input However by setting any of the optional arguments the user may partially or fully override the source search and or procedural steps as described below AutoOOF should only be used for observations above 26 GHz Details and recommended strategy It is important to choose a bright calibrator preferably at least 7 K in the observed band which is about 4 Jy at Q band You should not rely on the catalog flux to be accurate as it is often many years 74 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS out of date If you are not sure then run a point focus scan on the calibrator first in order to confirm its strength Remember you need to be able to detect the source when the subreflector is 5 out of focus which typically reduces its peak intensity by a factor of 8 The AutoOOF procedure will obtain three on the fly maps each taken at a different focus position and each requiring 5 minutes of observing time plus nearly a minute of initia
289. rving Projects that require observers to visit Green Bank for training are excluded from this guideline until the observers are trained for remote observing Caution Regarding Blackouts If a project has only one observer that observer should be particularly conscientious of blackouts It can be easy for an observer to inadvertently hamper observing opportunities too much by setting blackout dates too freely particularly repeating blackouts So repeating blackouts should be used with care Targets with low declinations such as the Galactic Center have tightly constrained observing opportunities to begin with so observers on such tightly constrained projects should be particularly careful with blackouts that would further limit their observing opportunities Consider as an example a project that has a session with a 4 hour minimum duration to observe the Galactic Center If the observer has a repeating 1 hour blackout date that intersects the window the entire session becomes ineligible each time the blackout intersects the 4 hour window 3 4 CANONICAL TARGET POSITIONS 13 When entering blackouts keep in mind too that projects do expire so it is in the interest of the observer to keep the projects eligible for scheduling as much as possible 3 4 Canonical Target Positions The DSS keeps track of a project s scheduling requirements via the session parameters which can be viewed on the project page The PI should check that session param
290. rving Se quence An example observing sequence would be as follows e mustanginit e TweakTargets amp FindBest Biases e savetuning e calandblank e ona 1 Jy or brighter point source 172 CHAPTER 13 MUSTANG quickdaisy check the gain and beam size on a calibrator autooof establish GBT surface corrections quickdaisy check gain and beam size after applying surface corrections e quick daisy on primary flux calibrator if this is a large slew over 60 degrees in az over 30 degrees in el you might want to run focus daisies centered on the current LFCY just to be safe e quick daisy on secondary flux calibrator within 15 degrees of science target if this is a large slew you might want to run focus daisies centered on the current LFCY just to be safe e half hour of observing boxmap or parfulldaisy e quickdaisy on nearby secondary pointing focus calibrator If the beam gain has gone down by 15 or more or the beam become 10 fatter in one or both directions repeat an AutoOOF on the pointing calibrator and verify results with a quickdaisy e calandblank e half hour of observing boxmap or parfulldaisy e quickdaisy to check gain and focus e calandblank e et cetera e mustangshutdown 13 4 Quick Look Data Reduction It is essential to monitor the quality of your data as you are collecting it A suite of tools has been written in IDL to make this possible This section outlines its use We highly recommend
291. s target_values is a corresponding array with list of RF values E For example if one wants to adjust to an RF value of 2 5 and 5 to 3 5 then one says E BalConvRack 1 5 2 5 3 5 E E This adjusts the converter module attenuators such that the target power levels are attained to within a threshhold of 0 15 volts as read by the RF power samplers The second method is to specify the attenuation settings of the Converter Rack attenuators All of the Converter Rack attenuators can be set to the same value using ji make the function available execfile users tminter astrid SetConverterRackAttenuation py set all the attenuators to 15 5 dB Set ConverterRackAttenuation 15 5 7 7 OBSERVING STRATEGIES FOR STRONG CONTINUUM SOURCES 115 7 7 Observing Strategies For Strong Con tinuum Sources Spectral line observations of strong continuum sources leads to a great amount of structure i e ripples in the observed spectra So observations of strong continuum sources requires careful consideration of the observing setup and the techniques used If you are trying to observe broad spectral lines wider than a few MHz toward a source with strong continuum emission more than 1 10th the system temperature then you should consider using double position switching This technique is discussed in an Arecibo memo by Tapasi Ghosh and Chris Salter which can be found at http www naic edu
292. s a comma separated list of floats with units of MHz There should be nwin entries for this keyword value 66 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS 6 2 2 3 Resetting Astrid The configuration tool in Astrid remembers all the keyword values defined during a session This feature occasionally results in Astrid being unable to validate an otherwise correct configuration because of previously set values To reset the configuration parameters to their default state you can issue the ResetConfig command in a script This command will reset the configuration tool values to their defaults 6 2 3 Scan Types A Scan is a pattern of antenna motions that when used together yield a useful scientific dataset This section describes the various scan types that are available for use within GBT Observing Scripts Each scan type consists of one or more scans which are the individual components of the antenna s motion on the sky The scan types listed below are the functions within your Observing Script where data will be obtained with the In Table 6 4 we show the available built in Scan Types for the along with a short description of what each Scan Type does More details on each Scan Type can be found in the subsequent text after the table Please note that the syntax for all Scan Types is case sensitive Location Offset Horizon and Time objects are defined in while Catalogs are defined in Seldom used
293. s 20 Raw data gt 150 40 30 100 E 2 10 50 s 10 5 E 0 E 0 0 E 10 5 100 20 10 0123456 6 7 8 9 10H 2 D B M 15 16 H 18 Time minutes Elev Offset arcsec e 150 100 50 50 100 150 200150100 50 0 50 100 20615610050 0 50 100 200150100 50 0 50 100 Cross Elev Offset arcsec Figure 5 8 A plot of the raw OOF data on a fairly clean Ka CCB dataset When you are ready to accept the solution being displayed it will need to be manually sent to the active surface A new feature added in October 2009 is the ability to compute the new local pointing and focus offsets from the OOF map It is recommended that when sending the solutions you use the yellow button labeled Send Selected Solution with Point and Focus Corrections new recommended method If you use this option you do not have to perform a peak focus after the OOF map While it is still good practice to run a peak focus at the beginning of your observing run particularly during the day you can let AutoOOF compute subsequent point focus corrections 5 1 THE ASTRID DATA DISPLAY TAB 45 Afocus 0 00 _ Afocus 38 00 mm Afocus 38 00 mm 455 434 440 450 i32 438 430 a s i 434 428 432 5 435 430 a 426 430 s 425 424 426 420 422 a24 LT 012 34 56 5 678 9101112 12 BM 15 16 17 B Time minutes orn 1 2 3 After baseline removal 4 012345 6 6 7 89 10 12 D DB M 15 HV B Tim
294. s and that the pointing solution is within twice the FWHM of the nominal location of the source For the relaxed heuristics this becomes within 50 of the expected FWHM of the Gaussian fits and three times the FWHM for the pointing correction 5 1 3 3 Data Processing Options X Pointing Options lt Fitting Acceptance Criteria Heuristics Processing Polarization Total Power X Left Raw Y J Right Both lt 3 ok Cancel Figure 5 5 The pop up menu to change the polarization and calibration used in pointing and focus fitting The user may change the data processing strategy beams and or polarizations used by GFM in reducing pointing or focus scans This is not needed typically since the software picks the proper default settings under normal conditions However for example if the X polarization channel is faulty for some reason one can use the Y channel instead This can be done by 42 CHAPTER 5 NEAR REAL TIME DATA AND STATUS DISPLAYS Step 1 Select the Data Display Step 2 Selecd the Pointing Tab or the Focus Tab see note below Step 3 Click on the Tools pull down menu Step 4 Select Options Step 5 Select the Data Processing tab in the pop up window Step 6 Make the new data processing selections in the pop up window see Figure 5 5 This options dialog is available only to for Pointing and Focus plugins Please note that the values are set independently f
295. s have been below these criteria for 15 minutes will observations be allowed to resume Safety measures for high winds will take precedence over those for snow and ice 16 4 2 Snow If snow is sticking to any of the GBT structure the operator will move the GBT to the snow dump position The decision to halt and resume observations is solely the responsibility of the GBT operator If dry snow appears to be accumulating the operator may periodically interrupt operations to dump snow and then resume observations 16 4 3 Ice If ice is accumulating on any part of the GBT structure the operator will move the GBT to the survival position The decision to halt and resume observations is solely the responsibility of the GBT operator 16 4 4 Temperature When the air temperature drops to 16 Fahrenheit the Azimuth slew rate of the GBT will be reduced to half of its normal rate This is due to the changing properties of the oil used in the Azimuth drive bearings Half rate speed 18 min instead of 36 min will be utilized until the temperature returns above 17 Fahrenheit When the temperature drops below 10 Fahrenheit observations will be ceased until the temperature is above 0 Fahrenheit and the operator has determined that the Azimuth drive motors are ready for use 16 4 5 Feed Blowers The feed blowers blow warm air over the radomes of the feeds to prevent condensation and frost Al though beneficial for most receivers they
