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HAWK-I User Manual

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1. Organisation Europ ene pour des Recherches Astronomiques dans Hemisphere Austral A Europ ische Organisation f r astronomische Forschung in der s dlichen Hemisphare ES EUROPEAN SOUTHERN OBSERVATORY o A ESO European Southern Observatory Karl Schwarzschild Str 2 D 85748 Garching bei M nchen Very Large Telescope HAW K I User Manual Doc No VLT MAN ESO 14800 3486 Issue 96 10 Jun 2015 Giovanni Carraro and the HAWK I IOT Ed EES C Dumas APprOVed scans Sa nek Se Dee ee hk Dyin yee ete es Name Date Signature A Kaufer ee a bettel Sym Sieste e whe a Gta Rae E HAWK I User Manual Issue 96 Change Record Issue Rev Date Section Parag Reason Initiation Documents Remarks affected Issue 1 25 May 2007 all First release for PAE Issue 81 31 August 2007 prepared for CfP P81 6 Dec 2007 all update after end of commissioning Issue 82 06 March 2008 P82 Phase version bump Bug in over head table corrected Minor changes to introduction Issue 82 1 06 March 2008 minor bug Issue 82 2 06 March 2008 Added warning about sky subtraction Issue 83 0 01 Sep 2008 P83 Phase 1 cal plan Issue 83 1 27 Nov 2008 P83 addenda for the IP83 release Issue 84 0 29 May 2009 P84 addenda New read out mode and persistence study Change of offset scheme Issue 84 1 27 Jun 2009 P84 addenda cleaning and Phase II Issue 85 0 09 Dec 2009 P85 Phase and Il Issue 85 1 28 Feb 2010 Fas
2. East and 0 4 South of the telescope pointing HAWK I User Manual Issue 96 26 The common reference point for all four quadrants taken as the centre of the telescope pointing and centre of rotation has the following pixel coordinates to 0 5 pix in the respective quadrant reference system Quadrant CRPIX1 CRPIX2 Ql 2163 2164 Q2 37 5 2161 5 Q3 42 28 Q4 2158 25 5 The CRVAL1 and CRVAI2 have the on sky coordinates of the telescope pointing FITS keywords TEL TARG ALPHA TEL TARG DELTA in all quadrants C 2 Vignetting of the field of view The Hawaii2RG detectors have 4 reference columns rows around each device which are not sensitive to light In addition due to necessary baffling in the all reflective optical design of HAWK I some vignetting at the edges of the field has turned out to be inevitable due to positioning tolerances of the light baffles The measured vignetting during commissioning on the sky is summarised in the following table Edge No of columns or rows vignetted gt 10 Maximum vignetting Y 1 14 Y 8 54 X 7 36 X 2 15 The last column represents the maximum extinction of a vignetted pixel i e the percentage of light absorbed in the pixel row or column with respect to the mean of the field Note although the Y edge vignetting is small in amplitude it extends to around 40 pixels at lt 10 HAWK I User Manual Issue 96 27 D The HAWK I calibration
3. 0 75 HAWK 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 In the case of MoveToPixel the exact integration time is dependent on the number of images one needs to take at least 2 and of course the corresponding integration time For 3 images of Detector Integration Time DIT 2 NDIT 1 the overhead is 1 5min 4 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 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 HAWK I User Manual Issue 96 14 IJ Telescope offsets J Delta Alpha Quit Figure 3 Offset execution along the template Table 3 Sky background contribution amp Useful integration times Filter Contribution from sky RON limitation linearity limit Recommended DIT electrons sec DIT sec DIT sec sec Broad band filters Ke 1600 lt 1 30
4. 10 H 2900 lt 1 20 10 J 350 1 15 140 10 Y 130 3 400 30 Narrow band filters CH4 1200 lt 1 40 10 NB2090 60 7 900 60 NB1190 3 6 110 14000 300 NB0984 Visitor filter now removed NB1060 3 4 120 14000 300 H2 140 17 400 30 BrG 180 15 300 30 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 4 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 near the zenith and the pupil was rotating by 2 45 degrees minute Being the VLT an alt azimuth telescope the image rotates with respect to the pupil This is noticed as a rotation of the diffraction spikes seeing HAWK I User Manual Issue 96 15 Figure 4 The annotation indicate the difference in pupil angle between the two frames being subtracted and the difference in start time between the two exposures 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 96 16 Part Il Reference Material A The HAWK I filters The 10 filters in HAWK
