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ISAAC User Manual

1. Not Guiding Readout Mode Double Cor Autoguider Sidereal time SETUP STOP MORE CANCEL SETUP DATA CANCEL Rotator on sky 0 00 4 Comments Z ActionLog w Disk Space w Exposure History SETUP finished 0 12 sec RTDDRAW command received SETUP function OCS RTD DRAW ST F RTDDRAW finished v SETUP START CANCEL Figure 5 OS Graphical User Interface Left panel instrument control Middle panel detector control Right panel telescope control 5 2 The Real Time Display RTD The Real Time Display is central to observing with ISAAC Like a video camera every frame taken by the detector is continuously displayed on the RTD It is important to realize that the continuous display of images on the RTD is not related to saving the data to disk An image is stored to disk only if the adequate action is taken to do so i e when a Start Exposure is sent This is what the templates do The RTD provides a number of tools for measuring statistics measuring the position and FWHM of objects in the field and for storing an image to be subtracted from incoming images This latter tool is referred to as store a fixed pattern and is very frequently used during acquisition quality control etc ter of slit TOSLIT Store FIXPAT FIXPAT On Off SW Rapid Frame
2. A 11 6 ISAACLW_spec_obs_GenericOffset This template works in an identical manner to ISAACSW_spec_obs GenericOffset Please refer to Sec for a description of what the template does This mode is available for MR spectroscopy only A 11 7 ISAACLW img cal GenericOffset This template is used for standard star observations in imaging It should only be used to calibrate observations that were taken with the Aladdin templates that do not use chopping The template is very similar to ISAACLW_img_obs_GenericOffset with the difference that the offsets are defined in detector coordinates Table 57 Parameters of ISAACLW_spec_obs_GenericOffset P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of sub integrations Number of Exposures SEQ NEXPO Number of exposures Return to Origin SEQ RETURN Return to Origin flag X offset list arcsec Y offset list arcsec Obs Type 0 or S SEQ OFFSETX LIST SEQ OFFSETY LIST SEQ OBSTYPE LIST X offset list arcsec Y offset list arcsec List of observation types S or O Instrument Mode Slit Central Wavelength microns INS MODE INS SLIT INS GRAT WLEN Instrument Mode Long Slit Central Wavelength microns Table 58 Parameters of ISAACLW_img_cal_GenericOffset P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of DITs Number of
3. e e 84 89 89 89 89 91 List of Figures 1 ISAAC Optical Layout 3 A 5 3 Atmospheric and Filter Transmission curves SW 17 4 Atmospheric and Filter Transmission curves LW 18 Ce DRAG E ERE A amp ee ee Ss oe Ee 21 v aoe He ae oe ee ee A e 22 7 Orientation conventions e 45 Putus Kex do UN AUR S AAA o Ros doe UE ad 48 MITIS 54 10 Illustration of the ISAACSW img obs AutoJitterOffset template 57 11 Illustration of the ISAACSW img obs FixedSkyOffset template 59 12 Illustration of the ISAACSW img obs_GenericOffset template 60 13 Illustration of the ISAACSW_img_obs_GenericOffset template 61 sad aaa 64 15 Illustration of the ISAACSW_spec_obs_AutoNodOnSlit template 66 16 Illustration of the ISAACSW_spec_obs_GenericOffset template 68 17 Chopping and Nodding 00 es 75 18 Filter curves for spectroscopic Dier 84 19 Filter curves for BB e 85 20 Filter curves NB filters 2 86 21 Filter curves NB filters ww voce o Roxy coeur non USA I ee X Kos RI Ee E 87 22 Filter curves NB filters 0 a 88 List of Tables A II 4 Me an ios e RM A het Ea Gay oy SAGE eaten ae ev Gath ne a 9 PLUIE TII 9 SE Te E DLP IPS 10 5 ISAAC SITES Fy Ob ee ROO a oy v OY P RC Tec RR roe e a 10 TT 10 n AI ee ee ee TA 10 LETT 11 9 ISAAC detectors 5 oop s sos Se RR UR m ox UE OR uo
4. Figure 6 Real Time Display 5 3 Target Acquisition 5 3 1 Imaging The pointing accuracy of the VLT is very good and usually a blind preset to the field is suffi cient in imaging the templates for the Hawaii and Aladdin arms are ISAACSW img acq Preset and ISAACLW img acq Preset respectively If users would like a finer pointing so as to position an object in a particular region of the detector they should use ISAACSW img acq MoveToPixel for the Hawaii arm and ISAACLW img acq MoveToPixel if chopping or ISAACLW img acq MoveToPixNoChop non chopping for the Aladdin arm These templates provide interactive tools such as arrows to define telescope offsets see figure 6 Use of the finer pointing acquisition templates should be accompanied by precise instructions in the Phase II README file Observers in service mode shall provide together with their OBs all necessary infor mation regarding the centering of the field if they have special requirements 5 3 2 SW Spectroscopy Blind centering of objects in the slits based on coordinates is not supported Neither the pointing accuracy of the telescope nor the coordinate accuracy of most targets would guarantee that the objects go straight into the slit It is mandatory to use the ISAACSW img acq MoveToS1lit or ISAACSW img acq MoveToSlitrrm acquisition template in all SW spectroscopic program OBs and to use the same slit in both the acquisition and observing templates This tem
5. However if large telescope offsets are used the guide star changes The telescope will not resume guiding automatically and the operator will be prompted to resume guiding More importantly after changing guide stars the telescope may not come back to precisely the same position This is a potential problem when doing spectroscopy of extended objects This particular problem will be dealt with by the operator during such observations by ensuring that the same guide stars are used when the telescope returns back to the object Flexures and tracking stability The flexure of ISAAC at the detector plane is very small around 0 5 pixel over a full instrument rotation In most circumstances the image stability of both tele scope and instrument is so good that there is usually no need to reacquire the target during long integrations up to two hours in spectroscopy This is not the case when crossing the meridian near Zenith and it is advised not to schedule trans meridian observations on fields with Zenith distances lower than 10 For such fields it is advised to do e g standard star observations during the 15 minutes surrounding the transit 5 Observing with ISAAC 5 1 Observation Software OS is the high level software controlling the instrument It has its own GUI which allows one to access all instrument parameters Figure 5 shows the ISAAC OS GUI The users only use templates to control the instrument and therefore have no dire
6. 3 5 Influence of the Moon The Moon is usually not a problem in the IR In Broad Band SW and LW imaging most of SW Narrow Band imaging LW Narrow Band imaging SWS LR spectroscopy LWS LR and LWS MR spectroscopy moonlight does not significantly affect the background There is therefore no point in requesting grey or dark time for programs that involve these modes However the moonlight contributes to the sky background when observing between the OH lines in J and H i e NB imaging in J in the low background NB filters NB 1 06 NB 1 19 and SWS MR spectroscopy in J and H Measurements done during an eclipse of the Moon showed that at more than 70 from the Moon the sky background remains approximately constant regardless of the phase Typically when ultimate performances are sought in MR spectroscopy below 2 0 um it is advisable to constrain the distance to the Moon to be above 50 70 while the Fractional Lunar Illumination can remain relatively unconstrained lt 0 7 a eM e a7 _ d G Im K n L A Ke 7 T To fx E 2 C e D 2 e e T a E c o n e o Y c x KI AM Ki A E E E t lt Kei lt Ke E E 2 LP o n 5 amp 5 S H o o o o gt gt qm jm o je o 4d E o CU A Lis Li Li Libido L SO o L co g so o UDJSSIUSUDJ UOSEILUEU DA JOISSILUSUDA UDISS WSUD Figure 3 Atmospheric Transmission spectrum in the SW region Most of the SW filter
7. ISAACSW img acq MoveToSlit ISAACSW spec obs AutoNodOnSlit 300 seconds 1 6 1 T ISAACSW spec cal NightCalib T F Execution time minutes Preset Instrument setup int time detector overhead Telescope offsets Flat field Total 10 0 2 0 5 0 13 x 1 NDIT x 12 6 AB cycles 0 25 x 8 8 offsets for 6 cycles 4 79 5 minutes for 60 minutes of integration Table 20 Overheads Example 5 LW Imaging with chopping L band Template parameters Acquisition Template Observation Template Integration time minutes ISAACLW img acq Preset ISAACLW img obs AutoChopNod 60 Execution time minutes Preset Instrument setup Integration time Global overheads Total 6 0 0 5 60 40 x 60 90 5 minutes for 60 minutes of integration Table 21 Overheads Example 6 LW Spectroscopy with chopping Template parameters Acquisition Template Observation Template Integration time minutes ISAACLW img acq MoveToSlit ISAACLW spec obs AutoChopNod 60 Execution time minutes Preset Instrument setup Integration time Global overheads Total 10 0 2 0 60 30 x 60 90 minutes for 60 minutes of integration Table 22 Overheads Example 7 LW Spectroscopy without chopping Template parameters Acquisition Template ISAACLW img acq MoveToSlitNoChop Observation Template ISAACLW spec obs AutoNodUnSlit DIT 0 4 seco
8. Spectroscopy with chopping and nodding ISAACLW spec obs AutoChopNod MR spectroscopy without chopping ISAACLW spec obs AutoNodOnSlit ISAACLW_spec_obs_GenericOffset Standard Stars Standard Star imaging with chopping ISAACLW img cal AutoChopNod Standard Star imaging without chopping ISAACLW img cal GenericOffset ISAACLW spec cal AutoChopNod Standard Star spectroscopy with chopping Standard Star spectroscopy without chopping ISAACLW spec cal AutoNodOnSlit ISAACLW spec cal GenericOffset Spectroscopic Night Time Calibration Night time flat fields and or arcs ISAACLW spec cal NightCalib The allowed imaging acquisition templates for subsequent science observations have changed since P70 The simple preset ISAACLW img acq Preset can be used for any subse quent imaging observation The chopping preset ISAACLW img acq MoveToPixel can only be used for subsequent imaging observations with chopping and the non chopping preset ISAACLW img acq MoveToPixNoChop can only be used for subsequent imaging observations without chopping Table 14 Hawaii Templates cookbook Action Template s to use Acquisition Simple telescope preset same for RRM ISAACSW img acq Preset ISAACSW img acq Presetrrm Preset telescope and center field ISAACSW img acq MoveToPixel Preset telescope and center object s in slit spectrosc
9. Table 11 Minimum DIT for the Rockwell and Aladdin Arrays Detector Readout Mode Minimum DIT s Hawaii SW DCR and NDR 1 77 3 55 Aladdin LW DCR LB 0 3447 Aladdin LW DCR HB 0 2771 Aladdin LW UCR 0 1073 For NB 3 21 amp NB_3 28 non chopping observations with this mode the minimum DIT is 0 3447s 3 Observing in the NIR 3 1 Atmospheric Transmission The transmission of the Earth s atmosphere from 0 8 to 5 1 jum is shown in Figures 3 and and overplotted are the transmission curves of most of the filters available in ISAAC The J H K L and M bands correspond to the main transmission windows All bands particularly J L and M are also affected by atmospheric absorption within the band The amount of telluric absorption varies with zenith distance and the amount of precipitable water vapor PWV 3 2 Background Emission There are two regimes in the sky background emission Below 2 2 um the sky emission is domi nated by OH emission taking place at an altitude of 80 km Detailed sky spectra with OH line identifications are available on the ISAAC web page http www eso org instruments isaac Beyond 2 Zum the thermal background dominates The thermal background consists of atmospheric and telescope emission An overall telescope emissivity of 17 has been recently measured Between the OH lines in J and H the background is very low and has been measured to be 0 1 to 0 15 e s during dark condi
10. leen O 5 4 2 SW Spectroscopy sosoo ee 5 4 8 LW Imaging and Spectroscopy rn EG ehh ee at ek OA Ee das Be 5 6 Chopping 5 Calibration Plans oea ics a feos e ee EE Re E oe ew POS vex 5 8 Pipelines 6 Template cookbook and overhead calculations 6 1 Templates General description and summary 2l 6 2 Overheads 13 13 13 13 14 16 19 19 19 21 21 21 22 22 22 24 24 24 24 25 25 25 26 27 27 7 Short Wavelength Imaging Hawaii SWI1 amp Aladdin LAND 36 1 Characteristics x s ye aa woe we Bow a aera diar DOE x Rcx N T Bean ee a a 36 1 2 Recommended DITs and NDITS eR 36 A eee Pas Ges che ee ey de sh chs hcg Ce ah wear eee oe 36 BE Me ese eek AS Bh ee a ee ee ee ee ee eek d 37 A E oy Anne ede eho a oe Od ee a Bae eee a 37 8 Long Wavelength Imaging LWI3 and LWIA 38 8 1 Characteristics 38 8 2 Recommended DITs and ND 38 MTM Tuc 38 La ed ak A ee ee A a RO a 38 Moe ok o a dr ee ee ee A Ba E 38 9 Short Wavelength Spectroscopy 1 SWS1 39 9 1 Characteristics RR Rss 39 9 2 Recommended DITs and ND 39 Rute mune RP RN EUR ETEeDIEMM EE EE m E 40 CV 40 e a e da e dais Se Gh es a Gee Get 40 10 Long Wavelength Spectroscopy 3 LWS3 41 10 1 Characteristic 4 llle 41 10 2 Recommended DITs and NDITS A 41 AA AR ae eee eh eh Ae a be 41 SCC A A AA a A A 42 abria a e a aaa e rae ay tees Sean Gt ee a Gey Get a 42 11 Short Wavelength
11. 109 1 044 1 009 1001 LA 1 009 1093 1050 11460 1 0 1000 tow 1 109 Lie Yare ere h Gen Waselengih um NB 1 19 NB 121 12 LE 10 10 o 08 oe 08 94 Di Lr 02 o oo Az 05 1 18 ite 139 jae IB 140 18 134 Varelergih an Parelengih Qum NB 1 28 NH 1 28 12 12 10 10 es os oe os o4 Di oz nz D oo E 08 15 1 148 13 1 1 136 1 Nwvalargth arm Varelengih um NB 1 84 NA 1 71 n4 no Eo 4 Ecog 4 zog gt l e E E o e E 3 Lae ne pn 1 70 me Vovelergsn om Wawelengih Qum Figure 20 Narrow band filter curves NB 2 07 12 10 E cs py Sg 201 em Sp 208 zw 210 ew 27 Yare e reh een NB 2 13 12 19 E 2 E Y 208 210 212 ei 210 Sg 220 Navelergih arm NB 2 19 12 10 G S de x 2128 an e 218 330 8 an tas Wavelength arm NB 2 29 14 10 E a A ki y zm um tm om zw 228 em Yara reh Ger 10 Di 00 Ki m 20 m sm vo zio E 214 216 Waselengih ue Na 217 LE 10 08 08 t oz oo 02 210 212 2 14 216 aia am 428 ea Terrier Qum ns Di D g B E ad E B a L 218 240 an 23M 1236 gw 23 am Wavelength Gum NH 234 os og n4 ng oo 2 E e L 225 zx ES em Sa om Waselengih Gum Figure 21 Narrow band filter curves Toremasion Taenia as os 04 o 212 214 as os o2 4 55 216 B321 5 EJ E 218 22 22 224 326 328 ss rasiert microns ilter NB_3 80 transmission curve T m
12. for Phase II Preparation Note calibration templates dealing with darks flats and arcs are not available in the ISAAC In strument Package for P2PP All the required calibrations are executed by the Operation Staff at the end of the night according to the setups that were used during the night The only calibra tions that can be taken at night if desired are spectroscopic flat fields and arcs taken with the ISAACSW spec cal NightCalib or ISAACLW spec cal NightCalib templates see Section 5 5 6 2 Overheads Since Period 65 overheads are charged to the users Special care should therefore be taken when estimating the overheads The execution time report produced by P2PP computes the overheads according to the rules given in this manual Users especially those in service mode should check it to make sure that the overheads have been taken into account Preset operations The overhead for preset and acquisition depends on the template as shown in Table 15 These times include the telescope preset closing the active optics loop and acquiring the target if necessary Hawaii overheads During the execution of an Observation Template most of the overheads come from frequent telescope offsets inherent to IR observations One should allow for approximately 15 seconds of time for the telescope to offset a few arcseconds and for the next exposure to start A strict minimum of 1 minute per telescope position including overheads is mandato
13. AutoJitter ffset This template moves the telescope alternatively between object and sky positions The object positions of the telescope are randomly distributed around the object initial telescope position and within a box whose dimensions are set by the parameter Jitter Box Width in arcsec The minimum value for this parameter is 10 arcsec The sky positions are at a constant distance defined by the parameter Sky Offset Throw from the original telescope position but at an angle randomly distributed between 0 and 360 degrees i e the sky exposures are distributed on a circle surrounding the initial telescope position Table 34 Parameters of ISAACSW img obs AutoJitter ffset P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs Jitter Box Width SEQ JITTER WIDTH Random offset box width arcsec Return to Origin SEQ RETURN T Return to Origin Sky Offset Throw SEQ SKYTHROW Sky Throw arcsec Rotate Pupil SEQ ROTPUPIL T Pupil rotation compensation Number of AB or BA cycles SEQ NABCYCLES Number of AB or BA cycles NDIT for the OBJECT positions SEQ NDIT OBJECT NDIT used on OBJECT positions NDIT for the SKY positions SEQ NDIT SKY NDIT used on SKY positions SW Filter wheel 1 INS FILT1 NAME i Filter name in wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter name in wheel 2 Figure illustrates what the template does By default there is no tel
14. Guide 9 5 Performance The user should refer to the ETC for estimating the performance of this mode NTT and VLT Instrument Exposure Time Calculators 10 Long Wavelength Spectroscopy 3 LWS3 10 1 Characteristics See Section 2 3 for a description of the mode Chopping is essential for LR observations and can be used for all observations For more information about chopping see Section 5 6 The chopping templates produce a data cube for each nod position which contains the two half cycle frames For MR observations non chopping observations can also be taken 10 2 Recommended DITs and NDITs For observations that use chopping DIT and NDIT are not parameters they are automatically set in the templates based on the instrument mode in use For non chopping observations the optimal DIT values are between 0 35 and 5 seconds NDIT should be set so that the total exposure at any one position is between one and a few minutes Users should note that some spectral regions in the M band will saturate the detector with the minimum integration time More detailed information is provided on the ISAAC web page 10 3 Calibration Plan For the LR grating only two grating settings that correspond to 3 55 and 4 75 um are supported Users should not use any other central wavelength in LR mode In LR mode telluric standards spectroscopic flats and arcs will only be taken at the supported wavelengths A variety of calibration frames will
15. IIS PAY ANANSI PAPAS LALALINS PASS SASS NS SA SASS PAPAS S ALAS ANANSI APAPALALAYS ANANSI SANA SA SASS ASS SS PALPAALAALAYYS PASSA SSNS NSS SSNS SS PAALAAALYYYS PASSA SSS NSS SS SNA SNS SNS SANS SA SA SS SA A SSS OS PSA SA SSNS NSS SASS SSSA SNS SA SASS Sd AS IPSAS PASSA SSS NS SSSA SSNS SANS SA SA SS Sd A SSS OS PASSA SSNS NSS SANS SSSA SANS SA SASS Sd AS IPSAS PASSA SSNS NSS SSNS SNS SNS SANS SA SA SS SA ASS PSPS SSP NS SSNS NISSAN SS SA SS SA A SANS SE PASSA SSS NS SSNS SNS SNS SANS SA SA SS Sd A SSS OS x PAS SSS IN IN INES PAAAAALAYLYYAS x ge x 1 un 7 aD Figure 17 Combination of chopping and nodding in the opposite direction On the left is a schematic of a chopped image so called position A with one star image positive in white and one star image negative in black The chop throw is assumed here to be smaller than the field size In the central figure the telescope has been nodded to the B position in the opposite direction of the chop There are background residuals on both A and B chopped images Subtracting the B from A right image provides an image free of background residuals with a central positive image twice as bright as the 2 negative images For observations that use chopping the bias voltage of the array is set so that the well depth is large This leads to a very large number of hot pixels whose flux is changing on the timescale of a few seconds Thus it is very important in long exposures to set Jitter Box W
16. MoveToPixel 7 ISAACSW img acq Polarimetry 7 ISAACLW img acq MoveToPixNoChop G ISAACLW img acq MoveToPixel if ISAACSW img acq MoveToSlit 10 ISAACSW img acq MoveToSlitrrm 10 ISAACLW img acq MoveToSlitNoChop 10 ISAACLW img acq MoveToSlit 10 Both Instrument Setup Spectroscopy 2 Average Both Instrument Setup Imaging 0 5 Average Both Instrument Setup per additional 1 Average after the 1st template in the same OB Both Telescope Offset 0 25 Average Hw imaging Detector readout per DIT 0 04 0 07 Approximately Al nochop imaging Detector readout per DIT Negligible Hw spectroscopy Detector readout per DIT 0 07 0 13 Approximately Al nochop spectroscopy Detector readout per DIT Negligible Al LW Imaging with chopping 40 Al LW Spectroscopy with chopping 30 Both Night time flat 4 For one on off pair Both Night time arc 3 For one on off pair T Depends on read speed see text 7 Global overheads in percent should be used for LW chopping observations Table 16 Overheads Example 1 SW Imaging with the Hawaii Template parameters Acquisition Template Observation Template DIT NDIT Number of Exposures ISAACSW_img_acq_Preset ISAACSW img obs AutoJitter 10 seconds 10 36 Execution time minutes Preset Instrument setup int time detector overhead Telescope offsets Total 6 0 0 5 0 167 0 07 x 10 NDIT x 36 0 25 x 36 101 minutes for 60 minutes of integration Table 17 Overhe
17. Number of sub integrations Number of Exposures SEQ NEXPO B Number of exposures Jitter Box Width SEQ JITTER WIDTH Random offset box size arcsec Return to Origin SEQ RETURN T Return to Origin Filter name in wheel 1 Filter name in wheel 2 LW Filter wheel 1 INS FILT3 NAME LW Filter wheel 2 INS FILT4 NAME A 11 2 ISAACLW img obs AutoJitter0ffset This template works in an identical manner to ISAACSW img obs AutoJitterOffset Please refer to Sec for a description of what the template does This mode is available for imaging with the J Block H amp Ks broadband filters and 3 21 and 3 28 narrow band filters only Table 53 Parameters of ISAACLW img obs AutoJitterUOffset P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs Jitter Box Width SEQ JITTER WIDTH Random offset box width arcsec Return to Origin SEQ RETURN T Return to Origin Sky Offset Throw SEQ SKYTHROW Sky Throw arcsec Rotate Pupil SEQ ROTPUPIL T Pupil rotation compensation Number of AB or BA cycles SEQ NABCYCLES Number of AB or BA cycles NDIT for the OBJECT positions SEQ NDIT OBJECT NDIT used on OBJECT positions NDIT for the SKY positions SEQ NDIT SKY NDIT used on SKY positions LW Filter wheel 1 INS FILT3 NAME Filter name in wheel 1 LW Filter wheel 2 INS FILT4 NAME Filter name in wheel 2 A 11 3 ISAACLW img obs FixedSkyOffset This template works in an identical manner to ISAACSW img