296. s of nwin deltafreq and restfreq were implemented The syntax uses a python dictionary for the restfreq and deltafreq keyword values for configurations The restfreq dictionary maps beams and frequencies of the spectral windows The delta frequency is a map of deltafreq to restfreq The list of values syntax continues to be supported for simpler modes When the dictionary is used to specify the rest frequencies this dictionary must contain a key named DopplerTrackFreq The value assigned to this key is the rest frequency that will be used by the LO as the Doppler tracking frequency Next a few paragraphs give examples of configtool frequency settings Example 1 beam all restfreq 24000 1 2 3 4 23400 5 6 7 25500 1 DopplerTrackFreq 25500 deltafreq 24000 0 23400 0 25500 0 requests that beams 1 2 3 and 4 have a rest frequency of 24000 that beams 5 6 7 have a rest frequency of 23400 and the 2nd beam 1 IF band has a rest frequency of 25000 There are no delta frequencies used in this observation For non zero delta frequencies the delta freq values should be specified in the same manor as the restfreq Example 2 For simple configurations the syntax for the existing receivers would also be supported For example restfreq 24000 nwin 1 beam 1 2 3 4 results in the routing of 4 beams 2 polarizations with each tuned to a rest frequecny of 24000 Example 3 Comparison of two configtool inputs where restfr
297. s of the Prime Focus Receivers Freq Range GHz Polarization Beams Polns Beam 0 290 0 395 Lin Circ 1 2 12 46 0 385 0 520 Lin Circ 1 2 22 43 0 510 0 690 Lin Circ 1 2 12 22 0 680 0 920 Lin Circ 1 2 21 29 0 910 1 230 Lin Circ 1 2 10 17 2 1 OVERVIEW OF THE GREEN BANK TELESCOPE 5 fm ae ED pa Er TE ee A Ae SEDE L o md ELON fa q o 6 4 A ax Sg E i fi N c T V xx 2 37 450 Figure 2 2 The National Radio Quiet Zone Table 2 2 Properties of the Gregorian Focus Receivers Freq Range GHz Polarization Beams Polns Beam 1 15 1 73 Lin Circ 1 2 6 20 1 73 2 60 Lin Circ 1 2 8 12 22 3 95 8 0 Lin Circ 1 2 5 18 8 00 10 1 Circ 1 2 13 27 12 0 15 4 Circ 2 2 14 30 18 0 26 5 Cire 7 2 15 25 30 45 26 0 31 0 Lin 2 1 20 35 30 5 37 0 Lin 2 1 20 30 36 0 39 5 Lin 2 1 20 45 38 2 49 8 Circ 2 2 40 70 67 134 68 92 Lin Cric 2 2 40 80 65 150 80 100 64 2 1 3 1 Prime focus receivers The Prime focus receivers are mounted in a Focus Rotation Mount FRM on a retractable boom The boom is moved to the prime focus position when prime focus receivers are to be used and retracted for Gregorian receivers The FRM holds one receiver box at a time Currently there are two receiver boxes and A change from PFI to PF2 receivers requires b
298. s recommended to use the Astrid GbtStatus display See Section 4 5 50 CHAPTER 5 NEAR REAL TIME DATA AND STATUS DISPLAYS 5 2 4 Weather Launch Weather This displays the current temperature humidity pressure and wind speed 5 2 5 CLEO Clock Launch Utilities Tools Clock A simple display of both the UTC and LST times and the Julian Date 5 2 6 Messages Launch Messages This shows all system status messages Its often useful to identify problems that might arise with any of the GBT devices 5 2 7 Other screens Launch Receivers Mustang PAR Mustang users will need to bring up the Mustang CLEO screen as explained in Chapter 13 Chapter 6 Introduction To Scheduling Blocks And Observing Scripts Here is an example of what a simple Observing Script looks like The first thing that the script does is to load in the definitions for configuring the S receivers Intermediate Frequency system and backends for the observations This is debet re Next a catalog that contains information on the sources to observe containing the source positions and radial velocities etc is loaded This is described in 8 6 2 4 The Configure runs the configuration that was defined in myconfigurations txt to select the requested receiver and backend and set switches and frequencies The telescope is then moved to the desired source with the Slew procedure see 6 2 3 and the power levels in the and the bac
299. s to provide the ACS with signals of the proper bandwidth The signals from this rack can also be sent to the DCR ASTRID Astronomer s Integrated Data Software Used for all observing processes baseline Baseline is a generic term usually taken to mean the fitted extrapolated across spectral lines continuum emission in an observed spectrum 112 beam width The FWHM of the Gaussian response to the sky the beam of the GBT Cw The speed of the wind C band A region of the electromagnetic spectrum covering 4 8 GHz Converter Rack A rack in the GBT IF system that recieves the signal from the optical fibers sent from the IF Rack mixes the IF signal with LO2 and LO3 references and then distributes the IF signal to the various backends Dynamic Corrections A system that uses temperature sensors located on the backup structure of the GBT to correct for deformations in the surface and deformations that change the pointing and foucs of the GBT IDL The Interactive Data Language program of ITT Visual Information Solutions IF Rack A rack in the GBT IF system where the IF signal is distributed onto optical fibers and sent from the GBT receiver room to the GBT equipment room where the backends are located 55 FT rugen 233 234 Glossary K band A region of the electromagnetic spectrum covering 18 26 GHz Ka band A region of the electromagnetic spectrum covering 26 40 GHz 6 KFPA New seven beam K band fo
300. sed to execute more complicated observing strategies In the following example we have many sources to observe and we desire a different amount of total integration time for each source To accomplish this we add two new columns to the Catalog We will call these columns sourcetime and status A few lines of the Catalog lets call it mycatalog cat would look like head name ra dec velocity sourcetime status SrcA 00 01 02 03 04 05 22 0 300 done SrcB 06 07 08 10 11 12 56 3 120 waiting The Observing Script would look like c Catalog mycatalog cat sourcenames c keys for s in sourcenames if c s status waiting dwelltime float c s sourcetime Track s None dwelltime Note that we have to convert the value that c s sourcetime returns from a string into a float before it can be used in the Observing Script 6 2 4 6 EPHEMERIS format Tables for moving objects A Catalog can also be used as an Ephemeris for the position of a moving object such as a comet or asteroid To make the Catalog into an Ephemeris the first non comment line of the Catalog must contain FORMAT EPHEMERIS The header of the Catalog for an Ephemeris can also contain the NAME COORDMODE VELDEF and HEAD keywords The data lines in the Catalog must contain at least the date the time and a pair of coordinates for an Ephemeris Optional parameters are coordinate rates radial velocity and radial velocity
301. sent to the active surface The default solution displayed in Astrid is the sixth order Zernike fit 26 The most aggressive fit is z7 while z5 is less aggressive A reasonable solution should contain broad features of less than 1 5 radians in early to mid morning to a few radians in the afternoon If the z6 solution shows large excursions over a significant area at the edge of the dish then you may wish to drop back to z5 If the calibrator is strong then you may try to use z7 unless the solution begins to show regularly spaced features around the circumference of the dish The values of reduced x for the z5 z6 and z7 fits are shown in the Fitted beam map plot It is important to check the quality of the beam map images before sending the solutions To do this click the Show raw data box The top row is the raw timestream from the receiver in the three maps The second row has the baselines removed and the bottom row shows the corresponding beam maps You should see several detections of the source in all three timestreams and a symmetric right positive negative pattern in all three images If you do not then the source was not bright enough Examples of these plots are shown in Figures and 5 9 Afocus 0 00 mm Afocus 38 00mm Afocus 38 00 mm 650 500 475 600 490 470 m 480 465 470 460 500 460 455 450 450 450 400 440 45 430 440 350 420 435 300 410 0 430 12345 6 567891011 2 111213 15161718 Time minute
302. sources for instance Due to the fact that MUSTANG instantaneously samples many points on the sky and the GBT beams traverse nearly identical paths through the atmosphere the spurious emission contributed by the atmosphere can be effectively removed by variants of a common mode subtraction implemented in the data reduction routines The penalty which results is that astronomical structures on scales much larger than one instantaneous FOV are removed from the map If the weather is clear and stable however the common mode subtractions can be less aggressive and larger structures can be reliably imaged The main effects of degraded weather will therefore be loss of large scale structure in the maps and further attenuation of the astronomical signal In the case of poor weather rain heavy and variable cloud cover a large and variable attenuation can prevent reliable flux calibration so observing is not recommended A device measuring the net near IR irradiance of the sky called a pyrgeometer has been installed near the GBT and provides an approximate indication of cloud cover Its data are shown on the 165 166 CHAPTER 13 MUSTANG GBTSTATUS screen near the wind information Values more negative than 70 watts m indicate clear skies while values more positive than 15 watts m indicate thorough cloud cover Wind and solar illumination affect the telescope structure and therefore influence 90 GHz obser vations with the GBT as well Refe
303. specifies the length of the calibration subscans in seconds The default is 10 0 The following example generates subscan points around 1258 6126 starting the first circle at the source s right Z17 1258 6126 Offset AzEl 00 09 00 00 00 00 cosv True 60 0 Appendix G Advanced Use of the Balance Command You can specify which devices are to be balanced This overrides the default behavior of Balance and should only be used when absolutely necessary The syntax for specifying the balancing of individual de vices is Balance DeviceName where DeviceName can be any of the following IFRack Spectrometer SpectralProcessor RevrPF_1 and RcvrPF 2 An optional parameter to the Balance can be a python dictionary that contains one or more of the balancing options listed below Items which are not in the dictionary are assigned their default values Non applicable options are ignored An example of using balancing options is Balance SpectralProcessor target level 6 which balances the inputs to a level of 6 dB rather than the default The first argument is DeviceName and is the name of the device which you would like to have bal anced Possible values for DeviceName are IFRack Spectrometer SpectralProcessor 1 and 2 The second argument allows you to control the balancing The supported keywords for this and their default values are
