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PACS Observer`s Manual

1. Observation Est Add Comments Visibitity OK Cancel Help Figure 6 20 Line spectroscopy step 2 Retrieve spectral line from database or add a line manually Once the Line Editor is filled spectral line parameters can be modified by clicking on Modify Line button An editable window will appear and show the current settings for the selected line The black mandatory fields have to be provided in order to get a valid line request Optional para meters are highlighted in green leaving default zero values mean the observer does not want to spe cify these values 60 Using HSpot to create PACS observations PACS Line Spectroscopy Unique AOR Label Pspecl 0000 Target NGC7027 Type Fixed Single Position 21h07m01 59s 42d14m10 2s 5 Update a line New Target Modify Targ Target List Spectral line parameters Line ID IN II 3P2 3P1 Number of visible stars for the target 23 v 1 Star tracker target Ra 136 757 degrees Dec 42 236 degrees Lui Wavelength qim 121 900 Line flux unit 104 18 W mA2 L4 t Wavelength Settings on 5 kinatha 0 00 feleqtion of wavelength ranges al Conti flux di 0 00 D CJ Rene
2. 17 Scientific capabilities 3 5 4 3 5 5 Spectrometer spatial resolution The spectrometer and in particular its image slicer is used over a large wavelength range The pho tometer pixel size of 9x9 arcseconds is a compromise between resolution at short wavelengths and observing efficiency mapped area at long wavelengths Full spatial sampling requires a fine raster with the satellite for spectral line maps with full spatial resolution For the sensitivity calculation this is neglected as the line flux will always be collected with the filled detector array Spectrometer spectral resolution Note Ce The main thrust of the PACS spectrometer resides in its high spectral resolution The spectrometer i is aimed at the study of emission absorption lines rather than continuum sources although a SED mode in the Range Scan spectroscopy AOT is available too The spectrometer resolution versus wavelength and order is given in Figure 3 9 An effective resolu tion of A A 940 5500 c A X 55 320 km s can be obtained The instantaneous 16 pixel spectral coverage is 600 2900 km s corresponding to 0 15 1 0 um wavelength coverage Effective Resolution SORT dv pix 2 grating resolution 2 T T T T T T T T T T T T T T T T T 300 Grating size 80x320 mm Collimated beam size 120 mm Grating consioni 8 50 0 05 grooves mm Grating spacing 117 65 micron Total number of grooves 2720 250 Groting ongle ronge 28 6
3. Wavelength ranges 72 105 and 105 210 microns Qnd 1st orders v Line width unit km s 4 Line width FWHM 1 00 PACS Line Editor E e lengt Redshifte Line Flux Line Flux Continuu Line Width Line Wid Line Repe PRE e RC EE 180 63 18 o00 104 18 0 00 1 00 kms l aah 900 12190 0 00 10 18 0 00 1 00 kms l The relative line strength fraction of on source time per p 741 15774 9 00 104 18 0 00 1 00 km s 1 line can be set by the line repetition factor for each line Note the sum of line repetition factors affects the 0n source time per integration cycle Cancel ES ine Manually Add Line From Database Modify Line Delete Line Redshift selection Unit Redshift z w Value 0 000000 Observing Mode Settings Nodding wavelength switching cycles EP Observatid Source type chopping and wavelength switching Number of cycles 1 Target NGC Setthe Observing Modes To control the absolute sensitivity consider 75 0 0 to adjust the number of integration cycles K observation Est Add Comments Visibility OK Cancel Help Figure 6 21 Line spectroscopy step 3 Modify spectral line parameters if necessary The observing mode has to be selected click on the Pointed tab You have access to the chopper angle set it to Medium 61 Using HSpot to create PACS observatio
4. To control the absolute sensitivity consider to adjust the number of repetitions Observation Est Visibility Add Comments RA 16h35m54 00s Use Proper Motion Dec 66d13m00 05 PM RA Cyn 0 000 Epoch PM Dec yn 0 000 Ca Cancel_ Lu ez Figure 6 7 Raster map step 1 start up HSpot select PACS Photometer AOT and provide target in formation ox Cancel File Edit Targets Observation Tools Images Lines Overlays Options Window Help 0 m3 T Observations nT ta Astronomical Observation Requests AORs Label Target Positi Type T G F Instrum Mode Information Durati Stat On 218 raste abell2218 16h35 fixed Single C1 C C PACS Phot Chopped raster 1911 mew 0 PACS Photometry Unique AOR Label 422 18 raster 7 3 Target abell2218 Type Fixed Single Position 16h35m53 99000s 66d13m00 2000s i j nr New Target Modify Taran Twgetibt Number of visible stars for the target 12 Star tracker target Ra 68 975 degrees Dec 66 217 degrees x Source Flux Estimates Optional Enter source estimated data for S N calculation Warning Specifying a very bright source induce a change in gain settings Please check applicable flux limits
5. amp x File Edit Targets Observation Tools Calibration Images Lines Overlays Options Window Help eB 0 AIHA OLES Q Mouse Control Mouse Shift Left Button Centre the Image at point x 3c273 POSS2 UKSTU Red PPhoto 0000 xme Base Image Y xiu E Observations r 3c273 POSS2 UKSTU Red Target 3c273 Type Fixed Single Total Duration hrs 0 1 Figure 6 6 Photometer AOT point source mode step 6 From the main HSpot panel click on Over lays gt AORs on current image to overlay the footprint of the AOR on the sky 6 2 1 2 Example of a raster map entry In this example we create an AOR targeting the galaxy cluster Abell 2218 A relatively small area is to be observed on the cluster core of 7x7 arcmin For this purpose the appropriate mode is the raster mode The idea here is to make very small step sizes along the chopping direction to chop out of the raster map as much as possible but larger step sizes in the perpendicular direction in order to achieve a square map By repeating the rasters several times in the AOR with the repetition factor but also repeating the AOR for slightly different raster map centre coordinates drizzling the sensitivity will increase With any Herschel AOR the first step is to enter target information The reference position provided in the target dialogue has
6. Herschel Plan File Edit Targets Observation Tools Images Lines Overlays Options Window Help LE n Rae Ox a 1 Pixel 1 009 Mouse Control Mouse Any Shift Left Button Centre the Image at point Select Observation Date Target Visibility by Herschel Select Observation Date Date 2009 Dec 15 Time 00 00 00 _ cancer Observations abell2218 POSS2 UKSTU Red Target abell2218 Type Fixed Single Total Duration hrs 0 5 S Net up Total AORs 1 Active 1 Proposal File Name ObsMan a2218 aor Figure 6 13 Raster map step 7 Create AOR overlay Herschel Plan ool File Edit Targets Observation Tools Images Lines Overlays Options Window Help BE 0 RIE 9 a L Controls Hide all Animation Animation w Trail save On Field Of View RA Dec Detail v PO1 O raster chop fov 248 9312 66 1684 248 9278 248 9167 66 1819 _ 248 9200 66 1822 248 9234 66 1825 248 9156 66 1966 248 9122 66 1963 _0 raster chop_fov 3088 66 1960 PO1 0 raster chop fov 248 9010 66 2101 PO1 0 raster chop fov 248 9044 66 2104 0 raster chop fov PO1 0 raster 1248 8 2248 Base Image PO1_0_raster_chop_fov 248 8966 66 2245 Cab ES EE PO1 0 raster chop fov 248 8932 66 2242 248 8854 66 2383 6 248 8921 662389 248 8842 66 2530 66 2526 P1 0 raster chop fov Y
7. The three major fields of PACS calibration are 1 Photometric Calibration 2 Spectral Calibration 3 Spatial Calibration The PACS calibration plan for both ground and in orbit calibration is described in depth in the PACS calibration plan 42 Chapter 6 Using HSpot to create PACS observations 6 1 Guidelines to AOT use The purpose of this chapter is to provide detailed step by step guidelines on how to create and op timize PACS observation requests Working examples of typical PACS observations are selected for the three AOTs Before starting the measurement design you need to install the HSpot software from the HSC AO website System installation and first step guidelines can be found in the HSpot Observers Guide HSpot is the client software of the HSC Proposal Handling System what is responsible for interfa cing to observers managing proposals including observation requests and it provides input to the Scientific Mission Planning System The necessary steps are common to creating any observing proposal Assuming you have settled on the science goals and sorted out which AOT to use see Chapter 4 the mandatory steps are the fol lowing e Select target or map central position for the AOR e Select band or grating order in which you wish to observe e Select observing mode and specify its parameters e Run the PACS Time Estimator to determine required observing time sensitivities and overheads e If required
8. H Observations Target None Specified Total Duration hrs 0 0 Figure 6 1 Photometer AOT point source mode step 1 Start up HSpot select PACS Photometer AOT and provide target information by clicking on the New Target button The target can be resolved either with SIMBAD or NED As a second step select the blue band 60 85 um or 85 130 um and enter flux estimates is applic able Pressing the Source Flux Estimates button brings up a table in which you may enter details of your source Note that it is optional to enter data here if you do enter information then you will be presented with signal to noise S N information in the Observation Estimates result panel and in the PACS Time Estimation report This table depends on the observing mode selected in Point source photometry the fields for extended source are disabled Note for very bright sources the dynamic range for the bolometer detectors has to be changed via gain settings If you specify a very bright source HSpot will warn you the gain settings will be changed The low gain settings are not ideal for faint sources 45 Using HSpot to create PACS observations v Herschel Planning Tool File Edit Targets Observation Tools Calibration Images Lines Overlays Options Window Help zB o ORAS EA observations 777 PACS Photometry Unique AOR Label PPhoto 0000 Target 3c273 Type Fixed Single Position
9. PACS Time Estimation With the specified NOD count 1 the total OBS time amounts to 890 sec AOT PointMode and Nodding info PACS AOT PacsLineSpec Instrument performance summary Time Estimation Breakdown On source time s 1055 Pointing mode Point source nodding with 1 nod cycles Calibration time s 306 i Instrument and observation overhead s pt Nod pattern nominal position or A S B xA etc Observatory overhead s 180 A B Kerr ume en im Global AOT durations PACS Time Estimator Messages 6 757 de AOT total duration 1361 sec ngth CalSlew with overheads 306 sec SRC REF with overheads 1055 sec d Wavelength ranges 55 72 and 105 21 HSPOT cost 1055 180 sec 1235 sec PACS Line Setup and CAL summary Line Id Wavelengt Redshifte Line Flux Line Flux AOT i 34 sec prologue duration sec 63 180 63 18 0 00 EDU E 2 E KeyWave 148 0 mic CAL duration 121 sec 3P2 121 900 121 90 0 00 10 18 e KeyWave 62 7 mic CAL duration 150 sec cuc 57741 157 74 0 00 10 18 SpecLine summary Line 63 18 mic Add Line Manually Add Line From Datai Continuum RMS at 63 18 mic 747 mJy Redshift selection e Line RMS at 63 18 mic 12 05E 18 w m2 Total duration 272 sec SRC REF no overheads 96 sec Unit Redshift Observing Modine 157 74090504516303
10. Unique AOR Labet PSpecL 0000 Target NGC7027 Type Fixed Single Position 21h07m01 59s 42d14m10 2s File Edit Taj I New Target Modify Targ Target List n l gt B Observati Number of visible stars for the target 23 Star tracker target Ra 136 757 degrees Dec 42 236 degrees Wavelength Settings f wavelength ranges Origin Name Transition Wavelength Line Width EE ine EIEH ranges 72 105 and 105 210 microns nd 1st orders DEFAULT o 3PO 3P1 145 52 DEFAULT O1 3P1 3P2 63 18 1 1 88 A PACS Line Editor al a edshifte Line Flux Line Flux Continuu Line Width Line Wid Line Repe DEFAULT 2P3 2 2P 57 32 DEFAULT 32102 22 119 44 al Ll E You can add transitions and modify spectral line attributes via the HSpot Line Manager facility HSpot Menu gt Lines gt Manage Lines Add Line Manually ll Add Line From Database Modify Line Delete Line Redshift selection Unit Redshift Lx Value 0 000000 Observing Mode Settings Nodding wavelength switching cycles Fi Observatid Source type chopping and wavelength switching Number of cycles 1 Target NGC Set the Observing Modes To control the absolute sensitivity consider to adjust the number of integration cycles
11. Figure 2 5 Bolometer matrices assembly 4x2 matrices from the focal plane of the short wave bolometer assembly The 0 3 K multiplexers are bonded to the back of the sub arrays Ribbon cables lead to the 3K buffer electronics In a similar way 2 matrices of 16x16 pixels are tiled together on for the long wavelength focal plane array The matrices are mounted on a 0 3K carrier which is thermally isolated from the surrounding 2K structure The buffer multiplexer electronics is split in two levels a first stage is part of the indium bump bonded back plane of the focal plane arrays operating at 0 3K Ribbon cables connect the out put of the 0 3K readout to a buffer stage running at 2K 7 The PACS instrument 2 3 3 For science observations the multiplexing readout samples each pixel at a rate of 40 Hz Because of the large number of pixels data compression by the SPU is required The raw data are therefore binned to an effective 10 Hz sampling rate After that the same lossless compression algorithm is applied as with the spectrometer data Cooler The photometer operates at sub Kelvin temperatures which are achieved using a He cooler This type of refrigerator uses porous material which absorbs or releases gas depending on the mode cooling or heating The use of the He isotope instead of the common He is dictated by two reasons it is not super fluid at cryogenic temperatures below 2 2 K and it is a superior cryogen This
12. Observing with PACS diffraction or wavelength full range full range um highest sensitiv FWHM um der um km s ity range um 1 175 2337 1 363 0 654 0 124 1 210 1314 0 92 0 441 0 098 The full wavelength ranges covered by the scan and the ranges covered to the highest sensitivity 1 e the wavelength seen by all 16 spectral pixels are shown in Table 4 5 and compared with respective FWHM of the spectrometer at these wavelengths for an unresolved line Chopping and nodding is imposed by the design of the AOT in other words if chopping nodding is deselected the frequency switching is selected instead see following section as both observing techniques are mutually exclusive A classical 3 positions chopping nodding is performed to elimin ate inhomogeneities in the telescope and sky background Three chopper throws are available Small Medium and Large refer to 1 3 and 6 arcmin chopper throws on the sky respectively The chopping direction is determined by the date of obser vation the observer has no direct influence changing this parameter In case some disturbing sky features would fall in within the chopper throw radius around the target the observer has to consider to setup a chopper avoidance angle constraint The angle can be specified in Equatorial coordinates counterclockwise with respect the celestial north The avoidance angle range can be specified up to 360 degrees with a minim
13. 66 2523 RII KJ KHR E 16 16 Rol Angle 167 41 Date 2009 Dec 15 00 00 GMT Done Help E Observations fp abell2218 POSS2 UKSTU Red Target abell2218 Type Fixed Single Total Duration hrs 0 5 S net up Total AORs 1 Active 1 Proposal File Name ObsMan_a2218 a01 Figure 6 14 Raster map step 8 Pointing table 54 Using HSpot to create PACS observations os Note Cer The raster map is centered in the middle of the grid of the chop on positions displayed in green Figure 6 14 As the position angle rotates by about 1 degree a day on this high ecliptic latitude tar get the orientation of the chop off area cannot be controlled unless a constraint is put on the on the raster line direction with the orientation constraint 6 2 1 3 Tutorial of Photometer scan map entry The first AOR example attempts to illustrate how to design a large area deep mapping measurement using the PACS Photometry AOT Our goal is to make a two band extragalactic scan map on the COSMOS field For such a wide area 2 square degrees the only suitable mode is the scan map mode bd Herschel Planning Tool mix File Edit Targets Observation Tools Calibration Images Lines Overlays Options Window Help BE 59 SP OHOX Mouse Control PACS Photometry Unique AOR Label Cosmos array FINAL _ Target COSMO
14. Fnu 9 Ss pu pn TOO Laura daa ee a doa ca ca d a ca ca d a ca ca d a a ca d a a au d 60 80 100 120 140 160 180 200 Wavelength um Figure 3 10 PACS spectrometer relative spectral response function PACS QM Spectrometer RSRF Note that relative normalisation between orders is arbitrary Scientific capabilities 3 5 7 Spectrometer sensitivity Photoconductors of the type used in PACS have been demonstrated to have dark noise equivalent powers NEP of less than 5 x 10 WHz Such a noise level would ensure background noise lim ited performance of the spectrometer Tests of the high stress detectors done at module level in a test cryostat and with laboratory electronics indicate a significant noise contribution from the readout electronics These measurements can be consistently described by a constant contribution in current noise dens ity from the CREs and a noise component proportional to the photon background noise where this proportionality can be expressed in terms of an apparent quantum efficiency with a peak value of 26 The NEP of the Ge Ga photoconductor system is then calculated over the full wavelength range of PACS based on the CRE noise and peak quantum efficiency determination at detector mod ule level for the high stress detectors The quantum efficiency as a function of wavelength for each detector can be derived from the measured relative spectral response function Similarly the abso
15. but ton to bottom left of the AOT window The PACS Time Estimator calculates the time that the obser vation should take and calculates sensitivities If flux estimates were provided the signal to noise calculation is done as well The Time Estimation Summary gives the return information for the most essential performance numbers In this working case we get 6 and 6 8 mJy 1 6 for a repetition factor of 1 You can click further on PACS Time Estimator Messages to get further information on the AOR You can get an estimate of the local confusion noise in the bottom of the Time Estimator window The confusion noise is specific for the AOR settings and is derived considering the two main astro physical components in the far infrared the Galactic cirrus and the cosmic infrared background How confusion noise estimator calculates the confusion noise is described in the Herschel Confu sion Noise Estimator Science Implementation Document The depth of the observation is controlled by the Repetition Factor For a point source observation it increases the number of ABBA nodding cycles 47 Using HSpot to create PACS observations x Herschel Planning T Y Messages File Edit Targets Observation Tools Calibration Images PACS Time Esti Info derived from HSPOT input Instrument performal minoBstime no overheads for filter blue2 120 0 sec dwell time minimum 1 nod cycle considered Band Point Source Point Source Point Sour
16. or other image The AOR you created can be overlayed now on the background image From the main HSpot panel navigate to Overlays and select AORs on current image from the pull down menu First you have to select which AOR to visualize if more then one AORs are stored in the main HSpot panel Select the current AOR You will be prompted to specify the date of observation If you do not have any preference than click OK with the default settings and the overlay image will appear in the HSpot window You may notice changing the observing day the overlay image will rotate on the sky This is be cause the spacecraft position angle is locked at a certain Observing Day and varies from 0 degree to 360 degrees over a year In case you want to avoid a certain region on the sky the chopper avoidance angle can be specified in the observing mode tab To enter a chopper avoidance range of angles If you want to avoid chopping on to a region at 20 40 degrees east of north then you should enter 20 in the From box and 40 in the To box Note if you want to avoid something to the North say 350 to 10 then you should enter 350 in From and 10 in To Also because of the nature of chopping the angles 180 degrees away from the pair you enter will also be avoided It is very important that you visualize your observation at different dates to make sure that you observation is still possible 49 Using HSpot to create PACS observations Herschel Planning Tool