18. The nodding frequency is also automatically defined in the templates to give optimum performance for each instrument mode e The detector acquisition system is synchronized in a transparent way with the M2 chopping e One chop cycle corresponds to one ON OFF cycle i e one period of the M2 chopping motion Only the acquisition frame is saved on disk as the subtracted ON OFF image Several chop cycles can be averaged by the pre processor to deliver only one image This is referred to as the Number of chop cycles in the template parameters and applies only to acquisition templates For the observing templates this parameter is automatically set e LW chopping data From P69 onwards we have delivered the two half cycle frames for each chopped image ie an ON frame and an OFF frame both averaged over the number of chop cycles These data are stored in a cube There is one cube containing these two half cycle frames for each chopped image This change is transparent at the template level for the user The pipeline has been updated accordingly The subtracted image ON OFF image can still be displayed on the RTD but is not saved on disk Storing the half cycle frames allows checking of the sky background levels to operate the detector at the optimum level ranges and easier application of the non linearity corrections during data reduction The format of the data issued from non chopping templates are un changed e DIT and NDIT are not para
19. and not with telescope presets In general acquisition templates dump an image to disk only the ISAACSW img acq Preset template does not These dumped images are aimed at keeping track of the field position and orientation before starting the observation All Hawaii acquisition templates use the SWI1 mode See also sections 7 and 9 for more information on target acquisition and on the Hawaii imaging and spectroscopic modes In general it is not necessary for the acquisition and the subsequent observation templates to have the same DIT and NDIT However not doing so may lead to unnecessary overhead A 6 2 ISAACSW_img acq Preset This template does a simple telescope preset It is the easiest template to use when objects can be easily identified against the sky background An identical version for RRM observations is available see Section A 6 3 It should NOT be used for subsequent spectroscopic observations and it should not be used if the user wants a pointing accuracy that is better than few arcsec The instrument parameters can be set to values used in the subsequent imaging template so that the instrument will be already set at the start of this template This will save time Table 27 describes the parameters of this template Table 27 Parameters of ISAACSW img acq Preset P2PP label Keyword Default Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT i Number of DITS Add Velocity A
20. each OB This is for the following reason the acquisition is always done at the same position on the array i e center of the slit Therefore different executions of the same template will position the targets at the same positions along the slit and the spectra will fall at the same positions along on the detector Therefore even if you define some non zero value for the Jitter Box Width parameter it is recommended to give the Nod Throw Along Slit parameter different values between OBs so as to get the spectra at different positions across the array When defining the nod throw users are requested to ensure that other objects in the slit do not cause the spectra to overlap when the throw is executed The total number of frames correspond to the product Number of AB or BA cycles x NINT x 2 The total integration time excluding overheads is defined in seconds by DIT x NDIT x NINT x 2 x Number of AB or BA cycles A 8 2 ISAACSW spec obs GenericOffset This template is for spectroscopy and has the flexibility to allow any sequence of telescope offsets It is essentially intended for programs requiring large offsets off the slit or slit scanning across one object Table 40 Parameters of ISAACSW spec obs GenericOffset P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of sub integrations Number of Exposures SEQ NEXPO Number of exposures Return to Origi
21. enters the entrance window on the left hand side of the figure the slit is then out of the beam The Telescope Focal Plane is 80 mm behind the entrance window The Mode Selector Mirror M1 directs the light to the collimator and the collimated beam is sent to the M7 mirror which selects between the Hawaii SW and Aladdin mostly LW but also JHK imaging arms The collimated beam is then imaged onto the detector by the objective in place on the Hawaii or Aladdin arm There are two filter wheels just in front of the objective wheels In spectroscopy M1 is retracted and light is diverted by M2 onto the 3 mirror collimator M3 M4 and M5 Light then reaches the grating in Littrow mode and is reflected back to M6 via the 3 mirror collimator An intermediate spectrum is formed on M6 which is conjugated with the slit plane The rest of the optical path is identical to the imaging path 2 2 Imaging Modes The characteristics of the imaging modes are summarized in table I and they are described in greater detail in Sections 7 and Table 1 ISAAC Imaging Modes Mode Array Spectral Range Pixel Scale Maximum Field Of View Detector Size arcsec arcsec pixels SWT Hawai 0 98 2 5 um 0 1484 152 x 152 1024 x 1024 LWI3 Aladdin 1 1 5 1 pm 0 1478 151 x 151 1024 x 1024 LWI4 Aladdin 3 0 5 1 um 0 0709 73 x 73 1024 x 1024 1 TWI3 is used for J Block H Ks NB 3 21 and NB 3 28 imaging without chopping and for acquisition of LW spec
22. hot stars spectral type B4 or earlier or solar type stars spectral types GOV to G4V These calibrations are taken so that telluric features can be removed from science spectra They can also be used for flux calibration with a relative accuracy of 5 10 and an absolute accuracy of 5 20 A detailed discussion on this topic is given in Sec Should users need more accurate results or require telluric standards of a particular spectral type they should provide the corresponding OBs and detailed instructions The spectro scopic standard star templates e g _cal_ must be used to prepare these OBs In this case the time executing the OBs will be charged to the user and the observatory will not observe a separate telluric standard e Spectroscopic Flats Flats corresponding to the set ups used during the night are taken by the operation staff the next day e Detector darks Darks are taken at the end of each night with the DIT values used during the night e The necessary arcs are taken by the operation staff the next day e Star traces These calibration frames are aimed at tracing spectra at different positions along the slit and providing the co ordinate transformation between imaging and spectroscopy They are archived for both the LR and MR modes 9 4 Pipeline The AutoNodOnS1it templates are supported by the pipeline The GenericOffset templates are not supported by the pipeline Further details are given in the ISAAC Data Reduction
23. it is positive from North to East Note that the opposite is true for FORS1 The slits are oriented along detector columns y axis on the figures In fact there is a small angle which ensures that night sky lines and arc lines are vertical This angle is totally transparent to the user The Y axis between images and spectra is flipped See figure 7 for illustrations of the orientation convention lt 11 y A Slit m 1024 1024 Slit 1024 1024 E y U N N x ge X 1 1 a b Figure 7 Orientation convention for images including acquisition images a Field orientation on detector at 0 rotation angle on sky b Field orientation at 30 rotation angle on sky The slit position is overlaid In spectra the Y axis is flipped T he circular arrow indicates the direction the field will rotate after a positive position angle is applied A 3 Chopping conventions and definitions e Chop Throw arcsec This is the throw of the chopping in arcsec The formal allowed range is 10 30 arcseconds however we strongly recommend that the throw is kept to 20 arcseconds or less If the chop throw is between 20 and 30 arcsec guiding is only possible on one beam leading to a deterioration of the image quality due to intermittent loss of AO corrections e Chop Position Angle This is the chopping position angle in degrees If the Chop Angle Coordinate is set to SKY then the choppin
24. its original spatial position The parameter Number of Exposures gives the number of exposures at each rotator position The offsets in X offset list arcsec and Y offset list arcsec will be repeated until SEQ NEXPO exposures have been taken Note that the telescope is only returned to its original spatial position after Number of Exposures exposures Be very careful if the lengths of X offset list arcsec and Y offset list arcsec are not equal to the number of exposures If the cumulative offset at the end of the list is not equal to zero it is easy to inadvertently move the object behind the polarimetry mask At the end of the template the rotator offset can optionally be returned to the value at the beginning of that template by setting Return to original rotator position to true T note that this option only returns the rotator to its original position at the end of the entire template With this scheme it is possible for the user to sample the object and sky as desired for a sequence of rotator positions within one template At least two different orientations separated by 45 degrees are required for computing the Stoke s parameters The most likely situation will be to set the Rotator Offset list parameter to 0 45 The template has been coded so the rotation occurs about the center of the mask which is approximately at x y 512 540 To image the entire field of view at one position angle one must take great care wi
25. need accurate flat fields or arcs Note that the arcs should usually not be necessary since the sky leaves plenty of telluric features for wavelength calibration In the M band it is not possible to do accurate wavelength calibration with the arc spectra Although we do provide an arc that is taken with the grating in third order the telluric features should prove to be more accurate 5 6 Chopping For LW broad band imaging and LW LR spectroscopy chopping is the only offered mode For other LW instrument setups the user can choose not to use chopping The basic characteristics and definitions of chopping are The chopping throw is distance between the two beams The maximum chop throw is 30 arcsec The chopping angle can be defined with reference to the SKY or to the DETECTOR see appendix A 3 Guiding can be achieved on both beams provided that the throw is approximately less than 20 arcseconds which corresponds to the field of view of the guide probe If the throw is greater than this guiding will be performed on only the central ON beam This will result in significantly poorer image quality in the OFF beam Thus we generally recommend that the chopping throw be kept to 20 arc seconds or less The chopping frequency is automatically defined in the templates and is based on the instrument mode in use It typically varies between 0 1 and 0 5 Hz e Chopping is always associated with nodding in the opposite direction of the chop
26. objects Blind offsets from a reference object should be limited to approximately 1 arcminute Offsets that are too large could cause the T CS to change the guide star which would result in a less accurate acquisition Experience has shown that the offsets from the reference star are often inaccurately defined For example if the offsets are computed from a previously taken ISAAC image the distortion at the edges of the field can affect the accuracy of the offsets if one has assumed a constant plate scale Also users tend to choose the brightest object in the field which can be far from the target Fainter reference objects still bright enough to satisfy the limits mentioned above are often closer to the target and make much better choices To minimise offset errors users should use reference objects that are as close as possible to the target rather than trying to use the brightest reference objects It is recommended to position a reference object in the slit together with the target so one can determine the position of the target on the spectral image It also allows one to monitor the image quality across the spectrum and to monitor the flux through the slit etc In service mode it is mandatory that all the relevant information is given in advance to the operation staff This information should consist of Finding charts with clear definition of the field orientation and of the scale Overlay of the slit e Clear identification of th
27. of the template will be executed by the night operator based on the indications provided by the user In service mode it is mandatory that the users send detailed information for centering the object into the slit The instrument mode for this template is LWI3 which is not an offered imaging mode Consequently the detector may have to be windowed down to a field of view of 1 arcmin if the acquisition filter is either L or narrow band M Therefore acquisitions involving objects separated by more than 1 arcmin should be acquired with either the narrow band LW or SW filters This template uses chopping All LW spectroscopic templates that use chopping should use this template The template can also be used for LW spectroscopic templates that do not use chopping although we recommend that the ISAACLW img acq MoveToSlitNoChop template is used for acquiring such targets The chopping parameters to be defined are e Chop Throw arcsec This is the throw of the chopping in arcsec it is limited to the 10 30 arcsec range A chop throw of lt 20 arcsec is recommended e Number of Chop Cycles This is the number of chop cycles to be averaged in the acquisition system preprocessor The higher the value the better the detection limit but the longer the integration time One chop cycle will typically last 2 to 10 seconds of time depending on chopping frequency The minimum number of chop cycles is 1 This parameter may be adjusted by the op
28. spectroscopy This section mentions several standard star lists that can be used for LW observations either for imaging or for spectroscopy They can also be used for SW spectroscopy The optimal magnitude ranges for LR and MR spectroscopic standards are L 4 to L 6 and L 2 to L 4 respectively For L band imaging standards should be fainter than L 6 magnitude and for narrow band imaging standards should be fainter than L 5 e the MSSSO infrared photometric standards McGregor 1994 PASP 106 508 Transformations from the Caltech system to the original MSSSO and AAO systems are given in McGregor 1994 PASP 106 508 e the IR photometric data of ESO calibration stars van der Bliek et al 1996 A amp AS 119 547 e An extensive list of bright stars of known spectral type and magnitude taken from a vari ety of sources MSSSO photometric standards IRPS FIGS G dwarfs spectroscopic standards UKIRT spectroscopic standards NASA Infrared Catalog Bright Star Catalog and have corre spondingly uncertain photometric magnitudes Photometric magnitudes in this list come from the following references M McGregor 1994 PASP 106 508 C Carter 1990 MNRAS 242 1 B Bouchet Manfroid amp Schmider 1991 A amp A Suppl 91 409 A Allen amp Cragg 1983 MNRAS 203 777 Stars with magnitudes listed but lacking a reference annotation are taken from the NASA Catalog and their photometry should be considered uncertain at the 0 0
29. standard through both a wide slit e g 2 arcsec or slitless and the slit used for the program object in order to get an estimate of the slit losses by comparing the spectra obtained with the two slit widths Alternatively if the broad band magnitudes of the object are known the absolute flux calibration can be derived by convolving the measured spectrum with the broad band filter curves In this case the IR magnitude of the standard is irrelevant only the spectral type is important This works at Low Resolution but not at Medium Resolution where the spectral coverage is smaller than the filter bandwidth Locating spectra Because ISAAC uses two different optical paths in imaging and spectroscopy the formats in imaging and spectroscopy are different E g if an object is along the slit at pixel Yimg its position along the slit in spectroscopy is Y spec Note for instance that the images are inverted between imaging and spectroscopy The relationship Y spec function Yimg is calibrated and maintained by ESO At the end of each acquisition see appendix A the image that is displayed on the RTD which usually consists of a moderately deep sky subtracted image is dumped to disk The locations of the slits are accurately known so it is always possible to know exactly what was observed from the acquisition images For faint objects it is not always easy to locate the spectrum on the spectroscopic images It is strongly recommended to t
30. to be flipped with respect to imaging Table 6 shows the correspondence between wavelength range grating order filter and spectral resolution in the LR and MR modes The order is automatically set by the templates and the user only needs to define the central wavelength of the observations 2 4 Polarimetric Mode ISAAC offers SW imaging polarimetry in the Hawaii arm A Wollaston prism in one of the two filter wheels splits the incoming parallel beam into two beams which are perpendicularly polarised The beams are separated by 21 arcseconds Thus an image taken with the Wollaston prism will contain two images of every object To avoid sources overlapping a special mask consisting of alternating opaque and transmitting strips 24 arc seconds as opposed to about 20 arc seconds is inserted at the focal plane Thus in a single exposure at least half the field will be missing so three exposures with telescope offsets in between are required to image one field see Section for more details The Wollaston prism is not achromatic so the exact separation between the two beams is a function of wavelength In J the separation is 22 5 arcseconds while in Ks the separation is 21 arcseconds The beam separation is also a function of position from the top to the bottom of the image the separation varies by 3 pixels To measure the Stokes parameters and hence the degree and position angle of polarisation a second set of images with the Woll
31. used as an order sorting filter however it can be used for imaging as well 3 This filter has leaks in the K band and the atmosphere defines the red edge of the filter For accurate photometry the Js filter is recommended The narrow band 1 06u4m and 1 19um filters correspond to regions of low OH emission and therefore enhanced sensitivity 5 The blocking filter is to prevent red leaks Table 3 LW Imaging filters See appendix B for the filter curves Name Line Central wavelength um Width um Width 96 LA 3 78 0 58 15 NBM 4 66 0 10 2 NB 3 21 3 21 0 05 1 6 NB 3 28 PAH 3 28 0 05 1 6 NB 3 80 3 80 0 06 1 6 NB 4 07 Bra 4 07 0 07 1 7 the central wavelength varies slightly across the field of view 2 the ESO L filter is centered at 3 8m and is closer to L filter Bessell and Brett 1988 than it is to the original Johnson L filter Table 4 ISAAC Spectroscopic Modes H Mode Array Spectral Range Pixel Scale Resolution for arcsec 1 arcsec slit SWSI LR Hawaii 0 98 2 5 um 0 147 500 SWSI MR Hawaii 0 98 2 5 um 0 147 3000 LWS3 LR Aladdin 3 0 5 1 um 0 147 400 LWS3 MR Aladdin 2 0 5 1 um 0 147 2500 ll See Sections o and 10 for more detailed information Table 5 ISAAC slits Slit width arcsec Slit Height arcsec 0 3 120 0 6 120 0 8 1208 1 0 120 1 5 120 2 0 120 1 Defects on the slit limit the usable length to 90 arcsec Table 6 Wav
32. 3m Be RUN ed x 11 10 ISAAC detector readout mode 11 LIS Minimum DITS s 2o soe x hom x x EC Rem eR he RIA EUR Rd Ah uU XU mode Rs 12 12 Acquisition filters versus target magnitude a 25 13 Aladdin Templates cookbook o aoa a aaa 30 14 Hawaii Templates cookbook 31 15 Overheads 2 ee 32 16 Overheads Example 1 SW Imaging with the Hawali 32 17 Overheads Example 2 SW Imaging with the Aladdin 33 18 Overheads Example 3 SW Standard star in spectroscopy o 33 19 Overheads Example 4 SW Spectroscopy of fainter object 34 20 Overheads Example 5 LW Imaging with chopping L band 34 21 Overheads Example 6 LW Spectroscopy with chopping 34 22 Overheads Example 7 LW Spectroscopy without chopping 35 23 Recommended DITs and NDITs for modes SWII amp LWIB 36 24 LW detector settings for imaging 24 2 ls 38 25 Recommended DITs and NDITs for mode SW 39 20 FITS files mamesl gt sc 23 kaaa ponr ani aaa 309 a 390 3 39 ee R Ay gU 47 27 Parameters of ISAACSW img acq breet 49 28 Parameters of ISAACSW img acq Presetrrm e 50 29 Parameters of ISAACSW_img_acq_MoveToPixel o 51 30 Parameters of ISAACSW img acq MoveToSlit o 52 31 Parameters of ISAACSW img acq MoveToSlit 53 32 Parameters of ISA
33. 5 mag level Other stars lacking measured photometric magnitudes should be used only as telluric standards to remove terrestrial absorption features flux calibration should be obtained separately Important note We had reports of incorrect visible magnitudes in this list Users are encouraged to choose only standard stars for which the IR magnitude is available in the photometric band corresponding to their observations and not to rely on the visible magnitude The table will be corrected for the errors as time permits D Acronyms ASM BB BOB CCD DCR DCR LB DCR HB DIT ETC GUI ISAAC LR LW LWI LWS LWS LR LWS MR MR NB NDIT NDR NINT NTT OB OS P2PP P70 P71 P72 P74 RRM RTD SOFI SW SWI SWS SWS LR SWS MR ToO UCR UT VLT Astronomical Site Monitor Broad Band Broker for Observation Blocks Charge Coupled Device Double Correlated Read Double Correlated Read Low Bias Double Correlated Read High Bias Detector Integration Time Exposure Time Calculator Graphical User Interface Infrared Spectrometer and Array Camera Low Resolution Long Wavelength Long Wavelength Imaging Long Wavelength Spectroscopy Long Wavelength Spectroscopy Low Resolution Long Wavelength Spectroscopy Medium Resolution Medium Resolution Narrow Band Number of Detector Integration Time Non Destructive Read Number of integrations New Technology Telescope Observation Block Observation Software Phase 2 Pr