304. specifies the source upon which to do the nod scanDuration A float It specifies the length of each subscan in seconds beamName A string It specifies the receiver beam pair to use for nodding beamName can MR12 or MR34 nodLength A number integer for integrations and float or integer for seconds Type depends on value of nodUnit It specifies the half cycle time This is the time spent in one position plus move time to the second position nodUnit A string either integrations or seconds The default is seconds An example SubBeamNod 3C48 scanDuration 260 0 beamName MR12 nodLength 4 4826624 Alternatively one can specify the nod time in units of the primary backend s integration times integer by setting the periodicity units to integrations instead of the default seconds e g SubBeamNod 3C48 scanDuration 260 0 beamName MR12 nodLength 3 nodUnit integrations If the backend s actual integration time is obtainable then a warning is issued if the alignment between the integration times and the nod times shift over the duration of the scan by more than 1096 of the nod time A warning is issued in any case if the backend s actual integration time is not obtainable Attempting to use integrations as the unit when the integration time cannot be obtained from the selected backend will cause a failure In either case when the subreflector is moving the en
305. ss Observers can see the most critical session parameters on the DSS web pages Completing the observations for a session may require scheduling multiple segments Each contiguous block of scheduled time is called a telescope period As telescope periods are completed the project and associated sessions will be billed the time If any time is lost to weather or an equipment failure the observer may consult with the telescope scheduler via the NRAO support center and request that the project not be billed for the lost time 3 3 Controlling the Scheduling of a Project Users can access their DSS account by logging in to the system at The DSS username and password are the same as those used for NRAO Interactive Services i e the Proposal Submission Tool From the DSS web site users can view and manage the scheduling information for their projects Users can control when their project is scheduled by enabling or disabling sessions individually Sessions are enabled for observing simply by clicking a check box Once enabled an observing session enters the pool of sessions eligible for scheduling Note that astronomers intending to observe remotely must be trained and approved by GB staff before the project can be authorized and made eligible for scheduling Observers can enter personal blackout dates Blackouts can be entered either as onetime events e g May 1 20 00 to May 4 05 00 UT or as repeating events e g every Monday from 15 3
306. ss release or a press release from your home institution For more information see page 30 of the January 2007 version of the INRAO Newsletter http www nrao edu news newsletters nraonews110 pdf 209 210 CHAPTER 19 AFTER YOUR OBSERVATIONS 19 5 Publishing Your Results Finally you should publish your results The will help with page charges for the publication of the results from your observations Please see http www nrao edu library page charges shtml for more details Please inform your scientific contact person of any publication resulting from your observations Appendix A The GBTSTATUS IF Path Nomenclature The nomenclature used for the IF path information in the Astrid Status Tabs IF The displayed is the number corresponding to the IF Rack switch in use The value displayed is the RF power in Volts detected by the lF Rack CM The displayed is the number corresponding to the Converter Module in use The value displayed is the RF power in Volts coming out of the Converter Module after the and Third LO LO3 mixers and before the Converter Module filters CF The displayed is the number corresponding to the Analog Filter in use The value displayed is the RF power in Volts coming out of the Analog Filter Rack after all filters have been applied used with 100MHz Converters SG The displayed is the number corresponding to the Analog Filter in use The value displayed is the RF power in Volts c
307. sser weather Note that this capability will not be used to accelerate scheduling of projects that truly do benefit from the most appropriate weather 3 13 Other DSS Control Parameters There are a number of additional contrals and parameters which can be used within the DSS system These parameters are fully described in DSS Project Note 10 The parameters can be used through contacting the GBT scheduler via the NRAO support center https help nrao edu 20 CHAPTER 3 INTRODUCTION TO THE DYNAMIC SCHEDULING SYSTEM Chapter 4 Introduction To Astrid 4 1 What Is Astrid The Astronomer s Integrated Desktop Astrid is a single unified workspace that incorporates the suite of applications that can be used with the Astrid provides a single interface from which the observer can create execute and monitor observations with the Some of the features of are e Creates and executes Scheduling Blocks which perform astronomical observations from Observing Scripts e Provides a real time display of data e Provides an update on the status of the e Provides an area to edit Observing Scripts They may be edited offline and saved before observing e Allows a second observer to monitor an observation that is in progress Astrid is a GUI Graphical User s Interface that is built from python code Many aspects of Ob serving Scripts will thus contain python commands along with specialized functions designed specifically for the GBT As
308. ssion will be scheduled if it has not run in advance of that date 3 12 Projects that can Tolerate Degraded Weather The DSS is designed to schedule projects in weather that is appropriate for the frequency being observed Some projects can tolerate lesser weather conditions than the DSS would assign by default For example consider a project at K band that observes many targets each for a short duration say 10 seconds The observing time for this project is dominated by overheads in slewing from one position to the next so marginal K band weather might be acceptable The observing team may prefer not to wait for very good K band weather which is rare and would delay their scheduling 3 13 OTHER DSS CONTROL PARAMETERS 19 To enable more aggressive scheduling the observer should send an email to the DSS helpdesk requesting that the project be considered for scheduling in lesser weather conditions The DSS support team can enter a session specific factor xi that effectively elevates the score for this session in marginal opacity conditions The xi parameter is tunable so the observer can request that the project be scheduled very aggressively or modestly so The factor only affects scoring related to atmospheric opacity so high frequency projects that are sensitive to high winds will still not get scheduled when the forecasted winds preclude accurate pointing The DSS support team will help observers decide if their project can tolerate le
309. st stage of post processing to recover the full bandwidth GUPPI can be record baseband data in expert user modes If you are interested in this capability contact Scott Ransom sransom nrao edu Ryan Lynch rlynch nrao edu or Paul Demorest pde mores nrao edu Additional resources can be found at https safe nrao edu wiki bin view CICADA GUPPIAstridGuide and Detailed information https safe nrao edu wiki bin view CICADA GUPP ISupportGuide 11 1 Summary Basic control of GUPPI is fully integrated into Astrid A typical observing script will consist of 1 loading a catalog of sources 2 setting up the IF LO path and GUPPI via Configure 3 slewing and balancing the system and 4 taking data mostly likely using a a Track command Depending on your science goals you may also wish to take calibration scans either through an OnOff or separate Track commands If you are observing at C band or above then you should also run an AutoPeakFocus Each of these Astrid functions are described elsewhere in this guide Here we will focus on GUPPI configuration and tips and strategies specific to pulsar observing with GUPPI tools are available for checking that the system is properly balanced monitoring power levels and RFI and checking that GUPPI is properly configured and successfully taking data 145 146 CHAPTER 11 PULSAR OBSERVING WITH GUPPI 11 2 Details of GUPPI Configuration Pulsar observers w
310. t Notes Observers can specify how they should be contacted prior to and during their observations The GBT operations staff stress that it is critical to keep contact information current Each observer can provide dynamic contact information in a free format text box Here the observer should provide any contact information not available through the person s static NRAO contact information which is also listed on the page Observers can also specify the order in which they should be contacted by GBT operations in the event of any schedule changes or in case there is need to contact the observer for any reason prior to the scheduled start time Specify the order by clicking the arrow icons next to the list of team members on the DSS project page Finally observers can record Project Notes on the DSS project web page Project notes provide observers a place to store and share observing instructions The notes are visible to all project team members as well as the GBT operations staff and GBT schedulers Observers who need to share instruc tions or other information with the GBT operator prior to the start of an observation can provide these instructions in the project notes area Project notes are not intended to be a log for observations but rather a place to store brief instructions or news that should be shared among observers and the GBT operator 3 6 The DSS Software Upon logging in to the DSS system users arrive at their DSS home page
311. t is 1 unidirectional A Boolean It specifies whether the map is unidirectional True or boustrophedo nicallyP False Default is False start An integer It specifies the starting row for the map The default value for start is 1 This is useful for doing parts of a map at different times For example if map has 42 rows one can do rows 1 12 by setting start 1 stop 12 and later finishing the map using start 13 stop 42 stop An integer It specifies the stopping row for the map The default value for stop is None which means go to the end This example produces a map with 6 rows each 120 long using a spacing of 6 and scan rate of 720 min that moves to a reference position every 7 rows RALongMapWithReferene center of map Offset J2000 2 cosv True Offset Offset ii 120 cos dec width 172000 0 i cosv True 30 height J2000 0 cosv True 6 vertical spacing Offset J2000 4 cosv True 4 deg cos dec ref offset 7 ref every 7th column 10 0 10 seconds per row RALongMap A Right Ascension Longitude map or RALongMap does a raster scan centered on a specific lo cation on the sky It is similar to RALongMapWithReference except that it does not make periodic observations of a reference position Syntax RALongMap location hLength vLength vDelta scanDuration beamName unidirec tional start stop RALongMap