17. 12h29m06 70s 2d03m08 6s New Target Modify Targ Target List Number of visible stars for the target 8 Star tracker target Ra 7 278 degrees Dec 2 052 degrees Instrument Settings Blue channel filter selection F Source flux estimates and gain settings 60 85 microns band 5 Source Flux Estimates 85 130 microns band Observing Mode Settings Repetition factor Source type and mapping mode settings Repetition 1 Set the Observing Modes To control the absolute sensitivity consider to adjust the number of repetitions Observation Est Add Comments Visibility Cancel Source Flux Estimates Optional Enter source estimated data for S N calculation Warning Specifying a very bright source will induce a change in gain settings Please check applicable flux limits in the HSpot User s Guide Band microns Point source flux density mJy Extended source surface brightness MJy sh 85 130 Blue band 20 0 Blue band 0 0 130 210 Red band 30 0 Red band 0 0 Cancel Figure 6 2 Photometer AOT point source mode step 2 Select one of the two bands of the blue photo meter channel Then click on button Source Flux Estimates and enter estimated flux densities in the 2 selected bands to later get signal to noise estimates optional Clicking on the Set the Observing Modes
18. Grating Drive sGe Ga Detector Red Spectromete Chopper sGe Ga Detector Calibrators and II Blue Spectrome Entrance Optics Filter Wheel II Figure 2 1 Left Optical layout After the common entrance optics with calibration sources and the chopper the field is split into the spectrometer train and the photometer trains In the latter a dichroic beam splitter feeds separate re imaging optics for the two bolometer arrays In the spectrometer train the image slicer converts the square field into an effective long slit for the Littrow mounted grating spec trograph The dispersed light is distributed to the two photoconductor arrays by a dichroic beam splitter which acts as an order sorter for the grating Figure 2 1 shows how the functional groups are distributed in the spatial instrument envelope Figure 2 2 shows an optical circuit block diagram of the major functional parts of PACS At the top The PACS instrument the entrance and calibration optics is common to all optical paths through the instrument On the right the spectrometer serves both the short wavelength blue and long wavelength red pho toconductor arrays A fixed dichroic beam splitter separates blue from red spectrometer light at the very end of the optical path On the left the bolometer fixed dichroic beam splitter comes before the blue and red imaging branches since they require different magnification Directly in front of their b
19. Herschel observatory PACS provides the Herschel Space Telescope with the capabilities for spectroscopy and imaging photometry in the 55 210 um range PACS has been designed and built by a consortium of institutes and university departments from across Europe under the leadership of the Principal Investigator Albrecht Poglitsch at Max Planck Institute for Extraterrestrial Physics Garching Germany Consortium members are from Austria UVIE from Belgium IMEC KUL CSL from France CEA OAMP from Germany MPE MPIA from Italy IFSI OAP OAT OAA CAISMI LENS SISSA from Spain IAC The PACS web site is http pacs mpe mpg de Introduction 1 3 Acknowledgements The PACS instrument is the result of many years of work by a large group of dedicated people in several institues and companies across Europe It is their efforts that have made it possible to create such a powerful instrument for use in the Herschel Space Observatory We would first like to ac knowledge their work This manual is edited by Bruno Altieri and Roland Vavrek ESAC and includes help and inputs from a number of people Particular help and contributions to this manual have come from Thomas M ller Marc Sauvage Ulrich Klaas J rgen Schreiber and Bart Vandenbussche This Observer s Manual also uses the knowledge contained in numerous PACS technical documents and various dis cussions 1 4 Acronyms AOR Astronomical Observation Request AOT Astro
20. Noise Confusion Noise Confusion Noise I Repetition factor Level for Level for Level per Pixel A n Point Sources Extended Sources my Source type and mapping mode settings Repetition 1 my Mysi Set the Observing Modes To control the absolute sensitivity consider 85 130 25 8 0 0445 27 0 to adjust the number of repetitions 130 210 0 3 0 0006 UE Observation Est Ada Comments Vi Update Confusion Noise Estimation Confusion Noise Estimator Messages pone Cancel Figure 6 10 Raster map step 4 Provide map repetition factor and run the PACS Time Estimator and the Herschel Confusion Noise Estimator 52 Using HSpot to create PACS observations x SIDE o x9 S File Edit Targets Observation Tools Images Lir PACS Time Estimation Instrument performance summary Band Point Source Point Source Point Source Extended Extended Extended um Flux SIN 1 0 Surface S N 1 0 Density noise Brightness noise ml my Mvis MIy sn 85 130 1o 0 2 5 2 10 0 1 9 5 3 130 210 2 0 0 3 5 9 20 0 10 4 im Time Estimation Breakdown On source time 6 1344 Calibration time s 32 Instrument and observation overhead s 387 Observatory overhead s 180 Total time 6 1911 PACS Time Estimator Messages Confusion noise estimation summary Note the predicted confusion noi
21. Repetition factor Number of AB nod cycles per raster position to adjust the absolute sensitiv ity maximum 32 Source flux estimates Optional point source flux density in mJy or surface brightness in MJy 28 Observing with PACS Parameter name Signification and comments sr for each band It is used for signal to noise calculations and to change the ADC to low gain if the flux in one of the two channel is above the ADC saturation threshold increasing the dynamical range by a factor 4 See Sec tion 4 1 1 for more details 4 1 3 Large area or extended source mapping This will likely be the most widely used observing mode of the photometer Herschel was build to make large scale surveys and such observations are not made by pasting together postage stamp ob servations such as the ones obtained in the two previous modes There are two ways to make large maps with the PACS photometer Raster the satellite goes through a rectangular grid pattern of points in the satellite reference frame that can be repeated Scanning the satellite slews continuously along parallel lines at a user specified speed 10 20 or 60 arcsec s Scan maps are intended to cover larger areas than raster maps For mapped areas smaller than 15 x15 the observation overheads in scan mapping one munute or more between scan legs depend ing on the scan speed become prohibitive and raster mapping is advantageous Conservatively
22. angle to 160 degrees allows an orthogonal coverage in a second AOR to be concatenated with all other parameters identical 57 Using HSpot to create PACS observations 6 2 2 Herschel Planning Tool mix File Edit Targets Observation Tools Calibration Images Lines Overlays Options Window Help BE 11550 GSC S Mouse Control Mouse Any w Shift Left Button Centre the Image at point H Observations Astronomical EEE Requests AORs Observing Modes Observing Mode Settings Choose one of the modes below Small source photometry Chopped raster Scan map Target COSMOS None selected Point source photometry Position 10h00m4 New Target Modi Observing mode parameters Scan Map Unique AOR Label Cosmos sky 51 Number of visible stars for Star tracker target Ra 330 1 Select the speed Scan leg lengths arcminutes Instrume Homogeneous coverage Blue channel filter selection Cross scan step arcseconds 60 85 microns band amp 85 130 microns band Square map Number of scan legs Ob serving Map orientation Orientation angle reference frame Sky Source type and mapping mode settings Orientation angle degrees 10 0 Set the Observing Modes Orientation constraint Angle from degrees 0 0 Observation Est Angle to degrees 360 0 Targe
23. bright cirrus fields star forming regions photo dissociation regions photo ionized regions in the vicinity of the selected line It is not advised to use frequency switching close to grating order cut offs or with a switch into a neighboring order as it might be difficult to calibrate Warning E The sensitivity reported by the current version of HSpot is underestimated by a factor V2 Users shall take this factor into account for the time estimation that would otherwise be wrong by factor 2 to reach the same sensitivity This will be corrected in phase II entry Range scan spectroscopy Mode Similarly to the Line scan spectroscopy mode this AOT allows to observe one or several spectral line features up to ten but the user can freely specify the explored wavelength range This AOT is mainly intended to cover rather limited wavelength ranges up to a few microns in high sampling mode see below to study broad lines larger than a few 100 km s which wings would not be covered sufficiently in Line Spectroscopy AOT or a set of closed lines But in the second case the relative depth of the of the line cannot be adjusted as in the Line Spectroscopy case The Range Spectroscopy AOT is also intended to cover larger wavelength ranges up to the entire bandwidth of PACS in SED mode in low sampling mode this time otherwise integration times get quickly prohibitive But one should remember that the power of the PACS spectrometer is its high spe
24. lute responsivity as a function of wavelength is derived from the relative spectral response function and an absolute reference point measured in the laboratory The achievable in orbit performance depends critically on the effects of cosmic rays in particular high energy protons Analysis of proton irradiation tests indicates that one will face a permanently changing detector responsivity cosmic ray hit lead to instantaneous increase in responsivity fol lowed by a curing process due to the thermal IR background radiation A preliminary analysis of the results indicates that with optimized detector bias settings and modu lation schemes chopping spectral scanning NEPs close to those measured without irradiation can actually be achieved It is therefore assumed that this will also apply to the actual conditions en countered in space The prediction of spectrometer sensitivity in the high sampling mode used in the AOTs line spec troscopy mode and range spectroscopy with the option high sampling are shown in figures Fig ure 3 11 and Figure 3 12 for the continuum and line detection respectively The prediction of spectrometer sensitivity in the SED mode used in AOT range spectroscopy with the option Nyquist sampling are shown in figures Figure 3 13 and Figure 3 14 for continuum and line detection respectively The best 50 1 hour sensitivity in the first order corresponds to about 0 2 Jy for the continuum and 5x10 Wm for the li
25. ngc7027 Ty Instrument Settings Sampling parameters Range sampling density Line Flux Continuum Line Width Line Width Range Rep D Red 72 00 210 00 72 00 0 00 40 18 0 00 0 00 km s 1 Add Range Modify Range I Delete Range Source type and Observing Mode Settings Nodding or map repetition cycles chopping I EN Set the Observing Modes Repetition 1 observation Est Add Comments Visibility To control the absolute sensitivity consider to adjust the number of integration cycles came Figure 6 27 Range spectroscopy step 3 Select Pointed observing mode and set up the appropriate chopper throw 67 Using HSpot to create PACS observations Time Estimation Breakdown On source time s 1885 Calibration time s 174 Instrument and observation overhead S 0 180 2065 Observatory overhead s Total time s PACS Time Estimati Instrument performance summary mages Lines Over Unique AOR La PACS Time Estimator Messages Done M Observations Target ngc7027 Num Star Range scan or S Range mode sel Figure 6 28 Range spectroscopy step 4 Run the PACS Time Estimator for the SED Red AOR by Range ID D Red Blue Edge um Red Edge 72 00 210 00 Instrument Setting Sampling parameters Range sam
26. observations The plural in line s and range s indicate that several lines or wavelength ranges can be observed within the scope of one AOT The PACS AOTs whether with the photometer or the spectrometer follow a similar pattern of events preparation of observation internal calibration and sky observations While slewing to the demanded celestial coordinates PACS is commanded from stand by mode to photometer set up or spectrometer set up ready for operations After the transition is accom plished PACS enters into an internal calibration sequence using the Internal Calibration Sources ICS and the data flow is started Since the calibration is performed while slewing an otherwise wasted time is being profitably used Currently the user is charged a flat rate of 3 minutes to account for the slew time regardless of its actual duration e At regular intervals during the science observation the spacecraft will remain idle while PACS repeats the ICS based calibration Note Ce 1 This feature has been disabled for the current HSpot release awaiting for more advanced instru ment calibration and characterisation of the internal calibration cycle If internal calibrations are later introduced within AOTs the observation overhead will obviously increase e PACS is commanded back to the relevant standby mode at the end of the observation and the data flow is stopped 4 1 PACS photometer AOT Three generic observing modes are
27. reduce crosstalk between left and rightmost pixels of adjacent slices see also Figure 2 8 Grating The grating blank has a length of 320mm with a groove period of 8 5 0 05 grooves mm with a total of approximatively 2720 grooves The reflection grating is operated in the first 105 210 um the second 72 105 um and the third diffraction order 55 72 um Grating deflections from 28 de 9 The PACS instrument 2 4 3 2 4 4 grees to 68 degrees are possible to cover the full wavelength range of each order A graphical correl ation of the grating angle of incidence versus order and wavelength is given in Figure 2 7 Grating angle wavelength relation in Littrow configuration T T T T T T T T T 3rd order 2nd order ur o ES o Angle grating normol light baom 1s1 order 30 Grating anale limit 50 199 150 200 Wavelengths in micron Figure 2 7 Relation between grating angle and wavelength Order sorting Filters The PACS order sorting filters enable the spectral purity of the selected band by suppressing contri butions by other orders the detector is sensitive to There are in total 3 bands in the PACS spectro meter 55 72 um 72 105 um and 105 210 um The filter transmission is shown in Figure 3 8 The filter train of both the photometer and spectrometer channels is illustrated in Figure 2 4 Photoconductor arrays The spectrometer employs two Ge Ga photoconductors arrays low and high st
28. relative response function was updated 81 References Herschel Observatory Observer s Manual HSC et al Herschel Observers Manual PACS Calibration Document Ulrich Klaas et al PACS Calibration Document PACS MA GS 001 January 5 2007 82
29. selected HSpot computes the ap propriate distance between scan legs cross scan step to achieve an homogeneous coverage which is a function of the array to map angle selected above Scan maps defined in instrument reference frame should in principle be used to cover square areas as the orientation of the scan map on the sky can not be known in advance it depends on the array position angle which itself depends on the exact observation day However in order to cover specific rectangular areas in the sky a constraint on the orientation of the scan map in the sky can be introduced by selecting a range for the map position angle i e the angle from the celestial equatorial north to the scan line direction counted positively east of north This corresponds to the option array with sky constraint in HSpot shown in Figure 4 6 Warning e Introducing a sky constraint puts a constraint on the scheduling and therefore shall be used only if necessary Moreover certain combinations of array to map angle and ranges of map position angle might not be feasible For instance for pointing close to the ecliptic plane the array position angle is close to 90 23 modulo 180 degrees as the Z axis is always pointing towards the sun 1 degree which is in the ecliptic plane Therefore the map orientation angle cannot be too different from the array to map angle 90 degrees modulo 180 This shall be checked with the overlay AOR facility i
30. sensitivity consider to adjust the number of integration cycles Observation Est Add Comments Visibility OK d Cancel Help Figure 6 19 Line spectroscopy step 1 Open Line Spectroscopy AOT window and select target coordin ates Select from the pull down menu of Wavelength settings the combination of grating orders in which the set of line can fit 3rd and 1st orders in this example HSpot provides an easy way to include spectral line transitions from online catalogues You have to click on Add line from database button to show the default selection of lines selected for PACS In case this selection does not include the transition you wish to observe under the Lines option on the HSpot main page additional lines can be retrieved from CDMS JPL servers The Manage Lines facility allows you to modify line attributes if necessary and save your own line database This tool can be used to merge line databases saved in the same HSpot format You may notice the default line list includes all three lines we want to observe in this AOR Only one line can be selected once to include more lines you have to repeatedly click on the Add Line 59 Using HSpot to create PACS observations from Database button The PACS Line Editor allows to set up to 10 spectral lines but this limit might be reduced if line re petition is applied PACS Line Spectroscopy
31. sky coordinates Values above 105 arcsec may lead to non overlapping legs depending on the ar ray to map angle In order to allow a minimum overlap between consecutive legs the user is ad vised not to select a cross scan distance above 105 arcsec to be immune against all possible values of the array to map angle am Note Ce I A cross scan distance of 51 arcsec i e the size of single blue array matrix gives relatively flat ex s posure maps for scan map in sky coordinates whatever the array to map orientation angle In ana logy to SPIRE terminology we call it the magic distance Conversely the array to map angle of scan maps in sky coordinates can be constrained with the op tion sky with array constraint in HSpot as shown in Figure 4 7 Again certain combinations of map orientation angle and constraints on array to map angle might be impossible this shall be checked by the user with the overlay AOR functionality of HSpot Table 4 4 lists the user input parameters required in HSpot in scan map mode 34 Observing with PACS Table 4 4 User input parameters for scan map mode Parameter name Signification and comments Filter which of the two filters from the blue channel to use In case observations in the two blue filter bands are required to be performed consecutively two AORs shall be concatenated Orientation reference frame The reference frame for the scan map orientation array or array wit
32. sorption cooler is run from a cold stage provided by the Herschel cryostat The refrigerator contains 6 litres of He and can in principle be recycled infinitely with an efficiency of more than 95 with a life time limited only by the cold stage from which it is run Gas gap heat switches which are coupled to the Herschel 3K system with thermal straps control the mode of operations The evaporation of He provides a very stable thermal environment under constant heat load The design of the cooler is well suited for work in space as there are no moving parts and the heat load is small This sorption cooler is nearly identical to the unit developed for SPIRE It provides a stable temper ature environment at 300 mK for more than 48 hours under normal observing and operational cir cumstances The recycling shall be performed during DTCP periods whenever the PACS photomet er will be selected for the following observing day 2 4 Spectrometer 2 4 1 The spectrometer covers the wavelength range from 55um to 210um in two channels that operate simultaneously in the blue 55 105um and red 105 210um band It provides a resolving power between 1000 and 4000 i e a spectral resolution of 75 300km s depending on wavelength for a fixed grating position The instantaneous coverage is 1500km s It allows simultaneous imaging of a 47 x47 field of view resolved in 5x5 pixels An image slicer employing reflective optics is used to re arrange the 2 d
