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1. 13 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 In Visitor mode is also possible to observe bright objects using BADAO say switching active optics off Telescope and or instrument defocussing are however not permitted 13 3 The influence of the Moon Moonlight does not noticeably increase the background in the NIR so there is no need to request dark or grey 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 Observation in AOF standard mode with a relatively faint T TS should request a Moon distance larger than 30 degrees to prevent problem with the TT sensing TBC Visitors should check their target positions with respect to the Moon at the time of their scheduled observations e g with the tools available at http www eso org sci observing tools 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 i
2. European Organisation Europaische Organisation Europ enne Organisation for Astronomical pour des Recherches f r astronomische Research in the Astronomiques Forschung in der Southern dans l H misph re s dlichen Hemisphere Austral Hemisph re VERY LARGE TELESCOPE HAWK I User Manual Doc No VLT MAN ESO 22200 6281 Issue 1 Date 04 03 2015 Function Name Date Signature Author Elena Valenti Job Manager Jerome Paufique PS Harald Kuntschner AOF PM Robin Arsenault Releaser Norbert Hubin Luca Pasquini L This document is under configuration control ESO Karl Schwarzschild Str 2 85748 Garching bei M nchen Germany HAWK Doc VLT MAN ESO 22200 6281 gt User Manual Date 4 3 15 Page 2 of 50 CO AUTHORS Co Authors Affiliation Division Ralf Siebenmorgen ESO INS HAWK I IOT ESO REVIEWERS Reviewers Affiliation Division Giovanni Carraro ESO LPO CHANGE RECORD ISSUE DATE SECTION PARA REASON INITIATION AFFECTED DOCUMENTS REMARKS 1 04 03 15 All Initial draft HAWK I User Manual Issue 1 HAWK I in a Nutshell Online information on HAWK I can be found on the instrument web pages in Casali et al 2006 and in Kissler Patig et al 2008 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 fu
3. 1 8 Abbreviations and Acronyms 2MASS 4LGS AO AOF DIT DMO DSM ESO ETC FC FoV FWHM GLAO GRAAL HAWK I NDIT NGS NIR OB P2PP PSF QC RTC RTD SM TT TIO USD UT VLT VM WF WFS Two Micron All Sky Survey 4 Laser Guide Stars Adaptive Optics Adaptive Optics Facility Detector Integration Time Data Management and Operations Division Deformable Secondary Mirror European Southern Observatory Exposure Time Calculator Finding Chart Field of View Full Width at Half Maximum Ground Layer Adaptive Optics GRound layer Adaptive optics system Assisted by Lasers High Acuity Wide field K band Imager Number of Detector Integration Time Natural Guide Star Near InfraRed Observing Block Phase Il Proposal Preparation Point Spread Function Quality Control Real Time Computer Real Time Display Service Mode Tip Tilt Telescope and Instrument Operator User Support Department Unit Telescope Very Large Telescope Visitor Mode WaveFront WaveFront Sensor HAWK I User Manual Issue XX 4 Part The instrument 2 Cold part the imager The HAWK I instrument design is presented by Casali et al 2006 and Kissler Patig et al 2008 a summary is provided in the following subsections Figure 1 Cut through HAWK I for an optical and mechanical overview Blue optical components black cold assembly filter wheels detector assembly green radiation shield red vessel structure cryogenic components electron
4. e Figure 7 represents the quantum efficiency curve for each of the detectors f bo Lu m d ot do 1 5 2 Wavelength micron Figure 7 Quantum efficiency of the HAWK I detectors See appendix A for further details on the detectors features and relative sensitivity 4 1 Threshold limited integration The normal mode of operation of the HAWK I 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 regression fit For these pixels only non destructive readouts having values below the threshold are taken into account The pixel values written into the FITS file is the value extrapolated to the integration time DIT and is calculated from the slope using only readouts below the threshold The pixels that have been extrapolated can be identified because their values are above DET SATLEVEL 5 Field of view The FoV of HAWK I is defined by four Hawaii 2RG chips of 2048 pixels each 1 pixel corresponds to 0 106 on the sky The detectors are separated by gaps of about 15 Figure 8 shows how the FoV looks like HAWK I User Manual Issue XX 12 15 217 gt KO gt 7 87 mS Figure 8 HAWK I FoV Note that it is very tempting to point right onto your favour
5. 0 2 128 25 6 28 159 1 0 1 128x32 4096 1 64x2 128 0 1037 255 0 1037 255 26 4435 28 164 4 6 1 128x32 4096 1 128x2 256 0 2074 127 0 2074 127 26 3398 28 166 11 2 1 128x32 4096 1024 32x2 64 0 066186 511 0 066186 511 33 821046 35 199 3 4 1 128x32 4096 1024 64x2 128 0 1180 255 0 1180 255 30 0900 32 181 4 4 1 128x32 4096 1024 128x2 256 0 2217 127 0 2217 127 28 1559 30 176 7 6 1 128x32 4096 2016 32x2 64 0 080074 511 0 080074 511 40 917814 43 236 2 6 1 128x32 4096 1984 64x2 128 0 1315 255 0 1315 255 33 5325 36 200 3 4 1 128x32 4096 1920 128x2 256 0 2342 127 0 2342 127 29 7434 32 182 2 0 For convenience we list the integration time for a single data cube equal to NDIT DIT the execution time for a single cube and the execution time for a template that generates five cubes NEXP 5 The test were carried out with NJITT 1 JITTER BOX 0 the Read speed factor was 8 and the Read speed add was 0 The last two parameters are low level detector con troller parameters they are controlled by the observing templates and they are fixed at these values for technical reasons beyond the scope of this document we list them here just for completeness The filter for the observations was set up in the acquisition template if it must be changed in the science template there will be additional overheads related to the filter movement The overhead per template is typically 30 33 sec Let s consider the last case in the table five exposures of NDIT x DIT 29
6. A Br ee BOE E EURO Y eg 6 Filters 7 TT star properties 8 Limiting magnitudes WN NNN KF KF KF A aon 2 A ON DDD C 10 10 11 11 12 13 13 14 14 14 HAWK I User Manual Issue 1 9 Image quality and astrometry Ill Observing with HAWK I from phase 1 to data reduction 10 Introduction 11 Phase 1 applying for observing time with HAWK I 11 1 Getting reasonable photometry with HAWK 11 1 1 Consider the 2MASS calibration fields ou onen 11 1 2 HAWK I extinction coefficients 2 2 a 11 2 The Exposure Time Calculator 2 2222 oa a 11 3 Proposal POM cee oec en wo 11 4 Overheads and Calibration Plan 2 ee 12 Phase 2 preparing your HAWK I observations 12 1 HAWK I specifics to templates OBs and p2pp 2 004 121 p2pp and the GuideCam tools 2 2o x wi 12 12 Obserine Blacks OBS 2s uw ew Rx ey eA wee ae 12 123 Templates o v os Bars er Apa mo dede s eR E ub ek 12 2 Finding Charts and README Files zz sos or o es 13 Observing strategies with HAWK I INNO TIU MMC 13 2 Visitor Mode Operations oaoa 13 3 The influence of the Moon 2 2222 CL m one 134 Twilight soc ee baa i Was See eb be REG ESE OR 13 5 Orientation offset conventions and definitions 0004 13 6 Instrument and telescope overheads 2 2 m m nn 13 7 Recommended DIT NDIT and Object Sky pattern 2 2 22 2 lll IV Reference Material A Detectors A 1 Struc
7. 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 probably want to move the target on the detector 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 see Fig 10 PA 0 PA 90 LL tn GLI LL Figure 10 Definition of position angle 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 right star appears in the upper left i e in Q4 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 see left panel of Fig 11 In the above example Fig 11 left panel 7 offsets are requested and the way the are perfo
8. a clear indication of the field orientation HAWK I User Manual Issue XX 23 e Ideally the FC should show the field in the NIR or at least in the red and the wavelength of the image must be specified in the FC 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 e he FC should show the position of the target at the end of the acquisition template Note that for AOF standard mode where the use of the Guide Cam tool is mandatory the FC is generated by the tool itself and it is automatically attached to the OB The tool can be of course used also to generate FC for TTS free and no AOF observations HAWK I User Manual Issue XX 24 13 Observing strategies with HAWK I 13 1 Overview As with all other ESO instruments users prepare their observations with the p2pp software Ac quisitions observations and calibrations are coded via templates and 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 Real Time Display RTD is used to view the raw frames Calibrations including darks sky flats 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
9. a given position on the sky is observed by each of the four chips of the HAWK I detector The jitter sequences are reduced following the standard two pass background subtraction workflow described in the HAWK I pipeline manual Objects have been detected with the SExtrac tor software courtesy of Gabriel Brammer including a 0 9 gaussian convolution kernel roughly matched to the average seeing measured from the reduced images Simple aperture photometry is measured within 1 8 diameter apertures The resulting number counts as a function of aperture magnitude observed by each chip are shown in Fig 16 As expected the co addition of the four jitter sequences reaches a factor of 2 0 8 mag deeper than do the individual sequences The limiting magnitudes here taken to be the magnitude where the number counts begin to decrease sharply and a proxy for the chip sensitivities are remarkably similar between the four chips We conclude that any sensitivity variations between the chips are within the 10 While they do not appear to affect the overall sensitivity the image artefacts on CHIP2 caused by radioactivity events see Fig 15 do result in an elevated number of spurious detections dashed lines in Fig 16 at faint magnitudes reaching 20 at the HAWK I User Manual Issue XX tie 31 Figure 15 The field around the z 2 7 quasar B0002 422 as seen in the 4 HAWK I quadrants Radioactive effects are clearly v
