HAWK-I User Manual
Contents
1. Photometry with HAWK lt o o a oe s ca beee4 42444 58465 bbw es 2 2 1 Two ways to get reasonable photometry 2 2 2 Consider the 2MASS calibration fields The Exposure Time Calculator 2 2 24854 8652 Re ee Ge GP Sigri we Propasal EENEG Overheads and Calibration Plan 2 6 5 468465444 e444 e 4 ey 8 3 PHASE 2 Preparing your HAWK I observations 3 1 3 2 4 1 4 2 4 3 44 4 5 4 6 HAWK I specifics to templates OBs andp2pp Ol EE a4 22 es 6 eek ODER OS OE BAS SA AOS CSS a 3 1 2 Observing Blocks OBs Sis Templates gt io sad dcx nma Reh Eee Ree EEE Eee GG Finding Charts and README Files Observing Strategies with HAWK I CORE as ak oe a eo a ee eae ee a A Visitor Mode Operations The influence of the Moon 2 a 2 a a a Orientation offset conventions and definitions Instrument and telescope overheads 2 1 a a Recommended DIT NDIT and Object Sky pattern Il Reference Material A The HAWK I filters enerne N Cn On OO Om A A GO GO GO M kA bM oNN NNN HAWK I User Manual Issue 84 B The HAWK I detectors B 1 Threshold limited integration B2 Detectors structur s lt o ec g soati oe oe SEE eee Eee LR ei ES The HAWK I Field of View C 1 Relative position of the four2. Organisation Europ ene pour des Recherches Astronomiques dans H misph re Austral A Europ ische Organisation f r astronomische Forschung in der s dlichen Hemisphare ES r EUROPEAN SOUTHERN OBSERVATORY o A ESO European Southern Observatory Karl Schwarzschild Str 2 D 85748 Garching bei M nchen Very Large Telescope HAWK I User Manual Doc No VLT MAN ESO 14800 3486 Issue 84 1 27 June 2009 Prepared See ee eee A AEST UO at cea eebe HAWK I User Manual Issue 84 Change Record Issue Rev Date Section Parag Reason lnitiation Documents Remarks affected Issue 1 25 May 2007 all First release for PAE Issue 81 31 August 2007 prepared for CfP P81 6 Dec 2007 all update after end of commissionnings Issue 82 06 March 2008 P82 Phase version bump Bug in over head table corrected Minor changes to introduction Issue 82 1 06 March 2008 minor bug Issue 82 2 06 March 2008 Added warning about sky subtraction Issue 83 0 01 Sep 2008 P83 Phase 1 cal plan Issue 83 1 27 Nov 2008 P83 addenda for the IP83 release Issue 84 0 29 May 2009 P84 addenda New read out mode and persistence study Change of offset scheme Issue 84 1 27 Jun 2009 P84 addenda cleaning and Phase II HAWK I User Manual Issue 84 HAWK I as a CAD drawing attached to the VLT and in the integration hall in Garching HAWK I in a Nutshell Online information on HAWK I can be found
3. 2 2 2 Consider the 2MASS calibration fields The 2MASS mission used a number of calibration fields for the survey Details are given at http www ipac caltech edu 2mass releases allsky doc seca4_1 html In particular the sect II 2 http www ipac caltech edu 2mass releases allsky doc sec3_2d html provides a list of fields that you could use as photometric fields in order to calibrate your obser vations 2 3 The Exposure Time Calculator The HAWK I exposure time calculator can be found at http www eso org observing etc it returns a good estimation of the integration time on source needed in order to achieve a given S N as a function of atmospheric conditions A few words about various input variables that might not be quite standard also read the online help provided on the ETC page e the parameters to be provided for the input target are standard The input magnitude can be specified for a point source for an extended source in which case we compute an integration over the surface defined by the input diameter or as surface brightness in which case we compute values per pixel e g 106x106 mas e Results are given as exposure time to achieve a given S N or as S N achieved in a given exposure time In both cases you are requested to input a typical DIT which for broad band filters will be short 10 to 30s but for narrow band filters could be long exposures between 60 and 300s before being sky background limited
4. Table 1 Acquisition and science HAWK I templates acquisition templates functionality comment HAWKI_img_acq_Preset Simple telescope preset recommended HAWKI_img_acq MoveToPixel Interactive target acquisition HAWKI_img_acq_PresetRRM Simple telescope preset for RRM offered starting P82 HAWKI_img_acq_MoveToPixelRRM Interactive target acquisition for RRM offered starting P82 HAWKI img acg AD Acguisition in Adaptive Optics mode foreseen for future implementation science templates HAWKI_img_obs_AutoJitter imaging with jitter no offsets recommended for low density fields HAWKI_img_ obs_AutoJitter0ffset imaging with jitter and random sky offsets recommended for extended objects HAWKI_img_obs_FixedSky0ffset imaging with jitter and fixed sky offsets when random sky is not suited HAWKI_img_obs_GenericOffset imaging with user defined offsets The calibration and technical templates are listed in Table 2 The only calibration template accessible to the service mode SM user is the one to take standard stars The calibration templates are foreseen to acquire darks flat fields and simple standard star obser vations to calibrate the zero point The technical templates are used for the periodical characterization of the instrument The illu mination frames are used to determine the variation of the zero point as a function of detector position The astrometry and flexure template are needed to compute the distortion map the plate sca