312. t second A mean level of around 20 30 is optimal 11 4 TAKING DATA 151 11 4 Taking Data In most cases you will use a Track command to take data This is most easily accomplished by loading a catalog and specifying the source name in your call to Track e g Slew balance then take data bright_MSPs Catalog pulsars_bright_MSPs_GBT Configure config_g Slew 7 B19374 21 Balance Track is how we take data now Scan duration is in sec Recommend you add 5 sec to account for some delays in the system Track B1937 21 endOffset None scanDuration 65 As shown in the example above it is usually a good idea to add 5 seconds to the scan duration when using fold mode This ensure that the last sub integration will be written to disk If you wish to take drift scan data or observe during maintenance time you can pass the current encoder position to track instead of an astronomical object e g Take Drift scan data Configure config g Balance loc GetCurrentLocation Encoder Track loc endOffset None scanDuration 20000 When observing flux calibrators it can be useful to use the OnOff function e g Slew balance then take data fluxcal Catalog fluxcal Configure config g Slew 30286 Balance Track is how we take data now Scan duration is in sec Recommend you add 5 sec to account for some delays in the system Track
313. ta without being logged into one of these machines the filler will fail with the error message VEGAS data expected but not found this workstation is not a lustre client For a list of public lustre client workstations see http www gb nrao edu pubcomputing public shtml In this case ssh to one of the above machines and fill your data there 10 3 6 Processing VEGAS data using GBTIDL Processing VEGAS data with GBTIDL is extremely similar to processing GBT Spectrometer data At the time of writing December 2014 we recommend that gbtidl test be used for all vegas data reduction It s required if there are more than 10 spectra in the output sdfits directory across all banks And it also will get the user the new showiftab procedure and new default behavior for the calibration routines as described in this MR https safe nrao edu wiki bin view GB Software ModificationRequest5bQ214 Filling using sdfits directly instead of the output online sdfits might also be useful if there are a lot of spectra to be processed in GBTIDL simply because it improves the response times in GBTIDL if there are not as many spectra to search through So if there s a convenient way to divide up the scans then this sort of syntax works sdfits help for more details sdfits backends vegas scans lt scan list gt PROJECT SESSION OUTPUT PREFIX Where scan list gt is a list of scans to fill a range would be something like 5 25 filling
314. target level Default value is 6 This keyword is applicable only when balancing the Spectral Pro port Default is to balance all active ports This keyword is applicable to the Spectrometer The keyword value is an integer list e g 1 5 7 22 34 which values between 1 and 40 sample time Default is sample every 2 seconds This keyword is applicable only when balancing the Prime Focus Receivers The value is an integer between 1 and 41 seconds cal Default value is off This keyword is applicable when balancing the Prime Focus Receivers Possible keyword values are on or off other values will be treated as if on was specified Examples of this advance use of Balance are 225 226 APPENDIX G ADVANCED USE OF THE BALANCE COMMAND Appendix H Operator Run Observing Guidelines We will consider having the operators run the observing for simplistic programs The following guidelines must be met in order for a project to be considered for being run by the GBT operators 1 The project must use only the GBT Spectrometer or the DCR Other backends do not currently have near real time displays which the operators can use to make sure that the data quality appears acceptable 2 The Astrid scripts should be as basic as possible 3 It should be easily determined by the operator which script should be run 4 The operator will not edit scripts The PI must keep all scripts up to date For m
315. tegration is always shown 46 File Edit View Tools Help ObservationManagement 1 DataDisplay 1 GbtStatus 1 PAE Y IP ARIK O A v Astrid OFFLINE 0 CHAPTER 5 NEAR REAL TIME DATA AND STATUS DISPLAYS Observation State GBT State GBT Status Queue Control Observation Control 0 080 offset 2 575mm Old DFC 0 603mm New LFC 1 973mm LIUZZU 19 L1622U RALongM Pointing Focus Continuum Spectral Line Beta 20 L1622U RALongMal Beams 21 L1622U RALongMal 2 550 29 116220 1 22 L1622U RALongMal STE signal No Car 1370 02 23 116220 RALongMal 2 545 Polarizations 24 L1622U RALongMal Met 25 L1622U Track 1 of OR 2 540 26 L1622U RALongMal Phases 27 L1622U RALongMal Z Signal No Cal 28 116220 RALongMal g 2 535 Signal Cal g 3 Frequencies GHz 30116220 RALongMal 2 530 13 70 31 116220 RALongMal 32 L1622U RALongMal 2 525 33 116220 RALongMal 34 116220 RALongMal 2 520 35 116220 RALongMal 36 116220 RALongMal 2 515 37 116220 RALongMa v 5 10 15 20 25 lt Time 2 352 deli 0 150 2 374 del 0 175 0 000 0 080 ObservationManagement Log 1 DataDisplay Log 1 GbtStatus Log 1 Command Console Idle Offline Figure 5 10 The Astrid Data Display Tab showing continu
316. tem for freq switched HI observations Configure vegas ps config now we balance the IF system and use a Break to check the IF system Balance Break Check the Balance of the IF system specify which source we wish to observe srcs Objectl now we set the parameters for the map the size of the map along the major axis majorSize Offset 2000 0 5 0 0 0 5 degrees in RA the size of the map along the minor axis minorSize Offset 2000 0 0 0 5 0 5 degrees in Dec the size between two points in a row of the map 6 3 WHAT MAKES A GOOD OBSERVING SCRIPT 109 pointStep Offset J2000 0 05 0 0 3 arcminutes expressed in degrees the size between two rows of the map rowStep Offset J2000 0 0 0 05 3 arcminutes expressed in degrees specify how far away from the map center that the off position should be two degrees of arc in Right Ascension direction myoff Offset J2000 2 0 0 0 how many points to observe between off observations refInterval 2 the time to scan each point in the map scanTime 120 seconds which beam to use mybeam 2 now observe for the map PointMapWithReference srcs majorSize minorSize pointStep rowStep myoff refInterval scanTime mybeam 6 3 What Makes a Good Observing Script Rarely does an observing session exactly follow one s plans A useful philosophy is to consider the work
317. tes The parameters used to determine these states are known as the configuration and the act of setting these states is known as configuring B Slew to your source C Balance the In this step you adjust amplifier and attenuator settings in the to ensure that all components operate within their linear regime D Execute your observations using one of the Observing Script Scan Types see Chapter 6 E If problems develop let the operator know and they will contact the on call support scientist for assistance Step 12 Once you are done observing you should close log out of the computer you were using and leave the control room 10 CHAPTER 2 THE GBT OBSERVING PROCESS Step 13 During and after your observing run you will reduce your data You will generally use GBTIDL for data reduction of spectral line data This can be done either at or at your home institution Only rudimentary continuum data reduction support is available for the at this time and you should contact your contact scientist for more information A pulsar data reduction package PRESTO is available from Scott Ransom Use one of the data reduction machines not the workstations used for running the observations Refer to http www gb nrao edu pubcomputing data reduction shtml for a list of data reduction machines at Green Bank Step 14 Once you are ready to leave Green Bank you will want to take home your data see Chapter 19 Step 15 Finally you will
318. that put the balance near the mid point of the observed power range Note that the balance is determined only to within 0 5dB owing to the integer settings of the IF Rack attenuators Syntax BalanceOnOff location offset beamName The parameters for BalanceOnOff are location A Catalog source name or Location object It specifies the source upon which to do the scan offset An Offset object It moves the beam to an optional offset position that is specified relative to the location specified in the location parameter value The default is None See 8 for information on Offset objects beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 2 3 A or any valid combination for the receiver you are using such as MR12 and MR34 The default for each receiver is listed in Table The following example balances on 3C48 and remeasures 1 degrees off Catalog fluxcal BalanceOnOff 3C48 Offset J2000 1 0 0 0 6 2 3 2 AutoOOF OOF Out Of Focus holography is a technique for measuring large scale errors in the shape of the reflecting surface by mapping a strong point source both in and out of focus The procedure derives surface corrections which can be sent to the active surface controller to correct surface errors The procedure is recommended for high frequency observing at frequencies of 26 GHz and higher AutoOOF has the same paramete
319. that would be involved in editing an Observing Script if something were to go wrong during its execution and you wanted to resume its execution where you left off You should break apart any long scripts into smaller individual scripts to reduce the need for edits During your observing you will make decisions as to how to proceed with the next observations You should break apart large scripts to increase your flexibility in being able to react to the circurmstances that arise during your observing Choose the Optimal Size for your Observing Script When preparing your science program you should construct several Observing Scripts An Ob serving Script should ideally contain from 5 to 30 minutes worth of observations A good example is the following Observing Script which sets up a source list configures for the observation slews to the source balances the IF power levels and then does the observations this is the set up for MYPROJECTID first load the catalog with the flux calibraters Catalog home astro util astridcats fluxcal cat now load the catalog with the L band pointing source list Catalog home astro util astridcats lband_pointing cat which source to use myCalibrator 3C123 calOffset Offset J2000 0 58 0 0 cosv True galOffset Offset J2000 1 45 0 0 cosv True set things up for a spectral line frequency switched observation of the calibrator source Comment