34. AACLW spec cal AutoChopNod This template is used for standard star observations in spectroscopy It should only be used to calibrate observations that were taken with the Aladdin templates that use chopping It is strictly equivalent to the ISAACLW spec obs AutoChopNod template with the only difference that some DPR keywords in the FITS header of the images are set to different values This allows pipeline processing archiving and quality control The user is referred to the description of the ISAACLW spec obs AutoChopNod template for the description of the parameters This template must be used by users request ing calibrations beyond the ones provided by the Calibration Plan of this mode This template should not be used to calibrate observations that were taken with Aladdin templates that do not use chopping A 10 5 ISAACLW spec cal NightCalib This template allows one to take night time calibrations right after any Aladdin spectroscopic tem plate See section 5 5 for more information regarding the need for night time calibrations This template is not autonomous It must follow a spectroscopic observation Furthermore it only calibrates the wavelength setting that is used in the preceding template and not the wavelength settings in all preceding templates Table 50 Parameters of ISAACLW_spec_cal_NightCalib P2PP label Keyword Def Description Flatfield at end of template SEQ FLATFIELD T Night flat field at end of template A
35. AACSW spec cal NightCalib for SW If used these tem plates must be attached at the end of each spectroscopic template They are not autonomous they must not be used on their own It is believed that the flat field non reproducibility problem only affects observations at high signal to noise ratio S N gt 100 It is therefore recommended that users use the night time calibration templates if they want high signal to noise data In this case one should also take night time flats for the telluric standards As this is not part of the ISAAC calibration plan users will have to provide the appropriate OBs To get the highest signal to noise ratio one should set the nod throws of the telluric standard and the science target to be the same Observers who do not wish to obtain such high signal to noise data this applies to most obser vations done with ISAAC can safely ignore the night time flat field calibrations Requesting night time arcs is usually not necessary for observations below 2 2m since the OH lines provide an in situ wavelength calibration Above 2 2 microns there are few OH lines but there are many telluric features and they can either be used as in situ wavelength calibration or as a means of determining the wavelength offset for observations calibrated with the daytime arcs Little experience has been obtained with similar problems in the LW arm However the same template has been created for the LW channel in case users feel they
36. ACSW img acq Polarimetry e 53 33 Parameters of ISAACSW img obs AutoJitter 54 34 Parameters of ISAACSW img obs AutoJitter ffset 56 35 Parameters of ISAACSW img obs FixedSkyO0ffset o 58 36 Parameters of ISAACSW img obs Generic0ffset lees 60 37 Parameters of ISAACSW img obs Pol ar imet rl 62 38 Parameters of ISAACSW img cal GenericO0ffset lees 63 39 Parameters of ISAACSW_spec_obs_AutoNodOnSlit 65 40 Parameters of ISAACSW_spec_obs_GenericOf Setl 2s 67 4 Parameters of ISAACSW spec calNightCalib o a 69 42 Parameters of ISAACLW img acq Breser 70 43 Parameters of ISAACLW img acq MoveToPixel o 71 44 Parameters of ISAACLW img acq MoveToSlit 005000000 73 45 Parameters of ISAACLW img acq MoveToPixNoChop 2004 73 46 Parameters of ISAACLW img acq MoveToSlitNoChop o o 74 a A a e R BE 75 48 Parameters of ISAACLW_img_obs_AutoChopNod o e e 76 49 Parameters of ISAACLW spec obs AutoChopNod o e e TT 50 Parameters of ISAACLW_spec_cal NightCalib 51 Aladdin non chopping template es 79 52 Parameters of ISAACLW img obs AutoJitter 79 53 Parameters of ISAACLW img obs AutoJitterOffset 80 54 Parameters of ISAACLW img obs FixedSkyOffset len 80 55 Parameters of ISAACLW img
37. EUROPEAN SOUTHERN OBSERVATORY VERY LARGE TELESCOPE ISAAC User Manual Doc No VLT PLA ESO 14100 0841 Issue 76 March 1 2005 J G Cuby C Lidman R Johnson A Jaunsen E Mason C Moutou March 1 2005 Prepared gt dada Eo N O EAS LR ER A JA NEC OS EN E P m a Change Record Issue Rev Date Section Parag affected Reason Tnitiation Documents Remarks 75 0 Feb 15 2005 Update for new web pages 76 0 Feb 27 2005 Updated for P76 CfP Contents 1 Introduction SE EE EE E E EE A E et 1 2 Current version of this User Manual 1 3 Reminders eco ib A a E Rae eee AA ee 14 Content of this mamuall 2 22 lees n E Contact xo dete ida Bee koX A X E Ae der M A ne Be ee 2 ISAAC Infrared Spectrometer and Array Camera 2 1 Optical Layout rrr 2 21 Comparison of JHK imaging in Hawaii and Aladdin arms E A ARTE es ae See ck Be a nd A die R eo T oe R E ub AE AR AAA TRR Ge A A doe ad Ss a jew O RE gk Maat T R E eee K T E 3 39 TT IT 3 4 e T IT s RG gri A AA EH AER ee a hee Me pee ERT oR Ak R en oe T Fe PO Bea ae hoses dem aen Ba Mey eo og ee a ica us E end ae ae ee 5 2 The Real Time Display RTD 2 412 164 4040844 oe e444 IR RUN oR E a acc cT AA MMA CINE 3x eot im aoe e E ks E e Cent dg 5 3 2 SW Spectroscopy 2 2 lh s sss 5 3 3 LW spectroscopy 2 4 2 2 ee 5 3 4 Rapid Response Mode RRM llle 5 4 Maximum Brightness of Observable l argets
38. Exposures SEQ NEXPO Number of exposures Return to Origin SEQ RETURN Return to Origin Flag X offset list arcsec SEQ OFFSETX LIST X offset list arcsec Y offset list arcsec SEQ OFFSETY LIST Y offset list arcsec LW Filter wheel 1 INS FILT3 NAME Filter wheel 1 LW Filter wheel 2 INS FILT4 NAME Filter wheel 2 A 11 8 ISAACLW spec cal AutoNodOnSlit amp ISAACLW spec cal GenericOffset These templates are used for standard star observations in spectroscopy They should only be used to calibrate observations that were taken with the Aladdin templates that do not use chopping They work in an identical manner to ISAACLW spec obs AutoNodOnSlit amp ISAACLW spec obs GenericOffset The only difference is that some keywords in the FITS headers are set to different values allowing pipeline processing and archiving These templates must be used by users requesting calibrations beyond the ones provided by the Calibration Plan of this mode A 11 9 ISAACLW spec cal NightCalib This template allows one to take night time calibrations right after any Aladdin spectroscopic tem plate See section 5 5 for more information regarding the need for night time calibrations This template is not autonomous It must follow a spectroscopic observation Furthermore it only calibrates the wavelength setting that is used in the preceding template and not the wavelength settings in all preceding templates Table 59 Parameters of ISAACL
39. NIS JUN j i f 6 j 5 H N A d EN j ere A SN 3 80 3 85 3 90 3 95 Wavelength microns nem 46 465 7 475 as rasiert order ere B22 as os a4 23 am 234 226 228 Worsiercth microns AOT as os 04 4 05 41 Worsiercth aE Figure 22 Narrow band filter curves C Standard stars See the ISAAC web pages for a list of standard stars C 1 SW Photometric Standards Only stars fainter than K 12 mag should be used as standards to calibrate the broad band filters A number of stars in the JHK Persson and UKIRT fundamental and extended lists are suitable Note however that many stars in these lists are too bright and may saturate the detector especially when the seeing is good C 2 SW Telluric Standards Telluric standards are used to remove telluric absorption features In most cases they can also be used for flux calibration A more detailed discussion as to which stars are best to use is given in Sec We prefer to use very hot stars earlier than type B4 or solar analogues The Hipparcos catalogue is an excellent source for such stars Many of the stars in the Hipparcos catalogue have IR magnitudes from either the 2MASS or DENIS IR surveys See also section C 3 for more star lists The optimal magnitude ranges for SW LR and MR spectroscopic standards are K 7 to K 9 and K 5 to K 7 respectively Stars brighter than this will saturate the detector C 3 Bright standards for LW imaging and
40. NS SLIT Which slit e g slit_1 The total integration time excluding overheads is defined in minutes In general the user will get slightly more or slightly less time that what was specified in the OB This is because the DIT is set so that the detector does not saturate the number of NDITs is set by the chopping frequency and the number of cycles is set so that approximately one minute is spent at each end of the nod To compute the actual integration time from the information provided in the FITS header you need to compute DIT x NDIT x 2 x Number of cyclesx Number of AB or BA cyclesx 2 Note again that if chopping nodding is done in the direction perpendicular to the slit only half of this time will be spent on target A 10 3 ISAACLW img cal AutoChopNod This template is used for standard star observations in imaging It should only be used to calibrate observations that were taken with the Aladdin templates that use chopping It is strictly equivalent to the ISAACLW img obs AutoChopNod template with the only difference that some DPR keywords in the FITS header of the images are set to different values This allows pipeline processing archiving and quality control The user is referred to the description of the ISAACLW img obs AutoChopNod template for the description of the parameters This template should not be used to calibrate observations that were taken with Aladdin templates that do not use chopping A 10 4 IS
41. P74 allows approved RRM programs to automati cally trigger target of opportunity ToO observations Please see for more information about RRM To facilitate the RRM two new ac quisition templates are provided ISAACSW img acq Presetrrm and ISAACSW img acq MoveToSlitrrm It is required that any RRM OB contains one of these acquisition templates The templates are essentially identical to the ISAACSW img acq Preset and ISAACSW img acq MoveToSlit templates but contain fewer param eters See Section 5 4 for brightness limits applied to RRM observations 5 4 Maximum Brightness of Observable Targets Direct imaging of very bright objects in the Hawaii arm results in residual images that can last up to several hours due to persistence effects in the Hawaii In service mode this problem can affect subsequent observations of other programs In visitor mode and provided that the nights are not shared the potential problems related to the persistence effects are left to the responsibility of the user We have less experience with the effect of bright stars on the Aladdin array Hence we request that users follow the same SW imaging rules as with the Hawaii Note RRM observations will be turned down if the field contains objects brighter than 9th mag nitude in J H or K This is done in order to protect the array from remnant effects and changes in the gain properties resulting from saturation As the field and OB contents is not known apriori a ge
42. Polarimetry 1 SWP1 43 11 1 Characteristics 43 11 2 Recommended DITS and NDITS 0 0 0 0 0 0 00 00 0000 0000084 43 yee Le Pe oa ee a ee eee ee ae ee ee 43 a eee be AR ee a ee ee eee 43 e Gs pra Dect dd de ad eet e He eg ay tes Sues es GE Seat Gee Geet A 43 44 hn pane 44 Se ee eG a Aa eee ee 45 SECHSTEN 46 La O A AA A AA E 46 LB A Boa a ad See da ee ee Se a 46 EE og sete eae E 49 Ld ae he i Bh OS Ge A Gon oe BO Se a e ee ale ae 49 Si ap nee eae ee ew Be ed Be ee es TT 49 TOE 50 AA 50 e ah E e KE woke Sb cece hy at 52 Porcio raid cian ac 53 SE E de a Ale a et ee 53 EEN 54 A 7 1 ISAACSW img obs AutoJitter 4 5 4 e es 54 A 7 2 ISAACSW img obs AutoJitterO0ffset 56 SE E EE EE SE rr EE ier vend ener er ERNE uie Aree nde R ta A 7 ISAACSWimg calPolarimetry o EE EE O OS EE EE EE sb Ee A 8 3 ISAACSW spec cal AutoNodUnSlit amp ISAACSW spec cal GenericOffset CRIAM SENE RE E wok A A o a dd TR E ii del dd s X Euh ED Rex am e E AE Ro eed aa be Bula EN SI ERE PIT RE e A Ur EENS i Be ee E ah E E MM cc CMM T TT e ERA d EA die ue TII STT AA TIPP a dir sin EE a hen ee wh a a A LE A EE A 11 8 ISAACLW spec cal AutoNodUnSlit amp ISAACLW_spec_cal_GenericOffset A 11 9 ISAACLW spec cal NightCalib eA B Filter curves C 1 SW Photometric Standard C 2 SW Telluric Standard C 3 Bright standards for LW imaging and spectroscopy
43. T It is therefore preferable to use a high NINT rather than a high NDIT At Low Resolution the noise is essentially limited everywhere by the photon noise from the OH lines after 1 minute of integration Therefore DITs of a few minutes e g from 1 to 3 are adequate It is then advisable to offset the telescope as many times as possible during the execution of the template Table 25 Recommended range for DIT in seconds and NDIT for SWS1 LR and SWS1 MR modes LR MR DIT recommended 60 200 300 900 NDIT 1 1 9 3 Calibration Plan For the LR grating only four grating settings that correspond to 1 06 1 25 1 65 and 2 2 jm are supported Users should not use any other central wavelength in LR mode In LR mode telluric standards spectroscopic flats and arcs will only be taken at the supported wavelengths A variety of calibration frames will be archived and updated through the execution of the Calibration Plan e LR and MR Telluric Standard Stars Observations of telluric standards will be performed whenever the LR and MR gratings are used Whenever possible we will limit the airmass difference between the standard and science tar get to 0 2 airmasses The standard will be observed with the slit that was used during the observations and either the 2 arcsec slit or in slitless mode Flats and arcs will not be taken immediately after the standard The stars are generally chosen from the Hipparcos catalog and are either
44. The second NodThrowAlongSlit 2 exposure B is therefore arcsec from the initial position along the slit In addition to nodding random offsets can be added in the middle of a cycle A sequence of 6 cycles with jittering will result in the following sequence A B e1 B e1 A e2 A e2 B e3 B e3 A e4 A e4 B e5 B e5 A e6 where n are random offsets In general n should be much smaller than the nod throw The random offsets are generated inside an interval defined by the parameter Jitter Box Width in arcsec Offsets are randomly distributed between terBoxWicth anq KESE It is strongly recommended to define some non zero value for the Jitter Box Width param eter as this allows one to get several images with the spectra lying at different positions on the detector However it should be smaller that the Nod Throw Along Slit otherwise spectra on either side of the throw could overlap To better exploit the jittering facility offered by this template it is also recommended to define Number of AB or BA cycles to some value higher than e g 4 or 5 so as to get several AB pairs of images with the spectra lying at different positions across the array If the parameter Jitter Box Width is set to zero then the template will just nod between A and B At the end of the template the telescope returns to the original position if the parameter Return to Origin is set to true T If not the
45. Tx NDIT for the SKY positions plus overheads shall each exceed one minute of time ISAACSW_img_obs_AutoJitterOffset Sky positions Sky offset throw FA 4 ter box Template Parameters bj ct positions Number of AB or BA cycles 3 Jitter box Width 40 Sky offset throw 250 Rotate Pupil F Figure 10 Illustration of the ISAACSW img obs AutoJitterOffset template The black dots in the central square represent the position of a star which was originally at the center of the field The other squares represent the position of the SKY frames A 7 3 ISAACSW img obs FixedSky0ffset This template moves the telescope alternatively between object and sky positions The object positions of the telescope are randomly distributed around the object initial telescope position and within a box whose dimensions are set by the parameter Jitter Box Width in arcsec The minimum value for this parameter is 10 arcsec The sky positions are also randomly distributed around a fixed offset position defined by the pa rameters Sky Offset in Alpha and Sky Offset in Delta from the original object telescope position The box dimensions of the random sky positions are set by the parameter Jitter Box Width i e the sky exposures are distributed in a box offset from the initial telescope position Table 35 Parameters of ISAACSW img obs FixedSkyUffset P2PP labe
46. W_spec_cal_NightCalib P2PP label Keyword Def Description Exposure Name DET EXP NAME Exposure Base filename Flatfield at end of template SEQ FLATFIELD T Night flat field at end of template Arc at end of template SEQ ARC F Night arc at end of template B Filter curves Filter SH tranamission curve Pier SK trarem sdon arve H H B 8 13 1 4 15 16 1 7 18 19 18 2 22 26 Worstercth imicror Wanslereth iria oe Ater SL trasmission cure 56 8 Figure 18 Filter curves for order sorting filters ransmission T Toeman Toremssion Toeman Filter Js transmission curve iarr ArT eg rr x e 4 M IRE d NN a ad f pt Ww a n E yor ec 0 8 0 8 Tu 1 1 y 1 I o o gt a e Transmission L l EE l 0 2 l j L j f y BRE Aeon A AN oO r T E d sen 1 0 95 1 00 1 05 1 10 15 1 20 1 10 1 15 1 20 1 25 1 30 1 35 1 40 Wovelength microns Wovelength microns Fiter J raremidon arve Alter Hiram don arve Toremssion 1 05 1 1 115 12 1 25 13 1 35 1 4 145 145 15 155 18 1 65 1 7 1 75 18 185 Toraman o 19 105 2 205 21 215 22 235 23 235 24 Wonslercth mia ora Filter M tranamission arve 1 9 5 51 52 43 44 45 46 47 48 Wasler h micron Figure 19 Filter curves for broad band filters NB 1 06 X8 1 08 Di 00 LEE E g k amp S e E
47. ads Example 2 SW Imaging with the Aladdin Template parameters Acquisition Template Observation Template DIT NDIT Number of Exposures ISAACLW_img_acq Preset ISAACLW img obs AutoJitter 10 seconds 10 36 Execution time minutes Preset Instrument setup int time detector overhead Telescope offsets Total 6 0 0 5 0 167 x 10 NDIT x 36 0 25 x 36 76 minutes for 60 minutes of integration Table 18 Overheads Example 3 SW Standard star in spectroscopy Template parameters Acquisition Template Observation Template DIT NDIT Number of AB or BA cycles NINT Return to Origin Night time Calibration Template Flatfield at end of template Arc at end of template ISAACSW img acq MoveToSlit ISAACSW spec cal AutoNodOnSlit 20 seconds 3 1 1 T ISAACSW spec cal NightCalib T T Execution time minutes Preset amp Acquisition Instrument setup int time detector overhead Telescope offsets Flat field Arc Total 10 0 2 0 0 33 0 13 x 3 NDIT x 2 1 AB cycle 0 75 3 telescope offsets 4 3 22 5 minutes for 2 minutes of integration Table 19 Overheads Example 4 SW Spectroscopy of fainter object Template parameters Acquisition Template Observation Template DIT NDIT Number of AB or BA cycles NINT Return to Origin Night time Calibration Template Flatfield at end of template Arc at end of template
48. allows to use the functionality of the template without presetting the telescope It is possible in this template to use the J Block H or Ks filters which are likely to allow an easier identification of the field these filters are not available for the subsequent observation templates Table 43 Parameters of ISAACLW img acq MoveToPixel P2PP label Keyword Default Description Preset Telescope SEQ PRESET T Preset telescope Chop Throw arcsec SEQ CHOP THROW M2 Chop Throw arcsec Number of Chop Cycles SEQ CHOP NCYCLES Number of chop cycles Chop Position Angle SEQ CHOP POSANG Chop Position angle deg Chop Angle Coordinate SEQ CHOP COORDS SKY or DETECTOR coords Add Velocity Alpha TEL TARG ADDVELALPHA 0 Additional tracking vel in RA Add Velocity Delta TEL TARG ADDVELDELTA 0 Additional tracking vel in DEC Angle on Sky deg TEL ROT OFFANGLE 0 Position angle DDD TTT LW Filter wheel 1 INS FILT3 NAME zs Filter wheel 1 LW Filter wheel 2 INS FILT4 NAME Filter wheel 2 1 In arcsec sec At the end of the template the image displayed on the RTD consisting of Number of Chop Cycles chopped images is dumped on disk A 9 4 ISAACLW img acq MoveToSlit All LW spectroscopy OBs that use chopping must use this template for target acquisi tion This template presets the telescope and allows the operator to interactively center objects into the selected slit In visitor mode the interactive part
49. alues used in the SWI1 mode see Section 7 should be doubled 11 3 Calibration Plan This mode is not supported within the ISAAC Calibration Plan The normal twilight flat fields without the Wollaston can be used to flat field the data 11 4 Pipeline This mode is not supported by a pipeline 11 5 Performance This mode is not supported by an ETC However the performance can be confidently estimated from the imaging case see section 7 by considering that the light from the object and from the sky is divided into two by the Wollaston To reach a given limiting magnitude in the background limited case therefore requires twice the time required in imaging Template description General remarks and reminders how to avoid common sources of error Only parameters specific to ISAAC are described The description of other parameters can be found in the P2PP Manual We strongly recommend that you consult the ISAAC web page for the latest information Templates using the Aladdin and templates using the Hawaii must not be mixed in the same OB All SW spectroscopic OBs must use the ISAACSW img acq MoveToSlit or ISAACSW img acq MoveToSlitrrm template for acquisition and all LW spectroscopic OBs must use either the ISAACLW img acq MoveToSlit or ISAACLW img acq MoveToSlitNoChop templates The SW polarimetric OBs must use the ISAACSW img acq Polarimetry template for acquisi tion LW imaging chopping templates must use either ISAACLW im
50. aston prism rotated 45 degrees with respect to the first pair are required The rotation is done by rotating the entire instrument The Stokes parameters are then determined as follows I i 90 1 0 2 45 1 135 Q 0 i 90 U i 45 i 135 where a is the intensity of the source which transmits light that is polarised at angle a We have assumed that the rotator is at a position angle of 0 degrees for the first measurement This need not be the case The degree of polarisation and the polarisation angle are given by VOTE P I U 0 0 5tan Q To derive the correct value of 0 attention needs to be paid to the signs of U and Q This algorithm neglects instrumental polarisation Preliminary measurements with ISAAC indicate that the instrument polarisation is 1 596 As this is partially caused by the tertiary mirror the vector defining the instrument induced polarisation will rotate relative to the sky A method to eliminate the instrumental polarisation is outlined by Sperello di Serego Alighieri 1989 Proceedings of 1st ESO ST ECF Data Analysis Workshop Table 7 shows the main characteristics of the Polarimetric Mode of ISAAC The filters available in the Polarimetric Mode are a subset of the filters available in imaging the Wollaston prism is on one of the two filter wheels making the filters on this wheel unavailable Available filters in SWP1 mode are listed in table 8 2 5 Detectors and Acqui