5. 2 3 1 HAWK I specifics to templates OBs and p2pp HAWK I follows very closely the philosophy set by the ISAAC short wavelength and NACO imaging templates 3 1 1 p2pp Using p2pp to prepare HAWK I observations does not require any special functions no file has to be attached except for the finding chart and possibly ephemerides all other entries are typed Step by step tutorial on how to prepare OBs for HAWK I with P2PP can be found at the following link http www eso org sci observing pahse2 SMGuidelines Documentation P2PP TutorialHAWKI HAWKI html 3 1 2 Observing Blocks OBs As an experienced ESO user it will come as no surprise to you that any HAWK I science OB should contain one acquisition template followed by a number of science templates If this did surprise you you may need to get back to the basics 3 1 3 Templates The HAWK I templates are described in detail in the template reference guide available through the instrument web pages A brief overview is given below If you are familiar with the ISAAC SW imaging or NACO imaging templates these will look very familiar to you and cover essentially the same functionalities The acquisition and science templates are listed in Table 1 Two forms of acquisition exist a simple preset when a crude accuracy of a couple of arcsec is enough and the possibility to interactively place the target in a given position on the detector The science templates provide four
6. 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 Kal Y 1021 970 1071 101 92 LEAKS 0 015 at 2300 2500 nm J 1258 1181 1335 154 88 H 1620 1476 1765 289 95 K 2146 1984 2308 324 82 CH 1575 1519 1631 112 90 Bry 2165 2150 2181 30 77 H 2124 2109 2139 30 80 NB0984 983 7 981 2 986 2 5 60 amp now removed NB1060 1061 1057 1066 9 70 NB1190 1186 1180 1192 12 75 NB2090 2095 2085 2105 20 81 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 Fig 5 the ghost images are 153 pixels in diameter and offset from the central star in the same direction however the latter varies with each quadrant and is not symmetric to the centre of the moisac The total integrated intensities of the ghosts are in both cases 2 but their surface brightnesses are a factor 10 of the peak brightness in the stellar PSF The figure 6 summarizes the HAWK I filters graphically HAWK I User Manual Issue 96 17 Figure 5 Sm
7. 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 128 x 32 4096 pixels e Only three values for the window height are allowed so DET 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 2048 DET WIN NY If the scientific goals of the program require different window sizes the users must contact the User Support Department to check if they are technica
8. Q2 Q3 Q4 Detector Chip 66 78 79 88 Operating Temperature 75K controlled to 1mK 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 t NDR 5 to 12 e Linear range 1 60 000 e 30 000 ADUs Saturation level between 40 000 and 50 000 ADUs DET SATLEVEL 25000 T The noise in Non Destructive Read NDR depends on the DIT the detector is read continuously every 1 6762s i e the longer the DIT the more reads are possible and the lower the RON For the minimum DIT 1 6762s the RON is 12e7 for DIT 10s the RON is 8e7 and for DIT gt 15s the RON remains stable at 5 Figure 7 represents the quantum efficiency curve for each of the detectors HAWK I User Manual Issue 96 20 r 1 Y dl Wavelength micro Navelength micro T Figure 7 Quantum efficiency of the HAWK I detectors BI Threshold limited integration The normal mode of operation of the HAWK detectors defined a threshold by setting the keyword DET SATLEVEL All pixels which have absolute ADU values below this threshold are processed normally Once pixels illuminated by a bright star have absolute ADU values above the threshold the values are no longer used to calculate the slope of the 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 extrapolat
9. and if the DIT is set to 0 1 0 2 secs which are often requested by the users HAWK I User Manual Issue 96 37 Table 5 Timing Parameters The execution times were rounded to 1sec The overheads are given for executing NEXP 5 exposures in stare mode 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 32x 32 1024 128x 32 4096 128x 32 4096 1 1 32x2 64 0 051096 511 0 051096 511 26 110056 28 160 1 2 1 1 32x2 64 0 051864 511 0 051864 511 26 502504 28 165 7 2 1 1 32x2 64 0 051864 511 0 1 511 51 1 53 286 1 3 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 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 5