5. 3 1 2 Observing Blocks OBs As an experienced ESO user it will come as no surprise to you that any HAWK I science OB should contain one acquisition template followed by a number of science templates If this did surprise you you may need to get back to the basics 3 1 3 Templates The HAWK I templates are described in detail in the template reference guide available through the instrument web pages A brief overview is given below If you are familiar with the ISAAC SW imaging or NACO imaging templates these will look very familiar to you and cover essentially the same functionalities The acquisition and science templates are listed in Table 1 Two forms of acquisition exist a simple preset when a crude accuracy of a couple of arcsec is enough and the possibility to position the target interactively at a given position in the image The science templates provide four forms of obtaining sky images small jitter patterns for un crowded fields random sky offsets for extended or crowded fields when the off position needs to be acquired far from the target field fixed sky offsets when random sky offsets are not suited and fi nally the possibility to define an arbitrary offset pattern when the standard strategies are not suited HAWK I User Manual Issue 84 8 For Rapid Response Mode we offer two acquisition templates They are exactly the same as the normal acquisition template but with the string RRM appended to the name
6. Note that it is very tempting to point right onto your favorite target and to lose it in the gap since this is where the telescope points HAWK I User Manual Issue 84 3 BEWARE of the gap between the detectors And see the details in Appendix C 2 1 2 Filters HAWK I is equipped with 10 filters 4 broad band filters and 6 narrow band filters see A for detailed characteristics and the URL to download the filter curves in electronic form The broad band filters are the classical NIR filters Y J H K The particularity of HAWK I is that the broad band filter set has been ordered together with the ones of VISTA There are thus identical which allows easy cross calibrations and comparisons The narrow band filters include 3 cosmological filters for Lya at z of 7 7 1 06um and 8 7 1 19um and Ha at z 2 2 i e 2 09um as well as 3 stellar filters CH4 H2 Bry Can you bring your own filters Possibly HAWK I hosts large 105mm7 i e expensive filters and was designed to have an easy access to the filter wheel However to exchange filters the instrument needs to be warmed up which usually only happens once per year Thus in exceptional cases i e for very particular scientific program user supplied filters can be installed in HAWK I within the operational constraints of the observatory Please make sure to contact paranal eso org before buying your filters provide your filters we would do our best to support you wit
7. e Do not hesitate to make use of the many graphical outputs In particular for checking your target line and the sky lines in the NB filters The screen output from the ETC will include the input parameters together with the calculated performance estimates Here some additional notes about the ETC output values e The integration time is given on source depending on your technique to obtain sky mea surements jitter or offsets and accounting for overheads the total observing time will be much larger e The S N is computed over various areas as a function of the source geometry point source extended source surface brightness Check carefully what was done in your case Most of the other ETC parameters should be self explaining and or well explained in the online help of the ETC HAWK I User Manual Issue 84 6 2 4 Proposal Form HAWK I allows only 1 set up direct Imaging Please indicate which filters in particular narrow band filters you intend to use This will allow us to optimize their calibration during the semester 4 INSconfig HAWK I Imaging provide HERE list of filters s Y J H K NB1060 NB1190 NB2090 H2 BrG CH4 2 5 Overheads and Calibration Plan When applying for HAWK I do not forget to take into account all the overheads when computing the required time e Make sure that you compute the exposure time including on sky time not only on source if your observing strategy requires it e Verify