320. that you review Observing Scripts with your project s contact support scientist Observing scripts can be written using Astrid s Observation Management Edit tab which contains asimple text editor reminiscent of Notepad MS Windows or you can choose to write your script outside of and use the Observation Management Import facility in to upload it into the database see 8 4 3 1 2 for details For the database you should choose a descriptive name for your Observing Script such as map_G11 0 or pointfocus which will remind you of the science you are trying to accomplish by running that particular script Names such as test or turtle p are not descriptive and should be avoided The name you choose can be up to 96 characters long and can contain white spaces so you may have an Observing Script name that consists of a few words such as K band frequency switched spectroscopy You do not need to add a suffix to your Observing Script name sb or py 6 2 Components of an Observing Script A typical Observing Script will include a a configuration for the system b specification of sources via a catalog c a slew to a source and then balancing the and maybe other Observing Directives and d the observational scan type commands It is highly recommended that the source catalog and the configuration definitions reside in files external to the Observing Script This will allow quick changes refinements without r
321. the process of observing with and analyzing the data from the CCB Much of the information in this chapter is also maintained at users bmason ccbPub README txt which is convenient for instance for cutting and pasting data analysis commands Template scheduling blocks are also in this directory Port Beam Polarization Frequency 9 1 Y 38 25 10 1 Y 34 75 11 1 Y 31 25 12 1 Y 27 75 13 2 X 38 25 14 2 X 34 75 15 2 X 31 25 16 2 X 27 75 Table 12 1 CCB Port labels and the astronomical quantities they measure 157 158 CHAPTER 12 THE CALTECH CONTINUUM BACKEND CCB 12 1 Observing with the CCB 12 1 1 Configuration Configuration of the CCB is straightforward and for most purposes the only two configurations needed are provided in the two configuration files users bmason ccbPub ccb conf and users bmason ccbPub ccbBothCalsLong conf These differ only in the duration of the integrations the former configures for 5 millisecond integrations which is useful for estimating the scatter in the samples to obtain meaningful x values in the analysis of science data the later configures for 25 millisecond integrations which is useful in peak focus obser vations to speed up processing of the data see Chapter 5 section 5 1 3 ccb conf is reproduced and explained below The following keywords tell ASTRID to expect beamswitched continuum observations with Ka and the CCB they do not have any practical effect on the
322. the source catalog Catalog home userid mycatalog cat target Wol tst a test location with line emission off WS51 Off a reference location with no emission mapTarget W51 ji Map center location Move to test target and balance Slew target Balance Set power levels Check the levels are correct Perform the test observation Check spectra ASAP Track target None 30 0 1 Break Check the spectra For position switching first observe the reference location Track off None 30 0 1 Then observe the mapping scans RALongMap mapTarget Offset Galactic 0 3 Galactic coordinate map Offset Galactic 0 0 Offset Galactic 0 0 140 0 1 140 second scans perform a second reference observation Track off None 30 0 1 Chapter 10 VEGAS 10 1 Overview The VErsatile GBT Astronomical Spectrometer VEGAS is a new FPGA based spectrometer built by NRAO and UC Berkeley that can be used with any receiver except Mustang It consists of eight independent spectrometers that can be used simultaneously Eight bit samplers and polyphase filter banks are used to digitize and generate the spectra together they provide superior spectral dynamic range and RFI resistance For details on the design of VEGAS please consult http www gb nrao edu vegas report URSI2011 pdf Observers can use between one and eight spectrometers or banks at the same time s
323. the start of the observing run may not be successful since the blind pointing errors can be similar to the beam size and the source may be missed in the simple Az El scans used by the Peak procedure Initial pointing offsets can be found with the AutoOOF procedure or users may want to point on Jupiter or another large source as needed Pointing and focus for W band requires special attention and users should not blindly accept the default solutions provided by the software system Users can enter solutions manually as needed as discussed in Section 5 1 3 4 14 4 CALIBRATION AND DATA REDUCTION 189 Fle Managers SamplerRates Help Power Supplies MMConverter2 J1 5v 503 Bias On YRI M 28V 28 00 vale o 15V 14 85 o0 15V 15 17 MMConverter J1 Cryo Monitor 15 13 18 SOK 79 59 Ambient 8 M E 2 us Dewar Vac V 048 2 3 oe Dewar Heat Mon 1 Vac Solenoid Mon Pump Req Mon 1 Cold2 Stationary g MMConverter4 J1 3 eo MMConverter3 J1 x Cryo Control Calibration Sequence Cryo Status 255 Cal Man MCB 1 Desired Positi osition Refrig Man MCB Ctl Mon 1 Cryogenics State Cooling Auto Amplifiers j 2 XLI AutoPrepare Unlocked Prepare 3 10 440 _438 3 52 721 Gate 5 6 0 28 0
324. ther requires about 4 hours because one feed must be physically removed and replaced with another It is recommended to allow for pointing and focus touch ups when observing at frequencies of 8 GHz and higher Table shows the recommended maximum intervals between pointings At the higher frequencies 18 26 GHz and 40 50 GHz also do a pointing check when the source elevation has changed by 15 degrees or more Table 7 2 Recommended maximum intervals between pointing observations during VLBI observerations Frequency Band Interval between pointing scans 8 10 GHz 4 5 hours 12 16 GHz 3 4 hours 18 26 GHz 1 5 2 hours 40 50 GHz 30 45 minutes 116 CHAPTER 7 OBSERVING STRATEGIES The observer should select as a pointing source a strong continuum source flux density gt 0 5 Jy within about 15 degrees and at similar elevation as the program source Include the pointing calibration source in the Very Long Baseline Interferometer observing schedule at the recommended intervals Allow about 8 minutes for the pointing and focus check in the schedule Note also that significant pointing errors at 7mm can happen when the wind speed is greater than 3 m sec 7 miles per hour For 1 3 cm significant pointing errors can occur for wind speeds greater than 6 m sec 14 miles per hour Refer to 5 for details To include a pointing and focus scan in your schedule put commands into your key file similar to the following c
325. ther sided of the spike The center spike is also interpolated over by the real time spectrum display We have chosen to interpolate over this spike as it is omnipresent and can cause problems for data reduction such as system temperature calculations If you are concerned about this process you may shift your line from the center of the passband using the deltafreq keyword in your astrid script 10 7 2 The Spurs When attempting to search for RFI with VEGAS by running a high pass filter through the data sig nificantly more spikes spurs were found than naively expected These spurs could be found in the same bins in relatively RFI free wavelengths such as Q band The spurs appear at the same location in bin space for a given mode and have relatively stable amplitudes These faint spurs are not always directly visible in the data but became clear when high pass filtered as shown in Figure 10 12 After significant testing it was determined that these spurs are below the spurious free dynamic range of 60dBc specified by the manufacturer and cannot be fully removed In overly simplistic terms the spurs are caused by the leaking of the FPGA clock into the four interleaved ADCs This causes a rail of thin spikes spurs to be inserted into the VEGAS IF spectrum at frequencies ix f Vspurs 64 10 1 where 0 lt i lt 64 and fs is the sample rate of the ADC Since the bandwidth of the FFT can only be half of fs i actually runs from 0
326. this file contains the configuration definitions configuration definition for continuum observations continuumconfig receiver beam obstype backend nwin restfreq bandwidth swmode swtype swper tint vframe vdef noisecal pol 79 27727 Revlon Continuum DCR 1 1400 80 tp 0 0 2 0 2 topo Radio 3 lo ri gt Linear The above configuration definition has been given the name continuumconfig and can be used for pointing and focusing observations or for continuum mapping For these observations we have selected continuum observations obstype Continuum using the single beam 1 to 2 GHz receiver receiver Revr1_2 beam B1 and the as the backend detector backend DCR We wish to 54 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS take data with a single band nwin 1 which has an 80 MHz bandwidth bandwidth 80 centered on 1400 MHz restfreq 1400 We wish to do total power observations swmode tp swtype none with the time to go through a full switching cycle being 0 2 seconds swper 0 2 We want the DCR to record data every 0 2 seconds tint 0 2 We do not wish to Doppler track the rest frequency since these are continuum observations vframe topo vdef Radio We would like to use the low power noise diode noisecal lo Finally we wish to take the data using linear polarizati
327. ting and Focusing How often you need to point and focus the GBT depends on the frequency of your observations the weather conditions whether or not it is day or night time and the amount of flux error that your experiment can tolerate from pointing and focus errors We will use good to refer to situations where the flux errors from pointing and focusing are less than 5 and usable for when these errors are between 5 1096 Note that this is not the total flux error limit of the system only the contribution from pointing errors In Table 7 1 the pointing and focus accuracies required to achieve usable and good performance as a function of observing wavelength are shown The approximate wind limits at which these flux accuracies can be achieved are shown along with the recommended observing strategy for performing peak and focus measurements The pointing error due to wind can be approximated by Fal wind 0 23 ef m arcsec 7 1 where ey is the wind speed If you are looking at extended sources then the pointing requirements can be relaxed from those in Table 7 1 You can use Equation 7 1 to estimate what the wind requirements should be when observing extended sources The recommended observing strategies are 7 4 STRATEGIES FOR POINTING AND FOCUSING 113 Table 7 1 Requirements limits and observing strategies for usable performance 10 rms flux errors from pointing alone and good pe