10. does only one thing but it does it well direct imaging in the NIR 0 97 to 2 31 jum over a large field 7 5 x7 5 It can be used in seeing limited mode but also it can make use of ground layer adaptive optics GRAAL achieved through a deformable secondary mirror and the laser guide stars facility 1 1 Science drivers So far HAWK I has been successfully used to study e the properties of medium redshift galaxy clusters see e g Lidman et al 2008 A amp A 489 981 e the outer solar system bodies see e g Snodgrass et al 2010 A amp A 511 72 e the very high redshift universe see e g Castellano et al 2010 A amp A 511 20 e exo planets see e g Gillon et al 2009 A amp A 506 359 e the properties of Galactic stellar populations see e g Valenti et al 2013 A amp A 559 98 and star forming regions see e g Preibish et al 2011 A amp A 530 34 The relatively recent implementation of Fast Photometry see Appendix F is probably going to boost more activity in the exo planets field as well as in the study of crowded fields through holographic imaging technique see Schoedel et al 2013 MNRAS 249 1367 1 2 Scope of this document The HAWK I user manual provides a description of the instrument characteristics as well as infor mation required for the proposal Phase 1 and the observation Phase 2 preparation Guidelines for the post observation phase are also summarised The instrument has started regular operations
11. field of view ask the operator if an adjustment is neces sary Note that the adjustment here includes both the telescope pointing and field of view orientation and the detector windowing parameters At this stage the operator is expected to press the draw button that draws on the RTD the windowing as defined in the acquisi tion template The operator can modify it at any time from now on by typing numbers on the pop up window but has to redraw to have the latest version shown on the RTD 4 If the operator gives a negative answer the template acquires an image saves it and then ends Otherwise an offset window is opened on the RTD to let the operator to define an offset and rotator angle offset and to modify the windowing parameters 5 The offsets including the rotator offset are sent to the telescope and after they are executed the template returns to item 3 where it takes another non windowed image and so on HAWK I User Manual Issue XX 47 FF Win FF NonWin1 FF Win FF NonWin2 FF NonWin1 FF NonWin2 Gaussian mean 1 sigma 0 02 log N 1 Ratio of different flat fields Figure 20 Histograms of the ratios between a windowed and two non windowed Kg twilight flats For comparison the ratio of the two non windowed flats and a Gaussian function is also shown HAWK I User Manual Issue XX 48 D 4 2 Acquisition HAWK I img acq FastPhotAOF When fast photometry is performed in AOF standard mode the
12. preparation of the OB requires the use of the Guide Cam Tool see sec 12 1 1 for instrument configuration pointing coordinates target and TTS coordinates color and magnitude of the TTS as well as PA The acquisition sequence in this case starts with telescope preset and target centring in full windowing mode ii TTS low order loop closure and iii LGS high order loop closure From now one the action sequence performed by this template is very similar to that described in the previous section In case the TTS free mode is used after the telescope moves to the preset position the LGSs are acquired and the loop is closed D 4 3 Science template HAWK img obs FastPhot This template is similar to the SAACLW img obs FastPhot except that it takes the detector win dowing parameters from the OS registers so these parameters can t be modified from within HAWKI img obs FastPhot The template operates in two modes Burst and FastJitter In Burst mode the telescope is staring at the target for the duration of the integration INT NDIT xDIT and only one data cube is produced In FastJitter mode the telescope can jitter in the sky and many data cubes one per offset can be produced within one template Action sequence performed by the template is identical to that of the HAWKI img obs AutoJitter template 1 2 4 Sets up the instrument including selection hardware detector windowing Performs a random offset most users are
13. 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 6 Filters HAWK I is equipped with 10 filters 4 broad band filters and 6 narrow band filters Please refer to appendix B 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 Ks 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 09 1m as well as 3 stellar filters CH4 H2 Bry Recently a visitor filter has been installed NB0984 0 98m Can you bring your own filters Possibly HAWK I hosts large 105mm 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 WELL before buying your filters The detailed procedure is described in a document available upon request please email to haw
14. sec J 23 9 24 8 10 0 H 22 5 23 9 10 3 Ks 22 3 24 2 9 2 Under the same average conditions 0 8 seeing 1 2 airmass HAWK I in combination with GRAAL AOF mode and TT star with magnitude 7 lt R lt 14 5 reaches for the same integration time 0 3 mag TBC fainter point sources at the same S N than without correction For more detailed exposure time calculation in particular for narrow band filters please use the exposure time calculator As for persistence on HAWKI detectors the following rules apply When using DITs smaller than 30 secs persistence effects can be neglected However when using larger DITs the maximum accepted saturation is 7 times the HAWKI saturation level TBC whether this is still the case in AOF mode and TTS free mode Therefore users are recommended to check carefully their fields against saturation using HAWKI ETC during Phase II and in case submit a waiver which will be evaluated on individual case basis 9 Image quality and astrometry The image quality of HAWK I is excellent across the entire field of view In seeing limited mode NoAOF distortions are below 2 over the full 10 diagonal and the image quality has always been limited by the seeing our best recorded images had FWHM below 2 2 pix i e lt 0 23 in the Ks band A reduction of the PSF diameter by a factor of 1 25 is achieve when HAWK I is used in combination with GRAAL TBC The photometric accuracy and homogeneity that we measured a
15. useful integration begins 2nd read of Ist DIT the first useful integration ends Ist read of 2nd DIT the second useful integration begins 2nd read of NDIT th DIT the last NDIT th useful integration ends Ist read of NDIT th 1 DIT not an actually useful integration begins INT an averaged frame Therefore if no frames are lost the generated cube contains NAXIS3 2 x NDIT 1 1slices 2 Frame loss that plagues some other fast instruments has not been noticed during the typical applications of the HAWK I fast photometry modes Most likely because of the slowing down of the detector read speed that increased the minimum DITs This problem usually occurs when the product of NX and NY is relatively large and DIT is close to MINDIT so the IRACE has to transfer large data volume quickly To check for frame losses verify that NAXIS3 header keyword is equal to estimates given above A feature of unknown nature causes a loss of two frames in the first cube after changing the Burst from True to False It is recommended to take a short bust after such a change before starting the actual science observations The HAWK I fast mode is subject to a maximum cube limitation similarly to ISAAC and Sofl The buffer size in this case is 512 Mb If the cube size exceeds the 512 Mb limit the observations will be split into multiple file extensions but the headers of all extensions will contain the DATA OBS information for th
16. which relies on the correction of the lowest layers of the atmospheric turbulence to improve the image quality delivered to astronomical observations A practical implementation of this type of AO faces numerous difficulties Indeed in contrast with classical on axis AO GLAO requires excluding the highest layers of the atmosphere from the correction brought by the system This can be done by using i Rayleight guide star for limited telescope diameters or ii with multiple Na Laser guide star for HAWK I User Manual Issue XX 7 larger telescopes The combination of powerful laser sources at the Na wavelength and low noise fast detectors makes possible today to implement GLAO systems on 8 m class telescope 3 2 Design of the module GRAAL is the widest FoV GLAO system developed for an 8 m class telescope with a free from optics scientific FoV of over 10 5 Its sky coverage exceeds 95 and allows 100 sky coverage with a slightly limited performance GRAAL offers an improvement of about 40 on the K band FWHM allowing routine observations with 0 3 FWHM 50 of the time with a seeing in the line of sight of 0 95 This represents a factor 2 with respect to the current situation where worse seeing conditions are used more often by HAWK I than by the AO instruments MUSE in narrow field mode and SINFONI located on other foci of the same telescope It also allows using the full potential of HAWK I and its sampling of 0 1 per pixel The UT
17. 7434 sec collect together 148 717 sec of integration leaving 33 sec in overheads up to the template execution time of 182sec These 33 sec are build up as follows 2sec to process the template and to send a set up command to the instrument this could be much longer if there is a filter change 10sec to set up the IRACE detector controller 2 3 sec to transfer every data cube and to merge the fits file and its header 10 sec to set up the IRACE detector controller back to the standard set up at the end of the template A detailed time line of the execution is shown in Table 5 The overheads listed above may vary by 1 2 sec Finally the HAWKI Fast Photometry mode suffers from frame loss especially if the DIT is close to the the MINDIT for the given windowing configuration Table6 lists the frame loss rate in percentages The frame losses increase with the size of the window and for a given window size they decrease with increasing DIT as can be seen from the few examples for NX 128 NY 32 Last bit not least the frame losses depend on the network load the experience shows that just HAWK I User Manual Issue XX 45 Table 6 Example Timing Parameters of the last case considered in Table 6 Action Time stat template 21 04 38 IRACE set up 21 04 40 start exposure 1 21 04 50 end exposure 1 21 05 22 start exposure 2 21 05 22 end exposure 2 21 05 54 start exposure 3 21 05 54 end exposure 3 21 06 26 start exposure 4 21 06 26 end expo