8. in the call for proposal that you have taken into account all listed overheads which can also be found in Sect 4 5 e Check whether you need any special calibration have a look at the calibration plan in Sect D this is what the observatory will give you as default Any additional calibration you might need should be mentioned in the phase 1 proposal and the corresponding night time to execute them must be included in the total time requested HAWK I User Manual Issue 84 7 3 PHASE 2 Preparing your HAWK I observations This sections provides a preliminary guide for the observation preparation for HAWK I in phase 2 both for Service mode SM or Visitor mode VM We assume that you are familiar with the existing generic guidelines which can be found at e http www eso org observing observing html Proposal preparation e http www eso org observing phase2 SMGuidelines html Service mode informations e http www eso org paranal sciops VA_GeneralInfo html VM informations We know that they are not super thrilling but a quick browse over them might save yes you some time during phase 2 3 1 HAWK I specifics to templates OBs and p2pp HAWK I follows very closely the philosophy set by the ISAAC short wavelength and NACO imaging templates 3 1 1 p2pp Using p2pp to prepare HAWK I observations does not require any special functions no file has to be attached except for the finding chart all other entries are typed
9. instrument parameters like DARK current detector characteristics photometric zero points and others can be followed via the continuously updated trending plots available on the HAWK I QC webpages HAWK I User Manual Issue 84 26 E The HAWK I pipeline We refer to the pipeline manual for a full description on the HAWK I pipeline This section provides only a very brief overview of what to expect from the pipeline The pipeline full documentation is available at http www eso org sci data processing software pipeli The planned data reduction recipes included in this delivery will be e hawki_img_dark The dark recipe produces master dark and bad pixel map e hawki img flat The flat field recipe produces a master flat a bad pixel map a statistics table the fit error image e hawki_img_zpoint This recipe provides the zero points for the UKIRT selected standards e hawki_img_detlin This recipe determines the detector linearity polynomial coefficients com putation as well as the error on the fit e hawki_img_illum The illumination map of the detectors is obtained by observing a bright photometric standard consecutively at all predefined positions over a grid e hawki_img_jitter All science data resulting from the jitter and generic offset templates The four quadrants are combined separately The four combined products are eventually stitched together The online reduction pipeline working on Paranal will not provide this sti
10. last column represents the maximum extinction of a vignetted pixel i e the percentage of light absorbed in the pixel row or column with respect to the mean of the field Note although the Y edge vignetting is small in amplitude it extends to around 40 pixels at lt 10 HAWK I User Manual Issue 84 24 D The HAWK I calibration plan D 1 Do you need special calibrations The calibration plan defines the default calibrations obtained and archived for you by your friendly Paranal Science Operations team The calibration plan is what you can rely on without asking for any special calibrations However these are indeed the only calibration that you can rely on without asking for special calibrations Thus we strongly advise all the users to carefully think whether they will need additional calibrations and if so to request them right in phase 1 For example is flat fielding very critical for your program i e should we acquire more flats e g in your narrow band filters Would you like to achieve a photometry better than a few percent i e do you need photometric standards observe right before after your science frames Is the homogeneity of the photometry critical for your program i e should you ask for illumination frames close to your observations Is the astrometry critical i e should we acquire a full set of distortion and flexure maps around your run We would be more than happy to do all that for you if you tell us s
11. 100 200 300 420 and 580 10 HAWK I User Manual Issue 84 12 Telescope offsets Offset execution along the template 4 5 Instrument and telescope overheads The telescope and instrument overheads are summarized below Hardware Item Action Time minutes Paranal telescopes Preset 6 HAWK Acquisition HAWK I Initial instrument setup for ACQ only 1 HAWK I Telescope Offset small 0 15 HAWK I Telescope Offset large gt 90 0 5 HAWK Readout per DIT 0 03 HAWK Filter change 0 35 The instrument set up is usually absorbed in the telescope preset for a simple preset In the case of MoveToPixel the exact integration time is dependent on the number of images one needs to take at least 2 and of course the corresponding integration time For 3 images of DIT 2 NDIT 1 the overhead is 1 5min 4 6 Recommended DIT NDIT and Object Sky pattern For integration time longer than DIT 120sec the service mode user has to use one of the following DIT 150 180 240 300 600 and 900sec Please note that these values are indicative and can change due to sky variability especially for H band whose flux for a given DIT can fluctuate by a factor of 2 due to variations of the atmospheric OH lines This effect also impacts the Y J amp CH4 filters The Moon has an effect on the sky background especially for the NB1060 and NB1190 filters Similarly the variation of the outside tempera