33. stack mosaic of frames is constructed 71 Pipeline description and data product expectations 7 1 2 Photometer processing levels In this section the different intermediate formats of the PACS data throughout the reduction process are described and the standard processing steps for the different photometry and spectroscopy ob servations of the PACS instrument are mentioned For a more detailed description of the pipeline refer to the PACS Data Processing User s Manual There is a Herschel wide convention on processing levels of the different instruments Raw Telemetry All telemetry packets produced by the instrument in the course of the observa tion In PACS IA we store manipulate this level as a PacketSequence Level 0 data Telemetry data as measured by the instrument minimally manipulated and stored as Data Frames For PACS this level is stored manipulated in a DataFrameSequence a se quence of PACS dataframes which are decompressed SPU buffers What is contained in every decompressed SPU buffer depends on the SPU reduction mode Typically there are several re duced readouts for every active detector averaged detector signals 40Hz or 20Hz readouts for a few selected pixels and mechanism status information sampled at 40Hz 20Hz by the DecMec the so called DMC Header Level 0 5 data The information contained in the Level 0 data is not sufficient to be able to pro cess those data The level 0 5 data is a bundl
34. step 5 Create the SED Blue AOR and run the PACS Time Estimat or 69 Using HSpot to create PACS observations Herschel Planning Tool Edit Targets Observation Tools Images Lines Overlays Options Window Help Constraint Editor Constraint Editor Tool Add Constraint then Drag AORs to Constraint Window Group Follow On Add Constraints Parameters Modify Paramete Add Comments Add Sequencing Add Group Within Add Concatenation Add AOR Timing Perform Action Remove GetAoR Moveup move Down Drop AORs app Observations Observations Target ngc7027 Type Fixed Single 5j Figure 6 30 Range spectroscopy step 6 Concatenate the two AORs Select from the main HSpot menu Tools and option Group Follow on Constraints In the pop up window you have to first click on Concatenation button then select the two AORs by clicking on Get AOR two times 70 Chapter 7 Pipeline description and data product expectations This chapter describes the standard processing steps pipeline for the different photometry and spectroscopy observa tion modes of the PACS instrument The pipeline steps are coded as java jython tasks using well defined interfaces To be able to use the most recent calibration information version con trolled cali
35. to 2 Hz The current chopper frequency for the photometer is 0 25 Hz but up to 4 Hz for the spectrometer where it is still expected to get a 90 duty cycle 3 3 Mirrors The PACS optics employs a large number of mirrors in each instrument channel Therefore the loss per mirror is an important number for the overall transmission of the system Losses occur by ab sorption in the mirror material by scattering at the mirror surface and by diffraction losses due to the finite mirror sizes Without diffraction which can be treated separately the combined scattering absorption losses per mirror surface can be less than 1 at FIR wavelengths but measurements also show that they vary with material and surface treatment and we assume a value of 1 From the number of reflections a loss of 26 for the spectrometer channels and of 15 for the photometer channels has been derived 3 4 Characteristics of the photometer 3 4 1 Photometer spatial resolution The photometer optics delivers diffraction limited image quality Strehl ratio gt 95 Therefore PACS shall preserve the image quality provided by the Herschel telescope and is diffraction limited on it whole energy range The FWHM s in the three filter bands together with main characteristics can be found in Table 3 1 Table 3 1 PACS photometer overall characteristics performances 75um 110um 170um wavelength range um 60 85 85 130 130 210 Resolution 3 2 pi
36. to refer to the required geometrical central position of the map with the chopper on footprints in green on Figure 6 14 The coordinates of the galaxy cluster can be re solved from one of the online available catalogues 50 Using HSpot to create PACS observations File Edit Targets Observation Tools Images Lines Overlays Options Window Help Elm 7 Ox r M Observations Po i zm Astronomical Observation Requests AORs Label Target Positi Type T GF Instrum Mode Information Durati Stat On x PACS Photomet a Unique AOR Labet PPhoto 0000 Target abell2218 Type Fixed Single Position 16h35m53 99000s 66d13m00 2000s New Target Modify Targ Target List Number of visible stars for the target 12 Star tracker target Ra 68 975 degrees Dec 66 217 degrees Instrument Settings Blue channel filter selection Source flux estimates and gain settings 60 85 microns band Target Name required SIMBAD Resolve the Name 02218 Visibility Background Fixed Moving Source Flux Estimates 85 130 microns band Observing Mode Settings Coord Sys Equatorial J2000 Proper Motion Repetition factor Repetition 1 Source type and mapping mode settings Set the Observing Modes
37. translate into the photometer sensitivities tabulated in Table 3 2 as implemented in HSpot Note LER If the Direct Mode can be used in orbit the sensitivities could be twice better in the blue band and 25 better in the red channel Table 3 2 PACS photometer predicted sensitivity 50 1 hour in mJy in DDCS mode central wavelength 75um 110um 170um off array chopping 7 7 7 8 8 8 on array chopping 2 5 53 6 25 scan mapping 4 7 4 7 5 3 The on array chopping technique is only used in point source photometry mode while the small source photometry mode and large raster mode make use of off array chopping The scan map mode as a slightly better sensitivity than the point source photometry mode because the chopper in not in volved the signal is modulated by the line scanning See chapter 4 for more information on the ob serving modes To a first order the sensitivity in all mode scales with the inverse of the square root of the on source observation time This scaling is used for the sensitivities and S N ratios reported by HSpot 3 5 Characteristics of the spectrometer 3 5 1 Diffraction Losses The image slicer is the most critical element of the PACS optics a simplified analysis for the less critical photometer as well as the effect of diffraction vignetting by the entrance field stop and Lyot stop have been included For the Lyot stop a worst case loss of 10 is used For the losses in the spectrometer the f
38. where chopping to an off position could introduce a considerably high contrast resulting from memory effects in the spectrometer s Ge Ga detectors Such an effect would lead to poorly calibratable data In wavelength switching mode the grating moves alternatively between an on line position and two close off line positions below and above with a shift of only two spectral pixels In this scheme the line always stays on the 16 spectral pixels A spectral dithering is also implemented shifting se quentially the line by a quarter of a pixel to improve the reconstruction of the unresolved line profile and the two calibration source are also observed shortly for each dither position to monitor the drift in sensitivities The frequency switching option is very efficient because 80 of the integration time is spent on target 20 on the calibration sources and it can be used for large extended sources since no clean 38 Observing with PACS 4 2 2 reference if needed But it shall be used with caution by definition this technique eliminates the continuum information Besides the baseline estimates will not be reliable if anoticeable gradient is present in the continuum flux over the performed wavelength throw blends of line forests disturb the wavelength switch interval In the frequency switching mode the observer shall also check the available spectral information of galactic extended sources as diffuse molecular clouds
39. with the chopper Both arrays are used at a time Line scan spectroscopy AOT This AOT is intended to observe one or several unresolved or narrow spectral line features on fixed wavelength range of about 1 micron but varying from 0 35 to 1 8 um depending on the wavelength and the grating order Only lines in the first 105 210 um and second order 72 105 um or first and third order 55 72 um can be observed within a single AOR to avoid filter wheels movements If lines of second and third grating order are to be observed on the same target at the same time two AORs shall be con catenated Depending on the requested wavelength grating order only the data of one of the two de tector arrays is normally of interest to the observer The fixed wavelength and its immediate neighborhood is observed for each chopper and grating po sition For improved flat fielding especially for long integrations the grating is scanned by a num ber of discrete steps around a specified centre position such that drifts in the detector responsivity between individual pixels are eliminated These grating scans provide for each line and for each of the 5 by 5 spatial pixels a short spectrum with a resolving power of 1700 in its highest resolution covering 1500 km s but dependent on the wavelength and order Up to 10 lines can be studied within one observation The relative sensitivity between the lines is controlled by using the line repetition factor in th
40. 8 deg Spectrometer scale 3368 2331 te obtain 80 km s pixel amp 175 micron Effective Resolution amp 175 micron ha o a a Effective resolution km s ist order 100 50 50 100 159 200 wavelengths micron Figure 3 9 The effective grating resolution Table 3 3 summarizes the grating characterisation in terms of velocity resolution spectral coverage and typical grating step sizes for a given order wavelength Table 3 3 PACS grating pixel spectral characterisation 18 Scientific capabilities grating order wavelength FWHM of an unresolved line instantaneous spectral cover pixel per age 16 pixels FWHM um km s um km s um 1 105 318 0 111 2856 1 000 1 78 1 158 239 0 126 1572 0 828 2 43 1 175 212 0 124 1280 0 747 2 65 1 210 140 0 098 720 0 504 3 11 2 72 164 0 039 1840 0 442 1 42 2 105 80 0 028 720 0 252 1 78 3 55 114 0 021 1448 0 266 1 26 3 72 55 0 013 615 0 148 1 42 3 5 6 Spectrometer relative spectral response function The tentative relative spectral response function RSRF for the QM model is displayed in Fig ure 3 10 Besides the overall trend of the RSRF one of the most important issue will be to calibrate with a high accuracy the ripples on short wavelength scales It is particularly important for faint line detection and identification CQM Relative Spectral Response Function Ss S N w Di iy Ly i Relative Response
41. CS observations ss 43 6 1 Guidelines to AOT Uses esi eR GP RT Ste mese te eee pee UU DN 43 6 2 Tutorial of an AOT entry an HSpot 1 o emite ertet eerte Pere oes eS EE ea sete 43 6 2 1 Tutorials of Photometer AOT entry ssse Hee 43 6 2 1 1 Tutorial of point source photometry mode entry 44 6 2 1 2 Example of a raster map entry eme 50 6 2 1 3 Tutorial of Photometer scan map entry sssse ee eeee eee eene eens 55 6 2 2 Tutorials of Spectrometer AOT entry sssssss ee 58 6 2 2 1 Example of line spectroscopy AOT entry sssse A 59 6 2 2 2 Example of range spectroscopy AOT entry 64 7 Pipeline description and data product expectations sssssssssseseeeene n ee eene 71 7 1 PACS photometry standard data processing e 71 7 1 1 Photometry processing steps meme hene rennen rene 71 7 1 2 Photometer processing levels pss kenyere eee i m eem memenmee rene 72 7 1 3 Photometer processing flow diagram ssssee eH 72 7 2 PACS spectrometry standard data processing ssssssseee e 76 7 2 1 PACS spectrometry processing steps 76 7 2 2 Spectrometer processing levels cseesseesecnsereeseeeceeecneseeesneecneseesees sees 76 7 2 3 Spec
42. HERSCHEL oro e Announcement of Opportunity for Key Programmes PACS Observer s Manual HERSCHEL HSC DOC 0832 Version 1 1 14 Mar 2007 PACS Observer s Manual Published version 1 0 01 February 2007 Published version 1 1 14 March 2007 Table of Contents 1 Introducti n LC A m 1 T 1 PUrpOse OF document c erre rre Ptr ex PRX er Suen PEENE EPIS REEF PRENNE E PORSE ewe named E PIO 1 1 2 IET duci M E 1 1 3 Acknowl dg ments 2 2 5 rrt sante in t ssa bed Mine tee ERE rente een REARS 2 T4 ACRONYMS En nt st np en IQ T T Um 2 2 The PACS mstrUment mec o ce a conga nep OPNS em rng 3 2 1 Overview instrument Concept icis epu detect inet lee voit ds eer odores 3 2 2 COMMON OPES 2 5er ee NER RF es eU dese Ud 3 2 2 Entrance OptiCs os Mines dates Rer eo erp use se trt ne tenore eoe Pe E uae sense 5 2 2 2 Calibration SOUrCes c ecu emet ee rre RE Ee can Rees oe ete eed oue 5 2 2 3 Chopper coe eset ne tbe tee nn TS esca er EC a lente el 6 2 3 Photometer oie oe nn aE MN rene nest REIR 6 2 3 1 Filters 55e er eter rte os eek D mre ete de E EE Rire 6 2 3 2 Bolometer arr ys eee te tdeo eere udo reete dota oo sd e esu edere eu conve 7 PESE 8 2 4 Sp ctroMeter 8 DAT Image slicer i irr Dre EP nr RR Ee rr ER EPERE KTSS 8 PAD Ofatng tette eerte ub hack es ceat ne et dou deat area tas hie NER TR Moe feat fy 9 2 43 Order Sorting Filters 1
43. Number of cycles 8 Cancel Set the Observing Modes To control the absolute sensitivity consider 10 adjust the number of integration cycles M Observations NG Target NGC7027 Type Observation Est Add Comments Visibility Figure 6 22 Line spectroscopy step 4 Select Pointed observing mode and chopper throw to Medium The PACS Time Estimator message includes sensitivity estimations for each line and for the con tinuum at the line centre Sensitivities can be improved by two ways increase the number of grating repetitions per line or increase the number of nodding cycles The relative line strength fraction of on source time per line is taken into account by specifying the grating scan repetition factor for each line This number can be specified in the line editor window A maximum of 10 repetitions in total can be given in the table For instance in the case that 10 lines are selected the Line repetition factor has to be 1 for each line if 3 lines are selected then the total of the 3 repetition factors has to be less or equal to 10 e g 4 5 1 or 2 3 3 If the sum of repeti tions exceeds 10 then you must either remove spectral line s or reduce the scan repetition factor s 62 Using HSpot to create PACS observations x Messages e Minimum required OBStime 890 sec F1
44. PACS photometer AO eset pet e re re etr p EORR Eee tees 23 4 1 1 Point source photometry ses 24 4 1 1 1 Gain setting for bright sources sse 25 4 1 1 2 Chopper avoidance angle ccc cece cece cence cece HH 25 4 1 2 Small source photometry ss 26 4 1 2 1 Chopper avoidance angle sese 27 4 1 3 Large area or extended source mapping 29 4 1 3 1 Raster mapping ModE iiss noceret toto ote reete ge eee Cogo epe oe tg 29 4 1 3 2 Scan mapping mode ss 31 4 1 3 2 1 Scan maps in instrument reference frame 32 4 1 3 2 2 Scan maps in sky coordinates 34 4 2 PACS spectrometer AO S ilie eot eth epe erra e pr ER Rare PO Ripe ena 36 4 2 1 Line scan spectroscopy AOT sssssssee HH mH III eher 36 4 2 1 1 Line scan with chopping nodding mode 37 4 2 1 2 Line scan in wavelength switching mode eee 38 4 2 2 Range scan spectroscopy Mode 39 ADD RangesCan oio deett rere oboe E UAR ehe thee este 40 4 22 22 SED MOE sie Ree e ES 40 4 2 2 3 Line mappiin E 2 16 coo eer mper er tore odore Eee ive eren aee e eder tees ey 4l lil PACS Observer s Manual 5 Calibration framework o nt Ed e trente td RR RR EROR REIR FR Rer 42 6 Using HSpot to create PA
45. S Type Fixed Single Position 10h00m28 60s 2d12m21 0s New Target Observing Modes Number of visible stars for t Star tracker target Ra 330 1 Observing Mode Settings Choose one of the modes below Small source photometry Chopped raster Scan map In strume None selected Point source photometry Blue channel filter selection n Observing mode parameters O 60 85 microns band 85 130 microns band Scan Map Select the speed Ob serving Scan leg lengths arcminutes Source type and mapping mode settings Homogeneous coverage Set the Observing Modes Cross scan step arcseconds Square map z Number of scan legs Observation Est Map orientation Orientation angle reference frame Array Orientation angle degrees 70 0 Orientation constraint Angle from degrees 0 0 Angle to degrees 360 0 Ei Observations 30273 POSS2 UKS Cancer Target COSMOS Type Fixed Single Total Duration hrs 44 8 Figure 6 15 Scan map step 1 A scan map is entered in array coordinate system with a low scan speed 10 s a scan leg length of 85 arcmin and an orientation angle of 70 degrees As the field is close to the ecliptic plane the position angle of the array is constrained to a small range and this effectively hence an array to map angle of 70 degrees constrain the orientation of th
46. affle enclosures the blue detectors have filter wheel mechanisms which contain the band pass fil ters for short wavelength photometry and the order selection band passes for 2nd and 3rd order op eration of the grating spectrometer respectively Telescope Entrance Optics Bolometer _ chopper Calibration optics Figure 2 2 Functional block diagram of PACS overall optics The focal plane sharing of the instrument channels is shown in Figure 2 3 The photometric bands which can be observed simultaneously cover the same field of view The field of view of the spec trometer is offset from the photometer field see Figure 2 3 However this has no effect on the ob serving efficiency The focal plane unit provides photometric and spectroscopic capabilities through five functional units common input optics with the chopper calibration sources and a focal plane splitter e a photometer optical train with a dichroic beam splitter and separate re imaging optics for the two short wavelength bands 60 85 um 85 130 um selectable via a filter wheel and the long wavelength band 130 210 um respectively two bolometer arrays with cryogenic buffers multiplexers and a common 0 3 K sorption cooler e a spectrometer optical train with an image slicer unit for integral field spectroscopy an ana morphic collimator a movable diffraction grating in Littrow mount anamorphic re imaging op tics and a dichroic beam splitter for separatio
47. als are multiplied by the absolute response The sky coordinates are calculated for each pixel The s c on board time is converted to UTC Calibrated 5x5xlambda data cubes are generated Spectrometer processing levels There is a Herschel wide convention on processing levels of the different instruments Raw Telemetry All telemetry packets produced by the instrument in the course of the observa tion In PACS IA we store manipulate this level as a PacketSequence Level 0 data Telemetry data as measured by the instrument minimally manipulated and stored as Data Frames For PACS spectroscopy this level is stored manipulated in a Data FrameSequence a sequence of PACS dataframes which are decompressed SPU buffers What is contained in every decompressed SPU buffer depends on the SPU reduction mode Typically there are several reduced readouts for every active detector averaged ramp readouts or fitted slopes 256Hz readouts for a few selected pixels and mechanism status information sampled at 256Hz by the DecMec the so called DMC Header Level 0 5 data The information contained in the Level 0 data is not sufficient to be able to pro cess those data The level 0 5 data is a bundle of Level 0 data and the data needed to fully pro 76 Pipeline description and data product expectations cess those data auxiliary data for the timespan covered by the Level O data such as the space craft pointing attitude history the time corre
48. ant to exclude some position angles of the chopping direction to avoid chopping into a bright close by infrared source For this purpose an interval of position angle to be avoided can be entered in HSpot The position angle is counted positive east of north i e counterclockwise in the sky from the north to the direc tion of the object to avoid i e the Y spacecraft axis As the chopper cannot rotate this effectively defines an avoidance angle for the satellite orientation Hence it is a scheduling constraint Moreover for pointings close to the ecliptic plane the position angle becomes constrained towards 23 5 de grees i e the inclination of the ecliptic plane chopping ecliptic south north direction Therefore values too different will make the observation impossible The range of position angles that will be available for a given target can be visualized with the AOR footprint overlay functionality And the exact angle values can be determined with the Herschel Fo cal Plane overlays Warning e The angle returned by HSpot in the AOR overlays is the roll angle which is counted from north counterclockwise i e also following the position angle convention but to the spacecraft Z axis The input angle Herschel Focal Plane overlay functionality is also the roll angle To get the position angle for the chopper avoidance 90 degrees must be subtracted to the roll angle 25 Observing with PACS Table 4 1 lists the user i