18. 8 DET WIN NX 128 and DET WIN NY 32 corresponding to windows on the stripes with sizes of 128x 32 px 13 3x3 3 arc secs gives MINDIT 20 milli secs Note that the stripes are 128 px wide so this is indeed a contiguous region on each of the detectors with size 2048 x 32 px 217 7x3 4 arcsec Typically the choice of window sizes is the result of a compromise between a few conflicting requirements e faster photometry i e smaller overheads smaller MINDIT higher time resolution requires smaller window sizes e more accurate photometry i e brighter and more reference stars wider clear area to measure the sky level wider margin for human errors during the acquisition leeway for target drift across the window because of poor auto guiding or atmospheric refraction since the target is observed in the NIR and the guiding is in the optical requires wider window sizes e smaller data volume requires smaller windows e higher data cadence i e less gaps between files for transfer fits header merging requires smaller window To simplify and standardize the observations and to minimize the day time calibration time the following constraints on the window parameters are imposed e Only contiguous windows that span entirely the width of the detectors are offered so DET WIN NX must always be set to 128 13 3 arcsec and DET WIN STARTX to 1 Therefore the total size of the output file along the X axis is always 128x 32 4096 p
19. I detector mosaic see Fig 3 is composed of four 2kx2k Hawaii 2RG arrays with 2 5 um cutoff Figure 3 HAWK I detector mount 3 Warm part the ground layer adaptive optics system GRAAL the ground layer adaptive optics system of HAWK I is presented and discussed in Paufique et al 2010 and Paufique et al 2012 The adaptive correction AO is provided by the deformable secondary mirror DSM nearly conju gated with the ground layers of the atmosphere at 90 m Therefore GRAAL is able to compensate for the lowest layers of the atmospheric turbulence up to 1 km depending on the spatial frequen cies considered carrying more than half of the turbulence variance GRAAL is a seeing improver and does not provide diffraction limited images at the focal plane To highlight the advantage of HAWK I User Manual Issue XX 6 combining GRAAL with HAWK I a PSF is shown in Fig 4 in AO open loop uncorrected and a close loop 20 20 40 40 60 60 a 20 400 100 120 e 120 140 10 460 160 180 180 200 200 ee E E zul NN 20 40 60 80 100 120 140 160 180 200 220 20 40 6 80 10 12 140 160 180 200 220 Figure 4 Simulated PSF without eft and with right GRAAL correction 3 1 Introduction The following section provides an introduction to the field of atmospheric turbulence and it is essentially taken from the NACO user manual For further reading see for example Adaptive Optics in astr
20. Note that the param eter DET WIN STARTK defines the starting point of the window counted from the beginning of each detector stripe not from the beginning of the detector All these parameters are defined in pixels although this figure is plotted in arc secs As examples four different sets of windows are shown in violet yellow solid and dashed black lines HAWK I User Manual Issue XX 42 between the individual windows such gap occur always because of the gaps between the detectors extra gaps occur if DET WIN NX is smaller than 128 and if DET WIN NY is smaller than 2048 The Burst sub mode describe here below only for historic reasons and to highlight the differences with jitter mode generates a single fits file containing a single cube the FastJitt generates as many files each containing a cube as the number of the jitters in the OB The cubes contain one extra slice i e NDIT 1 instead of NDIT because the last slice is the average of all NDITs In Fast Jitter mode the sliced in the generated cubes are Ist DIT a difference between the 2 reads separated by DIT seconds 2nd DIT a difference between the 2 reads separated by DIT seconds INT an averaged frame of all previous slices Therefore if no frames are lost the generated cube contains NAXIS3 NDIT 1 1 slices In Burst mode the slices in the generated cubes are 2nd read of Oth DIT not an actually useful integration Ist read of 1st DIT the first
21. TBD However GRAAL can work with stars as faint as R 18 mag but in the best seeing conditions TBD Observations with GRAAL require PHO or CLR conditions THN is to be still verified HAWK I User Manual Issue 1 Contents 1 Introduction LI Science drivers o ec oa ES E a 1 2 Scope of this document 2 ew scor o na daran ihn aan 1 3 Structiire of this document cc sr o eR PE wee ana 14 More important information uus a z wu Sew we ua a a anni L5 Contact Iniormatioh sp s s ra Ge oe me Ek ie ee SE RE d LO lU CC Ba NO s ek oe eo eee es SE Se EOS Se Eee oe he ee a 1 6 Abbreviations and Acronyms cocus uoo eom an a a en a The instrument 2 Cold part the imager Zi WOO M 22 WIBENONICS uus eee Go GO De aan a dies a Ro CR Ode doge ck pub E RE d 23 Detentor i doe xoxo we RR nece Eo diee E EL cS Wu eR 8 3 Warm part the ground layer adaptive optics system 31 INtrodu cHon ec hueso menus ou IR RR d RO RO Gb GIR A Rex eun x Udo ee 3 11 Atmospheric Turbulence a 3 1 2 Ground Layer Adaptive Optics 22 2 Como 32 Design of the module ee ae reu Roo RR RS RR E UE 2 2 Wayefront Sensors ou luos os a hele xA E RES Raw OE RATE UR Ad l Instrument Performance 4 Detectors 4 1 Threshold limited integration lll 5 Field of view 5 1 Relative position of the four quadrants ee ee 5 2 Center of Rotation and Centre of Pointing ll lln 5 3 Vignetting ofthe FOV ey heu E oso wx REY EY
22. User Manual Issue XX 46 D 3 4 Calibration Plan e Darks taken with the same windowing and readout mode e Twilight Flats non windowed and with the same filters as the science observations are offered the users only have to excise from them the necessary windows we compared windowed and non windowed Kg flats and found no significant difference Fig 20 D 3 5 FITS Files Names The file names for the fast mode contain FAST for clarity The extensions SAMPLE and DIT are also appended to the FITS file name D 4 Template Guide D 4 1 Acquisition HAWKI_img_acg_FastPhotNoAOF This section describes the acquisition procedure in case GRAAL is not use i e No AOF mode The detector windowing parameters DET WIN STARTX DET WIN STARTY DET WIN NX and DET WIN NY are defined in this template They are used to draw on the RTD the lo cations of the 32 windows These parameters are stored in OS registers and used by the science template later They can be accessed by the science template even if it has been aborted and restarted multiple times as long as the OS has not been stopped and restarted The action sequence performed by the template includes 1 Preset the telescope set up the instrument no windowing at this stage the full field of view is shown on the RTD 2 Move to the sky position take a non windowed image ask the operator to save it in the RTD and to turn on the sky subtraction 3 Take a non windowed image of the
23. Visiting astronomers do not need to submit OBs in advance of their observations However they should prepared them before arriving at the observatory or at latest at the observatory the nights before their observing run They will find further instructions on the the Paranal Science Operations web page and the Paranal Observatory home page In particular visiting astronomers are strongly encouraged to read this page 1 5 Contact information In case of specific questions related to Service Mode observations the use of the pipeline and the proposal preparation Phase 1 please contact the ESO User Support Department For general information on Visitor Mode observations please contact the Paranal Science Operation Team 1 6 News Please recall that the most up to date information on the instrument can be found on the HAWK I news web page 1 7 Glossary Active Optics This is the active control of the primary mirror of the telescope It is performed by using a telescope guide star Adaptive Optics This is the correction of the wavefront errors induced by atmospheric turbulence The wavefront is measured from laser spots and the corresponding corrections are sent to the deformable secondary mirror Laser Guide Star The artificial star created by the sodium laser at an altitude of 80 100 km Titp Til Star The star used to sense and correct the tip tilt aberrations which are not sensed by the lasers HAWK I User Manual Issue 1
24. ameters should be self explaining and or well explained in the online help of the ETC 11 3 Proposal Form Your proposal must be submitted by the respective deadline end of March and end of September using the supplied ESO Proposal Package and following the instructions given in the Call for Proposals The ESO Proposal Package can be downloaded from the User Portal Although HAWK I allows only direct imaging you need to specify the mode that is whether or not you intend to use GRAAL In case you want to use the AOF standard mode you must provide the magnitude of the TTS in R band in the target list Remember that the use of the lasers i e AOF standard and TTS free modes requires PHO or CLR conditions Please indicate which filters in particular narrow band filters you intend to use This will allow us to optimise their calibration during the semester For seeing limited operation ANINSconfig HHAWK IHnoAO0FJ provide HERE list of filters s Y J H K NB0984 NB1060 NB2090 H2 BrG CH4 4 If you plan to use the AOF standard mode please specify the TTS name and R mag in the target list INSconfigt HAWK I AOF provide HERE list of filters s Y J H K NB0984 NB1060 NB2090 H2 BrG CH4 4 lf you plan to use the TTS free mode then please leave the TTS name blank in the target list INSconfigt HAWK I noA0OF provide HERE list of filters s Y J H K NB0984 NB1060 NB2090 H2 BrG CH4 Finally the seeing condition to be requeste
25. and relative positions of the detectors and to quantify possible flexures Three further templates are used to characterise 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 no AOF imaging of standard field available to the SM user technical templates HAWKI img tec IlluFrame 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 DetLin detector test monitoring HAWKI img tec Focus telescope focus determination HAWKI img tec FilterWheel filter wheel positioning accuracy HAWKI img tec switchMODE to change the instrument mode 12 2 Finding Charts and README Files In addition to the general instructions on finding charts FC and README files that are available at http www eso org sci observing phase2 SMGuidelines FindingCharts html and http www eso org sci observing phase2 SMGuidelines ReadmeFile generic html respectively The following HAWK I specifics are recommended e The FoV of all FCs must be 10 by 10 in size with