12. bout 5 mas once the distortion model was applied a precision that should satisfy most purposes C 1 1 Center of Rotation and Centre of Pointing The center of rotation of the instrument is not exactly the centre of the detector array In the standard orientation North is Y East is X the center of the detector will be located 0 4 East and 0 4 South of the telescope pointing HAWK I User Manual Issue 84 23 The common reference point for all four quadrants taken as the centre of the telescope pointing and centre of rotation has the following pixel coordinates to 0 5 pix in the respective quadrant reference system Quadrant CRPIX1 CRPIX2 Ql 2163 2164 Q2 37 5 2161 5 Q3 42 28 Q4 2158 25 5 The CRVALI and CRVAI2 have the on sky coordinates of the telescope pointing FITS keywords TEL TARG ALPHA TEL TARG DELTA in all quadrants C 2 Vignetting of the field of view The Hawaii2RG detectors have 4 reference columns rows around each device which are not sensitive to light In addition due to necessary baffling in the all reflective optical design of HAWK I some vignetting at the edges of the field has turned out to be inevitable due to positioning tolerances of the light baffles The measured vignetting during commissioning on the sky is summarised in the following table Edge No of columns or rows vignetted gt 10 Maximum vignetting Y 1 14 Y 8 54 X 7 36 X 2 15 The
13. e Calculator Finding Chart Field of View Full Width at Half Maximum High Acuity Wide field K band Imager Near InfraRed Observing Block Phase II Proposal Preparation Point Spread Function Quality Control Real Time Computer Real Time Display Service Mode Telescope and Instrument Operator User Support Department Very Large Telescope Visitor Mode HAWK I User Manual Issue 84 2 Part Observing with HAWK I from phase 1 to data reduction 2 PHASE 1 applying for observing time with HAWK I This section will help you to decide whether HAWK I is the right instrument for your scientific project take you through a quick evaluation of the observing time needed and guide you through the particularities of HAWK I in the proposal form 2 1 Is HAWK I the right instrument for your project HAWK I does only one thing but does it well direct imaging in the NIR 0 97 to 2 31 um over a large field 7 5 x7 5 If this is what you intend to do HAWK I is the instrument you need If not you have probably downloaded the wrong manual The basic characteristics FoV pixel scale can be found in the nutshell at the beginning of this document 2 1 1 Field of View The Field of View of HAWK I is defined by four Hawaii 2RG chips of 2048 pixels each 1 pixel corresponds to 0 106 arcsec on the sky The detectors are separated by gaps of about 15 arcsec Thus the field of view looks like this 15 217 ke cf 7 5 n
14. eduction 6 Q2 chip 78 suffers from radioactive effects see Fig 6 HAWK I User Manual Issue 84 21 Master Flat Field in H Band cuts 0 8 1 2 Figure 5 Typical HAWK I twilight flat field H Band Figure 6 Radioactivity on Q2 chip 78 HAWK I User Manual Issue 84 22 C The HAWK I Field of View C 1 Relative position of the four quadrants The four quadrants are very well aligned with respect to each other Yet small misalignments exist They are sketched below Q4 chip 88 chip 79 8 0 03 8 0 04 02 Q1 chip 78 chip 66 8 0 130 Quadrants 2 3 4 are tilted with respect to quadrant 1 by 0 13 0 04 0 03 degrees respectively Accordingly the size of the gaps changes along the quadrant edges The default orientation PA 0 deg is North along the Y axis East along the X axis for quadrant 1 For reference purposes we use the partly arbitrarily common meta system Quandrant offset in X pix offset in Y pix Ql 0 0 Q2 2048 153 0 3 Q3 2048 157 2048 144 Q4 0 5 2048 142 It is valid in its crude form to within a few pixels The distortion corrections for a proper astrometry will be added to all image headers Distortions including the obvious rotation component will be defined with respect to the above system First qualitative evaluations with respect to HST ACS astrometric calibration fields re covered the relative positions of objects to a
15. hin the operational constraints of the observatory 2 1 3 Limiting magnitudes Limiting magnitudes are of course very much dependent on the observing conditions The exposure time calculator is reasonably well calibrated and we encourage you to use it In order to give you a rough idea of the performance to be expected we list here the limiting magnitudes S N 5 for a point source in 3600s integration on source under average conditions 0 8 seeing 1 2 airmass Filter Limiting mag Limiting mag Saturation limit Vega AB in 2 sec J 23 9 24 8 10 0 H 22 5 23 9 10 3 Ks 22 3 24 2 9 2 assumed 0 8 seeing For more detailed exposure time calculation in particular for narrow band filters please use the exposure time calculator Due to persistence effect of the detector in service mode no observation will be accepted for fields containing objects brighter than K 8 1 H 9 1 amp J 8 8 i e 5 times the saturation level This is really a generous lower limit brighter objects will produce persistence now more easily because of the increased minimum DIT 1 6762 secs 2 1 4 Instrument s performance We expect HAWK I to be used for plain imaging photometry and astrometry HAWK I User Manual Issue 84 4 The image quality of HAWK I is excellent across the entire field of view Distortions are below 2 over the full 10 diagonal and the image quality has always been limited by the seeing our best recorded i