51. be archived and updated through the execution of the Calibration Plan e LR and MR Telluric Standard Stars Observations of telluric standards will be performed whenever the LR and MR gratings are used Whenever possible we will limit the airmass difference between the standard and science tar get to 0 2 airmasses The standard will be observed with the slit that was used during the observations and the 2 arcsec slit Flats and arcs will not be immediately taken after the standard The stars are generally chosen from the Hipparcos catalog and are either hot stars spectral type B4 or earlier or solar type stars spectral types GOV to G4V These calibrations are taken so that telluric features can be removed from science spectra They can also use for flux calibration with a relative accuracy of 5 10 and an absolute accuracy of 5 20 A detailed discussion on this topic is given in Sec Should users need more accurate results or should users require telluric standards of a specific spectral type they should provide the corresponding OBs and detailed instructions The spectroscopic standard star templates e g _cal_ must be used to prepare these OBs In this case the time used in executing the OBs will be charged to the user and the observatory will not observe a separate telluric standard e Spectroscopic Flats Flats corresponding to the set ups used during the night are taken by the operation staff the next day e Darks Darks are ta
52. be windowed down to a field of view of 1 arcmin if the acquisition filter is either L or narrow band M Therefore acquisitions involving objects separated by more than 1 arcmin should be acquired with either the narrow band LW or the SW filters This template does not use chopping It should not be used to acquire targets if the subsequent LW spectroscopic template uses chopping Table 46 Parameters of ISAACLW img acq MoveToSlitNoChop P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of DITS Preset Telescope SEQ PRESET T Preset telescope Alpha offset from Ref Star SEQ REF OFFSETALPHA 0 Offset from Ref Star arcsec Delta offset from Ref Star SEQ REF OFFSETDELTA 0 Offset from Ref Star arcsec Alpha offset arcsec TEL TARG OFFSETALPHA 10 RA offset arcsec Delta offset arcsec TEL TARG OFFSETDELTA 10 DEC offset arsec Add Velocity Alpha TEL TARG ADDVELALPHA 0 Additional tracking vel in RA Add Velocity Delta TEL TARG ADDVELDELTA 0 Additional tracking vel in DEC Angle on Sky deg TEL ROT OFFANGLE 0 Position angle DDD TTT LW Filter wheel 1 INS FILT3 NAME LW Filter wheel 1 LW Filter wheel 2 INS FILT4 NAME LW Filter wheel 2 Slit INS SLIT Slit e g slit_1 T Tn arcsec sec This template is functionally identical to the ISAACSW_img_acq_MoveToS1lit template so users should refer to Sec for details A 10 Aladdin Observation and Cal
53. cquisition is made on reference objects That is once the reference object has been acquired and centered in the slit the offsets defined here will offset the telescope so as to bring the desired target into the slit At the end of the template the image displayed on the RTD consisting of Number of Chop Cycles chopped images is dumped on disk A 9 5 ISAACLW img acq MoveToPixNoChop The instrument mode for this template is LWI3 This template does not use chopping and can only be used to acquire targets for subsequent imaging observations that do not use chopping i e using J Block H Ks NB_3 21 or NB_3 28 Acquisition using LW broad band filters is allowed however Table 44 Parameters of ISAACLW img acq MoveToSlit P2PP label Keyword Default Description Preset Telescope SEQ PRESET T Preset telescope Alpha offset from Ref Star SEQ REF OFFSETALPHA 0 Offset from Ref Star arcsec Delta offset from Ref Star SEQ REF OFFSETDELTA 0 Offset from Ref Star arcsec Chop Throw arcsec SEQ CHOP THROW M2 Chop Throw arcsec Number of Chop Cycles SEQ CHOP NCYCLES Number of chop cycles ChopNod PARA of PERP to Slit SEQ CHOP SPEC Chopping along or perp to slit Add Velocity Alpha TEL TARG ADDVELALPHA 0 Additional tracking vel in RA Add Velocity Delta TEL TARG ADDVELDELTA 0 Additional tracking vel in DEC Angle on Sky deg TEL ROT OFFANGLE 0 Position angle DDD TTT LW Filter wheel 1 INS FILT3 NAME Filter w
54. ct interaction with OS However the OS GUI is useful for the visitors as a status display panel displaying all information from instrument detector and telescope ISAAC OS TYPE UNDEFINED INS_USER SYSTEM File Options Commands Tools Status Imaging Cam Type Tech Expo File Exp ld Exposure Count Down STATE SUBSTATE ISAAC Sw om skr ruar me jitterTest 0011 00 00 00 ONLINE Expo Name New Data ExposureTime 10 000 IDLE Instrument Mode Info jitterTest 0011 Phase Inactive Requestor swi W WCS W Seq Naming R S m Archive Header RTD Detector mavaiiscioz ICS ONLINE IDLE SIMULATION DCS ONLINE IDLE SIMULATION Tes ONLINE Functions Calibration Mirror Arml Window Chopping Preset Offsets No TCSY Chopping Telescope offset M Combined E 4 Chopping ON OFF Aab Dijo OFFSET slit_0 6_tilte b Throw xe vio OFFSET slit_1_tilted PupilObj Wavelength asa XY offset via RTD Idle Number of chop cycles mask_L2 Order Number of cycles SNE Rotator offset 45 OFFSET Chop frequency Hz M2 posune Throw offset 0 OFFSET mask_L3_1k wollaston e Pos Angle offset fo OFFSET focus_wedge DIT sec 7 JG MASK x jo Y Jo OFFSET NDIT XY via RTD ND Samples
55. ctor Integration Time secs Number of Exposures SEQ NEXPO Number of exposures List of NDIT SEQ NDIT LIST NDIT List Return to Origin SEQ RETURN T Return to Origin Flag Obs Type 0 or S SEQ OBSTYPE LIST Observation type list S or O List of offsets X or RA SEQ OFFSET1 LIST X or RA offset list arcsec List of offsets Y or DEC SEQ OFFSET2 LIST Y or DEC offset list arcsec Offset Coordinates SEQ OFFSET COORDS SKY or DETECTOR coords LW Filter wheel 1 INS FILT3 NAME Filter wheel 1 LW Filter wheel 2 INS FILT4 NAME Filter wheel 2 A 11 5 ISAACLW spec obs AutoNodOnSlit This template works in an identical manner to ISAACSW spec obs AutoNodOnSlit Please refer to Sec for a description of what the template does This mode is available for MR spectroscopy only Table 56 Parameters of ISAACLW spec obs AutoNodOnSlit P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of sub integrations Jitter Box Width SEQ JITTER WIDTH Jitter box width arcsec Return to Origin SEQ RETURN T Return to Origin flag Nod Throw Along Slit SEQ NODTHROW Throw of the nod arcsec Number of AB or BA cycles SEQ NABCYCLES Number of AB or BA cycles NINT SEQ NINT Number of frames at each position Instrument Mode INS MODE Instrument Mode Slit INS SLIT Which slit e g slit 1 Central Wavelength microns INS GRAT WLEN Central Wavelength microns
56. d Dealing with the moon If the object is very close to the moon less than 20 degrees away moonlight can prevent the telescope active optics system from working The effect is difficult to predict and quantify as it depends on too many parameters Just changing the guide star often solves the problem Visitors are encouraged to carefully check their target positions with respect to the Moon at the time of their scheduled observations Backup targets are recommended whenever possible and users are encouraged to contact ESO in case of severe conflict i e when the distance to the Moon is smaller than 30 4 2 The Telescope Telescope Focus This is a burden of the past In fact the telescope cannot be defoccussed For standard stars we can degrade the IQ by using a calibrated solution for the optics since standards are often too bright for the VLT However this procedure is not offered for science targets Telescope control Most interactions with the telescope consist of telescope presets for acquisition telescope offsets during observations and M2 chopping in LW observations Small offsets i e less than 1 arcminute are usually completed in 10 to 15 seconds of time The guide star is used for field stabilisation and optimising the performance of the optics active optics The active optics system runs continuously even when the telescope does an offset During the offset the guide star is lost for the duration of the offset Co
57. detailed explanation can be found at http www eso org projects dfs papers jitter99 Chopping This technique is reserved for the Aladdin arm above 3 um and it consists of moving the secondary mirror of the telescope M2 once every few seconds The typical throw is about 20 arcseconds Therefore in most circumstances the images corresponding to the two beams have some overlap An essential requirement of this technique is to combine chopping with telescope nodding i e offsetting in the direction opposite to that of the chop The chopped images usually leave strong residuals on the detector that are due to the different optical paths of the two beams These residuals subtract well between two chopped images taken with a telescope nod in between In addition chopping and nodding may be combined with jittering i e the telescope is slightly offset between nod cycles Photometric Calibration Because the strong IR atmospheric absorption varies with airmass and water vapor content see section in a slightly non linear manner accurate photometric calibration is more difficult in the IR than in the visible An accuracy of 1 can be obtained during stable nights provided that standard stars are observed frequently and with the same airmass as the object Standard stars have to be observed at least twice with a telescope offset in between allowing for the sky to be subtracted A list of photometric standard stars is provided in appendix C 1 The
58. ds for Object and assigns the DPR CATG to SCIENCE S stands for Sky and assigns the DPR CATG header keyword to SKY This template allows slit scanning across an object by defining a list of offsets in the X direction At the end of the template the telescope returns to the original position if the parameter Return to Origin is set to true T If not the telescope is not moved at the end of the template The lists can have any length however having lists of different lengths can become extremely confus ing It is good practice to use lists of equal length or lists with only one value when one parameter remains constant The total integration time exluding overheads is defined in seconds by DIT x NDIT x Number of Exposures ISAACSW_spec_obs_GenericOffset 1024 1024 OBJ N Position angle on the Sky 30 Template Parameters Number of exposures 6 X offset list 0 0 600 60 0 Y offset list 0 40 0 90 0 30 Obs Type oossoo ISAAC field of view Slit broadened x 1 1 Figure 16 Illustration of the ISAACSW_spec_obs_GenericOffset template The black dots represent the position of a star moved according to the lists of offsets in X and Y irrespective of the position angle on sky A 8 3 ISAACSW spec cal AutoNodOnSlit amp ISAACSW spec cal GenericOffset These templates are used for standard star observations in spectroscopy at SW They are strictly equivalent to the ISAACSW spec obs AutoNodOnS
59. e but the very high density of hot pixels and cosmic rays can seriously limit the data quality if the integrations are too long These bad pixels and cosmic rays are better removed when combining a large number of images The best compromise between data integrity and readout noise is difficult to find and somehow depends on the program It is advised to choose DITs of 10 15 minutes in J H and K band below 2 2 um medium resolution spectroscopy and smaller values above 2 2 wm in K band medium resolution spectroscopy If the total duration of the observation is short i e one single OB lasting less than one hour it is advisable to reduce the DIT to say 5 minutes or so and increase the number of exposures and telescope positions at which data is obtained This will make it easier to properly reject bad pixels If on the other hand the total duration of the observation is long i e several OBs each lasting 1 hr or so then it is advisable to increase the exposure time to 10 15 minutes Then by combining all the images from all OBs one will be able to adequately remove bad pixels In this case it is recommended to place the object at different positions along the slit The easiest way to do this is to give the different OBs slightly different values for the Nod Throw Along Slit parameter see Section A 8 1 The ISAACSW_spec_obs_AutoNodOnSlit template provides the possibility of storing individual frames at each telescope position NIN
60. e scale with what one may call a spectroscopic standard In general the spectroscopic standard and the telluric standard are the same star but this does not need to be the case The most prominent feature in IR spectra are the telluric lines of the Earth s Atmosphere Unfor tunately many of the telluric lines do not scale linearly with airmass so it is necessary to observe a standard at the same airmass and with the same instrument setup as that used for of the science target Furthermore the strength of the telluric lines varies with time so it is also necessary to observe the standard soon after or soon before the science target The spectrum of the telluric standard is divided directly into that of the science target Ideally the spectrum of the telluric standard should be known so that features belonging to it can be removed However this is never the case so one has to use standards in which the spectrum is approximately known In general we use either hot stars or solar analogs as telluric standards and generally these stars are selected from the Hipparcos Catalogue The spectra of hot stars those hotter than B4 are relatively featureless and are well fitted by blackbody curves So by knowing the spectral type of the star one uses a blackbody curve with the appropriate temperature to fit the continuum of the standard The spectra of stars that are cooler than AO start to have many more features and cannot be fitted with a blackb
61. e has proved to be efficient with SOFI It is the default configuration with ISAAC In addition the template provides the flexibility to adjust the number of NDIT subintegrations for the OBJECT and SKY frames NDIT for the OBJECT positions defines the number of subintegrations on the object and NDIT for the SKY positions defines the number of subintegrations on the sky The total integration time excluding overheads is defined in seconds by DIT x NDIT for the OBJECT positions NDIT for the SKY positions x Number of AB or BA cycles Thus the total integration time on the sky and on the object can be adjusted so that the S N on the object is optimised Remember that the 1 minute per telescope position rule means here that both DIT x NDIT for the OBJECT positions plus overheads and DITx NDIT for the SKY positions plus overheads shall each exceed one minute of time ISAACSW img obs FixedSkyOffset N Jd Sky positions E Sky offset Alpha a Pp r4 o a Pp o E H d Template Parameters Pa Ka Number of AB or BA cycles 3 Jitter box width 30 Sky offset Alpha 200 Sky offset Delta 170 Rotate pupil F Jitter box Object positions Figure 11 Illustration of the ISAACSW img obs FixedSkyOffset template The black dots in the central square represent the position of a star which was originally at the center of the field The other square represents the mean position of the SKY frame
62. e object e Clear identification of the reference object to be used for preliminary slit centering e The offset to be applied between the reference and the target This offset has to be entered in the ISAACSW img acq MoveToSlit template See Phase II Proposal Preparation P2PP for more detailed information on the format of the finding charts and README files to be provided at the time of OB submission Should this detailed information be missing the observations will not be scheduled 5 3 3 LW spectroscopy The same interactive tools available in ISAACSW img acq MoveToS1it are provided in the ISAACLW img acq MoveToSlit and ISAACLW img acq MoveToSlitNoChop templates Although the subsequent spectroscopic observations are at long wavelengths 734m short wavelength broad band filters J H and Ks are available for object acquisition It is believed that most of the targets will be acquired more easily in these SW filters than in the LW filters If the ISAACLW img acq MoveToSlit acquisition template is used then chopping is set by default even if SW filters are used during the acquisition A defect on the objective in the Aladdin arm produces a patch of lower counts in the bottom left quadrant of the array In order to avoid the subsequent spectra being at the same position on the array as this patch objects are acquired 150 pixels away from the centre of the slit 5 3 4 Rapid Response Mode RRM The rapid response mode RRM offered from
63. e stars not the telescope are moved in X and Y according to the list of offsets Telescope offsets are defined as lists with the parameters List of offsets X or RA and List of offsets Y or DEC The offsets are relative to the previous position in RA and DEC or in X and Y depending on the Offset Coordinates parameter and they are defined in arcsec Additionally the observation type can be defined for each image and is entered as a list in the parameter Obs Type 0 or S O stands for Object and assigns the DPR CATG header keyword to ISAACSW_img_obs_GenericOffset 1024 1024 Position Angle Sky 30 SS N Template Parameters Number of exposures 8 Obs Type List of Offsets in X or RA 0 7 5 0 7 5 0 0 7 5 List of Offsets in Y or DEC 0 0 45 D 45 45 0 45 Offset Coordinates SKY ISAAC field of view 1 1 Figure 13 Illustration of the ISAACSW_img_obs_GenericOffset template The black dots represent the position of a star which was originally at the center of the field In this example Offset Coordinates is set to SKY and the telescope is moved in RA and DEC according to the list of offsets the stars move in the opposite direction SCIENCE S stands for Sky and assigns the DPR CATG header keyword to SKY The total number of exposures is defined in the parameter Number of Exposures This number can be different from the number of elements in the aforementioned lists Lists do not need
64. ec Add Velocity Alpha TEL TARG ADDVELALPHA 0 Additional tracking vel in RA Add Velocity Delta TEL TARG ADDVELDELTA 0 Additional tracking vel in DEC 0 Angle on Sky deg TEL ROT OFFANGLE Position angle DDD TTT SW Filter wheel 1 INS FILT1 NAME Filter wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter wheel 2 T In arcsec sec ISAAC img obs AutoJitter 1024 1024 Position angle on the sky 30 E Template Parameters Number of exposures 8 Jitter box width 30 Jitter box width Isaac field of view x 1 1 Figure 9 Illustration of the ISAACSW img obs AutoJitter template The black dots represent the position of a star which was originally at the center of the field A 7 Hawaii Imaging Templates All Hawaii Imaging templates use the SWI1 mode except the ISAACSW img acq Polarimetry tem plate which uses the SWP1 mode For more information see section 7 A T ISAACSW img obs AutoJitter This template offsets the telescope between exposures according to a random pattern of offsets automatically determined within the template It is ideal for long integrations on empty fields and does not require a long list of offsets to be defined Table 33 Parameters of ISAACSW img obs AutoJitter P2PP label Keyword Default Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of sub integrations Number of Exposures SEQ NEXPO Number of exposures Jitter Box Wid
65. econds respec tively If the observations are to be done at the beginning of the night when the background in these filters is high then DITs at the lower end of the range should be used 7 For K band observations of objects that are crossing the meridian near Zenith within 10 degrees of Zenith it is better to use NDITx DIT that is nearer to the lower bounds of the recommended range This will result in better sky subtraction 7 3 Calibration Plan A variety of calibration frames will be taken archived and updated at regular intervals Nightly zero points provided it is clear in the Hawaii Js J H and Ks filters For the Al addin J Block H and Ks filters zeropoints will be taken on nights when these filters are used These zero points are aimed at providing photometric calibration accurate to 5 10 Hawaii Aladdin Should users need higher accuracy they should provide OBs for standards close to the object that will be executed either immediately before or after their observations In this case the time spent doing these observations will be charged to the user Zero points in all other filters are not supported by the calibration plan and users should prepare the necessary OBs Extinction coefficients for J J Block Js H and Ks filters The observatory does not measure the extinction every night Instead the observatory has calculated the average extinction from data that has been taken since operations began See this
66. ed in the ISAAC data reduction guide and in the ISAAC web pages Users are encouraged to consult these documents before submitting an ISAAC proposal and to assess carefully how these features may affect their scientific goals For example the Hawaii SW detector suffers from electrical ghosts along detector lines which are somehow proportional to the intensity integrated along the lines A procedure is_ghost to partially get rid of these features when reducing the data has been implemented in the eclipse data reduction package Table 2 SW Imaging filters See appendix B for the filter curves Name Line Central wavelength um Width um Width Filters available with the Hawaii SZ 1 06 0 13 13 Js 1 24 0 16 13 jel 1 25 0 29 23 H 1 65 0 30 18 Ks 2 16 0 27 13 NB 1 06 1 06 0 01 94 NB 1 08 He I 1 08 0 016 1 5 NB 1 1914 1 19 0 01 0 8 NB 1 21 1 21 0 018 1 5 NB 1 26 Fe II 1 26 0 019 1 5 NB 1 28 PG 1 28 0 019 1 5 NB 1 64 Fe II 1 64 0 025 1 5 NB 1 71 1 71 0 026 1 5 NB 2 07 He I 2 07 0 026 1 5 NB 2 09 2 09 0 02 1 0 NB 2 13 H2 S1 2 13 0 028 1 3 NB 2 17 Bry 2 17 0 028 1 3 NB 2 19 2 19 0 03 1 3 NB 2 25 2 25 0 03 1 3 NB 2 29 2 29 0 03 1 3 NB 2 34 CO 2 34 0 03 1 3 Filters available with the Aladdin J Block Same as Hawaii blocking filter with mean transmission of 75 H Same as Hawaii Ks Same as Hawaii H The central wavelength varies slightly across the field of view 21 This filter is primarily