26. at they work in a markedly different way with respect to the templates for other ESO instruments the windowing parameters are present only in the acquisition template and their values are carried over to the science template s by the Observing Software OS using designated common memory area So one can not skip the acquisition if it is necessary to modify the windowing parameters If the acquisition is skipped the science template will use the values from the last acquisition execution If an OB has been aborted the windowing parameters are remembered by the observing software as long as the Detector Control System DCS and OS panels have not been reset restarted so the OB can simply be restarted skipping the acquisition Occasionally during the execution of an OB a new acquisition image is not loaded automatically in the real time display RTD In this case one can re load the last acquisition image in that RTD and re draw the location of the windows by clicking on set up and draw from the pop up that BOB opens with the acquisition template Important a measure to reduce the load on the IRACE controller is to click on stop displaying the images on the RTD during the observations This is achieved by pressing the Stop button on the RTD panel NOTA BENE The IRACE is set to default at the end and this is critical for the observations HAWK I User Manual Issue XX 39 afterwards If an OB is aborted for some reason before this ste
27. ata in cubes The parameters for filter DIT and NDIT are lists allowing to obtain multiple darks in one go Specific details The new windowing parameters DET WIN STARTX DET WIN STARTY DET WIN NX and DET WIN NY define the detector windowing As in the science template they are used to window the detectors but unlike the science template they are explicitly definable and accessible by the users The previous parameters are not available in the calibration templates All the calibration are taken as reconstructed images in other words DET BURST MODE is internally always set to False Readout mode is set in the template implicitly to Double RdRstRd because for now this is the only one for which the new windowing is implemented The hardware windowing is set to True The store in cube option is set to True
28. cross 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 TBC whether this is still true with GRAAL 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 is auto calibrated on a monthly basis see HAWKI calibration plan using a sample of globular clusters as references The distortion map currently allows to recover relative position across the entire field with a precision of 1 arc sec TBC whether this is still true with GRAAL A note of caution as all current infrared arrays the HAWK I detectors suffer of persistence at the level of 1073 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 HAWK I User Manual Issue XX 16 Part Ill Observing with HAWK I from phase 1 to data reduction This part of the document helps you to decide whether HAWK I is the right instrument for your scientific project an
29. d at Phase 1 refers to the seeing in V band at zenith therefore you must use the value entered as input parameter for the ETC simulations HAWK I User Manual Issue XX 19 11 4 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 in the call for proposal that you have taken into account all listed overheads which can also be found in Sect 13 6 To do so you can either refer to Sect 4 5 or simulate the detailed breakdown of your program in terms of its constituent Observing Blocks OBs using the P2PP tutorial manual account see Sect 1 4 of P2PP user Manual The Execution Time Report option offered by P2PP provides an accurate estimate of the time needed for the execution of each OB including all necessary overheads e Check whether you need any special calibration have a look at the calibration plan in Sect C this is what the observatory will give you as default You might need more and we will be happy to provide you with more calibrations if you tell us in advance which Note however that night calibrations should be accounted for by the user 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 t
30. d it provides guidelines for Phase 1 and Phase 2 preparation 10 Introduction HAWK I performs direct imaging in the NIR 0 97 to 2 31 jum over a FoV of 7 5 x7 5 with a pixel scale of 0 106 per pixel The basic characteristics of the instrument are summarised in the nutshell at the beginning of this document whereas details on the instrument performance can be found in Part II HAWK I can be used in seeing limited mode or in combination with GRAAL which is a seeing improver allowing to enhance the instrument image quality In particular the following three operational modes are offered e AOF standard In this mode the full capabilities of GRAAL i e 4 LGS and TTS are used e AOF TTS free This mode allows the setup of the instrument when no GRAAL TTS is available but some degree of AO correction is still desired hence so it can be realised via the LGS only e no AOF In this case GRAAL is not used and the observation are performed in seeing limited mode 11 Phase 1 applying for observing time with HAWK I Now that you have decided that HAWK I is the right instrument to carry on your science project you must apply for observing time To do that properly there is a number of details that you must take into account ahead in time and this section will guide you through it 11 1 Getting reasonable photometry with HAWK 1 If good photometry is your goal you should go for one of the following options e Ask for special calibration
31. e Double Correlated where the sequence is cycle 1 read the detector reset the detector read the detector integrate for a time DIT sec cycle 2 read the detector reset the detector read the detector integrate for a time DIT sec etc The frame is reconstructed by subtracting the second read of the first cycle from the first read of the second cycle and so forth The difference between the Double correlated and ReadRstRead modes is that when one pixel is reset or read the rest of the pixels integrates in case of the normal Double Correlated readout HAWK I User Manual Issue XX 38 mode the pixel waits until all other pixels are reset read which implies a read time of MINDIT for every DIT ReadRstRead is therefore faster since this waiting phase is absent and the overheads are of the order of a few microseconds per DIT the time needed to reset read only one individual pixel The integrations of individual pixels in ReadRstRead mode are offset with respect to each other so the integration of the last to be reset read pixel starts MINDIT seconds after the integration of the first pixel to be reset read Usually it is safe to ignore this effect either because the DIT gt gt MINDIT as is usually the case for exoplanet observations or because the window is almost as small as the target size so the signal from the target is averaged over nearly all pixels from the window as is the case of the Lunar occulta
32. e observations in other words to shorten the MINDIT and to decrease the overheads for data transfer For example the MINDIT for a 64x64 px 6 x6 arcsec window which is about a reasonable minimum for observing is 0 1022 sec Historically the MINDIT was lower but increased noise in the detectors led to slowing down the readout speed and this increased it to the present value Unfortunately this effectively makes it impossible to carry out observational programs that require mili seconds scale resolution Archival users should be aware that initially from 2010 to mid 2012 the mode suffered from extra overheads of 0 15 sec plus one MINDIT the exact value depends on the detector windowing but for the most likely window sizes it is a few tens of a second or larger an upper limit for a non windowed detectors is MINDIT 1 8sec associated with each DIT This made observations with very high cadence requirements problematic but as of mid 2012 the new faster ReadRstRead detector readout mode described below was implemented Note that the windows are not located at the center of the HAWKI field of view i e if the telescope is preset to the target coordinates the target will fall into the central gap between the four detectors Therefore one must calculate an offset placing the target onto one of the detectors preferably close to where the detector windows are Second the new detector readout mode ReadRstRead is used It is similar to th
33. e start of the observation not for the start of the given extension Each extension will also have its own smaller header This poses a problem if the aim of the program is to achieve high timing accuracy because the data transfer time and the fits header merging time are subject to variations depending on the load on the local network and on the instrument workstation These HAWK I User Manual Issue XX 43 variations are hard to quantify so we recommend to keep the cube size below 512 Mb In addition the overheads are larger if the cube is split into individual files because they have to be merged so an extra time to copy the entire cube into a single file is necessary Finally the OS supports a maximum size of 2 Gb and if the combined size exceeds that the merging fails and the OB is aborted Therefore the NDIT must be limited to keep the file size below 512 Mb The user has two options to adjust the cube size e to change the window size defined by DET WIN NX or e to change the number of slices in the cube defined by NDIT Often the former is not possible because the size is set by other considerations i e the angular separation on the sky between a target and a reference source the required low MINDIT or the need to have large enough window to avoid slit like losses especially in case of poor seeing Therefore reducing the NDIT may be the only solution to this problem The cube size for FastJitt mode that stores rest
34. ear 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 diffraction 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 XX 28 Figure 12 The annotation indicate the difference in pupil angle between the two frames being subtracted and the difference in start time between the two exposures HAWK I User Manual Issue XX 29 Part IV Reference Material A A 1 Detectors Structures and features Figure 13 shows some of HAWK I s detector features clearly visible in the typical long gt 60s dark and twilight exposures Figure 13 Typical raw HAWK I dark frame with DIT 300sec right and twilight flat field taken with the Y band left Some features have been highlighted Some black features on chip 66 amp 79 Q1 and Q3 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 13 right panel On chip 88 Q4 there is an artefact on the detector s surface layer On chip 79 Q3 these are sort of doughnut shaped features More of these can be seen in Fig 13 left panel on chip 88 Both features are stable and removed completely by simple data reduction no extra step needed Detector