16. ify that you are handling the quadrant that you expect eg EXTNAME CHIP1 INT1 The characteristics of the four detectors are listed below Detector Parameter Ql Q2 Q3 Q4 Detector Chip 66 78 79 88 Operating Temperature 75K controlled to 1mK Gain e7 ADU 1 705 1 870 1 735 2 110 Dark current at 75 K e s between 0 10 and 0 15 Minimum DIT 1 6762 s Read noise NDR 5 to 12 e7 Linear range 1 60 000 e 30 000 ADUs Saturation level between 40 000 and 50 000 ADUs DET SATLEVEL 25000 1 The noise in Non Destructive Read NDR depends on the DIT the detector is read continuously every 1 6762s i e the longer the DIT the more reads are possible and the lower the RON For the minimum DIT 1 6762s the RON is 12e7 for DIT 10s the RON is 8e7 and for DIT gt 15s the RON remains stable at 5 E Figure 3 represents the quantum efficiency curve for each of the detectors HAWK I User Manual Issue 84 19 r i Wavelength micro Navelength micro 1 Figure 3 Quantum efficiency of the HAWK I detectors BI Threshold limited integration The normal mode of operation of the HAWK detectors defined a threshold by setting the keyword DET SATLEVEL All pixels which have absolute ADU values below this threshold are processed normally Once pixels illuminated by a bright star have absolute ADU values above the threshold the values are no longer used to calculate the slope of the regre
17. ing subtracted and the difference in start time between the two exposures HAWK I User Manual Issue 84 15 Part Il Reference Material A The HAWK I filters The 10 filters in HAWK I are listed in Table 4 The filter curves as ascii tables can be retrieved from the instrument web pages Note in particular that the Y band filter leaks and transmits 0 015 of the light between 2300 and 2500 nm All other filters have no leaks at the lt 0 01 level Table 4 HAWK I filter summary Filter name central cut on cut off width tansmission comments wavelength nm 50 nm 50 nm nm Kal Y 1021 970 1071 101 92 LEAKS 0 015 at 2300 2500 nm J 1258 1181 1335 154 88 H 1620 1476 1765 289 95 K 2146 1984 2308 324 82 CH 1575 1519 1631 112 90 Bry 2165 2150 2181 30 77 H 2124 2109 2139 30 80 NB1060 1061 1057 1066 9 70 Optical ghost NB1190 1186 1180 1192 12 75 Optical ghost NB2090 2095 2085 2105 20 81 Optical ghosts out of focus images showing the M2 and telescope spiders have been found only with the NB1060 Lya at z 7 7 amp NB1190 Lya at z 8 7 filters As illustrated in Fig 1 the ghost images are 153 pixels in diameter and offset from the central star in the same direction however the latter varies with each quadrant and is not symmetric to the centre of the moisac The total integrated intensities of the ghosts are in both cases 2 but their surface brightnesses are a fact
18. le and relative positions of the detectors and to quantify possible flexures Three further tem plates are used to characterize the detector to determine the best telescope focus and to measure the reproducibility of the filter wheel positioning Table 2 Calibration and technical HAWK I templates calibration templates functionality comment HAWKI_img_cal_Darks series of darks HAWKI_img_acq_TwPreset acquisition for flat field HAWKI_img_cal_TwFlats imaging twilight flat field HAWKI_img_cal_SkyFlats imaging sky flat field HAWKI_img_cal_StandardStar imaging of standard field available to the SM user technical templates HAWKI_img_tec_I1luFrame imaging of illumination field HAWKI_img_tec_Astrometry imaging of astrometric field HAWKI_img_tec_Flexure measuring instrument flexure center of rotation HAWKI img tec_DetTest detector test monitoring HAWKI_img_tec_Focus telescope focus determination HAWKI_img_tec_FilterWheel filter wheel positioning accuracy 3 2 Finding Charts and README Files In addition to the general instructions on finding charts and README files that are available at http www eso org observing p2pp the following HAWK I specifics are recommended e The field of view of all finding charts must be 10 by 10 in size with a clear indication of the field orientation HAWK I User Manual Issue 84 9 e Ideally the finding chart should show the field in the NIR or at least in the red and the wave