67. egrees The crosses represent the position of a star which was originally at the center of the field With this sequence the entire field of view would be imaged first at position angle of 45 degrees and then with 90 degrees A 8 Hawaii Spectroscopy templates A 8 1 ISAACSW spec obs AutoNodOnSlit This template nods the telescope between two positions A and B along the slit A cycle is a pair of AB or BA observations Cycles are repeated on ABBA sequences E g 3 cycles correspond to an ABBAAB sequence 4 cycles correspond to an ABBAABBA sequence etc Table 39 Parameters of ISAACSW spec obs AutoNodOnSlit P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of sub integrations Jitter Box Width SEQ JITTER WIDTH Jitter box width arcsec Return to Origin SEQ RETURN T Return to Origin flag Nod Throw Along Slit SEQ NODTHROW Throw of the nod arcsec Number of AB or BA cycles SEQ NABCYCLES Number of AB or BA cycles NINT SEQ NINT Number of frames at each position Instrument Mode INS MODE Instrument Mode Slit INS SLIT Which slit e g slit 1 Central Wavelength microns INS GRAT WLEN Central Wavelength microns Figure 15 illustrates what the template does The mean size of the nod is defined by parameter Nod Throw Along Slit in arcsec The first ex posure A is taken after offsetting the object along the slit by NodThcovALOngSiit arcsec
68. elength range order filter spectral coverage AA and spectral resolutions for the SWS1 and LWS3 LR and MR modes See appendix B for the filter curves Wavelength Or Fi LR MR Range de lt AA R 0 3 R 0 6 R 0 8 AA R 0 3 R 0 6 R 0 8 um r er um RQ R 1 5 R 2 um R 1 R 1 5 R 2 SWSI 0 98 1 1 5 SZ ful 1800 900 750 550 420 270 0 046 11500 5700 5000 3400 2700 1700 1 1 1 4 4 J full 1700 860 730 500 390 250 0 059 10500 5200 4700 3100 2500 1500 1 4 1 82 3 SH full 1600 840 690 500 380 250 0 079 10000 5100 4500 3000 2400 1500 1 82 2 5 2 SK ful 1500 750 600 450 330 200 0 122 8900 4400 3900 2600 2100 1300 LWS3 2 55 4 2 1 SL ful 1200 600 480 360 270 180 0 255 6700 3300 2600 2000 1500 1000 4 45 5 1 1 M full 1600 800 650 500 370 250 0 237 10000 5000 4000 3000 2300 1500 Table 7 ISAAC Polarimetric Mode Mode Spectral Range Pixel Scale Field Of View Detector Size arcsec arcsec pixels SWP1 0 98 2 5 um 0 1484 3 x 20x 150 1024 x 1024 Table 8 SW Polarimetry filters See appendix B for the filter curves Name Central wavelength um Width um Width SZ 1 06 0 13 13 Js 1 24 0 16 13 J Bl 1 25 0 29 23 H 1 65 0 30 18 Ks 2 16 0 27 13 NB 1 06 1 06 0 01 94 NB 1 1914 1 19 0 01 0 8 NB 2 09 2 09 0 02 1 0 NB 2 19 2 19 0 03 1 3 The central wavelength varies sli
69. en at different airmasses in all filters used during a night 8 4 Pipeline Chopping and most non chopping observations are supported by the pipeline The ISAACLW_img_obs_GenericOffset template is not supported 8 5 Performance The user should refer to the ETC for estimating the performance of this mode NTT and VLT Instrument Exposure Time Calculators 9 Short Wavelength Spectroscopy 1 SWS1 9 1 Characteristics See Section 2 3 for a description of the mode 9 2 Recommended DITs and NDITs The ISAAC array suffers from electronic pickup that is in some cases strong enough to dominate over the read noise We have tuned the readout of the array so that the pickup is minimised however this does not work for all DITs So we recommend that users use DITs for which the pickup is weak At the time of writing the recommended DITs are 30 60 90 100 120 150 180 200 250 300 400 500 600 750 and 900 seconds A more up to date list is available from the It is difficult to modify the array readout for DITs shorter than 30 seconds however such short DITs are generally reserved for standard star observations and in this case the pickup is insignificant Additionally the pickup can be removed at the data reduction stage See the Even with exposures as long as 900s the performance of MR spectroscopy between the OH lines in the J or H bands is readout noise limited It is therefore advisable to integrate for the longest possible tim
70. er that in the latter case the data are not calibrated e g flat fielded as they are in Garching for service observations Visitors can save the pipeline reduced data for themselves Pipeline reduced data are not part of the data package they receive at the end of their run The ISAAC pipeline is based on the eclipse library which can be downloaded from 6 Template cookbook and overhead calculations 6 1 Templates General description and summary The instrument detector and telescope are controlled by Observing Blocks OBs which are made up of templates Templates are divided into three categories acquisition observation and calibration Usually OBs consist of an acquisition template and one or more observation templates for science frames and one or more calibration templates for calibration frames One and only one acquisition template is allowed in an OB and therefore only one preset on sky It is not possible for example to group in the same OB observation templates on the science object and calibration templates on a standard star Tables 13 and 14 provide a short summary of the templates offered for period 72 These templates should cover most needs Should observers who have observing time with ISAAC consider that these templates do not cover their needs they must contact the User Support Group usg help eso org well before the obser vations start The template parameters are extensively described in appendix A
71. eration staff at execution time if the object is too faint ChopNod PARA of PERP to Slit This parameter allows the user to define chopping as either parallel or perpendicular to the slit If set to PARA the object will be continuously in the slit After completion of the preset the instrument and detector are set The observer is then prompted to either define an offset to the slit a drawing of which is overlaid on the RTD or to rotate the field by clicking on two objects Offsetting is simply done by drawing an arrow on the screen with the left hand button of the mouse If the offset is accepted the telescope offsets by the desired amount Finally the user is given the possibility of refining the position of the object Once the user is satisfied the template finishes An identical iteration loop is performed for rotating the field by clicking on 2 objects These 2 objects will be centered in the slit If the Preset Telescope parameter is set to F then the telescope will not move This can be useful in visitor mode to use the functionality of the template without presetting the telescope It is possible in this template to use the J Block H or Ks filters which are likely to allow an easier identification of the field these filters are not available for the subsequent observation templates The Alpha offset from Ref Star and Delta offset from Ref Star parameters allow the user to define a telescope offset when the a
72. escope offset before the first exposure If the parameter Return to Origin is set to true T the telescope moves back to its original position at the end of the template If not the telescope is not moved The Number of AB or BA cycles defines the number of OBJECT SKY or SKY OBJECT cycles to be executed These cycles are executed in ABBA sequences E g if Number of AB or BA cycles is set to 3 6 exposures will be taken in an ABBAAB sequence The template provides the possibility of rotating the instrument between object and sky frames so that pupil ghosts can be minimised all object frames have the same position angle on sky The technique has proved to be efficient with SOFI It is the default configuration with ISAAC In addition the template provides the flexibility to adjust the number of NDIT subintegrations for the OBJECT and SKY frames NDIT for the OBJECT positions defines the number of subintegrations on the object and NDIT for the SKY positions defines the number of subintegrations on the sky The total integration time excluding overheads is defined in seconds by DIT x NDIT for the OBJECT positions NDIT for the SKY positions x Number of AB or BA cycles Thus the total integration time on the sky and on the object can be adjusted so that the S N on the object is optimised Remember that the 1 minute per telescope position rule means here that both DIT x NDIT for the OBJECT positions plus overheads and DI
73. et ISAACLW img cal AutoChopNod ISAAC LWI STD ISAACLW img cal GenericOffset ISAACLW spec cal AutoChopNod ISAAC_LWS STD ISAACLW_spec_cal_AutoNodOnS1lit ISAACLW spec cal NightCalib ISAAC LWS NIGHTCALIB A A 1024 1024 1024 1024 Y Y l N N YN Sc Va d Slit _ x Slit x 1 1 1 1 a b L y A 1024 1024 1024 1024 f Pa P 1 1 e X Slit 1 1 c d Figure 8 Chopping orientation convention The star image in white is positive the star image in black is negative a 0 rotation on sky 0 chopping angle for SKY chopping coordinates or 90 chopping angle for DETECTOR coordinates b 0 rotation on sky 30 chopping angle for SKY chopping coordinates or 60 chopping angle for DETECTOR coordinates c 30 rotation on sky 0 chopping angle for SKY chopping coordinates or 60 chopping angle for DETECTOR coordinates d 30 rotation on sky 60 chopping angle for SKY chopping coordinates or 0 chopping angle for DETECTOR coordinates A 6 Hawaii Acquisition Templates A 6 1 Introduction Telescope presets can only be done via acquisition templates Telescope presets move the telescope to the requested coordinates and allow the telescope operator to select a guide star and start active optics Additionally these templates set up the detector and the instrument Conversely observation templates only deal with telescope offsets
74. eyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of DITs SW Filter wheel 1 INS FILT1 NAME Filter wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter wheel 2 Slit INS SLIT Slit e g slit_1 A 6 7 ISAACSW img acq Polarimetry All SW polarimetric OBs must use this template for target acquisition This template is very similar to the ISAACSW img acq MoveToPixel template The polarimetric mask is displayed on the RTD and is superimposed on the image of the field Therefore the offset can be defined so as to properly position the object into the transparent region of the mask The template has been coded so that the field of view will rotate around pixel x y 512 540 If the aim of the user is to measure the polarisation of a single target as opposed to measuring the polarisation in the entire field it is recommended that the target is placed on or close to this pixel Otherwise the target may move behind the mask after the field is rotated Service Mode users should make it clear where they wish their target to be placed Table 32 Parameters of ISAACSW img acq Polarimetry P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of DITs Preset Telescope SEQ PRESET T Preset telescope Alpha offset arcsec TEL TARG OFFSETALPHA 10 RA offset arcsec Delta offset arcsec TEL TARG OFFSETDELTA 10 DEC offset ars
75. g acq Preset or ISAACLW img acq MoveToPixel for acquisition and LW imaging no chopping templates must use either ISAACLW img acq Preset or ISAACLW img acq MoveToPixNoChop In those templates where 2 filters have to be defined SW Filter wheel 1 and SW Filter wheel 2 or LW Filter wheel 1 and LW Filter wheel 2 it is essential that at least one filter be set This includes acquisition templates The slit that is chosen in the acquisition template and the slit that will be used subsequently in the observation template must be the same If imaging and spectroscopic templates are combined in one OB it is required that the imaging template follows the spectrscopic template It is possible to submit a single OB which comprises several observing descriptions for example to observe a single target with different filters Night time calibration templates are not autonomous They must follow a spectroscopic obser vation Furthermore they only calibrate the wavelength setting that is used in the preceding template and not the wavelength settings in all preceding templates Some targets we are asked to observe saturate the detectors with the minimum DIT Please pay close attention to source brightnesses to ensure that this does not happen Use the verify button in P2PP this checks that individual parameters are within the defined ranges and also runs scripts to check the global logic of an OB With the exception of standards the minimum amoun
76. g will be in sky coordinates The convention is that 0 degree will result in chopping to the South i e the OFF beam will be to the South of the ON beam negative and positive images respectively on the acquisition images and that the angle of the chop is defined from North to West The direction of the chop on the array depends on the position angle of the instrument on the sky If the Chop Angle Coordinate is set to DETECTOR the chopping will be in detector coordinates The convention is that chopping will be along the X axis if Chop Position Angle is set to 0 and to the Y axis if Chop Position Angle is set to 90 This is independent of the position angle of the instrument on the sky e Chop Angle Coordinate Either SKY or DETECTOR See figure 8 for an illustration of the chopping orientation conventions A 4 Offset conventions and definitions The templates make extensive use of telescope offsets In some templates the offsets are set auto matically e g ISAACSW img obs AutoJitter but in others the offsets have to be entered manually as lists In this latter case the convention is that offsets are relative E g the following list of offsets RA offset list arcsec 0 10 10 20 20 will result in a first image at initial position in RA telescope offset 10 arcsec East for the second telescope offset 10 arcsec West for the third image i e the telescope is back to the initial position etc Sometimes offsets ma
77. ghtly across the field of view 2 This filter is primarily used as an order sorting filter however it can be used for imaging as well 3 This filter has leaks in the K band and the atmosphere defines the red edge of the filter For accurate photometry the Js filter is recommended 4 The narrow band 1 06u4ym and 1 19um filters correspond to regions of low OH emission and therefore enhanced sensitivity Table 9 ISAAC detectors Detector Format Pixel Size Q E RON Gain Well capacity pixels um Le e ADU e Hawaii 1024 x 1024 18 5 0 65 10 4 6 200 000 Aladdin 1024 x 1024 27 0 8 40 7 8 DCR HB UCR 290 000 8 7 DCR LB 170 000 Table 10 ISAAC detector readout modes Instrument mode configuration Detector readout mode Hawaii Hawaii SW Imaging SWI1 Double Correlated DCR Hawaii SW Spectroscopy SWS1 Non Destructive Read NDR Aladdin with chopping Aladdin LW Imaging LWI4 L M NB Uncorrelated UCR Aladdin LW Imaging LWI4 NB 3 21 3 28 3 80 4 07 Double Correlated High Bias DCR HB Aladdin LW Spectroscopy LWS3 MR and LR L band Double Correlated High Bias DCR HB Aladdin LW Spectroscopy LWS3 LR M band Uncorrelated UCR Aladdin without chopping Aladdin SW Imaging LWI3 J Block H Ks Double Correlated Low Bias DCR LB Aladdin LW Imaging LWI3 NB 3 21 NB 3 28 Double Correlated High Bias DCR HB Aladdin LW Spectroscopy LWS3 MR Double Correlated Low Bias DCR LB
78. grams we cannot guarantee that we will make the best choice as this depends on the science users wish to do If you think that a specific spectral type suits your program better than others we recommend that you submit calibration OBs The observatory selects telluric standards from four catalogues the IRIS Photometric Standards the MSSSO photometric standards a composite list of bright spectroscopic standards and the Hipparcos Catalogue The majority of the standards come from the Hipparcos Catalogue Although the Hipparcos Catalogue is an excellent source of telluric standards for ISAAC most of the stars in the catalogue do not have IR magnitudes which means that IR magnitudes have to be inferred from the spectral type Such an extrapolation leads to an uncertainty of 5 20 in the absolute flux calibration If users wish to have a more certain absolute flux calibration they should provide their own standards For absolute calibration slit losses have to be estimated This is usually a difficult task as the spectroscopic standard which is usually the telluric standard and the program object may not be positioned at exactly the same place in the slit If the object is a point source it can be assumed that the slit losses for the standard and the program object are the same If the program object is not a point source the slit losses have to be estimated on the basis of its morphology It is always good practice to observe the spectroscopic
79. he extent this is possible to orient the field so as to have a moderately bright object in the slit simultaneously with the program object This allows one to monitor slit losses during a long exposure while providing an extra means of locating the object spectrum through its position relative to this reference object The bright object can also be used as a secondary standard for the removal of telluric lines Wavelength calibration As mentioned in section ISAAC is equipped with a calibration unit allowing one to take arc spectra of Xenon and Argon However it is standard practice to use the OH lines for wavelength calibration The technique works very well at medium spectral resolution below 2 24m At low resolution the lines are too highly blended but can still be used for a zero point correction from a calibration performed with the arc lamps Detailed sky spectra with OH line identifications are available on the ISAAC web page http www eso org instruments isaac Above 2 2 um the OH lines are very weak and cannot be used so arc spectra should be used Telluric features can also be used Above 4 2 wm Xenon and Argon lines are too faint to be observed Although it is possible to use the grating in 3rd order to do the wavelength calibration the calibration is not very accurate An alternative method is to use the numerous telluric features This has been tested for MR and LR spectroscopy and has proved to be as accurate as using the arcs
80. heel 1 LW Filter wheel 2 INS FILT4 NAME Filter wheel 2 Slit INS SLIT Long Slit e g slit_1 T Tn arcsec sec in this case the detector may have to be windowed down to a field of view of 1 arcmin to avoid saturation The template presets the telescope and allows the operator to interactively center the field This template is functionally identical to the ISAACSW img acq MoveToPixel template so users should refer to Sec for details Table 45 Parameters of ISAACLW img acq MoveToPixNoChop P2PP label Keyword Default Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of DITs Preset Telescope SEQ PRESET T Preset telescope Alpha offset arcsec TEL TARG OFFSETALPHA 10 RA offset arcsec Delta offset arcsec TEL TARG OFFSETDELTA 10 DEC offset arsec Add Velocity Alpha TEL TARG ADDVELALPHA 0 Additional tracking vel in RA Add Velocity Delta TEL TARG ADDVELDELTA 0 Additional tracking vel in DEC Angle on Sky deg TEL ROT OFFANGLE 0 Position angle DDD TTT LW Filter wheel 1 INS FILT3 NAME LW Filter wheel 1 LW Filter wheel 2 INS FILT4 NAME LW Filter wheel 2 T Tn arcsec sec A 9 6 ISAACLW img acq MoveToSlitNoChop The template presets the telescope and allows the operator to interactively center objects into the selected slit The instrument mode for this template is LWI3 which is not offered for L and NB_M imaging Consequently the detector may have to
81. hrow in arcsec it is limited to the 10 30 arcsec range However we strongly recommend that users limit the throw to 20 arcseconds or less e ChopNod PARA of PERP to Slit Either PARA if chopping is done along the slit or PERP if perpendicular to it Nodding will always be done parallel to the chopping The first exposure is done without initially offsetting the telescope The first image A is a chopped subtracted image the second image B is taken with the telescope offset in the opposite direction to the chop etc Users of the LWS3 LR mode are requested to set the central wavelength to one of the following values 3 55 or 4 75 um Other values are not supported by the calibration plan see section HO If the parameter Return to Origin is set to true T the telescope moves back to its original position at the end of the template If not the telescope is not moved Table 49 Parameters of ISAACLW_spec_obs_AutoChopNod P2PP label Keyword Default Description Jitter Box Width SEQ JITTER WIDTH Random offset box size arcsec Return to Origin SEQ RETURN T Return to Origin Chop Throw arcsec SEQ CHOP THROW M2 Chop Throw arcsec ChopNod PARA of PERP to Slit SEQ CHOP SPEC Chopping along or perp to slit Integration time minutes SEQ TIME Integration time minutes Instrument Mode INS MODE Instrument Mode Central Wavelength microns INS GRAT WLEN Central Wavelength microns Slit I
82. ibration Templates With Chopping Chopping and Nodding The Aladdin templates are divided into those that use chopping LW and those that do not SW amp LW Chopping can be used for all LW observations gt 3ym It is the only mode of operations for imaging in L and M and LR spectroscopy The Aladdin templates that use chopping are listed in Table Table 47 Aladdin templates that use chopping P2PP Template Name ISAACLW_img_obs_AutoChopNod ISAACLW_spec_obs_AutoChopNod ISAACLW_img_cal_AutoChopNod ISAACLW_spec_cal_AutoChopNod If an observation is done with chopping then the calibration should be done with chopping as well Do not mix observing templates that use chopping with calibration templates that don t and vice versa Chopping is always combined with telescope nodding This is illustrated on figure y y y 1024 1024 1024 1024 1024 1024 AAS SIS PALPAALAAALYYS ee fe SSS NS SSN SNS SNS SANS SA SASS NINININI Sd PARAS SALYN ANAS SS YN ANAS SASS SA SASS SS SASS A SANA Sd I PALPLPAPAPPA LAL ALALAALAAYLYY PPAAPAAALALAALLALALAAYLA PASSA SSS NS SSSA NSN SANS SA SA SS SA ASS SS OS PASSA SSNS NSS SASS SASS SNS SA SANS Sd AS IPSAS PASSA SSS NSS SSSA SNS SNS SANS SA SA SS SA ASS OS PSA SA SSNS NSS SANS SASS SANS SA SASS Sd AS dE ASS SS PAS SNS SS SS PASSA S SSNS SASS SASS BN SA SANS Sd ASS Sd SS PPPPAASLAALI ANANSI PAPAS NINININI NAN ASSASSINS SA SASS PAY ANANSI PPASPLALALAI deefe fe SAS
83. ich ISAACSW img acq MoveToSlitrrm see Section A 6 6 must be used instead See also section and for more specific information regarding slit acquisition This template is very similar to the ISAACSW img acq MoveToPixel template A drawing of the selected slit defined with the Slit parameter is displayed on the RTD and is superimposed on the image of the field The centering of the target or reference objects is then done interactively with the tool described in appendix In most cases users will use the option to move the selected object to the centre of the slit The template also allows one to place two objects into the slit without the requirement of calculating the position angle beforehand There is no way of checking if the slit that is chosen in the acquisition template and the slit that will be used subsequently in the observation template are the same It is therefore of utmost importance that users ensure that they are identical Users should also ensure that the correct set of filters are used when acquiring bright targets See Section The Alpha offset from Ref Star and Delta offset from Ref Star parameters allow the user to define a telescope offset when the acquisition is made on reference objects That is once the reference object has been acquired and centered in the slit the offsets defined here will offset the telescope so as to bring the desired target into the slit These offsets should not be confused with the Al