328. tion Committee TAC uses these reviews to decide which proposals can be scheduled given the resources available Step 4 If your proposal is granted time on the by the TAC then your observations are scheduled Steps for Observing With the Step 5 Before you observe you need to prepare for your observations see Chapter 18 You will be assigned a scientific contact person GBT friend whom you should contact well in advance of your observing to determine optimum dates for a visit and ensure the telescope and hardware will be available for the project while you are on site Your friend will help you develop an appropriate observing strategy for your proposal see Chapter 7 They will also help you with any technical questions dealing with Radio Frequency Interference see Chapter 15 etc At this time you should review your project page s in the Dynamic Scheduling System and develop your Observing Scripts see Chapter 6 and 3 Step 6 If you are an experienced GBT observer you can observe remotely see Chapter 17 If you are new to the GBT you must plan to spend at least a week and preferably two weeks at the site to ensure appropriate weather conditions for the observations After hands on experience with observing you will qualify for remote observing 2 3 THE GBT OBSERVING PROCESS 9 Step 7 You will travel to Green Bank for your observations see 18 or if you are an experienced GBT observer you can observe
329. tions around the Observatory including some rooms in the Residence Hall Visitors should obtain a login account on the Green Bank system before arriving Before receiving your account you will have to go through a screening process The screening will automatically happen when you make a soom reservation in the BOS system You can also begin the screening process by filling in the form at https info nrao edu oas dpscompliance Accounts may be requested from Wolfgang Baudler wbaudler nrao edu or Chris Clark cclark nrao edu Any problems with connecting a personal computer to our network should be referred to these same two gentlemen 2 3 The GBT Observing Process The following list summarizes the general flow of how observing proceeds By the time you are reading this document you should have already been through several of the steps Steps for Proposing and Obtaining Time on the Step 1 You get a brilliant idea for an observation You research which telescopes would be best suited for the observations and find that the is the instrument for you Step 2 You read through the Proposers Guide http www gb nrao edu gbtprops man GBTpg GBTpg_tf html and determine which receivers and backends will be best for you to use You then write a proposal to use the using the Proposal Submission Tool https my nrao edu Step 3 Your proposal is sent to science referees for ranking and given a technical review by staff The Telescope Alloca
330. tire integration during which this occurs is flagged The scan will end at the end of the scanDuration once the current integration is complete regardless of the phase of the nod cycle The following example does a subreflector nod between beams 1 and 2 for 60 seconds each nod or half cycle lasts for three integrations where Rcvr26 40 was selected in the configuration with an integration time of 1 5 seconds SubBeamNod 1011 2610 60 0 MRI2 nodLength 3 nodUnit integrations In this example one out of every three integrations will be blanked because the subreflector is moving So the sequence will be Beam 1 2 intg Blanked while subreflector moving 1 intg Beam 2 2 intg Blanked 1 intg Beam 1 2 intg etc It takes about 0 5 seconds for the subreflector to move between beams but the entire integration time will be blanked If nodLength 5 then only one in five integrations would be blanked 80 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS The antenna uses the average position of the two beams for tracking the target and SDFITS reports the positions of the beams relative to the tracking position Although the SDFITS header postion will not match the target position the SubBeamNod mode successfully nods between the two beams during the scan Control of the subreflector may be done with any scan type using the submotion class This should only be done by expert observers Those
331. to JPL s HORIZONS system which can be used to generate ephemerides for solar system bodies Full access to HORIZONS features is available via the primary telnet interface HORIZONS system news shows recent changes and improvements A web interface tutorial is available to assist new users Current Settings Ephemeris Type change OBSERVER Target Body change Mars 499 Observer Location change Geocentric 500 Time Span change Start 2012 05 09 Stop 2012 06 08 Step 1d Table Settings change defaults Display Output change default formatted HTML Generate Ephemeris Special Options e set default ephemeris settings preserves only the selected target body and ephemeris type e reset all settings to their defaults caution all previously stored selected settings will be lost e show batch file data for use by the E mail interface ABOUTSSD _ GLOSSARY LINKS Fi GO 2012 May 09 18 14 UT Site Manager Donald K Yeomans FIRSTGOV server date time Q Webmaster Alan B Chamberlin Figure 6 2 The JPL Horizons website Your entries in the Current Settings should be 94 CHAPTER 6 INTRODUCTION TO SCHEDULING BLOCKS AND OBSERVING SCRIPTS Ephemeris Type OBSERVER Target Body SELECT YOUR OBJECT Clicking on the blue change link will open a form to search for the object of interest Observer Location Green Bank GBT 9 radar 280 09 36 7 E 38 25 59 1
332. tories and then combine the data Note that the scripts assume that a parfile exists in HOME tzpar lt source gt par where source is the source name you specified in Astrid Coherent search mode data require root privileges to combine so contact your project friend if you need help with that 11 7 Tips and Tricks e If you are searching for pulsars or observing a new source consider observing a well known pulsar as a test source at the start of your session to make sure that things are working properly A cal mode can also be used e If guppi status shows unexpected values the system seems to be having trouble balancing or you experience other issues ask the operator to do a conform params and prepare on GUPPI you can also do this yourself in Cleo if you know how This simple step can solve lots of problems especially if you are the first GUPPI project to observe following a maintenance period e If you are observing multiple sources with relatively short scan lengths and the operator needs to take control for a wind stow or snow dump ask if you can let the current scan finish and then use Pause to let the operator take control Once control is released back to you you can simply un pause and pick up where you left off But if the operator needs to take control immediately abort your scan and let them take over http www cv nrao edu sransom presto http sigproc sourceforge net http psrchive sourcefor
333. trid brings together many applications into a single unified GUI The GUI places each application into its own tab window Applications available in Astrid are Observation Management The Monitor and Control systems can roughly be thought of as a group of programs one for each hardware device and a master program the Scan Coordinator interfaces with the Observing Management Application in order to run Observing Scripts on the Data Display provides a real time data display by connecting to the GBT FITS Monitor GFM This allows the automatic processing of pointing and focus scans that can immediately update the GBT M amp C system with the determined corrections GFM can show raw uncalibrated continuum data as a function of time It can also show raw uncalibrated bandpasses for spectral line data Status also provides a screen that provides information on the real time status of the GBTI his provides meta information such as the LST UTC observer project ID etc information on the antenna such as current position etc and information on the current scan and setup Python Editor This application is a windows like text editor that features syntax highlighting for Python code This is the editor that is part of the Astrid Edit Tab see 4 3 1 where you can edit copy and save Observing Scripts 21 22 CHAPTER 4 INTRODUCTION TO ASTRID Command Line Interface also has a command line interface that allows some
334. um data Ele Edit View Tools S wosk1dbzazkEk t An ObservalenManagement 1 DataDisplay 1 GiStatus 1 Astrid OFFLINE 300 145947140 Peak 1 of Pointing Focus Continuum Spectral Line Beta 311 pol RALongMap 31 of 312 pol RALongMap 32 of 314 pol RALongMap 34 of 315 pol RALongMap 35 of 316 pol RALongMap 36 of 317 pol RALongMap 37 of 318 pol RALongMap 38 of 319 pol RALongMap 39 of 320 pol RALongMap 40 of 321 pol RALongMap 41 of 322 pol RALongMap 42 of 323 pol RALongMap 43 of 324 pol RALongMap 44 of 325 pol RALongMap 45 of 301 145947140 i ms 302 1459 7140 Peak 3 o 303 1459 7140 Peak 4 of AGBTO7A 104 03 313 0 304 145947140 Focussubn 7 Polarizations I xx v vv 305 pol RALongMap 25 of D 306 pol RALongMap 26 of Beam 1 P IFs 307 pol RALongMap 27 of 6 Pol XX Proc RALongMap 33 173 0 308 pol RALongMap 28 of IF 0 EL 39319 TED 309 pol RALongMap 29 of Phase 0 TSys 17 247 Reference Cal 310 pol RALongMap 30 of Signal Reference No Cal Signal No Cal Integrations o k Views ACF Channels ACFiFrequency Lags Keep Zoom Overlay Clear 326 pol RALongMap 46 of 327 pol RALongMap 47 of fy 0 6 0 8 1 0 1 2 1 4 1 6 18 xle4 Channels A9 ObservationManagement Log 1 Data
335. ur Observing Script into the Editor Otherwise you can just create your Observing Script in the Editor To save the Observing Script into 30 CHAPTER 4 INTRODUCTION TO ASTRID the database you just need to hit the Save to Database button This will run a validation check see 5 4 3 1 4 on your script and then a pop up window will appear which allows you to specify the name which you would like to use in the list for your Obsering Script Selecting an Observing Script If you perform a single click on any Observing Script in the Scheduling Block list the contents of the selected observing script will appear in the Editor The selected Observing Script will be highlighted with a blue background Mouse button Actions on the selected Observing Script If you perform a right mouse button click on the selected Observing Script a pop up window will appear that will let you rename create a copy or save the Observing Script to the database You can also delete the Observing Script from the Astrid database You may also rename the Observing script if you perform a left mouse button double click on the script name in the list 4 3 1 4 Validator The Validation area is where you can check that the currently selected Observing Script is syntactically correct This does not guarantee that the script will do exactly what you want it to do For example it can not check that you have the correct coordinates for your source You will also se