35. glow which is visible for long DITs but is removed by e g sky subtraction The darker area visible in Fig 13 corresponds to the shadow of the baffling between the detectors Emitting structure whose intensity grows with the integration time which is however fully removed by classical data reduction HAWK I User Manual Issue XX 30 e Chip 88 Q4 dark median has been found to be larger than the other detectors and to increase with NDIT see Fig 14 Thanks to Sylvain Guieu for detecting this e Chip 78 Q2 suffers from radioactive effects see Fig 15 CHIP 1 CHIP 2 T TTT TT 4 0 014 4 8r A tt 1 A A c S A 0 2 H 9 A Ee xX a 5 4 0 4 i 4 A 4r 4 A A A A A A A a A A L L 0 6 amp L 1 Lr 5 10 5 10 NDIT NDIT CHIP 3 CHIP 4 Arm T aa 0 014 A A 4 0 6 4 A S n n 01 a 4 o a i A o L E a a re A F A A 08 a F n a A 02 4 4 A A F A A A A A A A A L a 4 10r 4 A 0 3 H A 1 L 1 1 L 5 10 5 10 NDIT NDIT Figure 14 Right Trend of dark with NDIT in the 4 detectors A 2 Relative sensitivity We undertook a program to assess the relative sensitivities of the four HAWK I chips using ob servations of the high galactic latitude field around the z 2 7 quasar B0002 422 at RA 00 04 45 Dec 41 56 41 taken during technical time The observations consist of four sets of 11 x 300 sec AutoJitter sequences using the NB1060 filter The four sequences are rotated by 90 degrees in order that
36. have to run the ETC more than once to fine tune the value for the seeing input in order to achieve the image quality you want in your HAWK I data but at the same time not over constraining your observations HAWK I User Manual Issue XX 18 e among the instrument set up parameters needed as input for the ETC the mode is very important You need to specify whether the simulation should be run with or without GRAAL 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 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 he 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 par
37. he total time requested HAWK I User Manual Issue XX 20 12 Phase 2 preparing your HAWK I observations All scientific and calibration observations with HAWK I are prepared by OBs as a sequence of the available templates This is performed with the help of the phase 2 proposal preparation tool p2pp This sections provides a preliminary guide for the observation preparation for HAWK I in Phase 2 both for SM or VM We assume that you are familiar with the existing generic guidelines e Proposal preparation e SM informations e VM informations We know that they are not super thrilling but a quick browse over them might save you some time during Phase 2 12 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 12 1 1 p2pp and the GuideCam tools Using p2pp to prepare HAWK I observations does not require any special functions only when the AOF standard mode is NOT used Indeed for no AOF and TTS free mode no file has to be attached except for the finding chart and possibly ephemerides because all other entries are typed On the other hand when the AOF standard mode is selected the Guide Cam tool must be used to specify acquisition template entries In particular because the position of the TTS with respect to the target constraints the instrument PA as well as the FoV centre and telescope guide star the Guide Cam tool provide
38. ic rack 2 1 Optics The optical layout of HAWK I is given in Fig 2 The entrance window of the vacuum vessel is MIRROR 7 TM s Ve ENTRANCE WINDOW IRQ MRROR 1 COLD BAFFLE ID MRROR 4 DETECTOR FILTER 1 MFILTER 2 Figure 2 HAWK I optical layout used to image the pupil on the M3 mirror A cold baffle stops the light outside of the instrument FoV The first folding mirror M1 is used for beam accommodation Then the camera consists of one large spherical mirror M2 and two aspherical mirrors M3 and M4 allowing to adapt the HAWK I User Manual Issue XX 5 telescope beam to the required F 4 36 The two filter wheels are located directly in front of the detector mosaic The size of the filter needed to cover the whole FoV is 105x 105 mm The beam incidence angle versus the filter is quasi constant for all points of the field to keep the spectral filtering uniform over the whole FoV 2 2 Mechanics HAWK I is installed at the Nasmyth A of VLT UT4 Yepun and centred on the Nasmyth adaptor by the interface flange The vacuum vessel is split into three elements i vessel from part which extends to the interface flange diameter ii vessel centre part which offers all necessary supply ports and mechanical connections to support the cold mechanics iii access to the detector filter unit filter exchange the connection of the closed cycle coolers pre cooling lines and electronically cables 2 3 Detectors The HAWK
39. in period 81 operating exclusively in seeing limited mode until period XX Afterwards with the installation on UT4 of the Adaptive Optics Facility AOF the instrument has been equipped with GRAAL a seeing improver allowing to enhance the instrument image quality We welcome any comments and suggestions on the present manual these should be addressed to our user support group at usd help eso org 1 3 Structure of this document The document is structured as follows e Part provides a technical description of HAWK I and GRAAL e Part details the instrument performance e Part II describes the commonly used observing technique in the IR and provides guidelines for Phase 1 and Phase 2 preparation e Part IV contains collected useful reference material HAWK I User Manual Issue 1 2 1 4 More important information A handful of things that you must remember are e The TT star has to be fainter than R 7 e Phase 1 constraints are binding Because the use of the lasers requires CLR or PHO condi tions check in advance the presence of suitable TT star s All HAWK I related manuals are available on the HAWK I instrument web page together with the most updated information of the instrument For both Service and Visitor mode Observing Block OBs should be prepared with the latest version of the Phase 2 Proposal Preparation tool p2pp Information on the preparation of Service mode observation with HAWK I can be found here
40. isible in chip 2 limiting magnitude for this chip The number of spurious detections in the other chips is negligible see Fig 16 This rate of spurious detections on CHIP2 should be considered as a conservative upper limit as it could likely be decreased by more careful optimisation of the object detection parameters HAWK I User Manual Issue XX 32 CHIP 1 CHIP 2 CHIP 3 CHIP 4 Coadded stack N mag arcmin 033 34 15 16 17 18 19 MAG APER D 1 8 ZP 25 Figure 16 Number counts as a function of aperture magnitude for the four HAWK I chips The magnitudes as plotted adopt an arbitrary zero point of 25 plus the relative zero point offsets as monitored for the J filter 0 14 4 0 03 0 23 mag for chips 2 4 relative to chip 1 The limiting magnitudes i e the location of the turnover in the number counts of the four chips are essentially identical within the measurement precision of this exercise lt 10 Also shown are the number counts for a deep co added stack of the four rotated and aligned jitter sequences We use this deep image to assess the number of spurious sources detected on each chip objects matched from the single chip image to the deeper image are considered to be real while objects that only appear on the single chip images are considered spurious The number of spurious detections is negligible for chips 1 3 and 4 though for chip 2 it reaches 20 around the limiting magnitude HAWK I User Manua
41. ite target and to loose it in the gap since this is where the telescope points BEWARE of the gap between the detectors And see the details in Appendix 5 5 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 chip 79 8 0 040 Q1 chip 78 8 0 13 i43 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 HAWK I User Manual Issue XX 13 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 about 5 mas once the distortion model was applied a precision that should satisfy most purposes 5 2 Center of Rotation and Centre of Pointing The center of
42. ixels e Only three values for the window height are allowed so DE T WIN NY can be set to 32 64 or 128 pixels 3 3 6 7 or 13 3 arc seca respectively There is no restriction on where the windows are located so the users are free to set DET WIN STARTY to any possible value from 1 to 20048 DET WIN NY If the scientific goals of the program require different window sizes the users must contact the User Support Department USD to check if they are technically feasible acceptable and if this is the case to ask for a waiver D 2 2 Data Products and Cube Sizes The data product is a fits file containing cubes with slices made from the tiled together images of all windows windows in each stripe i e spliced together without the gaps that will be present HAWK I User Manual Issue XX 41 DET WIN STARTX1 DET WIN STARTX1 400 300 z 3 z 4 z Y arcsec 200 100 DET WIN STARTY1 G 100 200 300 460 Figure 19 Definition of the windows The location of the four HAWK I detectors on the fo cal plane is shown as well as the 16 stripes in which each detector is being read The sizes of the detectors and the gaps projected on the sky in arc secs are also given The binaries generated from quadrants 1 2 3 and 4 are usually but not always stored in fits extensions 1 2 4 and 3 Arrows indicate the direction in which the parameters DET WIN STARTX DET WIN STARTY DET WIN NX and DET WIN NY increase
43. kground 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 i 40 10 NB2090 60 7 900 60 NB1190 3 6 110 14000 300 NB0984 Visitor filter now removed NB1060 3 4 120 14000 300 H2 140 17 400 30 BrG 180 15 300 30 Table 3 lists the contribution of the sky background for a given filter and DIT 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 temperature impacts the sky contribution for the K 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 about 1 minute Figure 12 shows the quality of the sky subtraction as a function of pupil angle and time from the first frame A sequence of frames in the K band was obtained when the target was n
44. ki eso org 7 TT star properties TT sensing is done in the R band by using a star of magnitude 7 R 14 5 which must be located outside the instrument FoV see Fig 5 As a consequence the position angle PA of the instrument can be selected only according to the PAs of the available stars in the 1 wide annulus at radius 6 7 from the centre TTS as faint as R 18 should still provide a rather stable system performance TBC although a variety of steps performed during the acquisition as well as the required background subtraction become longer and more difficult The R I color of the TTS is important for precise atmospheric refraction compensation The AO system takes into account the differential atmospheric refraction between the wavelength used by the WFS and the central wavelength used for the science exposures in the calculation of the TT mirror orientation 8 Limiting magnitudes Limiting magnitudes are of course very much dependent on the observing conditions The exposure time calculator ETC is reasonably well calibrated and we strongly encourage you to use it In HAWK I User Manual Issue XX 15 order to give you a rough idea of the performance to be expected for NoAOF mode observations 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