19. length of the image must be specified in the finding chart and the README file e The IR magnitude of the brightest star in the field must be specified in the P2PP comment field of the OB HAWK I User Manual Issue 84 10 4 Observing Strategies with HAWK I 4 1 Overview As with all other ESO instruments users prepare their observations with the p2pp software Acqui sitions observations and calibrations are coded via templates and Observing Blocks OBs OBs contain all the information necessary for the execution of an observing sequence At the telescope OBs are executed by the instrument operator HAWK I and the telescope are setup according to the contents of the OB The HAWK I RTD is used to view the raw frames During acquisition sequences the RTD can be used for the interactive centering of the targets in the field Calibrations including DARKs skyflats photometric standard stars illumination maps etc are ac quired by the Observatory staff according to the calibration plan and monitored by the Quality Control group of ESO Garching 4 2 Visitor Mode Operations Information policy on the Visitor Mode operations at the VLT are described at http www eso org paranal sciops VA_GenerallInfo html Visitors should be aware that about 30 minutes night of night time may be taken off their time in order to perform the HAWK I calibrations according to the calibration plan 4 3 The influence of the Moon Moonlight does not
20. mages had FWHM below 2 2 pix i e lt 0 23 in the Ks band The photometric accuracy and homogeneity that we measured across one quadrant is lt 5 as monitored on 2MASS calibration fields We expect that with an even more careful illumination correction and flat fielding about 3 absolute accuracy across the entire field will be achieved routinely when the calibration database is filled and stable Of course differential photometry can be pushed to a higher accuracy Note in particular that given the HAWK I field size between 10 and 100 useful 2MASS stars calibrated to 0 05 0 10 mag are usually present in the field Finally the relative astrometry across the entire field was auto calibrated following Anderson et al 2006 A amp A 454 1029 and checked against ACS astrometric fields The distortion map cur rently allows to recover relative position across the entire field with a spectacular precision of lt 5 mas A note of caution as all current infrared arrays the HAWK I detectors suffer of persistence at the level of 107 1074 depending on how badly the pixels were saturated that decays slowly over minutes about 5min for the maximum tolerated saturation level in SM This might leave artifacts reflecting the dither pattern around saturated stars 2 2 Photometry with HAWK I As you will have noticed acquiring a single star per night does not allow to carry out high precision photometry but rather to monitor the i
21. noticeably increase the background in the NIR so there is no need to request dark or gray time However it is recommended not to observe targets closer than 30 deg to the moon to avoid problems linked to the telescope guiding active optics system The effect is difficult to predict and to quantify as it depends on too many parameters Just changing the guide star often solves the problem Visitors should check their target positions with respect to the Moon at the time of their sched uled observations e g with the tools available at http www eso org observing support html Backup targets are recommended whenever possible and you are encouraged to contact ESO in case of severe conflict i e when the distance to the Moon is smaller than 30 deg 4 4 Orientation offset conventions and definitions HAWK I follows the standard astronomical offset conventions and definitions North is up and East to the left All offsets are given as telescope offsets i e your target moves exactly the other way in arcseconds The reference system can be chosen to be the sky offsets 1 and 2 refer to offsets in Alpha and Delta respectively independently of the instrument orientation on the sky or the Detector offsets 1 and 2 refer to the detector X and Y axis respectively For jitter pattern and small offset it is more intuitive to use the detector coordinates as you HAWK I User Manual Issue 84 11 probably want to move the target on the detecto
22. nstrument performance 2 2 1 Two ways to get reasonable photometry If good photometry is your goal you should go for one of the following options e Ask for special calibrations Take into account as early as phase 1 i e in your proposal the fact that you want to observe more and other standard fields than the ones foreseen in the calibration plan In your README file you can then explain that you want your specified standard field observed e g before and after your science OB You can also specify that you want illumination maps for your filters close in time to your observations and or specify as special calibrations your own illumination maps e f a photometric calibration to 0 05 0 1 magnitude is enough for your program consider that the HAWK I field is large and that by experience you will have 10 100 stars from the 2MASS catalog in your field These are typically cataloged with a photometry good to lt 0 1 mag and would allow to deter mine the zero point on your image to 0 05 mag using these local secondary standards Extinction coefficients would automatically be taken into account and the colour terms for HAWK I are small 0 1x J K Check with Skycat or Gaia ahead of time whether good non saturated 2MASS HAWK I User Manual Issue 84 5 stars are present in your science field Skycat is available under http archive eso org skycat Gaia is part of the starlink project http starlink jach hawaii edu