336. ure by Tmo 14 4 where 7 is the zenith opacity and A is the airmass Assuming a Gaussian beam the main beam efficiency is given by Nmb 0 88997 ew mz y D A 14 5 where is the full width half maximum beam size in radians D is the diameter of the GBT 100m and A is the observed wavelength For the GBT the effective aperture efficiency is Na 0 3516T 4 4 5 14 6 where S is the flux density of a known calibration source The opacity as a function of time can be obtained by the weather database derived for Green Bank using the getatmos pro script Except for periods of rapidly changing weather conditions the predicted opacities are accurate to within 0 01 based on historical measurements 14 5 WEB DOCUMENTATION 191 Table 14 2 Effective Cold Load Temperature for W band Date Range Average Temperature 2010 May 2012 April 53 2012 May 2012 June 56 2012 October 2015 August 50 K 2015 September 54K Table Notes The estimated effective cold load temperature measured in the lab The temperature is estimated to better than 5 Note that a 10 error in the cold load measurement corresponds to only about 2 596 error in the measured T or Na 14 5 Web Documentation e 4mm Web Page http www gb nrao edu 4mm e 4mm Project Book http www gb nrao edu 4mm ProjectBook e 4mm Wiki https safe nrao edu wiki bin v
337. ure that the telescope and hardware will be available for the project You should plan on arriving in Green Bank at least one full business day before your observations are to begin This will allow you to meet with your scientific support person as well as the staff support person who will be on call during your observations If your observations are dynamically scheduled and dependent on weather conditions you should plan to spend at least a week and preferably two weeks to increase the likelihood that appropriate conditions for the observations will occur during your visit 18 2 Travel Support Some travel support for observing and data reduction is available for U S investigators on successful proposals More information on the travel support that INRAO provides can be found at http www nrao edu admin do nonemployee_observing_travel shtml 203 204 CHAPTER 18 PLANNING YOUR OBSERVATIONS AND TRAVEL 18 3 Trains Planes and Automobiles In principle observers may use a number of area airports for their travel to Green Bank These include Washington Dulles Pittsburgh Charlottesville Roanoke Va Charleston WVa Clarksburg WVa or Lewisberg WVa In addition limited AMTRACK train service is available to Charlottesville and White Sulphur Springs WVa Rental cars are available at most of the airports The Observatory can also send a driver for pickup at any of these airports or stations It is most convenient if visitors c
338. us When you leave the mouse situated over one of the Toolbar buttons for a few seconds a pop up will appear that tells you what action the Toolbar button will invoke 4 2 2 8 Application Component Tabs The Application Component Tabs are located under the Drop down menus and the Toolbar and at the very bottom of the GUI There is a tab for each Application that Astrid is currently running By clicking on the tabs you can switch the GUI so that it shows the contents of the selected Application 4 2 2 4 Application This comprises the majority of the space within the Astrid GUI This shows the contents of the Appli cation selected by the Application Component Tabs 4 2 2 5 Log Window The Log Window is located in the lower portion of the GUI underneath the Application display area It shows the log information for the currently selected Applications Note that each Application has its own logs Some Applications allow the contents of the logs to be saved to an external file 4 2 2 6 Observational Status The Observation Status area is located in the upper right corner of the GUI This provides information on whether or not is talking with the Monitor and Control M amp C system as well as the current state of the and Status of the Observation State The Observation State indicates Astrid s state The observation state is either e Not Connected e Idle e SB Executing e SB Paused 26 CHAPTER 4 INTRODUCTION TO ASTRID
339. us or minus 3 days In this example the window size is 7 days Currently windowed sessions are scheduled in the following way The cadence information from the proposal is used to preschedule all windowed sessions whereby all of the telescope periods are temporarily fixed in what are called default periods The user is given the window template e g 8 14 January 8 14 February 8 14 March 8 14 April and 8 14 May Within a windowed period a windowed session will be considered like an open session Near the end of each window range is a default period If the session has not been selected by the time the default period arrives the session will be scheduled in the default period The default period may be moved manually to a later time slot within the window if the human scheduler notices a problem with the original default period When the windowed period is scheduled the observer will be informed 24 48 hours in advance just like an open session The only difference is that the observer will be provided with the window template for planning purposes In the future historical weather data climate will be used to schedule such sessions more efficiently within the window Elective sessions are a restrictive form of windowed sessions Here rather than having a range of days on which the project session can be scheduled there is a list of possible days As with windows the list of possible days or opportunities has a default period on which the se
340. ut an array of dictionaries e g restfreq restfreq 1420 bank A restfreq 1665 bank B 3 The dictionary keys are restfreq bandwidth nchan deltafreq tint vpol bank and beam The nchan keyword is used to specify the number of channels in an individual window see Table 10 1 The bank keyword is used to specify a bank i e spectrometer and can have values from A to H All other keys have the same meaning as the standard keywords The minimum required key is restfreq If the value for a key is not specified then it will be taken from the corresponding value specified in the configuration block or the default values will be used Key values specified in the restfreq dictionary array override values specified in the configuration block bandwidth This keyword gives the bandwidth in MHz to be used by the specified backend The value of the keyword should be a float Possible values depend on the receiver and backend that are chosen see 6 3 Table 10 1 Table 6 1 receivers and their nominal frequency ranges Name Frequency Range GHz Notes Revr_342 290 395 Revr_450 385 520 Revr_600 510 690 Revr_800 680 920 Revr_1070 910 1 23 Rcvr1 2 1 15 1 73 Revr2_3 1 73 2 60 Revr4_6 3 95 8 Revr8_10 8 00 10 0 Rcvr12 18 12 0 15 4 RcvrArrayl8 26 18 0 26 5 7 beam focal plane array Revr 26
341. value pol Each of the prime focus receivers and receivers have a hybrid that can output either linear or circular polarization This keyword specifies whether linear or circular polarization is desired for these receivers The keyword value is a string Allowed values are Linear and Circular The default value is Circular for the Very Long Baseline Interferometer VLBI and Radar back ends and Linear otherwise noisecal All receivers below 12 GHz have two noise diodes for calibration signals one with an equivalent brightness temperature at roughly one tenth the system temperature lo value and one nearly equal to the system temperature hi value This keyword is a string which specifies which noise diode is to be used Allowed valued are lo and off The default value is lo except for the Radar backend for which the default values is off For the Ka band receiver there are three additional choices These are L R or LR T he Ka band receiver has two lo noise diodes one for each polarization for each of the two beams The D R and LR options specify which of these noise diodes are to be used with the receiver notchfilter There is a notch filter covering roughly 1200 1310 MHz in the L band receiver that filters out an FAA radar signal This keyword determines if this notch filter is in place and used by the system or is removed from the receiver s
342. values assume that the maps are sampled at twice Nyquist in the scanning direction and that there are four integrations per switching period Col 4 Recommended minimum switching period swper for Doppler tracked frequency switch observations with the noise diode turned off sp_nocal These values will yield less than 10 blanking in the first state of the switching cycle as well as less than 10 blanking overall This switching period will result in less than 10 of your data being blanked These values assume that the maps are sampled at twice Nyquist in the scanning direction and that there are four integrations per switching period Col 5 Recommended minimum switching period swper for Doppler tracked frequency switch observations with the noise diode turned on sp These values will yield less than 10 blanking in the first state of the switching cycle as well as less than 10 blanking overall These values assume that the maps are sampled at twice Nyquist in the scanning direction and that there are four integrations per switching period 10 5 BASELINE PERFORMANCE 139 Figure 10 10 VEGAS bandpass for the four families of VEGAS modes The upper left represents the 1500 MHz bandwidth of modes 1 and 2 the upper right is mode 3 the lower left shows the bandpass for mode 4 modes 4 9 all show a similar bandpass mode 17 representing modes 10 29 is shown in the lower right These shapes are all extremely stable and so are
343. verage 50 percentile winter conditions for Green Bank Thus high frequency observers can anticipate that the typical weather conditions under which they will observe will be best represented by the top 25 percentile conditions In contrast low frequency winter observers should expect they will observe under conditions that are worse than the 50 percentile and more like those of the 75 percentile conditions During the warm season June through September high frequency observing is much less produc tive and we almost exclusively schedule low frequency observing During these months low frequency observers can plan on observing under the average 50 percentile conditions 16 4 GBT Weather Restrictions During weather conditions that pose a risk for the safety of the GBT the GBT operators will cease all observations and take the appropriate action to ensure the safety of the GBT The operator is fully responsible for the safety of the GBT and their judgement is final The operators decisions should not be questioned by the observer 16 4 1 Winds The following guidelines exist for periods of high winds If the average wind speed exceeds 35 MPH over a one minute period the operator will stop antenna motion If wind gusts exceed 40 mph or if winds are expected to exceed 40 mph for a period of time the operator will move the antenna into the survival 200 CHAPTER 16 HOW WEATHER CAN AFFECT YOUR OBSERVING position Only after the wind speed