49. ard an Ariane 5 rocket to gether with Planck It will enter a Lissajous 700 000 km diameter orbit 1 5 million kilometers away from Earth at the second Lagrange point of the Earth Sun system The mission is named after Sir William Herschel who discovered the infrared radiation in 1800 It will be the first space observatory to cover the full far infrared and submillimetre waveband It will perform photometry and spectroscopy in the 55 670 um range with its 3 5m diameter radiat ively cooled telescope while its science payload complement of three instruments is housed inside a superfluid helium cryostat Herschel is designed to observe the cool universe The main scientific objectives of the mission are e to study the formation of galaxies in the early universe and their subsequent evolution e to investigate the formation of stars and their interaction with the interstellar medium to observe the chemical composition of the atmospheres and surfaces of comets asteroids plan ets and satellites e to examine the molecular chemistry of the universe Herschel will be operated as an observatory facility offering three years of routine observations which will be available for the entire scientific community Roughly two thirds of the observing time are open time and will be offered through a standard competitive proposal procedure The Photodetector Array Camera amp Spectrometer PACS is one of the three science instruments of the
50. aster Y direction 105 seconds to allow contiguous area mapping in all cases In order to be immune against field rotation due the changes of roll angle along the year the user should cover square areas For this purpose the number of steps and step size on both axis shall be computed However a constraint on the orientation of the raster in the sky can be imposed for in stance if rectangular area in the sky is to be covered and or a bright object is to be avoided This is achieved by selecting a range of map orientation angle in HSpot But this means a constraint in the scheduling as this limits the time window to carry out the observation Warning e Depending on the target coordinates some ranges in position angles are not possible this should be checked with the Overlay AOR functionality in HSpot For instance for targets close to the ecliptic plane the raster Y axis will be closely aligned with the ecliptic north hence a very narrow range of map position angle is physically possible If the PA constraint range does not overlap with the pos sible range the observation can not be scheduled Nodding is currently not implemented in this mode the observer can build a nodding like raster by choosing a raster step size along the raster X axis which is an integer divider of the chopper throw 30 Observing with PACS 3 5 arcmin The achieved sensitivity of the map depends on the number of times a sky pixel is seen by different ra
51. ble modulation in the background received by the instrument It also provides for an intermediate pupil position where the Lyot stop and the first blocking filter common to all instrument channels can be positioned It allows the chopper through two field mir rors adjacent to the used field of view in the telescope focal surface to switch between a chopped field of view on the sky and two calibration sources see also Figure 2 3 The chopped image is then re imaged onto an intermediate focus where a fixed field mirror splits off the light into the spectroscopy channel The remaining part of the field of view passes into the pho tometry channels A footprint of the focal plane splitter is shown in Figure 2 3 Calibration sources The calibration sources are placed at the entrance of the instrument to have the same light path for the sky observation and internal calibration This is essential for removing detector baseline drifts as best as possible a serious task with a warm telescope and the associated high thermal background To eliminate non linearity or memory problems with the detector readout system the calibration sources are low emissivity gray body sources providing FIR radiation loads slightly above and be The PACS instrument 2 2 3 low the telescope background respectively This is achieved by diluting the radiation from a small black source with a temperature near the telescope temperature inside a cold diffusor
52. bration files FITS format are loaded during the pipeline processing the different intermediate formats of the PACS data throughout the reduction For a more de tailed description of the pipeline refer to the PACS Data Processing User s Manual 7 1 PACS photometry standard data pro cessing 7 1 1 Photometry processing steps To summarize the data flow the most important pipeline steps for the photometer are described in the following 10 11 12 13 14 15 Raw telemetry data is decompressed and stored as science rotating raw signal data of 3 pixels stored in PhotRaw objects and averaged signal frames stored in Frames objects and house keeping data Bad saturated glitched pixels are flagged and corrected if possible The corrected signal readouts are converted to Volts Major observation blocks are summarized The chopper plateaux are cleaned from transition values and the chopper angle is converted to an the angle on the sky S C pointing is associated to each signal frame Valid signals on every chopper plateau are averaged The sky coordinates are calculated for each pixel The background is subtracted Signals of nodding position are averaged The flux is calibrated using differential calibration source measurements to populate absolute response arrays V W The zero level signal dark bias is subtracted The signals are divided by the absolute response The spacecraft on board time is converted to UTC A
53. bserving Mode Settings oes lt vo rue Nodding or map repetition cycles Sampling parameters Source type and chopping Repetition 1 Range sampling density Set the Observing Modes To control the absolute sensi consider to adjust the number of integration cycles Observation Est Add Comments Visibility canet Figure 6 26 Range spectroscopy step 2 Click on button Add Range to set up optional parameters for S N calculation 66 Using HSpot to create PACS observations Observing Modes Observing Mode Settings Choose one of the modes below None selected Pointed I Pointed with dither li Mapping Observing mode parameters Chopping nodding Chopper throw A Chopper avoidance angle Small a Angle to degrees 10 00 Large E Medium Angle from degrees 0 00 i lons Window Help CS Range Spectroscopy R SED Red et ngc7027 Type Fixed Single 21h07m01 59s 42d14m10 2s modify ranger Target ust ble stars for the target 23 get Ra 136 757 degrees Dec 42 236 degrees Cancel Wavelength Settings 210 microns 2nd 1st orders PACS Range Editor Range ID Blue Edge um Red Edge um Reference wa Line Flux M Observations Target
54. button you have to select Point source photometry tab in the pop up window 46 Using HSpot to create PACS observations v Herschel Planning Tool File Edit Targets Observation Tools Calibration Images Lines Overlays Options Window Help slg OHO l H Observations Target Positi PACS Photometry Unique AOR Label PPhoto 0000 Target 3c273 Type Fixed Single Position 12h2 906 70e 2d 3 New Target Observing Modes Observing Mode Settings Number of visible stars Choose one of the modes below Star tracker target Ra Small source photometry Chopped raster Scan map None selected Point source photometry Observing mode parameters Chopping and dithering settings Chopper avoidance angle Dithering Instru Blue channel filter selection 60 85 microns band S ka mens eee Angle from degree 0 00 On Observin Angle to degrees 0 00 Off Source type and mapping mode setti Set the Observing Modes to adjust the number of repetitions Observation Est Add Comments Visibility Duration hrs 0 0 Figure 6 3 Photometer AOT point source mode step 3 Click on the Set the Observing modes but ton and select the Point source photometry mode An accurate time estimate and associated noise is obtained by clicking the Observation Est
55. ce um Flux SIN 1 0 Density noise d my my 85 130 200 3 3 6 0 130 210 30 0 4 4 6 8 PACS Photometer AOT ObsMode Point source nodding and chopping You may increase the sensitivity for the current filter by setting the RepetitionFactor 2 3 to obtain OBStime repFactor 120 0 Chopper throw 52 0 arcsec Time Estimation Breakdown On source time s Map size 210 0 x 105 0 arcsec Calibration time s Map area 22 050 arcsec2 Instrument and observation overhead s Nod pattern as applicable A gt B Observatory overhead s Total time s Dithering information PACS T Dithering information is not applicable Confusion noise estim ion information Band Est 1 0 um Confusion Noise AOT duration w overheads 213 sec Level for Point Sources AOT duration comprises on sky plus setup and CAL Source my during siew q 85 130 130 210 Breakdown of AOT duration e On sky time w overheads 153 sec Update Confusion Noise Estimation e actual on sky time 120 Sec e Setup and CAL during slew w overheads 60 sec e actual calibration time 32 sec Cost of the AOT is calculated as on sky time 180 sec 153 180 333 sec Cancel Save messages Figure 6 4 Photometer AOT point source mode step 4 Click on the button Observation Est to get the sensitivity in the 2 bands It is advisab
56. ctral resolution rather than continuum sensitivity The use of the chopping nodding is imposed by the design of the AOT except in mapping mode where instead an off position can be defined if chopping nodding is de selected The chopping nod ding uses the same pattern as in line spectroscopy with a 3 positions chopping nodding to eliminate inhomogeneities in the telescope and sky background As in Line scan spectroscopy only ranges in first 105 210 um and second order 72 105 um or first and third order 55 72 um are allowed within a single AOR Note If ranges in the second and third order are to be covered at the same time then two AORs ought to be concatenated all As in line spectroscopy the spacecraft may be used in one of the three pointing mode pointed mode pointed with dither mode or in mapping raster mode Note Refer to the section line spectroscopy for the usage of these 3 pointing modes and their current lim itations Warning The map size is currently limited to 2x2 arcmin in size instead of 6x6 arcmin As in line spectroscopy 3 chopper throws are available small 1 arcmin medium 3 arcmin and large 6 arcmin except in the mapping mode where only the large chopper throw is allowed in order to chop out of the map In this case the map size is also limited to 4 arcmin except if an off 39 Observing with PACS position is selected All raster maps in range spectroscopy are defined i
57. e line editor of the wavelength settings in HSpot that allows to repeat a line scan several times While the absolute sensitivity is controlled by the re petition factor in the observing mode settings by dedicating a larger amount of time to this obser vation integer multiples Background subtraction is achieved either through standard chopping nodding for faint compact sources or through frequency switching techniques for line measurements of bright extended sources of the grating mechanism The observer can select either chopping nodding or frequency switching in combination with one of the three observing modes pointed pointed with dither and mapping For both observing mode settings three pointing modes are offered Pointed mode the default mode for point source spectroscopy a single pointing on the source The integral field concept allows simultaneous spectral and spatial multiplexing for the most ef ficient detection of weak individual spectral lines with sufficient baseline coverage and high tol erance to pointing errors without compromising spatial resolution The PACS spectrometer ar rays have 5 by 5 spatial pixels covering a squared 47 by 47 arcseconds field of view respect ively both channels viewing identical positions on the sky The line flux from a point source ob ject will always be collected with the filled detector array with most the source flux falling on the central pixel Therefore for the plain de
58. e of Level 0 data and the data needed to fully pro cess those data auxiliary data for the timespan covered by the Level O data such as the space craft pointing attitude history the time correlation selected spacecraft housekeeping etc It is also possible to include in this bundle the level O data of associated observations e g flatfields or photometric checks taken throughout the operational day The Frames class for reduced data and the PhotRaw class for additional raw channel data will be the basic data data products for this processing steps Level 1 data Detector readouts calibrated and converted to physical units in principle instru ment and observatory independent For PACS photometry this is a data cube with flux densities with associated sky coordinates The Frames class will be the basic level 1 product of photometer data Possibly the level 1 data generation can be done automatically to a large extend after the instru ment has been calibrated Level 2 data Further processed level 1 data to such a level that scientific analysis can be per formed For optimal results many of the processing steps involved to generate level 2 data may require human interaction based both on instrument understanding as well as understanding of the scientific aims of the observation Level 3 data These are the publishable science products where level 2 data products are used as input These products are not only from the specific
59. e scan legs to be north south An homo geneous coverage is selected to get a homogeneous exposure map 55 Using HSpot to create PACS observations x Me Herschel Planning Messages File Edit Targets Observation Tools Calibration Images Line PACS Photometer AOT ObsMode Large source line scan mode no chopping PACS Time Estimation Instrument performance summ ScanLeg 5100 0 arcsec number of legs 52 leg separation Band Point Source Point Source Point Source Extended Exter 98 7 arcsec scan speed 10 00 arcsec sec um Flux S N 1 0 Surface Density noise Brightness Map area 26 734 475 arcsec2 mJy mJy M y sr 85 130 0 0 o o 12 0 0 0 0 0 130 210 0 0 o o 13 7 0 0 10 0 No nodding C is in line scan mode Nod pattern as applicable Dithering information TELE ETE ES Dithering information is not applicable On source time s 26520 Duration information Calibration time s 32 Instrument and observation overhead s 2144 AOT duration w overheads 29724 sec Observatory overhead s 180 AOT duration comprises on sky plus setup and CAL Total time s 29844 during slew PACS Time Estimator Md Breakdown of AOT duration e On sky time w overheads 29664 sec i i i i actual on sky time 26520 sec Confusion noise estimation sum e Setup and CAL during slew w overheads 60 sec Band Est 1 0 Est 1 6 e actual calibration time 32 sec um Con
60. er positive east of north fol lowing the Position Angle convention The orientation constraint means a scheduling constraint and should therefore be used only if necessary Repetition factor number of times to repeat the raster map to adjust the absolute sensitivity maximum 100 Source flux estimates Optional point source flux density in mJy or surface brightness in MJy sr for each band It is used for signal to noise calculations and to change the ADC to low gain if the flux in one of the two channel is above the ADC saturation threshold increasing the dynamical range by a factor 4 See Sec tion 4 1 1 for more details 4 1 3 2 Scan mapping mode Scan maps will be the default to map large areas of the sky for galactic as well as extragalactic sur veys Scan maps are performed by slewing the spacecraft at a constant speed along parallel lines to cover a large area as illustrated in Figure 4 5 The lines are actually great circles which approxim ates parallel lines over short distances Scans mapping does not make use of chopping the signal modulation being provided by the spacecraft motion 31 Observing with PACS Cross scan distance a Scan leg length Figure 4 5 Example of PACS photometer scan map Schematic of a scan map with 6 scan line legs After the first line the satellite turns left and continue with the next scan line in the opposite direction just like in the ras
61. erving with PACS Figure 4 3 Chopper avoidance angle in small source photometry Illustration of the chopper avoidance angle In this particular case in order to avoid the bright source shown to enter the field of view of the Nod 1 Chop B position observations at position angle around 90 degrees shall be avoided for instance with a chopper angle avoidance interval of 70 110 degrees To achieve a higher sensitivity in this observing mode the number of nod cycles per raster position can be increased with the repetition factor in the observing mode settings but the 2x2 raster map is performed only once The sensitivity will then scale with the inverse of the square root of the re petition factor Table 4 2 gives the user inputs required in HSpot Table 4 2 User input parameters for the small source AOT mode Parameter name Signification and comments Filter which of the two filters from the blue channel to use In case observations in the two blue filter bands are required to be performed consecutively two AORs shall be concatenated Chopper avoidance angle Interval of position angles for the chopper avoidance zone The position angle is counted positive east of north i e counterclockwise in the sky from the celestial north to the direction of the object to avoid As the chop per cannot rotate this effectively defines an avoidance angle for the satellite orientation Hence it is a scheduling constraint
62. et Ra 136 757 degrees Dec 42 236 degrees Wavelength Settings Range scan or SED mode Range mode sep Red 72 210 microns Qnd 1st orders i PACS Range Editor Range ID Blue Edge um Red Edge um Reference wa Line Flux Line Flux Continuum Line Width Line Wictth Range Rep Add Range Modify Range Delete Range Gatonservatinns Instrument Settings Observing Mode Settings o Nodding or map repetition cycles Target ngc7027 Sampling parameters Source type and chopping Repetition J ah oi it Set the Observing Modes To control the absolute sensitivity consider to adjust the number of integration cycles Observation Est Add Comments Visibility cancel Help Figure 6 25 Range spectroscopy step 1 Start PACS Range Spectroscopy AOT and select SED Red range mode In the second step by clicking on Add Range button the Range Id Reference wavelength and Continuum flux density optional parameters appear in enabled mode The range Id is a mandatory field the other two are optional parameter and used for point source continuum signal to noise cal culation only Accepting the default zero values means the Time Estimator will not perform S N cal culation s Note EET In SED mode it is not mandatory to add a range manually If the range line is missing from the ue PACS Range Editor then HSpot wi
63. fusion Noise Confusion Noise Level for Level for Cost of the AOT is calculated as on sky time 180 sec Point Sources Extended Sources 29664 180 29844 sec my M Jy sr 85 130 Sensitivity information 130 210 Effective on sky time one spatial resolution element 21 9 sec Update Confusion Noise Estimation Confusion Noise Esti RMS red 13 7 m y RMS blu 12 0 m y RMS red 4 45 M y isr RMS blu 12 23 M y isr Observations 3c273 POSS2 UKSTU Red t ISSA Target COSMOS Type Fixed Single Cancel Save messages Figure 6 16 Scan map step 2 The observation duration is computed and the sensitivity estimated for the chosen scan map configuration in our case 12 mJy 16 in the 110 micron band 56 Using HSpot to create PACS observations v Herschel Planning Tool File Edit Targets Observation Tools Calibration Images Lines Overlays Options Window Help LE 0 8 53 02 08 FE Mouse Control SS Mouse Shift Left Button Centre the Image at point ae x ISSA 100 um COSMOS TOIT Cos mos array zie Base Image vixi Observations ISSA 100 um COSMOS Target COSMOS Type Fixed Single Total Duration hrs 36 5 Figure 6 17 Scan map step 3 Overlay of the above scan map AOR on the sky Changing only the ori entation