23. o i e if you mention it in phase 1 when submitting your proposal D 2 The HAWK lI standard calibrations in a nutshell Here is what we do if we do not hear from you HAWK I Calibration Plan Calibration number frequency comments purpose Darks 10 exp DIT daily for DITxNDIT lt 120 Darks 5 exp DIT daily for DIT lt NDIT gt 120 Twilight Flat fields 1 set filter daily broad band filters best effort basis 1 set filter as needed for narrow band filters Zero points 1 set broad band filter daily UKIRT MKO or Persson std Colour terms 1 set monthly broad band filters only best effort basis Extinction coefficients 1 set monthly broad band filters only best effort basis Detector characteritics 1 set monthly RON dark current linearity Please do not hesitate to contact us usd help eso org if you have any questions D 3 Quality Control All calibrations taken within the context of the calibration plan are pipeline processed and quality controlled by the Quality Control group at ESO Garching Appropriate master calibrations and the raw data they are derived from for reducing the science data are included in each Service Mode data package along with the raw science data and the science pipeline products More information about the HAWK I quality control can be found under http www eso org qc index_hawki html HAWK I User Manual Issue 84 25 The time evolution of the most important
24. on the instrument web pages and in Kissler Patig et al 2008 A amp A 491 941 HAWK I is a near infrared 0 85 2 5 um wide field imager The instrument is cryogenic 120 K detectors at 75 K and has a full reflective design The light passes four mirrors and two filter wheels before hitting a mosaic of four Hawaii 2RG 2048x2048 pixels detectors The final F ratio is F 4 36 1 on the sky correspond to 169 4um The field of view on the sky is 7 5 x7 5 with a small cross shaped gap of 15 between the four detectors The pixel scale is 0 106 pix The two filter wheels of six positions each host ten filters Y J H K identical to the VISTA filters as well as 6 narrow band filters Bry CH4 H2 and three cosmological filters at 1 061 1 187 and 2 090 um Typical limiting magnitudes S N 5 in 3600s on source are around J 23 9 H 22 5 and K 22 3 mag Vega HAWK I User Manual Issue 84 Contents 1 Introduction 1 1 1 2 1 3 14 Scope of KUA AA AA AAA SEE RE RSE Ke Structure of this document AA ee e e EEN EEE er g dere ge ett Neben Ee e EN Abbreviations and Acronyms Observing with HAWK I from phase 1 to data reduction 2 PHASE 1 applying for observing time with HAWK I 2 1 nz 2 3 24 2 5 21i WG 1 ae A Wa OEE Soe BSS e ai ene Aa A A cece oe See hs SS we eo AA 2 1 3 Limiting WARNES e q aos ee GE Ra ee ee 2 14 Instrument s performance
25. or 10 of the peak brightness in the stellar PSF The figure 2 summarizes the HAWK I filters graphically HAWK I User Manual Issue 84 16 Figure 1 Smoothed enhanced images of the optical ghosts visible in the four quadrants for the NB1060 left amp NB1190 right filters HAWK I User Manual Issue 84 17 100 L Y J H K 80 4 an li CH SS ent H gt 5 H Bry gt oO e az K 0 m NB NB1190 NBRO90 4 a 40 UI 20 4 0 K 1 1 L 1 1000 1500 2000 wavelength nm Figure 2 HAWK I Filters Black broad band filters Y J H Ks Green cosmological filters NB1060 NB1190 NB2090 Red CH4 H2 Blue Bry HAWK I User Manual Issue 84 18 B The HAWK I detectors The naming convention for the four detectors is the following 2000 PTT 2000 BT 1500 F 4 1500 E 4 E Q4 J E 93 1000 chip 88 E 0094 chip 79 500 H J 500 E 4 1 ay j o bee KUKUA KAA DIEN 0 500 1000 1500 2000 0 500 1000 1500 2000 X 2000 PITT 2000 PTT 1500 E 4 1500 E 4 8 oi J E Q2 1000F chip 66 E 1000 f chip 78 500 F 4 500 E 4 posi tir tisiitiiii I nl 0 500 1000 1500 2000 0 500 1000 1500 2000 Note that quadrant 1 2 3 4 are usually but not necessarily stored in extensions 1 2 4 3 of the HAWK I FITS file Indeed FITS convention forbids to identify extensions by their location in the file Instead look for the FITS keyword EXTNAME in each extension and ver
26. quadrants C 1 1 Center of Rotation and Centre of Pointing C 2 Vignetting of the field of view 0 000002 ee ee The HAWK I calibration plan D 1 Do you need special calibrations D 2 The HAWK I standard calibrations in a nutshell D3 Gan Controls e mee pes we ee ES ee ee Se HES ee o bled The HAWK I pipeline V 18 19 19 22 22 22 23 24 24 24 24 26 HAWK I User Manual Issue 84 1 1 Introduction 1 1 Scope of this document The HAWK I user manual provides the information required for the proposal preparation phase 1 the phase 2 observation preparation and the observation phase The instrument has started regular operations in period 81 We welcome any comments and sug gestions on the manual these should be addressed to our user support group at usd help eso org 1 2 Structure of this document The document is structured in 2 parts Part 1 1 takes you step by step through the essentials writing your proposal in phase 1 preparing your observations in phase 2 conducting your obser vations at the telescope and reducing your data Part 2 II contains collected useful reference material 1 3 Glossary 1 4 Abbreviations and Acronyms DMO ESO ETC FC FoV FWHM HAWK I NIR OB P2PP PSF QC RTC RTD SM TIO USD VLT VM Data Management and Operations Division European Southern Observatory Exposure Tim