45. l Issue XX 33 B 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 hawki instrument page 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 76 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 Ks 2146 1984 2308 324 82 CH 1575 1519 1631 112 9096 Bry 2165 2150 2181 30 77 H 2124 2109 2139 30 8096 NB0984 983 7 981 2 996 2 5 60 amp now removed NB1060 1061 1057 1066 9 70 NB1190 1186 1180 1192 12 75 NB2090 2095 2085 2105 20 81 Figure 17 Smoothed enhanced images of the optical ghosts visible in the four quadrants for the NB1060 left amp NB1190 right filters Optical ghosts out of focus images showing the M2 and telescope spiders have been rarely found only with the NB1060 Lya at z 7 7 amp NB1190 Lya at z 8 7 filters As illustrated in HAWK I User Manual Issue XX 34 Fig 17 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 i
46. likely to set the jitter box size to zero to keep the objects located on the same pixels which should reduce systematic effects from imperfect flat fielding Acquires images stored in a cube and continues as long as the number of the frames in the cube is equal to the value of the parameter DET NDIT this parameter defines the length of the cube The number of cubes acquired at each offset position is defined by SEQ NUMEXP Goes back to step and repeats the actions until SEQ NUMOFFSET offsets are executed Specific details The new windowing parameters DET WIN STARTX DET WIN STARTY DET WIN NX and DET WIN NY are not accessible to the user from this template The parameter DET BURST MODE selected between Burst True and Fast Jitter False modes Readout mode is set to DoubleRdRstRd because for now this is the only one for which the new windowing is implemented The hardware windowing is set to True implicitly for the user The store in cube option is set to True HAWK I User Manual Issue XX 49 D 4 4 Calibration templates HAWKI_img_cal_DarksFastPhot Twilight flats for this mode are obtained with the normal non windowing HAWKI img cal TwFlats template making the dark current calibration template HAWKI img cal DarksFastPhot the only unique calibration template for the fast mode It is similar to the usual dark current template HAWKI_img_cal_Darks with the execution of the hardware windowing and the storage of the d
47. ll reflective design The light passes four mirrors and two filter wheels before hitting a mosaic of four Hawaii 2RG 2048 x 2048 pixels detectors The final F ratio is F 4 36 1 on the sky correspond to 169 4um The field of view FoV 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 four cosmological filters at 0 984 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 can be used in combination with the GRound layer Adaptive optics system Assisted by Lasers GRAAL a seeing improver whose ultimate goal is to enhance the instrument image quality Under most seeing conditions 1 in visible band with the use of 4 lasers and a natural star for atmospheric and telescope tip tilt correction GRAAL reduces the 5096 encircled energy diameter by 12 in the Y and 21 in the K filters respectively over the entire FoV That is the FWHM of the PSF is typically reduced from 0 53 to 0 42 in K band The visible tip tilt star 7 lt R lt 14 5 is acquired outside the instrument FoV to avoid obscuration therefore it must be located between 6 7 and 7 7 FoV For best correction the star should be brighter than R 14 mag
48. mes 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 so i e if you mention it in Phase 1 when submitting your proposal C 2 The HAWK I 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 DITxNDIT 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 characteristics 1 set monthly RON dark current linearity The above list of calibration frames are taken exclusively in noAOF mode There are no reasons to use the laser and the TT star when observing standard fields as the corresponding zero points do not change TBC during commissioning Please do not hesitate to contact us usd help eso org if you have any questions C 3 Quality Control All calibratio
49. ns 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 HAWK I User Manual Issue XX 36 the raw data they are derived from for reducing the science data are available through the ESO User Portal More information about the HAWK I quality control can be found here The time evolution of the most important 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 XX 37 D HAWK I Burst and Fast Jitter Modes D 1 Description This section describes a mode for high cadence and high time resolution observations with HAWK the fraction of time spent integrating is typically 80 of the execution time and the minimum DIT MINDIT is in the range 0 01 0 1sec The mode is useful in two observing scenarios i studies of quickly varying sources that require good sampling of the light curves i e X ray sources ii studies if events with limited duration that can t be re observed so dead times are undesirable i e transit timing variations of extrasolar planets A good example of a combination of the two are Lunar occultations Richichi et al 20123 AJ 146 59 This is achieved by two measures First by windowing down the detectors to speed up th
50. ntensities of the ghosts are in both cases 2 but their surface brightnesses are a factor 1074 of the peak brightness in the stellar PSF The figure 18 summarizes the HAWK I filters graphically 100 80 be 60 2 o c D 9 40 NBI 19 D 20 B0984 ILAJI Lud LXI Ka LM l 1000 1500 2000 2500 wavelength nm Figure 18 HAWK I Filters Black broad band filters Y J H K Green cosmological filters NB1060 NB1190 NB2090 Red CH4 H2 Blue Bry magenta visitor filter NB0984 HAWK I User Manual Issue XX 35 C The HAWK I calibration plan C 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 fra
51. of 250 Hz The science HAWAII 2RG infrared sensors of HAWK I is as well used to correct slow drifts between visible WFS and IR imaging paths coming from flexures and uncompensated atmospheric dispersion taking the opportunity of continuous reading of the science detectors during integration HAWK I uses the adapter rotator of the Nasmyth focus to derotate its FoV On the opposite GRAAL LGS WFS must derotate the pupil therefore GRAAL includes an LGS ring a derotator carrying the LGS WFS which counteracts the adapter s effect to which is added the pupil rotation proportionnal to the elevation of the telescope Therefore to summarise GRAAL science mode is based on the use of e 4 LGS projected on sky with the help of 4 dedicated launched telescopes e The corresponding WFS located on a 12 diameter ring e one TT sensor using a NGS on a 14 5 ring e truth sensing is realized by the telescope guide probes a 21x21 Shack Hartmann sensor already in operation in Paranal since the telescope installation for active optics control Note that the active optics control will be superseded by the fast AO loop so that the active optics sensor will be blind to all modes but the ones invisible to the AO system the first of them being the focus mode e SPARTA an RTC platform sharing commonalities of hardware and software design with other AO systems GALACSI and SPHERE and e the DSM LGS TTs are filtered out and sent to the LGS launch systems to correc
52. onomy Rodier 1999 Cambridge University Press or Introduction to adaptive optics Tyson 2000 Bellinghan SPIE 3 1 1 Atmospheric Turbulence The VLT theoretical diffraction limit is 1 22x A D 0 7 at A 2 2um However the resolution is severely limited by the atmospheric turbulence to A ro 1 where ro is the Fried parameter ro is directly linked to the strength of the turbulence and it depends on the wavelength as For average observing conditions rg is typically 60 cm at 2 2 um Temperature inhomegeneities in the atmospheric induce temporal and spatial fluctuations in the air refractive index and therefore cause fluctuations in the optical path This leads to random phase delay that corrugate the wavefront The path differences are to a good approximation achromatic Only the phase of the wavefront WF is chromatic The coherence time of the WF distortions is related to the average wind speed V in the atmosphere and is typically of the order of ro V 60 ms at 2 2 um for V 10 m s 3 1 2 Ground Layer Adaptive Optics A technique to overcome the degrading effects of the atmospheric turbulence is real time com pensation of the deformation of the WF by AO Very schematically the wavefront sensor WFS measures the WF distortions which are processed by the real time computer RTC The RTC controls a deformable mirror to compensate the WF distortions A particular type of AO systems is the ground layer adaptive optics GLAO
53. ons by their location in the file Instead look for the FITS keyword EXTNAME in each extension and verify that you are handling the quadrant that you expect eg EXTNAME CHIP1 INT1 2000 PT 2000 PTT oe 1500 F j 1500 F j L Q4 J L Q3 J Tonne chip 88 E 1000 chip 79 4 500 E J 500 E 4 ay 1 o Laer iaa haret o Ee dias dansa 0 500 1000 1500 2000 O 500 1000 1500 2000 X 2000 PITT oF 2000 POTT 1500 J 1500 F 4 L Qi 1 L Q2 1 1000 chip 66 2 1000 7 chip 478 n 500 E 500 F 4 Q Cc Loc d ioca Loa dl o si lu ases Eis al 0 500 1000 1500 2000 0 500 1000 1500 2000 Figure 6 HAWK I detectors naming convention The characteristics of the four detectors are listed below Detector Parameter Q1 Q2 Q3 Q4 Detector Chip 66 78 79 88 Operating Temperature 75K controlled to lmK Gain e ADU 1 705 1 870 1 735 2 110 Dark current at 75 K e7 s between 0 10 and 0 15 Minimum DIT 1 6762 s Read noise NDR b5tol2e 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 HAWK I User Manual Issue XX 11 1 6762s the RON is 12e7 for DIT 10s the RON is 8e and for DIT gt 15s the RON remains stable at 5
54. ored images is NX 32 NY 2 NDIT 4 gt 512 x 1024 x 1024 536870912 3 The maximum acceptable NDIT is NDITmax 536870912 N X x 32 x NY 2 4 1 4 The 1 leaves space for the averaged image that is always stored in the last slice of the cube The Burst mode stores separately the two reads that form each images so for the same NDIT it generates twice more data than the FastJitt mode Therefore in Burst mode the maximum NDIT is half of that for the FastJitt mode D 2 3 Minimum DIT Overheads and Frame Losses The MINDIT depends strongly on the size and weakly on the location of detector windows The MINDITs and the execution times for some of the offered windowing parameter combinations are listed in Table6 The table shows that the overheads depend mainly on the window size because of the amount of pixels that need to be read and transferred while the location of the window has minor effects The faster windows are located close to the outer edges of the detectors i e with smaller values of STARTY However it is recommended to avoid setting START Y 1 px because the edges of the detectors usually suffer from stronger cosmetic defects The experience shows that these effects are smaller starting from START Y 100 150 px The time spent on the acquisition is a matter of how many fine adjustments are needed The absolute minimum of the acquisition without any telescope movement or movement of ins