64. g axis motion alone the horizontal gap between the 4 top and bottom matrices is still completely blind The Z axis motion allows to cover this area and leads to complete coverage The completely covered area 3 2 by 1 5 arcmin at the end of the ob servation is indicated as a hatched zone In this observing mode the chopping frequency is also fixed at 0 25 Hz and the dwell time per nod position to 64 seconds This leads to a minimal science time of about 8 minutes in this observing mode but only 4 minutes on target and a total AOR duration of about 15 min when all slew over heads are accounted In this configuration the predicted point source sensitivity in the covered area 3 2 x 1 5 the hatched area in Figure 4 2 is of the order of 21 mJy in the blue channel and 24 mJy in the red channel As the orientation of the arrays in the sky depends on the date of observation only the area inside a circle of radius 0 75 arcmin around the target celestial coordinates given by the observer is covered for sure to this depth 4 1 2 1 Chopper avoidance angle As the the area covered in the small source photometry mode is rectangular 3 2 x1 5 the user might want to exclude some position angles of the chopping direction to avoid chopping into a bright close by infrared source For this purpose an interval of position angle to be avoided can be entered in HSpot The position angle is counted positive east of north i e counterclockwise in the sky f
65. h sky constraint for instrument reference frame sky or sky with array con straint for sky coordinates scans Orientation angle Array to map angle if scan in instrument reference frame see Figure 4 6 or map orientation angle if scan in sky coordinates see Figure 4 7 in de grees Orientation constraint Map orientation angle range if scan in instrument reference frame see Fig ure 4 6 or array to map angle range if scan in sky coordinates see Fig ure 4 7 Scan speed Slew speed of the spacecraft high 60 arcsec s medium 20 arcsec s or low 10 arcsec s Scan leg length Length of a line scan leg the maximum length is 20 degrees homogeneous coverage Cross scan distance square map If selected Yes HSpot computes the exact cross scan distance in order to perform a homogeneous coverage i e a scan map where the time spent on each sky pixel of the map is approximatively the same discarding gaps between matrices This choice is available only when the scan map is per formed in instrument reference frame array Distance between two scan legs maximum 210 arcsec i e the long side of the bolometer array If selected Yes HSpot computes the number of scan legs in order to complete a square map in the sky which is recommended for scan maps performed in instrument reference frame where the orientation of the map in the sky is not known in advance Number of scan legs N
66. ideal for regions smaller than 15 arcminutes respectively and Scan map has to be used for efficient mapping of large areas These modes and their operational constraints are described in Chapter 4 6 2 1 1 Tutorial of point source photometry mode entry In this first working example we make use of the point source photometry mode get dual band photometry of an almost point source 3C273 With any Herschel AOT the first step is to enter target information The target of the observation can be entered in various ways see The HSpot User s Manual one of which is directly into the AOT that is being prepared via the New Target button near the top Press the button and then enter your target coordinates or the target name and resolve with SIMBAD or NED The AOT opens with a unique AOR label at the top however you can edit it to make it more mean ingful to yourself if you so wish 44 Using HSpot to create PACS observations v LL CRETE File Edit Targets Observation Tools Calibration Images Lines Overlays Options Window Help AH OO v Target Target Name required SIMBAD gt Resolve the Name 3c273 Visibility Background Fixed Moving Coord Sys Equatorial J2000 Proper Motion RA 12h29m06 70s v Use Proper Motion Dec 2d03m08 6s PM RA C yp 0 011 Epoch 2000 00 PM Dec yn 10 004 Cancel Help
67. imensional field of view along a 1x25 pixels entrance slit for the grating as schematically shown in Figure 2 3 This integral field concept allows efficient detection of weak individual spectral lines with sufficient baseline coverage and high tolerance to pointing errors without compromising spatial resolution as well as for spectral mapping of extended sources regardless of their intrinsic velocity structure The grating is Littrow mounted i e the entrance and exit optical paths coincide It is operated in first second or third order respectively to cover the full wavelength range The first order covers the range 105 210um the second order 72 105um and the third order 55 72um Anamorphic col limating optics expands the beam to an elliptical cross section to illuminate the grating over a length required to reach the desired spectral resolution The grating is actuated by a cryogenic motor with arcsec precision which allows spectral scanning stepping for improved spectral flat fielding and for coverage of extended wavelength ranges The light from the first diffraction order is then separated from the light of the two other orders by a dichroic beamsplitter and passed into two optical trains feeding the respective detector arrays stressed unstressed for the wavelength ranges 105 210um and 55 105um Anamorphic re imaging optics is employed to independently match the spatial and spectral resolution of the system to the square pixels of the de
68. in one single shot two AORs are to be concatenated for a total duration of about 50mn In the SED option only the Nyquist sampling density is allowed 4 2 2 3 Line mapping There is the possibility to use the range spectroscopy mode to make a fast line mapping with the raster map option if a very narrow wavelength range is entered in HSpot In this case the grating scan can be shorter than in line spectroscopy hence faster spending less time per raster position Warning There is no direct way to assess the line sensitivity for very narrow wavelength ranges in the range spectroscopy AOT with the current HSpot version Besides the map size is limited to 2x2 arcmin 41 Chapter 5 Calibration framework The calibration of the PACS observing modes is addressed centrally by the Observatory About 5 7 of the observing time will be spent on calibrating the PACS instrument The PACS Instrument Control Centre Team in collaboration with the Herschel Calibration Scientists will plan work out execute and analyse dedicated observations on celestial standards according to the In flight Calibra tion Plan in order to consistently and thoroughly characterise all instrumental effects They will generate the calibration files needed for the Standard Product generation as indicated in the flow diagrams in chapter 7 as well as for more sophisticated Interactive Analysis steps By the time of the launch the instrument will have undergone seve
69. in the HSpot Users Guide Point source flux density mJy Extended source surface brightness MJy s Blue band 1 0 Blue band 10 0 Red band 2 o Red band 20 0 Band microns 85 130 130 210 cancer Instrument Settings Blue channel filter selection 60 85 microns band Source flux estimates and gain settings Source Flux Estimates 85 130 microns band Observing Mode Settings Repetition factor Repetition 1 To control the absolute sensitivity consider to adjust the number of repetitions iiy Source type and mapping mode settings Set the Observing Modes observation Est Add Comments Hem ox Figure 6 8 Raster map step 2 Select blue channel filter and provide flux estimates 51 Using HSpot to create PACS observations B 0 8 9 89 Ox s File Edit Targets Observation Tools Images Lines Overlays Options Window Help M Observations Astronomical Observation Requests AORs Label Positi Mode Information Target Type ar G F Instrum Durati Stat On 218 raste abell2218 16h35 Fixed Single C O O PAGS Phot Chopped raster Observing Modes 2 Observing Mode Settings Choose one of the modes below Small source photometry Chopped ra
70. instrument but are usually combined with theoretical models other observations laboratory data catalogues etc Their formats should be VO compatible and these data products should be suitable for VO access 7 1 3 Photometer processing flow diagram 72 Pipeline description and data product expectations PACS photometer standard data processing PACS photometer standard data processing 1 Level 0 eSPU reduced Averaged readouts for each pixel estatus DEC MEC information Color coding input output object Calibration file CD Available method Prototype method available Method not yet available getConvertedMeasures parameter Figure 7 1 photometer pipeline colour coding More details gt next slide Figure 7 2 photometer pipeline data processing level 0 73 Pipeline description and data product expectations F N Bb gs Ee B ln e a e 9 a 3 s oO J c E o m ea gt c B 3 o 2 amp Le es a B B nm Figure 7 3 photometer pipeline data processing level 0 5 1 N T J 5E e ER in 3 A A E T a 8 Figure 7 4 photometer pipeline data processing level 0 5 2 74 Pipeline description and data product expectations o C o a T SE 32 a lt L3 z c a S E z 1 3 my x 8 3 Q 21 Keiry feueqns suorn1ojsiq2Seuip Ten TED doyp jou 3j ejSuy xs1oddoq ejS
71. ity mode mode are displayed in Sec tion 3 5 7 for a single up and down scan and one nodding cycle D Important In range spectroscopy AOT HSpot reports the sensitivity for the primary range entered in HSpot Another wavelength range is covered simultaneously in the other channel for free This parallel range can be estimated using Figure 2 7 or simply by multiplying the wavelength by 2 to go from the second to the first order or by 3 to go from the third to the first order However the sensitivity reached in this parallel range is currently not yet returned by HSpot It can not be derived either directly from the plots in Section 3 5 7 as the grating sampling density is dif ferent for the 3 orders but within 20 the answer shall be correct once scaling with the square root of the integration time 4 2 2 2 SED mode This observing mode is intended to cover the full PACS wavelength range in Nyquist sampling to get the far infrared SED Spectral Energy Distribution of a target It is split in two parts A full wavelength range is performed either in the red SED red first and second diffraction orders from 72 to 210 um for a dura tion roughly 30mn e or in the blue SED blue between 55 and 72 um plus a long wavelength range part in the 1st order 165 210 um for a duration of about 15mn 40 Observing with PACS Again if the full PACS spectrometer wavelength range is to be covered 55 210 um in SED mode
72. lation selected spacecraft housekeeping etc It is also possible to include in this bundle the level 0 data of associated observations e g flatfields or photometric checks taken throughput the operational day e Level 1 data Detector readouts calibrated and converted to physical units in principle instru ment and observatory independent For PACS spectroscopy this is an oversampled 5x5xn cube with flux densities associated wavelengths and sky coordinates for every flux density e Level 2 data Further processed level 1 data to such a level that scientific analysis can be per formed For optimal results many of the processing steps involved to generate level 2 data may require human interaction based both on instrument understanding as well as understanding of the scientific aims of the observation These data products are at a publishable quality level and should be suitable for VO access This level of PACS spectroscopy data consists of an image cube the depth of the cube being the wavelength frequency Each layer in the image cube has the same sky projection This cube is constructed by re sampling the integral field cube oversampled in wavelength different projec tion per layer due to distortions onto the same sky wavelength grid of the instrumental resolu tion Level 2 data will can also contain a set of 1 dimensional spectra Nyquist sampled to the instru ment resolution combining the data for one spatial pixel over diffe
73. le to visualize the AOR on an already existing background image Most of the available astronomical image servers can be accessed to download image in a relevant waveband Our ex ample shows the access to a DSS image 48 Using HSpot to create PACS observations ha Herschel Planning Tool File Edit Targets Observation Tools Calibration Images Lines Overlays Options Window Help blg 1 Hal est S PPhoto 0000 3c273 12h29 Fixed Single PACS Phot point source photometry 333 jew v DSS Image Target 3c273 Type Fixed Single Position 12h29m06 70s 2d03m08 6s New Target Modify Target Target List Survey Types amp POSS2 UKSTU Red POSS2 UKSTU Infrared O POSS2 UKSTU Blue POSS1 Red POSS1 Blue Where Put plot in new Frame Put plot in current Frame Quick V Survey HST Phase 2 Target Positioning GSC 2 HST Phase 1 Target Positioning GSC 1 D The best of a combined list of all plates Width Degrees 0 250 Height Degrees 0 250 Initial Zoom Level No Zoom v Three Colour Plots Make this a 3 Colour Plot E Observations Target 3c273 Colour Band Red Cancel Figure 6 5 Photometer AOT point source mode step 5 From the main HSpot panel click on Im ages gt DSS image to download a DSS
74. ll apply default SED values 65 Using HSpot to create PACS observations x Update a s Spectral range parameters Range ID Blue edge um Red edge im Reference wavelength for S N calo im 72 00 el Pla g Too Line flux unit ges Lines Overlays Options Window Help Line flux Continuum flux density mJy 0 00 D A Rande Spe LEBENS Line width unit UT PTT oo Unique AOR Label PSpecR SED Red Range repetition factor Target ngc7027 Type Fixed Single Range repetition Position 21h07m01 59s 42d14m10 2s The relative range strength fraction of on source time per range New Target Modify Target Target List can be set by the range repetition factor for each range Note The sum of repetition factors affects the on source time per integration cycle Number of visible stars for the target 23 Star tracker target Ra 136 757 degrees Dec 42 236 degrees Cancel Wavelength Settings Range scan or SED mode Range mode SED Red 72 210 microns nd 1st orders m PACS Range Editor Range ID Blue Edge um Red Edge um Reference wa Line Flux Line Flux Continuum Line Width Line Width Range Rep D Red 72 00 210 00 72 00 0 00 10 18 0 00 0 00 km s i Add Range Modify Range l Delete Range Observations Target ngc7027 Ty Instrument Settings O
75. logic On source time s 1019 Minimum 976 sec OBStime 54 0 72 0 mic with 1 repetition s Calibration time s 179 4 Observing time required Instrument and observation overhead s 0 Observatory overhead s 180 Minimum required OBStime 976 sec Total time s 1199 With the specified NOD count 1 the total OBS time amounts to 976 sec AOT PointMode and Nodding info PACS AOT PacsRangeSpec PACS Time Estimator Messages _Done_ Pointing mode Point source nodding with 1 nod cycles Nod pattern nominal position A or A gt B B gt A etc A gt B Global AOT durations AOT total duration 1198 sec CalSlew with overheads 179 sec SRC REF with overheads 1019 sec HSPOT cost 1019 180 sec 1199 sec _ Range ID _ Blue Edd Blue 55 00 Setup and CAL summary AOT prologue duration 34 sec e Key Wave 62 7 mic CAL duration 144 sec M Observations SpecLine summary Target ngc7027 Ty Instrun Eee akas d Line 54 0 72 0 mic Sampling parameters Best continuum RMS occurs at 60 32 mic 2370 mJy Rangesampiing dens Best line RMS occurs at 71 03 mic 31 56E 18 w m2 Worst continuum RMS occurs at 54 00 mic 12389 mJy Worst line RMS occurs at 54 00 mic 295 10E 18 w m2 Total duration 988 sec SRC REF no overheads 392 sec Cancel Save messages Figure 6 29 Range spectroscopy
76. make a single image Note that only the central 3x1 shaded area in Figure 4 1 is covered by all chop and nod positions As it is rectangular the user may want to put a constraint on the position angle with the chopper avoidance angle Figure 4 1 deals only with the blue array where 4 out of 8 matrices will be effectively used but the 24 Observing with PACS red side figure is simple to extrapolate the chopping alternates the source between the two matrices while nodding move the source from the bottom to the upper part of the matrix The chopping frequency is 0 25 Hz i e 4 seconds per chopper plateau for a duration per nod posi tion of 1 minute The minimal duration of this observing mode with calibration and slew overheads is 5 5 min including the fixed overhead of 3 min for the initial slew to target This initial slew time is used to performed internal calibrations The predicted sensitivity in this configuration is about 30 mJy 5 6 in the blue channel and 34 mJy in the red channel To achieve photometry of fainter sources the number of nod cycles is increased with the repetition factor in the observing mode settings to improve the sensitivity and reach faint er flux levels The sensitivity scales with the inverse of the square root of integration time and re petition factor 4 1 1 1 Gain setting for bright sources The standard ADC gain of the bolometers allows photometry on a large flux density dynamical ra
77. me one spatial resolution element 323 0 Sec RMS red 5 9 mJy RMS blu 5 2 mJy RMS red 1 92 MJy sr RMS blu 5 27 MJy sr OK Cancel Save messages Figure 6 11 Raster map step 5 Check the PACS Time Estimator Message 28 AO amp amp Herschel Plann File Edit Targets Observation Tools Images Lines Overlays Options Window Help ool gt Mouse Control Maps ang V Shift Left Button Centre the Image at point ES Target abell2218 Type Fixed Single Position 16h35m53 99000s 66d13m00 2000s New Target Modify Target Target List Survey Types POSS2 UKSTU Red POSS2 UKSTU Infrared POSS2 UKSTU Blue POSS1 Red POSS1 Blue Where Put plot in new Frame Put plot in current Frame E Quick V Survey HST Phase 2 Target Positioning GSC 2 HST Phase 1 Target Positioning GSC 1 A Observations S9 abell2218 POSS2 UKSTU Red The best of a combined list of all plates Target abell2218 Type Fixed Single width Degrees x 0 500 Height x o 500 Initial Zoom Level No Zoom m Three Colour Plots C Make this a 3 Colour Plot Colour Band Red Tr Ex Cancer Men S Figure 6 12 Raster map step 6 Select and download background image 53 Using HSpot to create PACS observations ool
78. mic Source type chopping and wavelength switching Continuum RMS at 157 74090504516303 mic 211 mJy _Setthe observing Modes e Line RMS at 157 74090504516303 mic 2 93E 18 w m2 Total duration 252 sec SRC REF no overheads 88 sec Observation Est Add Com Line 121 9 mic Continuum RMS at 121 9 mic 109 mJy Cancel e Line RMS at 121 9 mic 2 49E 18 w m2 Total duration 494 sec SRC REF no overheads 172 sec OK Cancel Save messages Figure 6 23 Line spectroscopy step 5 Run the time estimator by clicking on Observation Est but ton Check time estimation details in the PACS Time Estimator Message Similar as described in the photometer case the AOR overlay can be visualized on a background image Click on Images and select the image database from which you want to retrieve the back ground then navigate to option Overlays and AORs on current image 63 Using HSpot to create PACS observations x Herschel Planning Tool File Edit Targets Observation Tools Images Lines Overlays Options Window Help mE ABO ORA Q Mouse Control Mouse Any e Shift Left Button Centre the Image at point x NGC7027 POSS2 UKSTU Red I Ei Observations dx NGC7027 POSS2 UKSTU Red Target NGC7027 Type Fixed Single 5j Total Duration hrs 0 07 Figu
79. mps to Frames 2 SPU methods averaged sub ramps efitted slopes i Cal files OpenNoise Limits Dummy NoiseLimits Cal files DiscardRampHooks RampLinearisation Cal file GlitchThresholdCre Figure 7 10 spectrometer pipeline data processing level 0 5 2 3 Level 1 Calibrations on Frames Cal file LabelDescription Cal files ChopperAngle ChopperSkyAngle Cal file ChopJitterThreshold Cal file EffectiveCapacitance Figure 7 11 spectrometer pipeline data processing level 1 1 79 Pipeline description and data product expectations 3 Level 1 Calibrations on Frames Cal file GratingJitterThre shold Cal files Key wavelengths RSRF Cal files KeyWavelength Call13 V sec Jy Cal file Siam ImageDistortions Cal files SpecDistortions SpecAlignment Figure 7 12 spectrometer pipeline data processing level 1 2 80 Chapter 8 Change record Version 1 1 14 March 2007 e Third order wavelength range of spectrometer changed consistently in the manual to 55 72 mi crons Correction in Section 3 5 7 the SED mode uses the Nyquist sampling and not the high sampling density Improved spectrometer sensitivity plots in Section 3 5 7 including continuum sensitivity in second order with filter A in the range 55 72 micron 08 03 2007 e Chopper throw in Section 4 2 2 Range spectroscopy changed to 1 3 and 6 arcmin Figure 3 10 of the spectrometer