344. vers might need to reconfigure after each source if the change in velocity is larger than the bandwidth of a filter An example of how vlow and vhigh can be used is as follows Suppose that you are looking for water masers in extragalactic AGN Furthermore lets say that you are looking at 100 candidates with velocities from 1000 km s to 40000 km s The you would set vlow 1000 0 and vhigh 40000 0 and you would not have to change the IF configuration when you changed sources Note that if vdef Red i e redshift then you must give the redshift parameter z as the values for vlow and vhigh instead of velocity Your scientific contact person can help you decide if you should use vlow and vhigh 215 216 APPENDIX C USAGE OF VLOW AND VHIGH Appendix D Location and Offset Objects A Location is used to represent a particular location on the sky Locations can be specified in the follow ing coordinate modes J2000 B1950 RaDecOfDate HaDec ApparentRaDec Galactic AZE and Encoder A Location is specified by two values the meanings of which are dependent on the coordinate mode chosen E g For J2000 the two values are time and degrees Here is an example of how to specify a Location location Location J2000 16 30 00 47 23 00 An Offset object represents a displacement from a Location Here is an example of how to specify an Offset offset Offset J2000 0
345. w and the 13 5 TROUBLESHOOTING 175 3 Basic Options vanced Use subcommon2 Cutoff Frequency Roirad Poly fit Yes Default Automatic w No Skyscale RIT Data offsrcpolyfit al ea v Manual Fitters srtskip rm v 4 00000 1 00000 spskip p Force read write Coordinates v Yes DEC Hanually Plot Scan Scan Number Save FITS image Export Image Clear Error Clear Data _ Show Help E 3 Elev Rz az LPC el LPC LFC Y arcm s cal g 2 File name ScanTupe out of SB SrcName WindsHin Max Humid Temp 4 1 quickdaisy 1848 3219 0 86 1 92 94 9 0 7 7 1 fulllissdais 1 Z 1 fulllissdais vegaN 1 fulllissdais vegaN 1 fulllissdais vegaN Z 1 fulllissdais vegaN rac ae 1 fi E io 174 3 0 01 0 17 2 5 R Longap 1 R LongMap EI 33 TE 8 355555555 m Lig a RA Ee ean DOIA SE AS SESSSESSRER 222 bes amp fulllissdais vegal fulllissdais vegal fulllissdais vegal fulllissdais vegal fulllissdais vegal ipio to to to tp VIN foo fo fo fo fo fo fo fo fo fo ASRSBSIRRER boos ma cionb Nini Nine in acuta eeePPPPPPPP 2 5 PELPEPPPPI 1 1 d 1 1 y 1 d m 2255 Figure 13 5 Specifying the coordinate system for the maps in MUST
346. when the beef disks are under heavy use by another user which should not usually happen if people are being careful if there are network issues etc If you start to see many warnings about dropped packets ask the operator to contact the on duty support scientist Note that it is common to see a very small number of dropped packets 1 at the start of a scan This is not an issue and can be safely ignored You can also check the data that is being written to to disk by going to the output directory This will be in data 12 lt username gt lt projectID gt lt date gt where data 12 refers to either data1 or data2 whichever you specified with guppi datadisk username is your NRAO user name project ID is the GBT project ID as it appears in astrid e g AGBTI14A 507 and date is the UTC date in YYYYMMDD format 11 5 2 Monitoring Coherent Data Taking In coherent dedispersion mode data are written to one of eight GPU nodes This means that guppi status will not indicate that data is being written unless it is running on one of the GPU nodes The guppi daq server 1log file will also not update on beef Instead you should use guppi gpu status This will show the data taking status on each GPU node and show the last few lines from the server logs on each node Monitor this screen for messages about packet loss or errors on the various nodes The most common problems will be when a node is hung in Stopping or Waiting even while other nod
347. with a nod period of 6 seconds and 0 2 second integration times to minimize the blanking The high frequency ripples then present in VEGAS data and the spikes see 8 10 7 1 calibrate away nicely This spectrum consists of 4 overlapping Mode 1 spectra no special processing was required to stich the spectra together overlapping channels were simply dropped After the above processing was performed the scalar processing yielded a nice flat baseline and noise that is consistent with the radiometer equation 10 7 Instrumental Features and their Cure The architecture of the VEGAS hardware specifically the architecture of the ADC results in some characteristic features in the VEGAS spectrum Specifically these are e a strong spurious single channel wide wpike at the exact center of the ADC passband the so called center spike e weak single channel wide spurs at various locations in the bandpass the 32 spurs 10 7 INSTRUMENTAL FEATURES AND THEIR CURE 141 0 004 0 003 0 002 0 001 oo M i A M Wi M uh NOM 0 001 0 002 L o5 6 0 53 3 342 32 42 D a a pr or a d oa a a au 39 40 41 4 BAR Frequency CHz Figure 10 11 A deep integration with VEGAS 10 7 1 The Spike The center spike is caused by the FPGA clock By default the center spike is interpolated over by the SDFITS filler by taking the mean of the adjacent channel on ei
348. with another using the beamName parameter you can have very very bad data Make sure that if you configure with the same beam with which you Peak The following example does a peak in encoder coordinates with 90 minute lengths and a 30 second scan duration using beam 1 Peak 0137 3309 Offset Encoder 00 90 00 0 Offset Encoder 0 00 90 00 30 1 or with the defaults 6 2 COMPONENTS OF AN OBSERVING SCRIPT 71 Peak 0137 3309 Slew Slew moves the telescope beam to point to a specified location on the sky Syntax Slew location offset beamName The parameters for Slew are location A Catalog source name or Location object It specifies the source to which the telescope should slew The default is the current location in J2000 coordinate mode offset An Offset object It moves the beam to an optional offset position that is specified relative to the location specified in the location parameter value The default is None See for information on Offset objects beamName A string It specifies the receiver beam to use for the scan beamName can be C 1 2 3 A or any valid combination for the receiver you are using such as MR12 and MR34 The default is 1 Slew does the following based on the arguments provided 1 If only a location is given the antenna slews to the indicated position 2 Ifa location and offset are given
349. y 1 GbtStatus 1 nOfa Observation State 113 IR17208 0014 Continuum Spectral Line Beta 14 IR17208 0014 15 IR17208 0014 30 1L 2333 3901 focus GBT State 16 IR17208 0014 Ont 17 IR17208 0014 Wid 222 974 E Wid 223 448 GBT Status 18 IR17208 0014 Tsys 16 836 19 1R17208 0014 Ctr 133368 d 20 IR17208 0014 Hgt 0 847 21 IR17208 0014 Queue Control 22 IR17208 0014 23 IR17208 0014 24 DR210H OnOff 1 25 DR210H OnOff 2 Observation Control 26 2333 3901 Peak 1 27 2333 3901 Peak 2 28 2333 3901 Peak 3 29 2333 3901 Peak 4 SEARASZISG5 0 0 oaa aaaea 32 IRAS23365 3604 eed 200 100 0 100 200 300 34 IRAS23365 3604 7 2 Offset mm 35 IRAS23365 3604 d v gt cvm 6 Feeds 1 TotalPower Polarizations XL Center Sky Frequency 4 83 GHz pell 4 791 dell 0 252 tell 4 539 F pel2 4 783 del2 0 159 tel2 4 624 OldAz2 0 226 OldEl 0 200 dAz2 0 169 dEl 0 205 NewAz2 0 057 NewEl 0 005 warning Scan 30 does not have sufficient baseline present Fitting data to Gaussian with DC offset offset 13 368mm Old DFC 8 798mm New LFC 4 570mm I ObservationManagement Log 1 DataDisplay Log 1 GbtStatus Log 1 Command Console se Offline NEN 2 Figure 5 2 The Astrid Data Display Tab showing focus data 5 1 3 1 Fitting Acceptance Options GFM has several levels of determining whether or not the pointing and focus solutions will be up
350. ygor relockAstrid py for df in dfocus set focus ff df nomFocus Set Values Antenna local_focus_correction Y ff Set Values Antenna state prepare sleep 3 Daisy mySrc daisyRad daisyRadPd 0 0 daisyScanDur beamName C cos_v True coordMode Encoder calc dt 0 2 leave in nominal state Set Values Antenna local_focus_correction Y nomFocus SetValues Antenna state prepare 13 6 5 This SB applies pointing and focus offsets to the telescope The desired focus offset in millimeters is set in the python variable focusoff Typically it is not necessary to do this by hand any more as the autooof procedure takes care of the pointing and focus offsets in addition to the surface myLoc Get CurrentLocation Encoder offsetts to apply in arcmin LEAVE AT ZERO azoff 0 eloff 0 Y focus offset in mm focusoff 3 EET LLLLL LLLLLLL LLLLL azoff azoff 60 0 3 14159265 180 0 eloff eloff 60 0 3 14159265 180 0 SetValues Antenna localPointingOffsets azOffset2 azoff SetValues Antenna localPointingOffsets elOffset eloff SetValues Antenna local focus correction Y focusoff 1 180 CHAPTER 13 MUSTANG 13 6 6 quickdaisy collects a single quick map using the daisy scan pattern This is useful for instance to check your calibration every half hour It s not a bad idea
351. your project friend for advice on which value to use e guppi datadisk controls which RAID data are written to in incoherent modes Allowed values are datal or data2 In coherent modes data are written to eight HPC machines and this keyword is not used e guppi dm controls the DM used for coherent search mode It is not used by any other modes guppi fold parfile specifies the path to the ephemeris parfile used for either incoherent or coherent fold modes The parfile must exist and be visible from beef and readable by tempo guppi fold bins controls the number of phase bins used for either incoherent or coherent fold or cal modes Enough bins should be used to fully resolve fine profile structure Typical values are 256 in incoherent modes which are not typically used anymore and 2048 in coherent modes guppi fold_dumptime controls the length of a sub integration in either incoherent or coherent fold or cal modes The value is specified in seconds with 10 s being typical It must be shorter than the total scan length The following is a heavily documented configuration script As is it will configure for search mode at L band but it can be easily edited for other observing modes An example well documented L band obstype Pulsar usually Revr_342 Revr_800 Revrl_2 Revr2_3 receiver Revrl_2 pol Linear C band and below are native restfreq
352. z for modes 25 29 All the spectral windows from a single spectrometer must have the same bandwidth The 8 spectrometers can be tuned to different frequencies covering a bandwidth of up to 10 GHz although the GBT IF system typically limits this to 4 6 GHz depending the receiver 127 OVERVIEW 10 1 ZHIN 096 0 ZHIN OST t 31 6 0 9 107 ose g opour ZHIN 000T JO UIPIMpueq 10 ZHI OOFL O3 ZHIN OST St 0c 10 g 2 ZHI OOST JO YIpImMpueq pueqoseq 10 o8uex Aouonboy o qesn AL ZHIA OOOT pooe d oq ue spueqqns oq 6 O3 GZ sopour 10 o30u oos ZHN OOST JO YIpPImMpueq pueqoseq oy pooe d oq ued spueqqns oy vc 0 0c IO JoyouoIyoods ouo ST 1 poytoods oy y e q 3 OY UT poj3sr Y SOWING oq UINUITUTUT oY Ud Surtqo3rAS c sosn jr fo durexo 104 uorjedsoqur WINUITUTUL OY lt oq 9484S SuryoyIMs iod 8 eu T soqdq p Aq poquosoidol st e132ods ype potsiod uolyeisoyul UNUITUIUT oun 3e spouueqo re pue uorjezrre od 10 po3 e no eo sr p 270 Ze OT ZET 970 9899 6 91 8 8 6 9 0 Ze 6 69 Ie 0 8947 691 8 97 871 8 9POIN vo ze 9 2 oT PSE9T 6 9T 8 7 871 22

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