84. idth to some non zero value so that these hot pixels can be removed A 10 1 ISAACLW img obs AutoChopNod This template combines chopping and telescope nodding The number of nodding cycles is referred to as Number of AB or BA cycles and one cycle commonly called an AB cycle consists of two exposures one at each end of the nod Additionally it is possible to jitter between ABBA cycles but not between AB or BA cycles The amount of jitter between ABBA cycles is defined by the Jitter Box Width parameter in arcseconds For the removal of hot pixels it is essential that Jitter Box Width be set to a non zero value The orientation of the chopping is defined with the Chop Position Angle parameter This param eter can be defined in terms of SKY or DETECTOR coordinates with the Chop Nodding Coordinate 7 parameter see section A 3 The parameters dealing with chopping and nodding are e Integration time minutes This parameter allows one to define the total integration time excluding overheads See section 6 2 for how to compute the overheads The number of chop and nod cycles will be determined automatically in the template e Chop Throw arcsec This is the chopping throw in arcsec it is limited to the 10 30 arcsec range However we strongly recommend that users limit the throw to 20 arcseconds or less e Chop Position Angle See section This parameter can be defined in either SKY or DETECTOR coordinates e Chop Nodd
85. in array is intrinsically more non linear The Aladdin JHK images are more complicated to flatfield because the flatfield contains scattered light and also a central light concentration In some cases we have found that flat fielding can actually decrease the photometric accuracy of the observation Without illumination corrections the flat fielding accuracy is 23 improving to 1 5 with illumination corrections The corresponding values for the Hawaii are 22 without and 1 with illumination corrections Ks images taken with the Aladdin contain scattered LW light observed as circular arcs which is probably due to the open filter position which is immediately adjacent The scattered light is removed by normal IR sky subtraction techniques however sky subtraction is still better with the Hawaii The main advantage of JHK Aladdin observations is that they are much more efficient due to the negligible readout time This can mean a significant reduction in overheads for users with short DITs This also means that the minimum DIT is reduced compared to the Hawaii 0 3447s compared to 1 77 3 55 s The Aladdin arm also has higher throughput than the Hawaii arm in tests SW imaging with the Aladdin reached 0 15 mag fainter than with the Hawaii in the same exposure time In summary users who require very short integration times or who do not require such accurate photometry may be interested in using the Aladdin arm for JHK observations however
86. ing Coordinate Either SKY or DETECTOR Depending on which value is selected the chopping angle will be defined either on sky or relatively to the detectors rows and columns The nodding is slaved to the direction of the chopping If the parameter Return to Origin is set to true T the telescope moves back to its original position at the end of the template If not the telescope is not moved Table 48 Parameters of ISAACLW img obs AutoChopNod P2PP label Keyword Default Description Integration time minutes SEQ TIME Integration time minutes Jitter Box Width SEQ JITTER WIDTH Random offset box size arcsec Return to Origin SEQ RETURN T Return to Origin Chop Throw arcsec SEQ CHOP THROW M2 Chop Throw arcsec Chop Position Angle SEQ CHOP POSANG Chop Position angle deg Chop Nodding Coordinate SEQ CHOPNOD COORDS SKY or DETECTOR coords LW Filter wheel 1 INS FILT3 NAME Filter wheel 1 LW Filter wheel 2 INS FILT4 NAME Filter wheel 2 The total integration time excluding overheads is defined in minutes In general the user will get slightly more or slightly less time that what was specified in the OB This is because the DIT is set so that the detector does not saturate the number of NDITs is set by the chopping frequency and the number of cycles is set so that approximately one minute is spent at each end of the nod To compute the actual integration time from the information p
87. itude IR Magnitude Filters to use gt 11 Any gt 8 and lt 11 Any Narrow Band filter gt 6 and lt 8 Two close Narrow Band Filters on each filter wheel E g NB_2 19 on filter wheel 1 and NB_2 17 on filter wheel 2 lt 6 Two distant Narrow Band Filters on each filter wheel E g NB_2 09 on filter wheel 1 and NB_2 17 on filter wheel 2 Important note when the bright object in the field of view is not the target to center on slit the target may become too faint to see due to the use of the Narrow Band Filter s In this case see Sec 5 3 offsets from a reference star should be used 5 4 3 LW Imaging and Spectroscopy For NB_3 21 and NB_3 28 non chopping observations the maximum brightness is L 5 Users who wish to observe brighter stars in these filters should use chopping For LW spectroscopy objects brighter than 4th magnitude should be acquired with the NB filters 5 5 Night Flat fields and arcs Due to non reproducibility effects involving the grating and the slit there are usually slight differ ences between flats and arcs taken at different times As flats and arcs are taken the day after the observations this can limit the accuracy at which spectroscopic data can be flatfielded and wave length calibrated To circumvent this special templates have been created to allow flat fields or arcs to be taken at the end of the spectroscopic templates without moving the grating or slit wheel ISAACLW spec cal NightCalib for LW IS
88. ken at the end of each night with the DIT values used during the night e LRarcs LR arcs are taken in the L band In M it is not possible to take arcs with the grating in the 1st order so they are taken with the grating in 3rd order However the accuracy is poorer than using the telluric features themselves which are ubiquitous in M band spectra e MR arcs Arcs corresponding to the setups used during a night are taken by the daytime astronomer during the following day As in LR arcs are taken with the grating in 1st order for L and with the grating in 3rd order for M Alternatively the ubiquitous telluric features can be used This has been tested for all spectroscopic modes and has proved to be as accurate as using the arcs e Star traces These calibration frames are aimed at tracing spectra at different positions along the slit and providing the co ordinate transformation between imaging and spectroscopy They are archived for both the LR and MR modes 10 4 Pipeline All chopping and most non chopping templates are supported The GenericOffset templates are not supported 10 5 Performance The user should refer to the ETC for estimating the performance of this mode NTT and VLT Instrument Exposure Time Calculators 11 Short Wavelength Polarimetry 1 SWP1 11 1 Characteristics See Section 2 4 for a description of this mode 11 2 Recommended DITs and NDITs Since light is divided in two by the Wollaston prism the DIT v
89. l in blue the L filter in yellow the M filter 4 Observing at the VLT 4 1 Visitor Mode Operations Visitors arrive on Paranal 2 days ahead of their observing run and receive support from Paranal Science Operations PSO to prepare their OBs Users are requested to read the P2PP and ISAAC User Manuals before arriving During the night users do not have direct interaction with the instrument and the telescope The execution of their OBs is undertaken by the Telescope Instrument Operator and or the nighttime support astronomer Visitors should be aware that about 10 15 minutes of their time will be used by the observatory to take calibrations This usually involves twilight flat fields and imaging standards For spectroscopic observations the observatory will not automatically take telluric standards although they are es sential in removing telluric features and calibrating the data Visitors should think carefully about which telluric standards they should observe and observatory staff will help them make the right choice A brief overview of spectrophotometric calibration which includes the removal of telluric features is give in Sec Back up programs Even though Paranal is an excellent site bad weather can occur Therefore visitors should request backup programs in their telescope time proposal particularly if their main targets are in the North where on some occasions it is not possible to point the telescope because of strong win
90. l Keyword Def Description DIT DET DIT Detector Integration Time secs Jitter Box Width SEQ JITTER WIDTH Random offset box width arcsec Return to Origin SEQ RETURN T Return to Origin Sky Offset in Alpha SEQ SKYOFFSET ALPHA Sky Offset in Alpha arcsec Sky Offset in Delta SEQ SKYOFFSET DELTA Sky Offset in Delta arcsec Rotate Pupil SEQ ROTPUPIL T Pupil rotation compensation Number of AB or BA cycles SEQ NABCYCLES Number of AB or BA cycles NDIT for the OBJECT positions SEQ NDIT OBJECT NDIT used on OBJECT positions NDIT for the SKY positions SEQ NDIT SKY NDIT used on SKY positions SW Filter wheel 1 INS FILT1 NAME Filter name in wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter name in wheel 2 Figure 11 illustrates what the template does By default there is no telescope offset before the first exposure If the parameter Return to Origin is set to true T the telescope moves back to its original position at the end of the template If not the telescope is not moved The Number of AB or BA cycles defines the number of OBJECT SKY or SKY OBJECT cycles to be executed These cycles are executed in ABBA sequences E g if Number of AB or BA cycles is set to 3 6 exposures will be taken in an ABBAAB sequence The template provides the possibility of rotating the instrument between object and sky frames so that pupil ghosts can be minimised all object frames have the same position angle on sky The techniqu
91. l always give a better sky subtraction For more information about chopping see Section 5 6 The imaging mode for observations with chopping is LWI4 The chopping templates produce a data cube for each nod position which contains the two half cycle frames For the narrow band 3 21 and 3 28 um filters non chopping observations can also be used The imaging mode for NB_3 21 and NB_3 28 non chopping observations is LWI3 8 2 Recommended DITs and NDITs For observations that use chopping DIT and NDIT are not parameters they are automatically set by the templates and depend on the filter For observations without chopping the optimal DIT values are given in Table NDIT should be set so that the total exposure at any one position is one minute Table 24 LW detector settings for imaging Mode and filter DIT seconds LWIS3 3 21 um filter 0 35 to 0 7 LWI3 3 28 um filter 0 35 to 0 5 8 3 Calibration Plan Supported calibrations are e Zero points of the night provided it is clear in the L and M_NB filters These zero points aim to provide photometric calibration to an accuracy of 10 Users requiring higher accuracy should provide OBs that will be executed either immediately before or after their observations In this case the time spent doing these observations will be charged to the user Narrow band filter zero points are not supported by the calibration plan and should be requested by the users e Darks e Sky flats tak
92. lit and ISAACSW spec obs GenericUffset tem plates in the definition of the parameters The user is referred to the description of these templates for the description of the parameters appendix A 8 1 amp A 8 2 These templates must be used by SWS1 MR and SWS1 LR users requesting calibrations beyond the ones provided by the Calibration Plan of this mode The differences with ISAACSW spec obs AutoNodOnSlit amp ISAACSW_spec_obs_GenericOffset are 1 some DPR keywords in the FITS headers of the images are set to different values allowing pipeline processing and archiving 2 In the list of available slits Slit parameter a slitless slit can be selected for obser vation of the standard star in a slitless mode for absolute spectrophotometric calibration Note that the Nod Throw Along Slit parameter when selecting the slitless must be lt 20 arcsec Note also that this particular slit is not offered in the list of available slits in the ISAACSW img acq MoveToSlit template Any slit can be defined for the acquisition when slitless is selected in the present template A 8 4 ISAACSW spec cal NightCalib This template allows one to take night time calibrations after the ISAACSW spec obs AutoNodOnSlit ISAACSW spec obs GenericOffset and ISAACSW spec cal AutoNodOnSlit templates See section 5 5 for more information regarding the need for night time calibrations This template is not autonomous It must follow a spectroscopic observati
93. lpha TEL TARG ADDVELALPHA 0 Additional tracking vel in RA Add Velocity Delta TEL TARG ADDVELDELTA 0 Additional tracking vel in DEC Angle on Sky deg TEL ROT OFFANGLE 0 Position angle DDD TTT SW Filter wheel 1 INS FILT1 NAME Filter wheel 1 SW Filter wheel 2 INS FILT2 NAME e Filter wheel 2 T Tn arcsec sec No RTD image is dumped on disk at the end of this template A 6 3 ISAACSW img acq Presetrrm This template is functionally identical to ISAACSW img acq Preset apart from having fewer param eters see Table Del and is intended for acquisition of RRM imaging OBs Table 28 Parameters of ISAACSW img acq Presetrrm P2PP label Keyword Default Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT x Number of DITs SW Filter wheel 1 INS FILT1 NAME Filter wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter wheel 2 A 6 4 ISAACSW img acq MoveToPixel This template presets the telescope and allows the operator to interactively center the field In visitor mode the interactive part of the template will be executed by the instrument operator under the supervision of the visiting astronomer In service mode it is mandatory that users send detailed information for the field centering see Section 5 3 In general one should not put the object at the very center of the array One should aim to place it a few tens of pixels away In order for objects to be clearly seen one fixed pa
94. meters of the LW chopping templates as they are automatically set to the optimal values imposed by the chopping frequency and saturation levels 5 7 Calibration Plans The calibrations that the observatory takes are discussed in detail in sections 7 to Users are requested to read these sections carefully The time spent doing these calibrations is not charged to the user If the user wishes to do calibrations that are not specifically mentioned or if the user wishes to do calibrations in excess of those specified in the calibration plan then users must submit the OBs to do these calibrations together with precise instructions in the README file The time spent doing these calibrations will be charged to the user 5 8 Pipelines It is our long term aim to produce pipelines that reduce ISAAC data accurately At this point in time this is not the case and experienced observers will be able to do better than the pipeline Thus we recommend that users use pipeline products as a means of quickly assessing the data The pipeline recipes and their limitations are discussed in more detail in the ISAAC Data reduction guide See Sections 7 to for details of the pipelines associated with each template For the templates supported by the pipeline service observers will receive reduced data processed by the pipeline in Garching by the Quality Control Group Visitors will have direct access to the data processed automatically on line Note howev
95. most users will probably want to use the Hawaii arm 2 3 Spectroscopic Modes ISAAC is equipped with 2 gratings for Low and Medium Resolution LR and MR respectively spectroscopy 6 slits and order sorting filters for each spectroscopic band The main characteristics of the spectroscopic modes of ISAAC are summarized in table 4 Slits with widths ranging from 0 3 to 2 arcsec see table 5 are available The 0 8 slit has two defects on the slit which produce regions of reduced transmission in the spectra Figure 2 shows a plot of the transmission along the slit The two defects at 93 and 688 pixels from the bottom of the slit are clearly seen It is recommended that observers choose nod throws that avoid using these parts of the slit This limits the usable length of the 0 8 slit to 1 5 arcmin Ll We li d W j MM il H ON hi UR TI uk IW d ii on 0 8 Transmiss 0 200 400 600 B0 lixels from bottom of slit Figure 2 Transmission along 0 8 slit showing two slit defects A calibration unit allows calibration lamps to be used for both wavelength calibration and flat fielding in spectroscopy only The lamps used for wavelength calibration are Xenon and Argon Special acquisition templates are used for the spectroscopic modes in order to ensure that objects are properly acquired in the slits The spectroscopic arm of ISAAC involves additional mirrors which cause the spatial axis the vertical one
96. n 1 2 Current version of this User Manual This is version 76 of the ISAAC User Manual applicable to Period 76 CfP It is advisable to check the ISAAC web page for possible updates to this manual and for recent news 1 3 Reminders See P2PP ISAAC Information for recent reminders 1 4 Content of this manual This User Manual is organized as follows Section 2 describes the optical layout the offered modes the detectors the control software and the templates of ISAAC Section dl gives an overview of observing in IR Section 4 presents some general features of observing at the VLT and section 5 introduces observing with ISAAC Section 6 gives a cookbook of the ISAAC templates and has a discussion of overhead calculation Sections 7 to section 11 give details of the different ISAAC instrument modes Finally the appendices present a detailed description of the templates appendix A the filter curves appendix B and a list of acronyms appendix D The standard star lists previously in the appen dices are now available from the ISAAC web pages 1 5 Contact Should you have any questions regarding the operation of ISAAC the point of contact is the User Support Group usg helpCeso org in Garching 2 ISAAC Infrared Spectrometer and Array Camera 2 1 Optical Layout Figure 1 shows the ISAAC optical layout i Array detector Filter wheels Figure 1 ISAAC Optical Layout In imaging mode light
97. n SEQ RETURN T Return to Origin flag X offset list arcsec SEQ OFFSETX LIST X offset list arcsec Y offset list arcsec SEQ OFFSETY LIST Y offset list arcsec Obs Type 0 or S SEQ OBSTYPE LIST List of observation types S or O Instrument Mode INS MODE Instrument Mode Slit INS SLIT Long Slit Central Wavelength microns INS GRAT WLEN Central Wavelength microns Figure 16 illustrates what the template does Telescope offsets are defined as lists with the X offset list arcsec and Y offset list arcsec parameters Telescope offsets are relative defined along detector lines X and columns Y and are in arcsec Offsets in Y are along the slit offsets in X are perpendicular to the slit With large combined offsets the guide probe may not be able to follow the same guide star In such a case the guiding system will automatically find another star but not resume guiding A pop up window will instruct the operator to resume guiding If the guide star has changed during an offset the accuray of the offset will be poorer than the offset would have been if the same guide star had been used This will only occur when offseting from object to sky On the return offset the operator will make sure that the original guide star is reselected so that pointing accuray is maintained while on the object Additionally the observation type can be defined for each image and entered as a list Obs Type 0 or 8 O stan
98. nds NDIT 150 Number of AB or BA cycles 30 NINT 1 Return to Origin T Execution time minutes Preset 10 0 Instrument setup 2 0 int time 60 0 Telescope offsets 15 25 61 telescope offsets Total 87 25 minutes for 60 minutes of integration 7 Short Wavelength Imaging Hawaii SWI1 amp Aladdin LWI3 7 1 Characteristics See Section 2 2 for a description of this mode JHK imaging is possible with the Aladdin as well as the Hawaii See section for a comparison of these two modes For most users JHK imaging with the Hawaii will be superior 7 2 Recommended DITs and NDITs Table gives some recommended values for DIT and NDITxDIT These values are a compromise between being background limited and maximising efficiency while limiting the exposure level to below 10 000 5 000 ADU Hawaii Aladdin and not staring at the same position for too long It is important that the sky is sampled frequently and many times Users should err on the side of having too many sky frames rather than too few Exposure levels can be derived by using the NTT and VLT Instrument Exposure Time Calculators Table 23 Recommended DIT in seconds and NDIT ranges for mode SWI1 amp LWI3 J Js J Block H Ks NB filters in J NB filters in H and K DIT seconds 30 45 10 12 10 15 60 120 50 100 NDITx DIT seconds 60 180 60 120 60 120 180 300 120 300 T For visitor mode programs the ranges for the Js and H filters are 30 60 and 10 15 s
99. neral rule must be applied to all ISAAC RRM observations The brightness of field stars will be checked automatically with the final release of the 2MASS catalogue See Sections 5 4 1 and for more information on general brightness limits in service mode 5 4 1 SW Imaging Aladdin and Hawaii Observations involving fields with objects brighter than 11th magnitude BB imaging or 8th magni tude NB imaging cannot be guaranteed in service mode and in shared visitor nights ESO reserves the right to lower the overall priority of the OB in question in service and not to execute the observations in shared visitor nights Imaging observations not compliant with these limits must be approved via submission of a If the waiver is approved this should be stated in the README file along with an estimate of the brightest object in the field of view ESO will try to devise strategies so that the observations can be done for example scheduling the observations for the end of the night or scheduling other imaging OBs after the observations in question 5 4 2 SW Spectroscopy Table indicates the filter settings that must be used when acquiring targets This depends on the brightness of the sources in the instrument field of view during a spectroscopic acquisition Note that this typically applies not only to standard stars but also to science fields when there are bright objects in the field of view Table 12 Acquisition filters versus target magn