80. n HSpot Note In the case of a square scan map in instrument reference frame the orthogonal coverage to cover ad the same area is achieved by simply adding 90 degrees to the array to map angle and recomputing the cross scan distance If the array to map angle is 45 degrees the cross scan distance if even the same 33 Observing with PACS 4 1 3 2 2 Scan maps in sky coordinates a array to map angle p map orientation angle PA array position angle B a PA Line scan direction Sky with array constraint Figure 4 7 Scan maps in sky coordinates The map orientation angle in the sky D is fixed by the observ er therefore there is no control on the array to map angle which depends on the target coordinates and exact observation time However a constraint on the array to map angle can be put in HSpot Another way to define rectangular areas in the sky with scan mapping is to select mapping in sky coordinates with the option sky in HSpot In this configuration the map orientation angle is defined by the observer i e the angle from the equatorial celestial north to the line scan direction in the first leg However in this case there is no direct control of the homogeneity of the map coverage as the cross scan distance to achieve this purpose depends on the array position angle which itself depends on the exact observation day The user shall be very careful in selecting a cross scan distance when in
81. n of diffraction orders The blue channel contains an additional filter wheel for selecting its short or long wavelength part two photoconductor arrays with attached cryogenic readout electronics CRE The PACS instrument i Telescope Axis PACS FOV F ootprint to rasa ae Ltoengk in the Telescope Focal Plane as ca ai su Y Direction arcmin B 7 5 5 4 3 2 1 1 2 3 4 5 7 8 Z Direction mm Z Direction arcmin dog TEE 35 179 Central Fieid 4175 Chop 1 75 Chop PACS focal plane usage Long wavelength and short wavelength photometry bands cover practic ally identical fields of view The spectrometer FOV is offset in the Z direction closer to the optical axis of the telescope Chopping is done along the Y axis left right in this view and also allows ob servation of the internal calibrators on both sides of the used area in the telescope focal plane The maximum chopper throw for sky observations is 3 5 arcmin for photometry and 6 3 arcmin for spectroscopy In photometry object and reference fields are almost touching at 3 5 arcmin throw Figure 2 3 PACS field of view footprint in the telescope focal plane 2 2 Common Optics 2 2 1 Entrance Optics 2 2 2 The entrance optics fulfills the following tasks it creates an image of the telescope secondary mirror the entrance pupil of the telescope on the focal plane chopper this allows spatial chopping with as little as possi
82. n spacecraft coordinates therefore the user is ad vised to define square maps in order to get a mapped area of interest independent of position angle i e same number of raster points and step sizes on both axis Two observing modes are available the range scan mode and the SED mode 4 2 2 1 Range scan A number of wavelength ranges low and high wavelength pairs have to be entered either in the 72 210 um interval 2nd and 3rd order or in the 55 72 and 105 210 um interval 1st and 3rd order Two different sampling densities of the up down scan are offered either the high sampling density the same as in line spectroscopy but here for arbitrary ranges corresponding an objectives of more than 3 samples per FWHM of an unresolved line in each pixel at all wavelengths orthe Nyquist sampling considering the 16 spectral pixels with grating step size of 6 25 spec tral pixel In range spectroscopy integration times can be very long for instance a full up down scan in the first order takes more than 5 hours If the time scale of the detector drifts turn out to be shorter than expected such long scans might not be advised as the time spend on one nod position will be too long The Nyquist sampling shall therefore be the default for large wavelength range coverages as it al lows obviously faster scans than the high sampling density option but at the expense of sensitivity The sensitivities for the SED mode and high sampling dens
83. ne sensitivity 20 Scientific capabilities RMS continuum PACS full sampling range scan RMS Uy nee E t T 60 80 100 120 140 160 180 200 Wavelength um Figure 3 11 Spectrometer point source continuum sensitivity in high sampling density mode for both line range repetition and nodding repetition factors equal to one in the line spectroscopy or range spec troscopy AOTs Solid blue line third grating order filter A dotted blue line second order with filter A green second order with filter B red first order 1410 1 0 10 8 0107 6 0107 RMS W m2 4 010 2 010 0 0 line RMS PACS full sampling range scan ee ee a d a a a d a a a 1 a a al 60 80 100 120 140 160 180 200 Wavelength um Figure 3 12 Spectrometer point source line sensitivity in high sampling density mode for both line range repetition and nodding repetition factors equal to one in the line spectroscopy or range spectro scopy AOTs Blue third grating order filter A green second order filter B red first order 21 Scientific capabilities RMS continuum PACS SED range scan RMS Uy 60 80 100 120 140 160 180 200 Wavelength um Figure 3 13 Spectrometer point source continuum sensitivity in SED mode range spectroscopy AOT for both range repetition and nodding repetition factors equal to one Solid blue line third grating order with filter A dotted blue line second order
84. nge from the mJy level up to about 2000 Jy before the brightest pixel saturates ADC saturation and not the detector Hence the standard gain shall be appropriate for almost all types of scientific observations However for very bright sources such as planets or stars in star forming regions a low bias gain could be needed Driven by the point source flux density or surface brightness entered by the observer the AOT allows to change to a low gain setting that increases the flux dynamic range by a factor 4 However this is at the expense of losing sensitivity at low flux levels as the noise is not properly sampled anymore with the low gain due to the coarser digitalization This low gain setting applies also to all other photometer modes as well 3 Important D The low gain shall be used with caution and under exceptional circumstances only If the low gain is selected it applies to both the red and the blue channel entered in HSpot for any of the three photometer bands As this is well below the maximal value of the dynamical range of the high gain mode the low gain can therefore not be selected in phase I Warning 9 Due to a software bug the AOR time estimation cannot be run if a flux density higher than 10 Jy is entry 4 1 1 2 Chopper avoidance angle In the point source photometry mode the properly imaged field i e with chopping and nodding is rectangular about 52 arcsec x 2 5 arcmin see Figure 4 1 The user might therefore w
85. nomical Observation Template CRE Cryogenic Readout Electronics DDCS Double Differential Correlated Sampling DMC Detector and Mechanics Controller DTCP Daily TeleCommunications Period ESA European Space Agency FM Flight Model FOV Field Of View FPU Focal Plane Unit FWHM Full Width Half Maximum HSpot Herschel planning observations tool ICC Instrument Control Centre e CSS Internal Cals bration Source ILT Integrated Instrument Level Tests NEP Noise Equivalent Power OD Observation Day mode PACS Photodetector Array Camera amp Spectrometer QLA Quick Look Analysis QM Qualification Model RSRF Relative Spectral Response Function SED Spectral Energy Distribution GRUS Signal Processing Unit Chapter 2 The PACS instrument 2 1 Overview instrument concept The PACS instrument comprises two sub instruments which offer two basic and and mutually ex clusive modes in the wavelength band 55 210 um Imaging dual band photometry 60 85 um or 85 130 um and 130 210 pm over a field of view of 1 75 x3 5 with full sampling of the telescope point spread function diffraction wavefront er ror limited Integral field spectroscopy between 55 and 210 um with a resolution of 75 300km s and in stantaneous coverage of 1500 km s over a field of view of 47 x47 Photometer Optics Filter Wheel Blue Bolomete Slicer Optics
86. nputs required in HSpot Table 4 1 User input parameters for the point source AOT mode Parameter name Meaning and comments which of the two filters from the blue channel to use In case observations in the two blue filter bands are required to be performed consecutively two AORs shall be concatenated On dithering enabled or Off dithering disabled A fixed dithering pattern is applied with an amplitude of 1 pixel with the chopper such that 20s is spent per dither position 12s on chop A and 8s on chop B for the 3 dither positions per nod cycle This is intended to improve the flat field accuracy Chopper avoidance angle Interval of position angles for the chopper avoidance zone The position angle is counted positive east of north i e counterclockwise in the sky from the north to the direction of the object to avoid Repetition factor Number of AB nod cycles to adjust the absolute sensitivity maximum 120 Source flux estimates Optional point source flux density in mJy or surface brightness in MJy sr for each band It is used for signal to noise calculations and to change the ADC to low gain if the flux in one of the two channel is above the ADC saturation threshold increasing the dynamical range by a factor 4 See Sec tion 4 1 1 for more details 4 1 2 Small source photometry This observing mode is intended for mapping of sources with relatively small size as nearby galax ies or pr
87. ns PACS Line Spectroscopy Unique AOR Label PSpecL 0000 x Observing Modes 2 Target NGC7027 Type Fixed Single Position 21h07m01 59s 42d14m10 2s New Target Modify Targ Target List Observing Mode Settings Choose one of the modes below None selected Pointed I Pointed with dither Mapping Number of visible stars for the target 23 Observing mode selection Star tracker target Ra 136 757 degrees Dec 42 236 degrees Chopping nodding J Wavelength switching Wavelength Settings Observing mode parameters Selection of wavelength ranges Chopper throw Chopper avoidance angle Angle from degrees 0 00 Angle to degrees 0 00 IE Wavelength ranges 55 72 and 105 210 microns Grd 1st orders v Small PACS Line Editor Line Id Wavelengt Redshifte Line Flux Line Flux Continuu Line Width Line Wid Line Repe IO 3P1 63 180 63 18 0 00 104 18 0 00 1 00 km s t INII3P2 121 900 121 90 0 00 104 18 0 00 1 00 km s 2 ICI C 157 741 157 74 0 00 104 18 0 00 100 km s 1 Medium Large Add Line Manually J Add Line From Database J Modify Line Delete Line Redshift selection Unit Redshift value 0 000000 Observing Mode Settings Nodding wavelength switching cycles Source type chopping and wavelength switching
88. ntinue with the next raster line in the reverse direction and so on for number of raster lines entered in HSpot n An example of a PACS photometer raster map is shown in Figure 4 4 29 Observing with PACS RENE E sees pue X raster axis Y spacecraft axis 4 Figure 4 4 Example of a photometer raster map with m 4 and n 6 and raster step sizes of 100 arcsec in both directions giving a redundancy factor of 2 in the raster X axis direction The area covered by the raster chop on positions is shown with the blue rectangle about 8x10 arcmin But for symmetrical reas ons the nod off position is imaged in the fashion as the chop on position so the actual raster map area covered is the dashed blue rectangle about 11 5x10 arcmin The number of steps on the X and Y raster axis as well as the raster step sizes are left open to the user The observer can therefore choose the redundancy factor i e the number of raster positions that observe a given sky position a key factor for the detection of faint sources with previous IR missions It is advised to visualize the raster footprint on the sky with the Overlays menu in HSpot Small areas of the order of 3x3 arcmin can be covered with raster maps with very small step sizes a few arcseconds allowing to chop mostly out of the map Sparse sample maps are not allowed therefore the maximum step size in the raster X direction is 210 arcsec and in the r
89. nto the individual detectors Each module is attached to a 18 channel cold readout electronics CRE amplifier multiplexer cir cuit in CMOS technology The photocurrent from the detector crystals is integrated on a capacitor The capacitance is switchable between 4 values from 0 1 to 3pF to provide sufficient dynamic range for the expected flux range The integration process is reset after preset interval During the integra tion the voltage signal is regularly read in a non destructive way with a frequency of 1 256s leading to an integration ramp with 256 reset interval samples 11 Chapter 3 Scientific capabilities Based on the results from the QM Instrument Level Tests tests of FM components subunits and our present knowledge of the Herschel satellite the performance of the entire system can be estimated in terms of what the observer is concerned with i e an assessment of what kind of observations will be feasible with Herschel PACS and how much observing time they will require The system sensitivity of the instrument at the telescope depends mainly on the optical efficiency i e the fraction of light from an astronomical source arriving at the telescope that actually reaches the detector on the photon noise of the thermal background radiation from the telescope or from within the instrument and on detector electronics noise 3 1 Herschel telescope Ideally the telescope would be diffraction limited over the full PACS
90. offered with the AOT photometer Point source photometry This mode is devoted to target a source which is completely isolated and point like or smaller than one blue matrix A typical use of this mode is for point source photometry It uses chopping and nodding both with amplitude of 1 blue matrix and dithering with a 1 pixel amplitude keeping the source on the array at all times Small source photometry This mode is devoted to target sources that are smaller than the array size yet larger than a single matrix To be orientation independent this means sources that fit in circle of 1 75 arcmin diameter This mode uses also chopping and nodding but this time the source cannot be kept on the array at all times 23 Observing with PACS Large area or extended source mapping This mode is necessary to map sources larger than the array size or to cover large contiguous areas of the sky e g extragalactic surveys There are two ways to perform these kinds of observations raster mapping with chopping e scan mapping without chopping 4 1 1 Point source photometry The point source photometry observing mode shall be used for sources that are significantly smaller than a single matrix i e point sources mostly It makes use of a classical 4 positions on array chop ping with dithering along the Y axis combined with nodding along the Z axis to compensate for the different optical paths The chopper is used to alternate the
91. om the telescope is about 1 2 x 10 WHz depending on the bandpasses The post detection bandwidth thermal electrical of the bolometers is 3 Hz the noise of the bolo meter readout system has a strong 1 f component such that a clear 1 f knee frequency cannot be defined a factor of ten in post detection frequency i e 0 3 Hz 3 Hz is assumed to be sufficient to cover both chopped and continuously scanned observations and the noise in this band is con sidered as relevant for sensitivity estimates The quantum efficiency i e the fraction of the power incident on a pixel that gets actually absorbed by the pixel has been modeled for the PACS absorber structure and averages 8096 Scientific capabilities There are two modes of reading the bolometers arrays a so called Direct Mode DM and the Double Differential Correlated Sampling DDCS mode where an internal electrical reference is subtracted to the signal of the bolometer signal in order to get rid of external electromagnetic per turbations Although the direct mode shows less noise by up to a factor 2 in the blue channel the DDCS has been taken as the default mode because of unknown electromagnetic perturbations from the spacecraft wiring in orbit In DDCS mode the latest NEP measurements are 4 x 10 WHz in the blue channel and 8 x 10 WHz in the red band Including all components in the detection path as described in the previous sections these NEPs
92. on wider areas scan mapping is significantly more efficient than raster mapping and avoid the problem dealing with positive and negative source beams by chopping off within the raster map area 4 1 3 1 Raster mapping mode Rastering is intended to cover larger area than the PACS FOV yet not too large either A reasonable maximum size is probably of the order of 15 x15 as above a certain size the raster becomes difficult to handle and moreover it becomes very inefficient due to the large slewing overheads about 30 seconds between raster positions depending on the raster step size with respect to line scan map ping mode Rasters are only allowed in the instrument reference frame with the raster X axis along the spacecraft Y axis long edge of the detectors and the raster Y axis along the spacecraft Z axis small edge of the detector Chopping by one full FOV is performed on each raster position 3 5 ar cmin along the raster X axis Therefore for large rasters chopping is done inside the raster map which might complicate the data processing The target position entered in HSpot is the centre of the rectangular rastered area The dwell time per raster position is fixed to 64 seconds chopping every 4 seconds hence 8 chopper cycles on each raster position Then the spacecraft moves to the next raster position on the line raster X axis and so on for the number of steps m number of raster points entered in HSpot It turns then left to co
93. oto stellar disks The term small source is used here to refer to sources that are slightly smaller than the array i e 1 75x3 5 or to avoid problems with the array orientation inside a circle of 1 75 diameter but more extended than a single matrix Most star forming regions are probably too large for this mode and larger rasters or line scan mapping should be used instead In this observing mode a raster with small step size is performed to observe the target with a clas sical 3 positions chopping nodding for each raster position as illustrated in Figure 4 2 Therefore only half of the science time is actually used for on source integration in contrast to the point source photometry observing mode With the pattern of gaps between matrices the small 2x2 raster map allows to recover the signal lost between pixels This offers also the advantage of a larger fully covered area The parameters of this raster i e the displacement in both directions nod and chop throws are fixed and not left to the observer s choice peee pe ve p sr ose de sir e G GE poy Sandsa er UN ul a ni om a ee MN l l l f I I I l Teceeusee Bessoooos LN PEPPER db chopped on source nodded off source nod1 chop A off source nod1 chop B nod2 chop B nod2 chop A 26 Observing with PACS Figure 4 2 Footprint of detector on the sky in small source photometry The pointing sequence is colour coded and goes black red green blue By the Y axis lon
94. p can only be defined in celestial coordinates with a max imum size of 2 degrees and sparsely sampled maps are possible If the user wants to cover a contiguous area in the sky under any position angle he shall not define a step size larger than 34 arcsec i e the size of the array 47 divided by v2 Warning Q With the current HSpot version the map size in chopping nodding mode is unfortunately limited to 2x2 arcmin in size instead of 6x6 arcmin This shall be corrected for the Phase II entry As an al ternative users can meanwhile either use the wavelength switching mode in the line spectroscopy AOT as the limit of the map size is much higher 2x2 degrees in this case and the integration time per raster position similar or provisionally enter a smaller than intended step size to be changed later on in phase II entry 4 2 1 1 Line scan with chopping nodding mode For each user defined wavelength PACS performs an up down grating scan with an amplitude such that a given wavelength is seen successively by all 16 spectral pixels The sampling density is higher than 3 samples per FWHM at all wavelengths Table 4 5 spectral coverage in line scan diffraction or wavelength full range full range um highest sensitiv FWHM um der um km s 3 55 1880 0 345 0 021 3 72 799 0 192 0 013 2 72 2658 0 638 0 039 2 105 1039 0 364 0 028 1 105 5214 1 825 0 111 1 158 2869 1 511 0 126 37