55. p the IRACE remains in hardware windowing mode with the window size defined during the OB and with the store in data cube mode ON D 2 1 Detector Windowing For speeding up the observations the HAWK I detectors are windowed at hardware level so only the pixels that fall within the user defined windows are actually read In contrast in case of software windowing the entire detectors are read and only the pixel values within the user defined windows are stored so there is no gain in speed The hardware windowing is hard coded in the templates and does not require any further action from the user Each HAWK I detector is read in 16 vertical stripes The stripes span 128x2048 px and each of the detectors spans 2048 x 2048 px One window is defined in each stripe but the locations of the windows are not independent i e they all move together in a consistent manner that will be described further below Therefore the total number of windows for each HAWK I frame is 4x16 64 because HAWK U is a made of 4 detector arrays Along the X axis the windows can be contiguous or separated within each detector even contiguous windows within the detector offer only sparse coverage on the sky because the four detectors themselves only offer a sparse coverage of the focal plane i e there is space between the arrays gaps so one can not have a single contiguous window across the entire focal plane The situation closest to that are four contiguous window
56. re given at http www ipac caltech edu 2mass releases allsky doc seca4 1 html In particular the sect Ill 2 http www ipac caltech edu 2mass releases allsky doc sec3_2d html provides a list of fields touch stone fields that you could use as photometric fields in order to calibrate your observations 11 1 2 HAWK I extinction coefficients We measured HAWK I extinction coefficient for the broad band filters as a result of a year moni toring The results are J 0 043 0 005 H 0 031 0 005 K 0 068 0 009 Y 0 021 0 007 We plan to keep monitoring these coefficients on a monthly basis according to the calibration plan 11 2 The Exposure Time Calculator The HAWK I ETC 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 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 The seeing condition to be provided as input parameter is the seeing in V band at zenith As output parameter the ETC provides you the corresponding seeing at desired airmass and at the observing wavelength As a consequence you might
57. ripe For example if the user wants to define a window of 18x28 px on each stripe the corresponding values of DET WIN NX and DET WIN NY will be 18 and 28 respectively These values will produce a fits file that contains a 3 dimensional data cube with 576x56xNDIT because of the 16 stripes in each of the two detectors along the X axis 18x16x2 576 and the two detectors along the Y axis 28x2 56 The allowed values are 1 128 and 1 2048 for DET WIN NX and DET WIN NY respectively t However the users should take care that the starting point plus the size of the window HAWK I User Manual Issue XX 40 along each axis do not exceed the size of the stripe along that axis 128 or 2048 respectively for X and Y Figure 19 shows examples of various detector window definitions For instance an increase of the parameter DET WIN STARTX would move the violet set of windows towards the yellow set if the other parameters are kept fixed Similarly an increase of the parameter DET WIN STARTY would move the violet set towards the solid black set The dashed black line set corresponds to DET WIN NX 128 128x16 stripes x2 detectors 4096 px in total along the X direction that defines contiguous windows see below An interesting special case is to define contiguous regions i e the windows on the individual stripes are as wide as the stripes themselves so there are no gaps along the X axis one has to use for example DET WIN STARTX 1 DET WIN STARTY 4
58. rmed is shown in the right panel of Fig 11 The sequence of offset will be 10 10 90 10 100 200 HAWK I User Manual Issue XX 26 J zi Telescope offsets J Telescope offsets J 4 200 3 aa 300 220 6 250 210 110 i i 100 i g 20000 dae droom ES Pu CN Figure 11 Left Pop up window at the start of an example template it provides a quick check of your offset pattern Right Offset execution along the template 100 200 300 420 and 580 10 13 6 Instrument and telescope overheads The telescope and instrument overheads are summarised below Hardware Item Action Time minutes Paranal telescopes Preset 6 HAWK I Acquisition NoAOF HAWK I Acquisition AOF TBD HAWK I Acquisition TTS free TBD HAWK I Initial instrument setup for ACQ only 1 HAWK I Telescope Offset small 0 15 HAWK I Telescope Offset large gt 90 0 75 HAWK I Readout per DIT 0 03 HAWK I After exposure per exposure 0 13 HAWK I Filter change 0 35 The instrument set up is usually absorbed in the telescope preset for a simple preset a TBC whether the overheads associated to telescope offsets remain the same even when GRAAL in on 13 7 Recommended DIT NDIT and Object Sky pattern For DITs longer than 120sec the SM user has to use one of the following DIT 150 180 240 300 600 and 900sec HAWK I User Manual Issue XX 27 Table 3 Sky bac
59. 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 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 40 5 pix in the respective quadrant reference system Quadrant CRPIX1 CRPIX2 Q1 2163 2164 Q2 37 5 2161 5 Q3 42 28 Q4 2158 25 5 The CRVAL1 and CRVAI2 have the on sky coordinates of the telescope pointing FITS keywords TEL TARG ALPHA TEL TARG DELTA in all quadrants 5 3 Vignetting of the FoV 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 TBC upon commissioning results Edge No of columns or rows vignetted gt 10 Maximum vignetting Y 1 14 Y 8 54 ER T 36 X 2 15 HAWK I User Manual Issue XX 14 The last column represents the maximum extinction of a vignetted pixel i e the percentage of light absorbed in the pixel row or column with
60. s 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 HAWK I User Manual Issue XX 17 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 They are measured on a monthly basis Besides we remind that colour terms for HAWK I are small 0 1x J K Check with Skycat or Gaia ahead of time whether good non saturated 2MASS 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 11 1 1 Consider the 2MASS calibration fields The 2MASS mission used a number of calibration fields for the survey Details a
61. s of the Paranal observatory have been designed such as to minimize the non atmospheric sources of image degradation with for instance a closed loop active optics during science obser vations GRAAL therefore only correct further these disturbances at higher temporal frequencies excepted in the case of very good seeing where the telescope and enclosure residual seeing contri butions might become significant in the PSF formation Figure 5 GRAAL focal plane illustration The 4 LGS rotate with respect to the FoV The visible TT star is selected outside of the LGS ring The cones represent the Rayleight scattering areas from upwards propagation of the laser beams lasers are side launched GRAAL is based on a 4 Na LGS sodium Laser Guide Stars system launched from the corners of the centrepiece of UT4 As shown in Fig 5 the lasers are pointed towards areas located outside of the science FoV 7 5 x7 5 and the light re emitted by the 80 100 km altitude Sodium layer is collected by 4 WFS each with 40x 40 subapertures The slopes provided by the WFS are combined to provide an estimate of the WF error for the lowest layers this shape is then removed from the actual shape of the DSM The AO loop is closed at a 700 to 1000 Hz frequency As the LGS are not useful to sense Tip Tilt TT an additional visible Natural guide star NGS HAWK I User Manual Issue XX 8 WFS is embedded in GRAAL and the TT is corrected at a loop frequency
62. s one across each of the four detectors An additional constraint is that the windows must be centered within the stripes Since the stripes are 128 pixels wide an even number the width of the windows defined by DET WIN STARTX see below must also be an even number The detector windows are described by the following parameters e DET WIN STARTX and DET WIN STARTY define the starting point of the window within an individual stripe The X axis on all detectors increases in the same direction but the Y axis on the upper and the lower detectors increases in opposite directions so when the values of DET WIN STARTX and DET WIN STARTY increase the starting points of the windows move to the right along the X axis and towards the central gap along the Y axis Note that these parameters are different at the software level from the parameters DET WIN STARTX and DET WIN STARTY used to define the windowing in other HAWK I observing modes Values larger than 100 px are recommended for DET WIN STARTY because the back ground at the edges of the detectors is higher due to an amplifier glow The allowed value ranges for DET WIN STARTX and DET WIN STARTY are 1 128 and 1 2048 re spectively but if they are set to 128 and 2048 the window will only be 1x1 px so the users should select smaller starting values to leave room for an ample size of the windows e DET WIN NX and DET WIN NY define the sizes in pixels of the windows in each individual st
63. s smaller than 30 deg 13 4 Twilight Because HAWK I is an infrared imager observations of bright objects in no AOF or TTS free modes may be carried out in twilight From P91 onwards there is a new constraint in p2pp called twilight constraint This constraint can be used to define the earliest time with respect to the end of the astronomical twilight when the execution of the OB can be started While the relation between the HAWK I User Manual Issue XX 25 time difference from the evening twilight end and sun elevation varies during the year for Paranal due to its low latitude this difference is small Therefore the constraint is given in minutes as a difference in time with respect to the end of astronomical twilight i e the time when the solar elevation is 18 degrees The default value of twilight constraint is 30 A negative number means that it is allowed to start the observation before the end of the astronomical twilight The twilight constraint can take values between 45 and 0 minutes 13 5 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 arc seconds 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