100. nsequently offsetting the telescope too frequently can result in a significant loss of signal for the active optics and degraded performance This has the following important operational consequence The minimum time between telescope offsets must be at least one minute Observa tions not complying with this rule will be rejected by the operation staff at the time of execution Note that this rule does not apply to standard stars imaging or spectroscopy since some image degradation can usually be tolerated Provided that the previous rule is followed the control of the telescope active optics is totally transparent to the users Other important facts are e the offsetting accuracy of the telescope is 0 1 arcsec RMS as long as the same guide star is used when offsetting Offsets larger than a few arc minutes may involve a guide star change and in such a case the offsetting accuracy is less e defocusing the telescope is not an operational procedure e Scanning along the slit in spectroscopy during one exposure is not supported Guide Stars Guide stars are automatically found by the Telescope Control System and the users do not have to worry about finding them When small telescope offsets are used a few arcseconds to a few arcminutes the telescope keeps the same guide star this depends in practice on the position of the guide star in the Nasmyth field of view The offset accuracy is then excellent at the level of 0 1 arcsecond
101. nteractive part of the template will be executed by the instrument operator under the supervision of the visiting astronomer In service mode it is mandatory that the users send detailed information for target acquisition The chopping parameters to be defined are e Chop Throw arcsec This is the throw of the chopping in arcsec it is limited to the 10 30 arcsec range A chop throw of lt 20 arcsec is recommended e Number of Chop Cycles This is the number of chop cycles to be averaged in the acquisition system preprocessor The higher the value the better the detection limit but the longer the acquisition time One chop cycle will typically last between 2 to 10 seconds depending on chopping frequency The minimum number of chop cycles is 1 This parameter may be adjusted by the operation staff at execution time if the object is too faint e Chop Position Angle 7 See section A 2 e Chop Angle Coordinate Either SKY or DETECTOR After completion of the preset the instrument and detector are set The observer is then prompted to define an offset This is simply done by drawing an arrow on the screen with the left hand button of the mouse If the offset is accepted the telescope offsets by the desired amount Finally there is the possibility to redraw the arrow for refining the position of the object if necessary Once the user is satisfied the template finishes The Preset Telescope parameter if set to F
102. obs FixedSkyOffset Please refer to Sec for a description of what the template does This mode is available for imaging with the J Block H amp Ks broadband filters and 3 21 and 3 28 narrow band filters only Table 54 Parameters of ISAACLW img obs FixedSky0ffset P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs Jitter Box Width SEQ JITTER WIDTH Random offset box width arcsec Return to Origin SEQ RETURN T Return to Origin Sky Offset in Alpha SEQ SKYOFFSET ALPHA Sky Offset in Alpha arcsec Sky Offset in Delta SEQ SKYOFFSET DELTA Sky Offset in Delta arcsec Rotate Pupil SEQ ROTPUPIL T Pupil rotation compensation Number of AB or BA cycles SEQ NABCYCLES Number of AB or BA cycles NDIT for the OBJECT positions SEQ NDIT OBJECT NDIT used on OBJECT positions NDIT for the SKY positions SEQ NDIT SKY NDIT used on SKY positions LW Filter wheel 1 INS FILT3 NAME Filter name in wheel 1 LW Filter wheel 2 INS FILT4 NAME Filter name in wheel 2 A 11 4 ISAACLW_img_obs_GenericOffset This template works in an identical manner to ISAACSW_img_obs_GenericOffset Please refer to Sec for a description of what the template does This mode is available for imaging with the J Block H amp Ks broadband filters and 3 21 and 3 28 narrow band filters only Table 55 Parameters of ISAACLW img obs_GenericOffset P2PP label Keyword Def Description DIT DET DIT Dete
103. obs Generic0ffset len 8l 56 Parameters of ISAACLW_spec_obs_AutoNodOnSlit 8l 57 Parameters of ISAACLW_spec_obs_GenericOf set o 82 58 Parameters of ISAACLW img cal GenericOffset o 82 59 Parameters of ISAACLW spec calNightCalib een 83 1 Introduction 1 1 ISAAC ISAAC is an IR 1 5 um imager and spectrograph that lies at the Nasmyth B focus of UT1 It has two arms one equipped with a 1024 x1024 Hawaii Rockwell array and the other with a 1024 x 1024 InSb Aladdin array from Santa Barbara Research Center The Hawaii arm is used at short wavelengths 1 2 5 wm Prior to P70 the Aladdin arm was used exclusively at long wavelengths 3 5 um From P70 onwards this arm is also offered for JHK imaging ISAAC has several modes imaging and spectroscopy in both SW and LW and imaging polarimetry in SW only All modes are offered for both Service and Visitor Programs Target acquisitions obser vations and calibrations are done via templates A number of calibrations are regularly performed by ESO for general use Calibration Plan Finally data reduction pipelines are available for most modes of the instrument Important additional information to consult before preparing Phase I or Phase II proposals can be found at the following URLs ki e ISAAC web pages e Proposal Preparation and Submission e Phase II Proposal Preparation P2PP e P2PP ISAAC Informatio
104. observatory maintains a list of standard star OBs which visiting astronomers can use Flat fielding The VLT domes are not equipped with calibration screens so dome flats are not possible In imaging twilight flats are for the time being the only possibility offered to ISAAC observers Regular twilight flat fields are taken by the ISAAC operation staff as part of the Calibration Plan and are made available through the ESO archive ISAAC does have a calibration unit equipped with a tungsten lamp however the unit is adequate for spectroscopic flat fields only 3 4 Spectroscopy Nodding The classical technique in spectroscopy is to observe object s at two or more positions along the slit The sky is effectively removed by subtracting one frame from the other registering the two beams and then subtracting again This process is sometimes called double subtraction If the field is crowded or if the object is extended then a blank sky may be necessary and in this case the double subtraction is done slightly differently Spectrophotometric Calibration Calibration of spectroscopic data in the IR is a complicated procedure that requires care It is generally done in three steps The first step removes telluric features with what is commonly called a telluric standard the second step removes the spectral features of the telluric standard that are imprinted onto the science spectrum because of the first step and the third step sets the absolut
105. ody curve for wavelengths below 1 6 microns Unfortunately hot stars do contain some features usually lines of hydrogen and helium that can be difficult to remove If the region around the hydrogen and helium lines are of interest then one can also observe a late type star which should have weak hydrogen and helium lines This star is then used to correct for the helium and hydrogen absorption in the spectrum of the hot star Some hot stars also have emission lines or are in dusty regions These stars should be avoided The V I colour of the star can be used as an indicator of dust For stars hotter than A0 it should be negative And lastly hot stars tend to lie near the galactic plane so there may be situations where there are no nearby hot stars Solar analogs for the purpose of removing telluric features are stars with spectral type GOV to G4V These standards have many absorption lines in the IR particularly in the J band The features can be removed by dividing by the solar spectrum that has been degraded to the resolution of the observations This can be a bit tricky with ISAAC as the spectral resolution is variable In addition to hot stars and solar analogs IR astronomers have used other stellar types as telluric standards For example F dwarfs are commonly used We would like users to think carefully about which star is best for their program Although the observatory will automatically observe a telluric standard for service pro
106. on Furthermore it only calibrates the wavelength setting that is used in the preceding template and not the wavelength settings in all preceding templates Table 41 Parameters of ISAACSW_spec_cal_NightCalib P2PP label Keyword Def Description Flatfield at end of template SEQ FLATFIELD T Night flat field at end of template Arc at end of template SEQ ARC F Night arc at end of template A 9 Aladdin acquisition Templates A 9 1 Introduction Telescope presets can only be done via acquisition templates Telescope presets move the telescope to the requested coordinates and allow the telescope operator to select a guide star and start active optics Additionally these templates set up the detector and the instrument Conversely observation templates only deal with telescope offsets and not with telescope presets In general acquisition templates dump an image to disk only the ISAACLW_img_acq Preset template does not These dumped images are aimed at keeping track of the field position and orientation before starting the observation The acquisition templates to use depend upon the subsequent observation For imaging the sim ple preset ISAACLW_img_acq Preset can be used for any subsequent observation The chopping preset ISAACLW img acq MoveToPixel can only be used for subsequent imaging observations with chopping and the non chopping preset ISAACLW img acq MoveToPixNoChop can only be used for subsequent imaging observations wi
107. oposal Preparation ESO Observing Period 70 ESO Observing Period 71 ESO Observing Period 72 ESO Observing Period 74 Rapid Response Mode Real Time Display Son Of Isaac Short Wavelength Short Wavelength Imaging Short Wavelength Spectroscopy Short Wavelength Spectroscopy Low Resolution Short Wavelength Spectroscopy Medium Resolution Target of Opportunity Un Correlated Read Unit Telescope Very Large Telescope
108. opy same for RRM ISAACSW img acq MoveToSlit ISAACSW img acq MoveToSlitrrm Preset telescope and center field polarimetry ISAACSW_img acq Polarimetry Imaging Imaging of uncrowded fields ISAACSW_img_obs_AutoJitter Imaging of extended objects or crowded fields ISAACSW_img_obs_AutoJitter0ffset ISAACSW_img_obs_GenericOffset ISAACSW img obs FixedSkyOffset Imaging requiring special telescope offset sequences ISAACSW_img obs_GenericOffset Imaging Polarimetry ISAACSW img obs Polarimetry Spectroscopy Spectroscopy of point like or moderately extended objects ISAACSW spec obs AutoNodOnSlit Spectroscopy of extended objects i e wider than 1 arcminute or complex sequences of slit positions ISAACSW spec obs GenericOffset Standard Stars Standard Star imaging ISAACSW img cal GenericOffset Standard Star polarimetry ISAACSW img cal Polarimetry Standard Star spectroscopy ISAACSW spec cal AutoNodOnSlit ISAACSW spec cal GenericOffset Spectroscopic Night Time Calibration Night time flat fields and or arcs ISAACSW spec cal NightCalib Table 15 Overheads Channel Operation Time Comment minutes Both Full Preset amp acquisition varies with acq template ISAACSW_img acq Preset 6 times incl active optics ISAACSW img acq Presetrrm 6 ISAACLW img acq Preset 6 ISAACSW img acq
109. p NB 3 28 imaging and LW MR spectroscopy are more efficient The overheads come from instrument setups telescope presets object acquisitions and telescope offsets The overhead from detector readout is negligible Assuming DIT 0 4 seconds and NDIT 150 the elapsed time between two consecutive exposures is 0 4 x 150 15 75 seconds corresponding to overheads of about 25 Table provides some generic values for the main operations involved during operations They should be used when computing the ISAAC overheads Some examples tables 16 to 21 are given below to illustrate how to compute overheads with ISAAC Table 13 Aladdin Templates cookbook Action Template s to use Acquisition Simple telescope preset ISAACLW img acq Preset Preset telescope and center field with chopping ISAACLW img acq MoveToPixel Preset telescope and center field without chopping ISAACLW img acq MoveToPixNoChop Preset telescope and center object s in slit with chopping ISAACLW img acq MoveToSlit Preset telescope and center object s in slit without chopping ISAACLW img acq MoveToSlitNoChop Imaging with chopping and nodding ISAACLW img obs AutoChopNod Imaging without chopping J4 Block H Ks and narrow band imaging below 3 5 jum ISAACLW_img_obs_AutoJitter ISAACLW_img_obs_AutoJitter0ffset ISAACLW_img_obs_GenericOffset ISAACLW img obs FixedSkyOffset Spectroscopy
110. pha offset arcsec and Delta offset arcsec offsets which are used to define a sky reference for the first telescope position in order to subtract a fixed pattern Table 30 Parameters of ISAACSW img acq MoveToSlit P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of DITs Preset Telescope SEQ PRESET Preset telescope Delta offset from Ref Star SEQ REF OFFSETDELTA Offset from Ref Star arcsec T Alpha offset from Ref Star SEQ REF OFFSETALPHA 0 Offset from Ref Star arcsec 0 1 Alpha offset arcsec TEL TARG OFFSETALPHA 10 RA offset arcsec Delta offset arcsec TEL TARG OFFSETDELTA 10 DEC offset arsec Add Velocity Alpha TEL TARG ADDVELALPHA 0 Additional tracking vel in RA Add Velocity Delta TEL TARG ADDVELDELTA 0 Additional tracking vel in DEC Angle on Sky deg TEL ROT OFFANGLE 0 Position angle DDD TTT SW Filter wheel 1 INS FILT1 NAME Filter wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter wheel 2 Slit INS SLIT Slit e g slit_1 T Tn arcsec sec The image displayed on RTD at the end of the template is dumped on disk A 6 6 ISAACSW_img acq MoveToSlitrrm This template is functionally identical to ISAACSW img acq MoveToSlit apart from having fewer available parameters see Table B1 and is intended for acquisition of RRM spectroscopy OBs Table 31 Parameters of ISAACSW img acq MoveToSlit P2PP label K
111. plate provides interactive tools to rotate the field and or make telescope offsets to center objects into the selected slit which is overlaid on the RTD It can also be used to place two objects in the slit without having to precompute the position angle Service mode users requiring the rotation angle to be found in this way should make this clear in the finding chart and README and identify which stars to use OBs for which target acquisition cannot be completed within a few minutes of time will not be executed Acquisition can be done either on the target itself or on reference targets The object used for acquisition has to be brighter than approximately 17 18th magnitude in the IR when acquisition is done with the near IR Broad Band filters J H or Ks Exceptions will be tolerated for moving targets and special situations to be evaluated on a case by case basis When the science target is fainter than the above quoted magnitude the procedure for acquisition should rely on reference objects which are brighter than this limit These reference objects can either be positioned in the slit together with the target by defining the appropriate position angle on sky the recommended procedure or be used for initial centering on slit followed by a blind offset to move the target into the slit The ISAACSW img acq MoveToSlit template allows one to define relative offsets from the reference star These reference objects should be stars or point like
112. rc at end of template SEQ ARC F Night arc at end of template A 11 Aladdin Observation and Calibration Templates Without chopping For some modes one can take data in the Aladdin arm without chopping These modes are broadband imaging with the J Block H amp Ks filters NB imaging with the NB 3 21 and NB 3 28 filters and MR spectroscopy at all wavelengths The Aladdin templates that do not use chopping are listed in Table Table 51 Aladdin templates that do not use chopping P2PP Template Name ISAACLW_img_obs_AutoJitter ISAACLW img obs AutoJitterOffset ISAACLW img obs FixedSkyOffset ISAACLW img obs GenericOffset ISAACLW spec obs AutoNodOnSlit ISAACLW spec obs GenericOffset ISAACLW img cal GenericOffset ISAACLW spec cal AutoNodOnSlit If an observation is done without chopping then the calibration should also be done without chopping Do not mix observing templates that do not use chopping with calibration templates that do and vice versa A 11 1 ISAACLW img obs AutoJitter This template works in an identical manner to ISAACSW img obs AutoJitter Please refer to Sec for a description of what the template does This mode is available for imaging with the J Block H amp Ks broadband filters and 3 21 and 3 28 narrow band filters only Table 52 Parameters of ISAACLW img obs AutoJitter P2PP label Keyword Default Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT
113. requesting calibrations beyond the ones provided by the Calibration Plan of this mode Table 38 Parameters of ISAACSW img cal GenericOffset P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of DITs Number of Exposures SEQ NEXPO Number of exposures Return to Origin SEQ RETURN Return to Origin Flag X offset list arcsec SEQ OFFSETX LIST X offset list arcsec Y offset list arcsec SEQ OFFSETY LIST Y offset list arcsec SW Filter wheel 1 INS FILT1 NAME Filter wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter wheel 2 A 7 7 ISAACSW img cal Polarimetry This template is used for standard star observations in SW polarimetry It is strictly equivalent to the ISAACSW img obs Polarimetry template with the only difference that some DPR keywords in the FITS headers of the images are set to different values allowing pipeline processing and archiving The user is referred to the description of the ISAACSW img obs Polarimetry template for the description of the parameters Acquisition template Angle on Sky deg 45 IN N E Observation template parameters Number of exposures 9 X Offset List 1515150 15 15015 15 Y Offset List 300030003000 Rotator Offset List 045 DO E N E E 24 20 Figure 14 Illustration of the ISAACSW img obs Polarimetry template The rotator angle set in the acquisition image is 45 d
114. rovided in the FITS header you need to compute DIT x NDIT x 2 x Number of cyclesx Number of AB or BA cyclesx 2 Depending on the chop throw and whether or not the object is within the field of view in both chop positions the total integration time on the object may be reduced by a factor 2 A 10 2 ISAACLW spec obs AutoChopNod This template combines chopping and telescope nodding The number of nodding cycles is referred to as the Number of AB or BA cycles and one cycle commonly called an AB or BA cycle consists of two exposures one at each end of the nod Additionally it is possible to jitter between ABBA cycles but not between AB or BA cycles The amount of jitter between ABBA cycles is defined by the Jitter Box Width parameter in arcseconds For the removal of hot pixels it is essential that Jitter Box Width be set to a non zero value Chopping and therefore nodding can be either along the slit or perpendicular to it ChopNod PARA of PERP to Slit parameter It is important to realize that if it perpendicular to the slit only half the integration time will be spent on target The parameters dealing with chopping and nodding are e Integration time minutes This parameter allows one to define the total integration time excluding overheads See section 6 2 for how to compute the overheads The DIT NDIT and the number of chop and nod cycles will be determined automatically e Chop Throw arcsec This is the chopping t
115. ry in order to maintain image quality see Section 4 Another source of overheads is the detector read time which lasts approximately 2 3 4 1 E seconds per DIT for Hawaii imaging observations and 4 0 7 6 seconds per DIT for Hawaii spectroscopic observations The overheads then depend on the nature of the observations In Ks imaging for For service mode observations a read time of 4 1s should be assumed The Hawaii read time has alternated between these two values because of changes in the chip read speed made to reduce the amplitude of the odd even column effect Refer to the ISAAC web pages http www eso org instruments isaac Documentation for the current value instance DIT is typically 15s Assuming NDIT 6 the elapsed time between 2 consecutive exposures including one telescope offset is therefore 6 x 15 4 1 15 130 seconds corresponding to overheads of about 44 in case of a readout of 2 3 seconds the overheads are of the order of 30 Shorter DITs will accordingly increase the overheads In medium resolution spectroscopy in J or H the DIT can be as high as 15 minutes leading to readout time limited overheads of 2 only Aladdin overheads For the templates that involve chopping the overheads are given as a fraction of total integration time For imaging this fraction is 40 and for spectroscopy the overheads are 30 The newer Aladdin templates that do not involve chopping used for J Block H Ks NB_3 21 am
116. s AXA ISAACSW img obs GenericOffset This template is for imaging and has the flexibility to do any sequence of telescope offsets either in detector or sky coordinates Table 36 Parameters of ISAACSW_img_obs_GenericOffset P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs Number of Exposures SEQ NEXPO Number of exposures List of NDIT SEQ NDIT LIST NDIT List Return to Origin SEQ RETURN T Return to Origin Flag Obs Type 0 or S SEQ OBSTYPE LIST Observation type list S or O List of offsets X or RA SEQ OFFSET1 LIST X or RA offset list arcsec List of offsets Y or DEC SEQ OFFSET2 LIST Y or DEC offset list arcsec Offset Coordinates SEQ OFFSET COORDS SKY or DETECTOR coords SW Filter wheel 1 INS FILT1 NAME Filter wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter wheel 2 Figure 12 and 13 ilustrate what the template does ISAACSW_img_obs_GenericOffset 1024 1024 Position angle on the Sky 30 E N Template Parameters Obs Type 0 List of Offsets in Xor RA 0 7 507 5007 50 List of Offsets in Y or DEC 0 0 45 0 45 45 0 45 Number of exposures 8 Offset Coordinates DETECTOR ISAAC field of view 1 1 Figure 12 Illustration of the ISAACSW_img_obs_GenericOffset template The black dots represent the position of a star which was originally at the center of the field In this example Offset Coordinates is set to DETECTOR and th