95. performed either in the instrument reference frame or in sky coordinates 4 1 3 2 1 Scan maps in instrument reference frame When scan maps are performed in instrument reference frame an array to map angle is chosen ob server The array to map angle is the angle from the spacecraft Z axis to the line scan direction in the first leg counted positive counterclockwise in the sky This configuration corresponds to refer ence frame array in HSpot and is illustrated in Figure 4 6 PACS does not have a fixed magic angle like SPIRE it it left as a free parameter to the user It is however advised not to use 0 or 90 degrees as gaps between matrices would then stay in the final map if a sky position is visited only by one scan line leg An array to map angle of 45 degrees al lows to get the same depth in two scan maps with orthogonal mapping directions 32 Observing with PACS a array to map angle B map orientation angle PA array position angle B a PA Line scan direction Array with sky constraint Figure 4 6 Scan maps in instrument reference frame The array to map angle o is defined by the user This effectively defines the map orientation angle in the sky D as the array position angle is not a free parameter it is function of target coordinates and observation time However a constraint on the map orientation angle can be put in HSpot In this configuration if the homogeneous coverage parameter is
96. pling density x HSPOT decoding logic Hild Minimum 1766 sec OBStime 70 0 210 0 mic with 1 repetition s Observing time required Minimum required OBStime 1766 sec With the specified NOD count 1 the total OBS time amounts to 1766 sec AOT PointMode and Nodding info PACS AOT PacsRangeSpec Pointing mode Point source nodding with 1 nod cycles Nod pattern nominal position A or A gt B B gt A etc A gt B Global AOT durations AOT total duration 2059 sec CalSlew with overheads 174 sec SRC REF with overheads 1885 sec HSPOT cost 1885 180 sec 2065 sec Setup and CAL summary AOT prologue duration 34 sec e KeyWave 94 0 mic CAL duration 139 sec SpecLine summary Line 70 0 210 0 mic Best continuum RMS occurs at 131 78 mic 464 mJy Best line RMS occurs at 139 75 mic 8 75E 18 w m2 Worst continuum RMS occurs at 104 88 mic 772928 mJy Worst line RMS occurs at 104 88 mic 6 211 73E 18 w m2 Total duration 1854 sec SRC REF no overheads 708 sec ok cancer Save messages clicking on Observation Est button on the bottom of the main AOT window 68 Using HSpot to create PACS observations PACS Time Estimation x essage a Instrument performance summary Time Estimation Breakdown HSPOT decoding
97. raction of power arriving at the detector is shown in Figure 3 7 Grating efficiency The calculated grating efficiency i e the fraction of the incident power that is diffracted in the used grating order as a function of wavelength is shown in Figure 3 7 Scientific capabilities 08 08 3 B 2 amp 06 206 o E a pa c S 04 9 04 o es 02 02 E 60 80 100 120 140 160 180 200 60 80 100 120 140 160 180 200 Wavelength um Wavelength um Figure 3 7 PACS spectrometer optical efficiencies Left calculated grating efficiency Right Diffraction throughput of the spectrometer optics the diffraction losses mainly occur in the image slicer 3 5 3 Spectrometer filters The transmission of the filter chain in each of the instrument channels has been calculated from measurements of the individual filters see Photometer filters section The filter transmission curves for the three grating orders are plotted in Figure 3 8 ume Note Ce With the flight model dichroics there is a gap in wavelength coverage between the Ist and second ad order in the 100 105 micron range C ost n A E 06 o C LH 04 i D iL xL 0 60 80 100 120 140 160 180 200 Wavelength um Figure 3 8 Transmissions of the spectrometer filter chains The graph represents the overall transmis sion of the combined filters in each of the three grating orders of the spectrometer The vertical lines mark the nominal band edges
98. ral months of ground character isation and calibration making use of different kinds of stimulators like blackbodies for continuum emission vapour cells and a FIR laser for absorption emission lines and blackbodies with hole masks in front simulating point sources Once in orbit after instrument check out there will be a larger initial calibration block during the Performance Verification Phase verifying the in orbit performance of the instrument which can be compared against the ground performance and providing the baseline in flight calibration The feas ibility of the calibration strategy for the observing modes will be one aspect during the subsequent Science Verification Phase Refinement and extension of the calibration will then be done during the Routine Phase when the understanding in data processing will grow The issue of time dependence of certain calibration parameters will be handled two fold Shorter term time variations like e g the drift of detector responsivity will be addressed by the AOT design by incorporating at least one reference measurement on the internal calibration sources in the selected filters photometry or at key wavelengths of the selected grating orders spectroscopy Possible longer term variability of parameters will be monitored by repeating dedicated calibration measurements at regular time intervals Feedback triggering a stability check of calibration paramet ers can also come from data quality control
99. ration is given in the following section Tips and details on use of Range Spectroscopy AOT can be obtained in Chapter 4 6 2 2 1 Example of line spectroscopy AOT entry In this example we define a point source observation on planetary nebulae NGC 7027 Three spec tral lines are requested the OI line at 63 microns NII at 122 microns and C at 158 microns PACS Line Spectroscopy Unique AOR Label PSpecl 0000 x B Target None Specified File Edit m m New Target __ Modify Target Target List EN Number of visible stars for the targetNone Specified m Obse Target BRI EB vetength settings Target Name required simpap Resolve the Name ses NECTOR visiviy ackorouna Background 2 and 105 210 microns Qnd 1st orders v Fixed Moving PACS Line Editor 5 Flux Line Flux Continuu Line Width Line Wid Line Repe Coord Sys Equatorial J2000 Proper Motion RA 21h07m01 59s V Use Proper Motion Dec 42d14m10 2s PM RA fy 0 006 Epoch 2000 00 PM Dec yr 0 016 OK cancel Help Add Line Manually Add Line From Database Modify Line Delete Line Redshift selection Unit Redshift z y Value 0 000000 Observing Mode Settings Nodding wavelength switching cycles Source type chopping and wavelength switching Number of cycles 1 Setthe Observing Modes To control the absolute
100. re 6 24 Line spectroscopy step 6 Download a background image and create the overlay of the AOR 6 2 2 2 Example of range spectroscopy AOT entry In this example we define a point source observation on planetary nebulae NGC 7027 Full spectral energy distribution SED measurement is requested using the combination of SED Red and SED Blue range scan options The grating performs only one up down scan the measurement time is the shortest possible for the entire 55 to 210 microns spectral range in this fast scanning mode see Sec tion 4 2 2 for details Two AORs have to be created for the complete range coverage these AORs are being concatenated in the last step The measurement time with only one repetition single AB nodding cycle is 2065 seconds in the SED Red mode and 1119 seconds in the SED Blue mode In total the shallow full SED spec trum with overheads takes 53 minutes respectively The best continuum sensitivity at 132 microns is 464 mJy 64 Using HSpot to create PACS observations Herschel Planning Tool File Edit Targets Observation Tools Images Lines Overlays Options Window Help zB x PA Range Spectroscop a m Observations Unique AOR Label PSpecR SED Red Target ngc7027 Type Fixed Single Label Tar Position 21h07m01 59s 42d14m10 2s New Target Modify Target Target Listu Number of visible stars for the target 23 Star tracker targ
101. rent scans applying noise fil ters etc Level 3 data These are the publishable science products where level 2 data products are used as input These products are not only from the specific instrument but are usually combined with theoretical models other observations laboratory data catalogues etc Their formats should be VO compatible and these data products should be suitable for VO access 7 2 3 Spectrometer processing flow diagram a Z sl Y gt 5 lb un amp g S Ele v e Lan S a 5 S d a 2 A E lg e E gi S B 8 Lx lt o 5 A gt gt e 6 m o Q Q e A A o 2 zi 5 E PS 5 lt te z 2 a Q 5 amp F 3 3 l Q E 2e II uoneIque Suisso o1d g Figure 7 7 spectrometer pipeline colour code 77 Pipeline description and data product expectations PACS spectroscopy standard data processing 1 Level 0 SPU reduced Raw ramps for selected pixels Averaged sub ramp readouts Fitted ramp slopes estatus DEC MEC information getConvertedMeasures parameter More details gt next slide Figure 7 8 spectrometer pipeline data processing level 0 2 Level 0 5 From Ramps to Frames 2 SPU methods vaveraged sub ramps fitted slopes decomposeDataframes pdfs spectrometer pipeline data processing level 0 5 1 Figure 7 9 78 Pipeline description and data product expectations 2 Level 0 5 From Ra
102. reo ee eds Gaeta queste Ede 10 24 4 Photoconductoft Arrays 2 3 repr eot reet Ire nore E ETE PEE ede rte AU teen 10 3 Scientific capabilities re oU RE EO ete RR tpe s 12 3 1 Herschel telescope c x5 e te Een ted etu isto tie Lo ent do ue edens 12 3 2 Chopper ste EOD E Ade te pope uc eds 12 RM OU MP EET 13 3 4 Characteristics of the photometer sssessessee HH ee eren 13 3 4 1 Photometer spatial resolution sssssssee eem emen 13 3 42 Photometer filters 1 eet eere ere rep E EEOSE REES EEES 14 3 4 3 Photometer bad pixels ots peregre rh Rr P Eas E TR rere 14 3 44 Photometer sensitivity i ceste sant aden tenue Shs seins sage ent rei rdi geile Pie 15 3 5 Characteristics of the spectrometer ssr rroen e a E R IH He mee emere 16 3 5 T Diffraction LOSSES ssa coire eto etie eto Uer exe ee optet tedden ood Ufer wear sed 16 3 5 2 Gratin eFlcIency sn tee etes tog ette retos it ege nter 16 3 5 3 Spectrometer filters 3 eerie ete sert et decimae diste tet aen I deed nes 17 3 5 4 Spectrometer spatial resolution sess mem e eee 18 3 5 5 Spectrometer spectral resolution sess eee 18 3 5 6 Spectrometer relative spectral response function 19 3 5 7 Spectrometer sensitl V y i tete tet ebore e tI trie tI Fee EET wee 20 4 Observing with PAGS ionerne erp EEE oon eec Pea y ere De Te Hep ope ee seu ee ER M epe re bep te seeds 23 4 1
103. reset repetition factors in order to tune the sensitivity Examples in the tutorial session are intended to illustrate the use of the above scheme in the flavour of the various observing modes 6 2 Tutorial of an AOT entry in HSpot 6 2 1 Observations are generated by filling out AOTs in HSpot these AOTs lead the observer through the possible choices for setting up a PACS measurement so that the final request an Astronomical Ob serving Request AOR contains all the necessary information for the observation to be made There are three PACS AOTs available in HSpot s Observation pull down menu e PACS Photometer e PACS Line Spectroscopy e PACS Range Spectroscopy Each of the AOTs are provided with various observing modes available as sub windows of the main AOT front end pages Detailed information about the underlying AOT logic can be obtained in Chapter 4 Tutorials of Photometer AOT entry The initial choice that you need to make is to decide in which Observing Mode you wish to observe 43 Using HSpot to create PACS observations This decision has to be based on the source extent Clicking on the Set the Observing Modes but ton you find four tabs of four choices e Point source photometry e Small source photometry e Chopped raster e Scan map You should select Point source photometry for bona fide point sources Small source photometry is for targets smaller than 4 arcmin in diameter Chopped raster option is
104. ressed with 16x25 pixels on which the 16 spectral elements of the 25 spatial pixels are imaged The Ge Ga photoconductor arrays have a modular design They are made of 25 linear modules of 16 pixels each are stacked together to form a 2 dimensional array Ge Ga photoconductors are sens itive in the wavelength range 40 110 120 um without any stress A stress is therefore applied to im prove the long wavelength sensitivity The stressing mechanisms ensures homogeneous stress on each pixel along the entire pile of 16 spectral elements The low stressed has a mechanical stress on the pixels which is reduced to about 10 of the level needed for the long wavelength response Light cones in front of the actual detector block provide an area filling light collection in the focal plane and feed the light into the individual integrating cavities around each individual mechanically stressed detector crystal The light cones also act as a very efficient means of straylight suppression because their solid angle acceptance is matched to the re imaging optics such that out of beam light is rejected The PACS instrument Figure 2 8 High stress module close up The 25 stressed modules corresponding to 25 spatial pixels in tegrated into their housing Stress is applied to the whole stack of 16 Ge crystals providing the instantan eous spectral coverage for each of the 25 spatial fields on the sky Light cones provide for area filling col lection o
105. rom the north to the direc tion of the object to avoid i e the Y spacecraft axis As the chopper cannot rotate this effectively defines an avoidance angle for the satellite orientation Hence it is a scheduling constraint Moreover for pointings close to the ecliptic plane the position angle becomes constrained towards 23 5 de grees i e the inclination of the ecliptic plane chopping ecliptic south north direction Therefore values too different will make the observation impossible The range of position angles that will be available for a given target can be visualized with the AOR footprint overlay functionality And the exact angle values can be determined with the Herschel Fo cal Plane overlays Warning e The angle returned by HSpot in the AOR overlays is the roll angle which is counted from north counterclockwise i e also following the position angle convention but to the spacecraft Z axis The input angle Herschel Focal Plane overlay functionality is also the roll angle To get the position angle for the chopper avoidance 90 degrees must be subtracted to the roll angle If a bright source is to be avoided on the chopped position or on the nodded position a range of chopper avoidance angles and only one can be introduced as illustrated in Figure 4 3 The func tionality overlays gt Herschel Focal Plane can be used for this purpose in HSpot selecting the right aperture in configure focal plane 27 Obs
106. s Window Help PACS Time Estimation Instrument and observation overhead s 387 Observatory overhead s Total time s 180 1911 PACS Time Estimator Messages Confusion noise estimation summary Note the predicted confusion noise level is higher than the estimated 1 0 instrument noise level Instrument performance summary servation Requests AORs Band Point Source Point Source Point Source Extended Extended Extended fee instrum Mode Information Duratiz Stat OH E um Flux SIN 1 0 Surface S N 1 0 Density noise Brightness noise O Fac vicc nappes raser ns cid my my Mysi Mv sr 85 130 10 0 2 5 2 10 0 19 5 3 PACS Photometry 0 i Beim Bo ez 53 Es Eos e Unique AOR Labet 422 18 raster 7 3 Time Estimation Breakdown On source time s 1344 Target abell2218 Type Fixed Single Calibration ti Position 16h35m53 99000s 66d13m00 2000s libration time s 32 C New Target Modify Targ Target Number of visible stars for the target 12 Star tracker target Ra 68 975 degrees Dec 66 217 degrees Instrument Settings Blue channel filter selection gt z Source flux estimates and gain settings 60 85 microns band Source Flux Estimates 85 130 microns band Band Et Ex Tm Et Observing Mode Settings um Confusion
107. se level is higher than the estimated 1 0 instrument noise level Band Est 1 0 Est 1 0 Est 1 0 um Confusion Noise Confusion Noise Confusion Noise Level for Level for Level per Pixel Point Sources Extended Sources m my MIyisr 85 130 25 8 0 0445 27 0 130 210 03 0 0006 11 Update Confusion Noise Estimation Confusion Noise Estimator Messages pone Info derived from HSPOT input minOBstime no overheads for filter blue2 64 0 sec dwell time no nodding demanded You may increase the sensitivity for the current filter by setting the RepetitionFactor 2 3 to obtain OBStime repFactor 64 0 PACS Photometer AOT ObsMode Large source raster mode chopping and no nodding Raster points lines 3 7 Step size 5 0 x 52 0 arcsec Map size 220 0 x 417 0 arcsec Map area 91 740 arcsec2 Nod pattern as applicable No nodding C stays at nominal position Dithering information Dithering information is not applicable Duration information AOT duration w overheads 1791 sec AOT duration comprises on sky plus setup and CAL during slew Breakdown of AOT duration e On sky time w overheads 1731 sec e actual on sky time 1344 sec e Setup and CAL during slew w overheads 60 sec e actual calibration time 32 sec Cost of the AOT is calculated as on sky time 180 sec 1731 180 1911 sec Sensitivity information Effective on sky ti
108. source between the left and right part of the array i e the ON and OFF positions and the satellite nodding is used to alternate it between the top and bottom part of the array i e the A and B positions see Figure 4 1 so that the target is always on the array Nod 1 chop A Nod 1 chop B Nod2 chop A Nod 2 chop B nod1 chop A nod1 chop B nod2 chop A nod2 chop B Point source AOT footprint on the sky Figure 4 1 Source positions in point source photometry AOT Sketch showing the source positions as a function of the nod and chopper positions The Y axis is to the left the Z axis to the top Chop positions are defined by the internal chopper while nod positions are defined by the satellite pointing Dithering at each chopper position performed with the internal chopper is not represented Figure 4 1 shows the positions of a point source in this centred chop nod configuration where chop ping and nodding axes are orthogonal Chopper positions A and B are subtracted from one another to suppress the background and deal with possible low frequency drifts differences obtained in nod position 1 and 2 are subtracted from one another to remove remaining telescope contributions The chopper can also be used to perform a small dithering through a pre determined sequence of small offsets along the Y axis with the chopper The same sequence is then applied to the nod off position These four images can be folded on one another to
109. sphere with a larger exit aperture The temperature of the radiator 80K is stabilized within a few mK Chopper In order to discriminate faint signals of celestial sources from orders of magnitude larger thermal background fluxes of the only moderately cooled Herschel telescope 80K differential measure ments are required For this purpose a small tilting mirror the chopper flips alternately on the astro nomical source and on a nearby sky position with a variable throw up to 6 arcmin on the sky for the spectrometer and 3 5 arcmin for the photometer This allows full separation of an object field and a reference field The chopper is also used to alternatively look at the two internal calibration sources ICS which are located at the left and right side of the instrument FOV see Figure 2 3 The chopper is capable of following staircase waveforms with a resolution of 1 and delivers a duty cycle of 90 at chop frequency of 5 Hz The chopper axis is stabilized in its central position by flexular pivots and rotated by a linear motor The chopper design allows a low heat load in the PACS FPU At larger elongations the chopper is used to reflect the beams from the ICSs within the PACS Focal Plane Unit enabling frequent photometric calibration of the detector arrays during the flight 2 3 Photometer 2 3 1 After the intermediate focus provided by the entrance optics the light is split into the long wavelength and short waveleng