64. s you an easy and safe way to select suitable star s for TT correction It provides an user friendly graphics interface that allows you to load an image of 10 x10 FoV centred on your target together with a catalog of suitable VLT guide stars and TTS to help you to configure the instrument set up as shown in Figure 12 1 1 Once the instrument configuration is ready all the relevant information e g target TTS and VLT coordinates magnitude and color of the TTS PA stored by the tool in a configuration file are automatically uploaded to the p2pp into the corresponding entries of the acquisition template Note that although not mandatory the tool can be used also for no AOF and TTS free mode observation preparation For a detailed description on the use of the Guide Cam tool we strongly invite the reader to check the manual available at the following link http www eso org link to the GuideCam Tool manual Step by step tutorial on how to prepare OBs for HAWK I with P2PP can be found here HAWK I User Manual Issue XX 21 Figure 9 Guide Cam Tool The location of the VLT guide star is displayed with the guide probe arm covering the blue shaded annulus The location of the GRAAL TT field is the pink square 12 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
65. sure 4 21 06 58 start exposure 5 21 06 58 end exposure 5 21 07 30 IRACE set up 21 07 40 end template 21 07 40 turning off the RTD during the observations can reduce the frame loss by 2 396 Unfortunately other loads on the network can not be controlled by the operators which can easily leads to uncertainty in the frame loss rate of 2 396 as our experiments has shown Frame losses for the window sizes listed in the Table6 practically disappear for DIT 0 5 1 0 sec D 3 Preparation and Observation D 3 1 OB Naming Convention Following the common convention for the fast modes FastJitter OBs BURST F should start with the prefix FAST in their name D 3 2 OB Requirements and Finding Charts The finding chart requirements are the same as for the other VLT instruments The typical accuracy of the VLT pointings is below 1 arcsec However the simple preset tem plate can not define the correct detector windowing for the fast mode The windowing is defined only in the specialized acquisition template HAWXK img acq FastPhotNoAOF and HAWKI img acq FastPhotAOF depending whether or not GRAAL is used There fore HAWKI img acq FastPhotNoAOF or HAWKI img acq FastPhotAOF must be executed at least once and the windowing parameters should be kept the same during the entire sequence Sec D 4 D 3 3 Observing Modes The Burst mode is not offered anymore while the FastJitter mode is now offered both in Service and Visitor mode HAWK I
66. t the jitter of each beam independently Slopes computed from each of the four LGS WFS at the loop rate 1000 Hz are split in two components respectively TT and high orders commands are then used to drive the LGS jitter actuators respectively the DSM 3 3 Wavefront sensors The LGS sensor unit consists of 4 identical systems Each one is composed of e One small pick up mirror placed with a fixed arm at 5 8 from the optical axis on the Nasmyth focal plane One trombone allowing focusing on the LGS e One re imaging objective composed of two lenses One 40x40 micro lenses array e One 240x240 L3 CCD and NGC controller Each pick up mirror redirects the LGS light to a classical Shack Hartmann WFS The system accepts focus variations from 80 to 180 km The visible TT sensor collects the the light of a NGS before the Nasmyth focal plane outside the HAWK I FoV A pick up mirror selects the NGS inside a FoV ring internal radius of 6 6 and external radius 7 6 The system is composed of HAWK I User Manual Issue XX e One pick up mirror with at least 50 FoV e One re imaging objective e One 240x240 CCD 9 HAWK I User Manual Issue XX 10 Part Il Instrument Performance 4 Detectors The naming convention for the four detectors is shown in Figure 4 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 extensi
67. the SM user is the one to take standard stars HAWK I User Manual Issue XX 22 Table 1 Acquisition and science HAWK I templates acquisition templates functionality comment HAWKI img acq PresetNoAOF Simple telescope preset For observation in no AOF mode HAWKI img acq PresetRRMNoAOF Simple telescope preset For RRM observation in no AOF mode HAWKI img acq PresetAOF Simple telescope preset For observation in AOF standard or TTS free mode HAWKI img acq FastPhotNoAOF Acquisition for windowed mode For observation in no AOF mode HAWKI img acq FastPhotAOF Acquisition for windowed mode For observation in AOF standard or TTS free mode science templates HAWKI img obs AutoJitter imaging with jitter no offsets recommended for low density fields 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 HAWKI_img_obs_FastPhot imaging with fast read out and windowing The calibration templates are foreseen to acquire darks flat fields and simple standard star obser vations to calibrate the zero point the latter only in noAOF mode The technical templates are used for the periodical characterisation 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 templates are needed to compute the distortion map the plate scale
68. tions The mode has two modifications 1 burst NOT OFFERED is intended for applications that require short high time resolution observations i e lunar and KBO occultations transits of extrasolar planets etc 2 Fast Jitter OFFERED is intended for observations of extremely bright objects that require short DITs to avoid saturation and small overheads to increase the efficiency i e exo planet transits The Burst mode is preferable when the DIT is equal or close to the minimum DIT because of the smaller frame loss and higher cadence due to skipping the image restoration from two detector reads The penalty is the complicated structure of the output file see below The distinction between burst and Fast Jitter sub modes was adopted for historical reasons the previous instruments with fast imaging required significant additional overheads to reconstruct the images taking a difference of two detector reads This is not the case for HAWKI and therefore only the Fast Jitter is offered Update The fast photometry may be familiar to the users of fast jitter and burst modes of ISAAC NaCo VISIR and Sofl The main advantage of HAWK I in comparison with these instruments is the wide field of view that allows a better selection of bright reference sources for relative photometry and the favorable pixel scale D 2 Implementation The Fast Photometry templates are discussed in details further but for clarity we will point out here th
69. trument wheel is 100sec This is important to remember in case of aborting and restarting the OB with acquisition Therefore if the OB has to be aborted for some reason and there is no need to make adjustments it is better to skip the acquisition template Table 5 also shows the execution times for a few extreme or typical cases if the DIT is set to the smallest available value for a given windowing configurations and if the DIT is set to 0 1 0 2 secs which are often requested by the users HAWK I User Manual Issue XX 44 Table 5 Timing Parameters The execution times were rounded to 1sec The overheads are given for executing NEXP 5 exposures in stare mode i e with jitter box size JITTER WIDTH 0 and NOFFSET 1 The 32 and 2 multiplication factors are given to remind the user that the NX and NY parameters are the total width of the detector windows across the entire set of stripes The readout mode is ReadRstRead STX and STY stand for STARTX and STARTY respectively this is a non standard case STX NX STY NY MINDIT Max DIT NDIT Integr Exec Times Frame px px px px sec NDIT sec Time lexp NEXP 5 loss sec sec sec 1 32x32 1024 1 32x2 64 0 051096 511 0 051096 511 26 110056 28 160 1 2 1 128x32 4096 1 32x2 64 0 051864 511 0 051864 511 26 502504 28 165 7 2 1 128x32 4096 1 32x2 64 0 051864 511 0 1 511 51 1 53 286 13 1 128x32 4096 1 32x2 64 0 051864 511 0 2 511 102 2 104 542 2 4 1 128x32 4096 1 32x2 64 0 051864 511
70. tures and features on A2 Relative Sensitivity eue se s soca eo ue koc Eo cR KO doom P ee ERY B The HAWK I filters C The HAWK I calibration plan C 1 Do you need special calibrations ee C 2 The HAWK I standard calibrations in a nutshell C3 Dus Control Jaco OO RA ORO xU RE oe RAK AS Dh eee a 15 29 29 29 30 33 HAWK I User Manual Issue 1 iv D HAWK I Burst and Fast Jitter Modes 37 DE Deero uu eu ioe deem mos RUM X ale x Vu ne de sd ar ae d 37 D 2 Implementation s s 2 sss 38 DL Detector Windowing ou us Vou ox oe Dana ox REOR RO R E BC 3C na 39 D 2 2 Data Products and Cube Sizes lll 40 D 2 3 Minimum DIT Overheads and Frame Losses 2 2222 222200 43 D 3 Preparation and Observation 2 2222 22 a one 45 D 3 1 OB Naming Convention 2 650444 04 be sea nen ee 45 D 3 2 OB Requirements and Finding Charts 45 D 3 3 Observing Modes eee eee eee 45 D34 Calibration Plam uuu eo oN ae ew ee m Ron wee He Rs 46 O35 FITS Files Names 4224 35 ee ewan eisen 46 DA Template Guide uou ouo sommo RS ee be ee we eee 46 D 4 1 Acquisition HAWKIimg_acq_FastPhotNoAOF 46 D 4 2 Acquisition HAWKIimg_acq_FastPhotAOF 0 4 48 D 4 3 Science template HAWKIimg_obs_FastPhot 48 D 4 4 Calibration templates HAWKI img cal DarksFastPhot 49 HAWK I User Manual Issue 1 1 1 Introduction HAWK I
71. you you may need to get back to the basics 12 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 Only one form of acquisition exist that is a simple preset with no possibility to to interactively place the target in a given position on the detector However each instrument mode has a dedicated acquisition template The science templates provide three forms of obtaining sky images small jitter patterns for un crowded fields fixed sky offsets for extended or crowded fields when the off position needs to be acquired far from the target field and finally the possibility to define an arbitrary offset pattern when the standard strategies are not suited Note that unlike the acquisition the science templates do not depend on whether or not GRAAL is used For Rapid Response Mode RRM we have only one dedicated acquisition template which is exactly the same as the one for noAOF observations but with the string RRM appended to the name RRM observation are only allowed without GRAAL i e in No AOF mode The calibration and technical templates are listed in Table 2 The only calibration template accessible to

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