117. satisfied the template finishes If the Preset Telescope parameter is set to F then the telescope will not move This can be useful in visitor mode to use the functionality of the template without presetting the telescope The interactive pop up windows are usually displayed before new images have arrived on the RTD Therefore users are strongly advised to carefully check that a new image has arrived before clicking on these windows e g for storing a fixed pattern for changing the DIT and NDIT The image displayed on RTD at the end of the template is dumped on disk Table 29 Parameters of ISAACSW img acq MoveToPixel P2PP label Keyword Default Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT S Number of DITs Preset Telescope SEQ PRESET T Preset telescope Alpha offset arcsec TEL TARG OFFSETALPHA 10 RA offset arcsec Delta offset arcsec TEL TARG OFFSETDELTA 10 DEC offset arsec Add Velocity Alpha TEL TARG ADDVELALPHA 0 Additional tracking vel in RA Add Velocity Delta TEL TARG ADDVELDELTA 0 Additional tracking vel in DEC Angle on Sky deg TEL ROT OFFANGLE 0 Position angle DDD TTT SW Filter wheel 1 INS FILT1 NAME Filter wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter wheel 2 T Tn arcsec sec A 6 5 ISAACSW img acq MoveToSlit All SW spectroscopy OBs must make use of this template for target acquisition The only exception is for RRM observations for wh
118. sition System Characteristics The detectors are an Hawaii 1024 x 1024 array from Rockwell used for SW observations and a 1024 x 1024 Santa Barbara Research Center SBRC Aladdin array used mainly for LW observations but also for JHK imaging from P70 onwards They are controlled by the ESO IRACE controller The main characteristics of the detectors are summarized in table 9 DIT and NDIT The IRACE controller controls the detector front end electronics and manages pre processing of the data before transferring it to the workstation The pre processor among other tasks averages the NDIT individual DIT integrations This significantly lowers the data rate between the IRACE con troller and the instrument workstation were the images are finally stored on disk particularly for L band imaging where the DIT is only a hundred milliseconds Note that the number of counts in the images always correspond to DIT not to the total integration time i e DIT x NDIT Readout Modes The offered readout modes with the Hawaii are Double Correlated Read DCR and Non Destructive Read NDR The offered readout modes with the Aladdin are Uncorrelated Read UCR Double Correlated Read with High Bias DCR HB and Double Correlated Read with Low Bias DCR LB DCR first resets the array and then performs two reads one at the beginning and one at the end after DIT seconds of integration The difference between these two reads is the image NDR first resets
119. t of time between telescope offsets is one minute Remember that for short wavelength imaging objects brighter than 11th magnitude must be justified in the README file Ensure that the correct set of filters are used when acquiring bright targets for SW spectroscopy See Section Ensure that spectra do not overlap when offsetting the telescope or nodding the secondary In particular make sure that jitter width is smaller than the nod throw Observation templates that use chopping should only be calibrated with calibration templates that use chopping Likewise observation templates that do not use chopping should only be calibrated with calibration templates that do not use chopping For observations that use chopping the bias voltage of the array is set so that the well depth is large This leads to a very large number of hot pixels whose flux is changing on the timescale of a few seconds Thus it is very important in long exposures to set Jitter Box Width to some non zero value so that these hot pixels can be removed When doing a blind offset from a bright reference object to a faint target the co ordinates of the reference object are the ones that should go into the acquisition template Orientation conventions and definitions East is to the right X of the images for zero position angle North is to the bottom Y7 of the images for a zero position angle Position angle on sky This angle is measured in the standard way i e
120. telescope is not moved at the end of the template ISAACSW spec obs AutoNodOnSlit 1024 1024 Position angle on sky 180 Jitter box A Template Parameters mM Nod throw Jitter box Width 20 Acquisition Nod Throw along slit 70 position Number of AB or B cycles 4 2 3 6 7 B ISAAC field of view peat broadened 1 1 Figure 15 Illustration of the ISAACSW spec obs AutoNodOnSlit template The black dots represent the different positions of a star originally at the center of the slit Note that the template starts with a telescope offset to move the star to one end of the nod along the slit Users of the SWS1 LR mode are requested to set the central wavelength to one of the following values 1 06 1 25 1 65 or 2 20 Other values are not supported by the calibration plan see section 9 The NINT parameter defines the number of frames stored per or B position If e g DIT 120s NDIT 1 NINT 8 8 images will be stored for each position If in addition Number of AB or BA cycles is set to 2 the template will deliver in total 32 images 8 for the first A position 16 for the B position and 8 for the second A position The total integration time excluding overheads is 64 minutes Note in the case where there are several OBs using this template on the same target for several hours of integration on the same target it is recommended to modify the Nod Throw Along Slit parameter by a few arcseconds between
121. th SEQ JITTER WIDTH Random offset box size arcsec Return to Origin SEQ RETURN T Return to Origin SW Filter wheel 1 INS FILT1 NAME Filter name in wheel 1 SW Filter wheel 2 INS FILT2 NAME Filter name in wheel 2 Figure illustrates what the template does The offsets are distributed randomly within a box whose size is defined by the parameter Jitter Box Width in arc seconds with the condition that the distance between any two points in a series of ten values is greater than a certain minimum This is intentionally done to ensure that the 5 frames before and after any frame are spatially not too close and can be safely used for creating skies without residual objects for sky subtraction The value of the Jitter Box Width parameter corresponds to the full width of the box in which the offsets are generated Defining too wide a box may lead to poor image overlap Conversely too small a value may lead to poor sky subtraction near extended objects A value of 30 arcsec or less is adequate for empty fields The minimum value is set to 10 arcsec By construction there is no telescope offset before the first exposure If the parameter Return to Origin is set to true T the telescope moves back to its original position at the end of the template If not the telescope is not moved The total integration time excluding overheads is defined in seconds by DIT x NDIT x Number of Exposures A 7 2 ISAACSW img obs
122. th the spatial offsets The opaque and transmiting parts of the mask have slightly different widths 24 arc seconds for the opaque ones and 20 arcseconds for the transmiting ones Thus three exposures with offsets of about 15 arcseconds in between the exposures are needed to cover the whole field Figure 14 illustrates what the template does Only the filters in filter wheel 1 are available for this template Table 37 Parameters of ISAACSW img obs Polarimetry P2PP label Keyword Def Description DIT DET DIT Detector Integration Time secs NDIT DET NDIT Number of sub integrations Number of Exposures SEQ NEXPO Number of exposures at each rotator position X offset list arcsec SEQ OFFSETX LIST X offset list arcsec Y offset list arcsec SEQ OFFSETX LIST Y offset list arcsec Rotator Offset list SEQ ROT OFFLIST 0 Rotator offset list degrees Return to original rotator position SEQ RETROTOFF T Return to original rotator position Flag SW Filter wheel 1 INS FILT1 NAME Filter name in wheel 1 The total integration time excluding overheads is defined in seconds by DIT x NDIT x Number of Exposuresx number of rotator offsets A 7 6 ISAACSW img cal GenericOffset This template is used for imaging standards and is similar to the ISAACSW img obs GenericOffset template appendix A 7 4 with the difference that the offsets are defined in detector coordinates This template should be used by all SWII users
123. the array and then non destructively reads the array N 1 times during the DIT seconds of integration where N depends on the DIT and is set by the software Longer DITs will result in more reads For each pixel a line is fit to the N reads the first read is discarded and the slope of the fit gives the pixel value in the image The readout modes are not parameters defined by the users The readout mode is automatically set according to the instrument mode Table 10 lists the detector modes that are assigned to instrument modes configurations LW observation modes Chopping is the default mode of operation for LW observations it is not used for SW observations Chopping is achieved by synchronizing the detector with the secondary mirror of the telescope M2 and by subtracting the images from the respective beams The result of a chopped image is therefore a background subtracted image with positive and negative images It is described in more detail in Section We deliver the two half cycle frames for each chopped image ie an ON frame and an OFF frame both averaged over the number of chop cycles These data are stored in a cube For LW narrow band imaging observations below 3 5 microns and for MR spectroscopic observations it is possible to get reasonable sky subtraction without resorting to chopping We have provided 6 observing templates 2 acquisition templates and 2 calibration templates that can be used to jitter and nod the telescope wi
124. thout chopping For spectroscopy observations using chopping must use ISAACLW img acq MoveToSlit for acquisition Non chopping observations can use either ISAACLW img acq MoveToSlit or ISAACLW img acq MoveToSlitNoChop A 9 2 ISAACLW img acq Preset This template does a simple telescope preset It is the easiest when a pointing accuracy of a few arcsec is enough for the purposes of the program It should NOT be used for subsequent spectroscopic observations No light reaches the detector during this template to avoid accidental imaging of warm objects as the telescope is presetting Consequently an image of the field will not be seen on the RTD when this template is used Table H2 describes the parameters of this template Table 42 Parameters of ISAACLW img acq Preset P2PP label Keyword Default Description Add Velocity Alpha TEL TARG ADDVELALPHA 0 Additional tracking vel in RA Add Velocity Delta TEL TARG ADDVELDELTA 0 Additional tracking vel in DEC Angle on Sky deg TEL ROT OFFANGLE 0 Position angle DDD TTT T Tn arcsec sec No RTD image is dumped on disk at the end of this template A 9 3 ISAACLW_ img acq MoveToPixel The instrument mode for this template is LWI4 The template uses chopping and can only be used to acquire targets for subsequent LW imaging observations that use chopping This template presets the telescope and allows the operator to interactively center the field In visitor mode the i
125. thout chopping These templates are identical to those used for SW imaging in the Hawaii arm The advantages of jittering and nodding over chopping are twofold Firstly the overheads are less and secondly there are no negative images so that unlike when chopping the whole field of view becomes available for science For all LW broad band and LR spectroscopic observations chopping is the only offered mode Windowing Windowing is not offered for either SW or LW observations However in some cases acquisition frames in the L band and some LW calibrations windowing may be used but this is automatically setup and transparent to the user Minimum DIT Table 11 indicates the minimum integration times for the Hawaii and Aladdin arrays which limit the magnitude of the stars to be used for e g photometric calibration In the Hawaii array the minimum DIT has alternated in the past between 3 55 and 1 77s This is due to changing the detector read speed to reduce the amplitude of the odd even column effect The current value of the minimum DIT in the Hawaii array can be found For service mode observations with the Hawaii array the allowed minimum DIT is 3 55s Users requiring shorter DITs should consider using the Aladdin array see Section 2 2 1 Note that DIT NDIT are not template parameters for the LW templates where chopping is used They are hardcoded in the templates Features ISAAC suffers from a number of features that are discuss
126. tions It is a sensitive function of the Moon phase and the distance to the Moon Even with DIT values of 900s the performance in MR spectroscopy is limited by the readout noise of the detector and not by the shot noise from the sky continuum Longer integration times are possible but lead to very poor cosmetics hot pixels and cosmic rays see Section 9 3 3 Imaging Jitter Because of the high sky brightness in the IR its rapid variability detector cosmetics and detector instabilities accurate sky subtraction is essential and this requires special attention and procedures The standard practice is to resort to the jitter technique also called shift and add and all ISAAC SW and some LW imaging templates make use of it When the field is uncrowded sky frames can be estimated from the object frames themselves In practice a running sky is built from the 5 frames that were taken immediately before and after the frame from which the sky is being estimated All sky subtracted frames are then co added with adequate shifts to form the final image When the field is crowded or the object extended i e covering a large fraction of the array the sky has to be sampled away from the object resulting in a loss of efficiency for the observations which can amount to 50 of the time if the sky has to be sampled as frequently as the object In this case all the object and sky positions are jittered between themselves A more
127. to have the same length If the number of exposures is larger than the number of elements in a list the list is restarted from the beginning as many times as needed until the correct number of frames have been acquired The lists can have any length however having lists of different lengths can become extremely con fusing It is good practice to use lists of equal length or lists with only one value if one parameter is not changed At the end of the template the telescope is returned to the original position if the parameter Return to Origin is set to true T If not the telescope is not moved at the end of the template The total integration time is defined in seconds by NumberofExposures DIT x 5 NDIT i 1 where NDIT i are the elements of the List of NDIT A 7 5 ISAACSW img obs Polarimetry This template is used for imaging polarimetry Telescope offsets are defined with the parameters X offset list arcsec and Y offset list arcsec and are defined along detector rows and columns so that users can move the object easily along the strips of the polarimetric mask which are along detector columns A list of rotator offsets is defined with the parameter Rotator Offset list The rotator offsets are relative to the current rotator position All the spatial offsets are performed for each rotator offset At the end of the sequence of spatial offsets at one rotator position the telescope is returned to
128. transmission curves are overplotted The atmospheric spectrum is represented here with a FWHM of 8 The atmospheric spectrum is a model corresponding to the typical situation at Paranal The Narrow Band Filters can be easily identified through the central wavelength of their response curves In green is part of the Z filter not offered since P70 in yellow the J filter in magenta the SH filter in blue the H filter in green the SK filter and in orange the Ks filter i L TS S Lal g a L Kal om J e et L _ mc b gt j b Mm P Q d Y EE E A m 2 95 2 85 b UDS UU Wavelength microns ECH 37 75 3 8 3 85 EY 3 95 3 45 35 55 36 3 4 Wavelength microns 4 45 4 25 4 3 4 35 4 2 4 05 L RD D UO SSILUSUDA 3 95 Wovelengin microns UA 4 95 49 AUI i op Wavelength microns 3 i m EX qu me E 9 Se i a e gt d o 7 ES sa o LO S5 SUD Figure 4 Atmospheric Transmission spectrum in the LW region Most of the LW filter transmission curves are overplotted The atmospheric spectrum is represented here with a FWHM of 2 5 The atmospheric spectrum is a model corresponding to the typical situation at Paranal The Narrow Band Filters can be easily identified through the central wavelength of their response curves In magenta is the SL filter the absorption dip at 3 1 jum is not rea
129. troscopic targets 2 LWIA is used for LW imaging with chopping L NB M NB_3 21 NB_3 28 NB_3 80 and NB_4 07 The filters available in SWI1 LWI3 and LWI4 modes are listed in tables 2 and Note that the filter central wavelengths are field dependent this is a general characteristic of filters due to the variation of the incidence angle on the filter across the field of view The effect is 0 3 of the central wavelength in some NB filters in K which represents a significant fraction of the bandwidth of these filters 2 2 1 Comparison of JHK imaging in Hawaii and Aladdin arms Due to technical problems in P69 it was necessary to transfer some SW observations to the Aladdin arm Although the technical problems are now fixed we have decided to keep and offer the possi bility of JHK imaging with the Aladdin arm Note however that as yet we have little experience with JHK Aladdin observations and in particular have not yet clarified some issues regarding flat fielding and photometric accuracy For these reasons we strongly suggest that users carry out SW imaging observations with the Hawaii arm The main cause of concern for Aladdin JHK observations is the photometric accuracy In test observations we find a difference which we do not currently understand of up to 0 1 mag rms between Hawaii and Aladdin magnitudes of the same field For JHK imaging with the Hawaii we achieve a photometric accuracy of 5 or better In addition the Aladd
130. ttern image is acquired in an offset position defined by the Alpha offset arcsec and Delta offset arcsec parameters This image is then subtracted from all images that are subsequently displayed on the RTD The telescope first goes to the offset position the operator is prompted to store a fixed pattern and when stored the telescope moves to the preset position The image displayed on the RTD then displays an image of the field minus the fixed pattern The integration time for these acquisition images is defined by the DIT and NDIT parameters and should be set according to the guidelines discussed in section At this point in time the user can change DIT and NDIT If the user changes these values the telescope offsets again and the user is required to store another fixed pattern before the telescope returns to the nominal position This loop can continue until the user has identified the target The observer is then prompted to define an offset This is simply done by drawing an arrow on the screen with the left hand button of the mouse At this point a window which lists the pixel co ordinates at the start and the end of the arrow will appear see figure 6 The user can either accept the offsets cancel or edit the co ordinates directly If the offsets are accepted the telescope offsets by the desired amount Finally the user is given the possibility to redraw the arrow for refining the position of the object if necessary Once the user is
131. web page Twilight Flat Fields in all filters as they are used Note that due to the limited number of narrow bands NB which can be observed during twilight each science OB is restricted to include at most two NB filters e Detector darks e Illumination corrections which are large scale difference between the true flat field and the twilight sky flat field These are determined in the Aladdin and the Hawaii for Js J J Block H and Ks only 7 4 Pipeline All AutoJitter and AutoJitterUOffset templates are supported by the pipeline ISAACLW_img_obs_GenericOffset is not supported ISAACSW_img_obs_GenericOffset is only partly supported sequences of observations with offsets larger than the field of view mosaicing are not reduced by the pipeline The SWI1 and LWI3 pipelines also calculate zero points and the read out noise and create master twilight flats and master dark frames See Infrared Jitter Imaging Data Reduction Algorithms for a description of the pipeline algorithm This pipeline has been used successfully since the start of the operations 7 5 Performance The user should refer to the ETC for estimating the performance of this mode NTT and VLT Instrument Exposure Time Calculators 8 Long Wavelength Imaging LWI3 and LWIA 8 1 Characteristics See Section 2 2 for a description of this mode Chopping is essential for observations with wavelengths gt 3 5um and can be used for all LW obser vations Chopping wil
132. y be defined in detector coordinates In that case a positive offset in X will move the image to the right X the telescope offset is therefore in the opposite direction All offsets are given in arcseconds even the offsets that are defined in detector coordi nates Therefore an offset of 10 in X will move the object 10 arcsec to the right of the image Reminder the minimum time between telescope offsets is 1 minute A 5 File names The names of the FITS files produced are fixed for each template and have names of the format ROOT _ nnnn _ ext fits where ROOT depends on the template used and is given in Table nnnn is a 4 digit incremental number and ext is a possible extension e g CUBE1 for LW obser vations Table 26 FITS files names Template ROOT ISAACSW img obs AutoJitter ISAAC SWI SCI ISAACSW img obs AutoJitterOffset ISAACSW img obs Generic Offset ISAACSW img obs Polarimetry ISAAC SWP SCI ISAACSW spec obs AutoNodUnSlit ISAAC SWS OCT ISAACSW_spec_obs_GenericOffset ISAACSW_img_cal_GenericOffset ISAAC_SWISTD ISAACSW spec cal AutoNodOnSlit ISAAC SWS STD ISAACSW img cal Polarimetry ISAAC SWP STD ISAACSW spec cal NightCalib ISAAC SWS NIGHTCALIB ISAACLW img obs AutoChopNod ISAAC LWI SCI ISAACLW img obs AutoJitter ISAACLW img obs AutoJitterOffset ISAACLW img obs Generic Offset ISAACLW spec obs AutoChopNod ISAAC LWS SCI ISAACLW spec obs AutoNodOnSlit ISAACLW spec obs GenericOffs

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