110. ster Scan map None selected Point source photometry Observing mode parameters Raster Map Number of raster points perline Number of raster lines Raster point step arcseo Raster line step arcseo Map orientation Orientation angle reference frame Array 1911 ew PACS Photometry Unique AOR Label A2218 raster 7 3 Target abell2218 Type Fixed Single Position 16h35m53 99000s 66d13m00 2000s Modify Tara New Target Target Number of visible stars for the target 12 Star tracker target Ra 68 975 degrees Dec 66 217 degrees Orientation constraint Angle from degrees 0 0 Angle to degrees 260 0 Cancel Instrument Settings Blue channel filter selection a 4 Source flux estimates and gain settings 60 85 microns band Source Flux Estimates 85 130 microns band Observing Mode Settings Repetition factor Repetition 1 To control the absolute sensitivity consider to adjust the number of repetitions Source type and mapping mode settings Set the Observing Modes Doservation Fst Ada Comments Vibe OK Cancer Heb Figure 6 9 Raster map step 3 Observing mode and raster map settings File Edit Targets Observation Tools Images em A D 9x ors Lines Overlays Option
111. ster positions Depending on the raster step sizes the sensitivity may not be homogeneous and will vary across the rastered area the sensitivity usually getting higher towards the centre of the map Note LE HSpot returns the mean sensitivity in the mapped area including the edge effects The sensitivity will be higher in the central area with higher spatial redundancy For rasters with very small step sizes this effect might be significant as the exposure map will have a small flat part in the centre Table 4 3 lists the user inputs required in HSpot Table 4 3 User input parameters for raster map mode Parameter name Signification and comments Filter which of the two filters from the blue channel to use In case observations in the two blue filter bands are required to be performed consecutively two AORs shall be concatenated Number of raster points per line number of raster points along a line raster X axis Number of lines number of lines i e number of raster point along a column raster Y axis raster point step distance between two raster points along a line raster line step distance between two raster lines Orientation constraint A constraint on the orientation in the sky of the raster can be entered by se lecting a range of map orientation angles for the observation to take place The orientation map angle is the angle measured from the equatorial north to the X raster axis long axis of the bolomet
112. t COSMOS Type Fixed Single Total Duration hrs 39 4 Figure 6 18 Scan map step 4 An alternative is to define the scan map in sky coordinates with scan legs oriented north south in equatorial coordinates orientation angle 0 and a cross scan distance of 51 arcsec magic distance that allows a rather homogeneous exposure map in all cases Tutorials of Spectrometer AOT entry The initial choice that you have to make is to decide in which AOT to observe The PACS Line Spectroscopy AOT is designed to detect unresolved lines in high grating sampling density see de tails in Chapter 4 Range Spectroscopy provides a flexible interface to set up custom defined wavelength ranges in two different grating sampling density as well as a predefined mode in which fast full range observation can be performed SED mode The second step is to decide in which Observing Mode you wish to observe This decision has to be based on the source extent Clicking on the Set the Observing Modes button you find three tabs of four choices e Pointed e Pointed with dither 58 Using HSpot to create PACS observations Mapping You should select Pointed mode for point sources Pointed with dither for faint point sources and Mapping to perform an extended coverage by defining a raster map These modes and their opera tional constraints are described in Chapter 4 In this spectroscopy tutorial a simple case of a Line Spectroscopy AOR gene
113. tection of a line source one pointing is sufficient 36 Observing with PACS Pointed with dither This mode is offered to take data for a point like object in a very similar way as in the Pointed observing mode see above In order to improve the spatial sensitivity the spacecraft is commanded to three close positions perpendicular to the chopper direction In such a configuration this observing mode can compensate for image slicer effects especially im portant for faint targets However as a consequence the minimum science time is increased by a factor three the total duration of the AOR is 1100s with respect to only 470s in the pointed mode Note CET When the dither pointed mode is selected the sensitivity returned by HSpot is only for one of the three pointings The sensitivity reached for the whole AOR can thus obtained by dividing the HSpot figure by V3 Mapping This mode allows the observer to set up a raster map observation in combination with chopping nodding or wavelength switching techniques In chop nod mode the map can only be defined in spacecraft coordinates and the map size shall be restricted to 6 arcminutes for clean offset positions with the large chopper throw for each ras ter position The user is therefore advised to build a square raster map to be position angle inde pendent This means to have the same number of raster points and step sizes on the X and Y ax is In wavelength switching mode the ma
114. tector arrays the filter wheel in the short wavelength path selects the second or third grating order Image slicer The image slicer s main function is to transform the 5x5 pixel image at its focal plane into a linear 1x25 pixel entrance slit for the grating spectrometer The slicer assembly consists of 3 set of mir rors e The slicer stack 5 identical spherical field mirrors individually tilted which forms separate pu The PACS instrument 2 4 2 pil images for each slice on the set of 5 capture mirrors The capture mirrors re combine the separate beams into the desired linear image on the set of 5 spherical mirrors at the exit of the slicer assembly The field mirrors at the exit re combine the pupils separated in the slicer into a common virtual pupil The collimators of the spectrometer will later form an anamorphic image of this virtual pupil onto the grating At the same time the field mirror apertures serve as the entrance slit of the grating spectrometer spectrograph _ slit d spectral dimension 16 x 25 pixel detector array Figure 2 6 Integral field spectrometer concept projection of the focal plane onto the detector arrays in spectroscopy mode The image slicer re arranges the 2D field along the entrance slit of the grating spec trograph such that for all spatial elements in the field spectra are observed simultaneously Note the blank space left between the slices to
115. ter map case The reference scan direction is the direction of the first leg Note that the turn around between line does take place as simplistically drawn in the figure Three scan speeds are offered a low speed 10 arcsec per second a medium speed 20 arcsec s and a high speed 60 arcsec s The highest speed default value is envisaged for galactic surveys with a serious degradation of the PSF due to the on board averaging of 4 frames final 10 Hz sampling The slow scan speed shall be used for extragalactic surveys it allows to cover square degree area in about three hours The PSF degradation and smearing due to the scanning should be almost negli gible with the two lowest scan speeds according to simulations It is suggested to perform two scan maps of the same area with orthogonal coverage in order to re move more efficiently the stripping effects of the 1 f noise For this purpose two AORs shall be con catenated in HSpot In the second AOR the map orientation angle is then increased by 90 degrees to get an orthogonal coverage Note Cer As for raster maps the sensitivity returned by HSpot is the mean sensitivity across the scan map j Due to edge effects the sensitivity in the central part of the scan map where the exposure map is flat will be slightly higher For scan maps with small cross scan distances the lower the number of scan legs the higher this effect as the exposure map becomes less homogeneous PACS scan maps can be
116. th channels by a dichroic beam splitter with a transition wavelength of 130 um and is re imaged with different magnification onto the respective Si bolometer arrays The blue channel offering two filters 60 85 um and 85 130 um has a 32x64 pixels arrays while the red channel with a 130 210 um filter has a 16x32 pixels array Both channels cover a field of view of 1 75 x3 5 with full beam sampling in each band The two short wavelength bands are selected by two filters via a filter wheel The field of view is nearly filled by the square pixels however the arrays are made of sub arrays which have a gap of 1 pixel in between The incident infrared radiation is registered by each bolometer pixel by causing a tiny temperature difference Filters The PACS filters in combination with the detectors define the photometric bandpass of the instru ment There are in total 3 bands in the PACS photometer 60 85 um 85 130 um and 130 210 um The transmission of the photometer filters is shown in Figure 3 4 The PACS instrument PACS Filter Schemes ial Md FLRS1 FBRP 2 FLRS2 FBRP 1 Figure 2 4 Overview of the filter arrangements in PACS The selection of the blue photometer filter is done via commanding of the filter wheel 2 2 3 2 Bolometer arrays Figure 2 5 shows a cut out of the 64x32 pixel bolometer array assembly 4x2 monolithic matrices of 16x16 pixels are tiled together to form the short wave focal plane array
117. trometer processing flow diagram ssssse teen seca eeea sean eeueeeee 77 8 Change record o rei be Paadaite koe EE ele ttes nues dif RS Pub PC OEE CREUSE se die 81 References EET 82 Chapter 1 Introduction 1 1 Purpose of document The PACS Observer s manual is intended to support astronomers to in the definition of their obser vations with the PACS instrument The purpose of this document is to provide relevant information about the PACS instrument on board Herschel Space Observatory The information is mainly tar geted to be a general overview of the instrument and its performance in order to help the astro nomer to plan prepare and execute scientific observations with PACS The structure of this observ er s manual is as follows we first describe the instrument Chapter 2 and its scientific capabilities Chapter 3 followed by the available astronomical observation templates AOTs Chapter 4 The calibration scheme and products are presented in Chapter 5 A cookbook for entering observations with HSPOT is given in Chapter 6 and the manual ends with a description of the pipeline Chapter 7 This initial version is written to support the first call for Herschel observing proposals by the European Space Agency ESA in February 2007 1 2 Background The Herschel Space Observatory is an ESA cornerstone mission for high spatial resolution observa tions in the FIR and sub millimeter regime to be launched in 2008 abo
118. tures but since not all of the actual filters could be measured we as sume their ambient temperature performance as a good and somewhat conservative estimate The filter transmission curves for the three photometer bands are plotted in Figure 3 4 0 7 07 07 e 1 0 6 o o 1 o in 0 5 o rs i 0 4 e io 1 0 3 o io 1 0 2 Filter transmission Filter transmission Filter transmission e 0 1 0 14 04 0 0 50 6 amp 0 70 80 90 100 M0 70 80 90 100 0 120 130 140 100 120 140 160 180 200 220 240 260 Wavelength um Wavelength um Wavelength um Figure 3 4 Filter transmissions of the PACS filter chains The graph represents the overall transmission of the combined filters in each of the three bands of the photometer The vertical lines mark the nominal band edges 3 4 3 Photometer bad pixels The flight model bolometer blue array displays about 2 of dead pixels or very low responsivity pixels including one row of 16 pixels as can be seen on Figure 3 5 and Figure 3 6 in the upper right matrix 14 Scientific capabilities Figure 3 5 FM blue array with low illumination Figure 3 6 FM blue array with high illumination 3 4 4 Photometer sensitivity The photometer sensitivity is driven by the foreground thermal noise emission mostly from the tele scope and the electrical noise of the readout electronics The estimated background noise fr
119. um range of 15 degrees to avoid too much constraints on mission plan ning Note LE Setting up a chopper avoidance angle requires an additional constraint on mission planning there fore this parameter should have to be used only for observations where it is absolutely necessary Up to 10 up down scans can be performed per nod position for different lines and or repeating a given line several times allowing to cover some lines to different depths The PACS focal plane chopper is moved between the on target and the off positions during the scan s Then the whole se quence of spectral line scans is repeated in the nod position In total one half of the science time is spent on source The absolute sensitivity is controlled by dedicating a larger amount of time to a given observation i e by repeating the nodding cycle AB or ABBA more times In order to take advantage of the best spectrometer sensitivity a ramp length of 64 readouts 1 4sec ramps has been selected two ramps per chopper plateau are foreseen and one chopper cycle per grating position 4 2 1 2 Line scan in wavelength switching mode The observer could consider the wavelength switching mode as an alternative to the chopping nod ding mode if by chopping to a maximum of 6 arcminutes the field of view is not placed in an emis sion free area for instance in crowded area Wavelength switching shall also be considered for very bright objects typically solar system objects
120. umber of parallel line legs in the scan map the maximum 1500 but there is additional limit of 4 degrees for the with of the scan map i e the total cross scan distance Repetition factor number of times to repeat the scan map to adjust the absolute sensitivity maximum 100 Source flux estimates Optional point source flux density in mJy or surface brightness in MJy sr for each band It is used for signal to noise calculations and to adjust the ADC to low gain if the flux in one of the two channel is above the ADC saturation threshold increasing the dynamical range by a factor 4 See Sec tion 4 1 1 for more details 35 Observing with PACS 4 2 PACS spectrometer AOTs 4 2 1 Two different observation schemes are offered with the PACS spectrometer line and range spectro scopy line spectroscopy mode A limited number of relatively narrow emission absorption lines can be observed for either a single spectroscopic FOV 0 78 x 0 78 or for a larger map Back ground subtraction is achieved either through standard chopping nodding for faint compact sources or through wavelength switching techniques for line measurement of the grating mech anism of bright extended sources range spectroscopy mode This is a more flexible and extended version of the line spectro scopy mode where a freely defined wavelength range is scanned by stepping through the relev ant angles of the grating synchronized
121. uy1eddoq Say ED Figure 7 5 photometer pipeline data processing level 1 1 Ceo aS g lt zo e 7 3 H amp 3 a 121 z o ge Le y lt Figure 7 6 photometer pipeline data processing level 1 2 Ta Pipeline description and data product expectations 7 2 PACS spectrometry standard data pro cessing 7 2 1 PACS spectrometry processing steps 7 2 2 10 11 12 13 14 15 16 Raw telemetry data is decompressed and stored as science rotating raw ramps of 3 pixels and averaged ramps stored in Ramps objects and housekeeping data Bad saturated glitched pixels are flagged and corrected if possible The corrected science data are reduced to signals volt sec stored in Frames objects Major observation blocks like e g nod positions grating scan directions are summarized The chopper plateaux are cleaned from transition values and the chopper angle is converted to an the angle on the sky gt Spacecraft pointing is associated to each signal frame Wavelength is calibrated and associated to each pixel Signal glitches are searched and corrected The background is subtracted at the same grating positions Signals of nodding position are averaged at the same grating positions Signals are divided by the relative spectral response function The flux is calibrated using differential calibration source measurements to populate absolute response arrays W V s The sign
122. wavelength range The present telescope design allows a wavefront error of 6um r m s The type of error is not known we have assumed spherical aberration for the analysis The main effect on the point spread function PSF is a transfer of power from the central peak to larger radii while the width of the central peak is not affected much The power concentrated in the central peak delimited by the first zero of the ideal telescope PSF as a function of wavelength is shown in Figure 3 1 It enters into the sensitivity calculation as telescope efficiency because for weak confused sources only the power in the cent ral peak will be detected OS T T Ne 65 0 6 0 x 1 L 1 L L L 60 80 100 120 140 160 180 200 wavelength Lum Figure 3 1 Telescope efficiencies defined as the fraction of power encircled within the central peak of the telescope PSF as a function of wavelength 3 2 Chopper Errors jitter in the chopper throw would spread out the power from the central peak The chopper accuracy of 1 arcsec on the sky is well within specifications With beam widths of over 6 arcsec the effect of pointing errors introduced by the chopper is negligible as the power will end up on the same array pixels that receive the power in the central peak in the ideal case The duty cycle is better 90 i e more than 90 of the observing time can be used for integration 12 Scientific capabilities at chopper frequencies up
123. with filter A green second order with filter B red first or der line RMS PACS SED range scan 4 210 3 510 2 8 10 24 107 RMS W m2 14107 7 010 TT 0 0 Lucca boa aca doa a ca dba a a d a a a d a a a d a a al 60 80 100 120 140 160 180 200 Wavelength um Figure 3 14 Spectrometer point source line sensitivity in SED mode range spectroscopy AOT for both range repetition and nodding repetition factors equal to one Blue third grating order filter A green second order filter B red first order 22 Chapter 4 Observing with PACS Either the photometer or the spectrometer will be used during dedicated Observation Days OD of 21 hours The reason for this is to allow uninterrupted observations with the photometer to optimize the time spent on recycling the photometer cooler which takes about 2 hours during the Daily Tele communication Period DTCP of 3 hours per day As the hold time of the cooler will probably be more than 48 hours the photometer might even be used for two consecutive ODs The Herschel observations are organized around standardized observing procedures called AOTs for Astronomical Observation Template Three different AOTs have been defined and implemen ted to perform astronomical observations with PACS one generic for photometry mapping and two for the spectrometer 1 Photometer observations 2 Line s spectroscopy observations 3 Range s spectroscopy
124. xel size arcsec 3 2 6 4 FOV arcmin 3 5 x 1 75 FWHM arcsec 5 2 7 7 12 ee ELL s BE D Figure 3 2 Snapshot a QLA screen during FM ILT testing where an external blackbody is seen through a 4mn aperture simulating a source much more extended than a point source Top red array bottom blue array m sine Scientific capabilities E i See ENE IENE eee amus 78H iam LE Figure 3 3 Simulation of point source observation showing the distribution of the flux as a function of position taking into account the insensitive part of the focal plane In this example the source is at the geometrical centre of the array which is not a particularly smart choice This a logarithmic display of the intensity falling on the detector dynamic range display is 10 no noise or instrument physics apart from the geometrical optical ones is included Note that with the source at the centre of the focal plane only 18 6 of its flux falls on the sensitive parts of the detector 3 4 2 Photometer filters The transmission of the filter chain in each of the instrument channels has been calculated from measurements of the individual filters All filters have been measured at room temperature some filters or samples taken from the same filter sheet as used for the flight filter have also been meas ured in a contact gas cryostat near Helium temperature Generally filters show a small gain in trans mission at cryogenic tempera

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