27. r or place it on a different quadrant in which case do not forget the 15 gap The sky reference system is probably only useful when a fixed sky frame needs to be acquired with respect to the pointing For a position angle of 0 the reconstructed image on the RTD will show North up Y and East left X The positive position angle is defined from North to East Note that the templates use always offsets relative to the previous pointing not relative to the original position i e each offset is measured with respect to the actual pointing For example if you want to place a target in a series of four offsets in the center of each quadrant point to the star then perform the offsets 115 115 telescope moves to the lower left star appears in the upper right i e in Q3 230 0 0 230 230 0 Note that HAWK I offers during execution a display that shows at the start of a template all the offsets to be performed see below It provides a quick visual check whether your pattern looks as expected JE Telescope offsets H i D Zem 7 280 210 110 200 4 500 220 6 100 1 1 10 nn Gemeen Zei gea Pop up window at the start of an example template it provides a quick check of your offset pattern In the above example Fig 4 4 7 offsets are requested and the way the are performed is shown in Fig 4 4 The sequence of offset will be 10 10 90 10 100 200
28. ssional fit For these pixels only non destructive readouts having values below the threshold are taken into account The pixel values writen into the FITS file is the value extrapolated to the integration time DIT and is calculated from the slope using only readouts below the the thershold The pixels that have been extrapolated can be identified because their values are above DET SATLEVEL Bi Detectors structures We present some of HAWK I s detector features in two examples Figure 4 is a typical long gt 60s exposure Some features have been highlighted e 1 some black features on chip 66 amp 76 For both of them when light falls directly on these spots some diffraction structures can be seen as shown in the corresponding quadrants in Fig 5 e 2 On the left chip 88 there is an artefact on the detector s surface layer On the right chip 79 these are sort of doughnut shaped features More of these can be seen in Fig 5 on chip 88 Both features are stable and removed completely by simple data reduction no extra step needed HAWK I User Manual Issue 84 20 Figure 4 Typical HAWK I dark frame DIT 340sec e 3 Detector glow which is visible for long DITs but is removed by e g sky subtraction e 4 The darker area visible here corresponds to the shadow of the baffling between the detec tors 5 Emitting structure whose intensity grows with the integration time It is however fully removed by classical data r
29. tched image if min offset lt 1500 or max offset gt 1500 Besides utilities will be provided to make it easier for the users to reduce the data by hand step by step This utilities list is not finalised yet but will contain among others e hawki_util_distortion Apply the distortion correction e hawki_util_stitch Stiches 4 quadrant images together e hawki_util_stdstars Generates the standard stars catalog from asii files e hawki_util_gendist Generates the distortion map used for the distortion correction
30. ture impacts the sky contribution for the Ks BrG H2 and NB2090 filters Due to the sky variations and in order to allow for proper sky subtraction we recommend to offset at least every 2 minutes Please be reminded that the minimum time at a position before an offset is 1 minute HAWK I User Manual Issue 84 Table 3 Sky background contribution amp Useful integration times Filter Contribution from sky RON limitation linearity limit Recommended DIT electrons sec DIT sec DIT sec sec Broad band filters Ks 1600 lt 1 30 10 H 2900 lt 1 20 10 J 350 1 15 140 10 Y 130 3 400 30 Narrow band filters CH4 1200 lt 1 40 10 NB2090 60 7 900 60 NB1190 3 6 110 14000 300 NB1060 3 4 120 14000 300 H2 140 17 400 30 BrG 180 15 300 30 The figure below show the quality of the sky subtration as a function of pupil angle and time 13 from the first frame A sequence of frames in the K band was obtained when the target was near the zenith and the pupil was rotating by 2 45 degrees minute Being the VLT an alt azimuth telescope the image rotates with respect to the pupil This is noticed as a rotation of the difraction spikes seeing around bright stars The sky subtraction error is larger when the pupil rotation angle between the two images is largest HAWK I User Manual Issue 84 14 The annotation indicate the difference in pupil angle between the two frames be
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