10. 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 4 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 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 1 PA 0 PA 90 L D E N aa SS E N S ai Figure 1 Definition of position angle Note that the templates use always offsets relative to the previous poin
11. forms of obtaining sky images small jitter patterns for un crowded fields random sky offsets for extended or crowded fields when the off position needs to be HAWK I User Manual Issue 96 9 acquired far from the target field fixed sky offsets when random sky offsets are not suited and fi nally the possibility to define an arbitrary offset pattern when the standard strategies are not suited For Rapid Response Mode we offer two acquisition templates They are exactly the same as the normal acquisition template but with the string RRM appended to the name Table 1 Acquisition and science HAWK I templates acquisition templates functionality comment HAWKI_img_acq_Preset Simple telescope preset recommended HAWKI_img_acq_ MoveToPixel Interactive target acquisition HAWKI_img_acq_PresetRRM Simple telescope preset for RRM offered starting P82 HAWKI_img_acq_MoveToPixelRRM Interactive target acquisition for RRM offered starting P82 HAWKI_img_acq_FastPhot Acquisition for windowed mode science templates HAWKI_img_obs_AutoJitter imaging with jitter no offsets recommended for low density fields HAWKI_img_obs_AutoJitter0ffset imaging with jitter and random sky offsets recommended for extended objects HAWKI_img_obs_FixedSky0ffset imaging with jitter and fixed sky offsets when random sky is not suited HAWKI_img_obs_GenericOffset imaging with user defined offsets HAWKI_img_obs_FastPhot imaging with fast read out and windowing
12. 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 6 The overheads listed above may vary by 1 2sec 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 Table5 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 turning off the RTD during the observations can reduce the frame loss by 2 3 Unfortunately HAWK I User Manual Issue 96 38 Table 6 Example Timing Parameters of the last case considered in Table5 Action Time start 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 exposure 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 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 3 as our experiments has shown Frame losses for the window s
13. plan D 1 Do you need special calibrations The calibration plan defines the default calibrations obtained and archived for you by your friendly Paranal Science Operations team The calibration plan is what you can rely on without asking for any special calibrations However these are indeed the only calibration that you can rely on without asking for special calibrations Thus we strongly advise all the users to carefully think whether they will need additional calibrations and if so to request them right in phase 1 For example is flat fielding very critical for your program i e should we acquire more flats e g in your narrow band filters Would you like to achieve a photometry better than a few percent i e do you need photometric standards observe right before after your science frames Is the homogeneity of the photometry critical for your program i e should you ask for illumination frames close to your observations Is the astrometry critical i e should we acquire a full set of distortion and flexure maps around your run We would be more than happy to do all that for you if you tell us so i e if you mention it in phase 1 when submitting your proposal D 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 D
14. points BEWARE of the gap between the detectors And see the details in Appendix C 2 1 2 Filters HAWK I is equipped with 10 filters 4 broad band filters and 6 narrow band filters see appendix A for detailed characteristics and the URL to download the filter curves in electronic form The broad band filters are the classical NIR filters Y J H 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 and 8 7 1 19um 1 06um respectively for Ha at z 2 2 2 09 1m and as well as 3 stellar filters CH4 Ho Bry Can you bring your own filters Possibly HAWK I hosts large 105mm7 i e expensive filters and was designed to have an easy access to the filter wheel However to exchange filters the instrument needs to be warmed up which usually only happens once per year Thus in exceptional cases i e for very particular scientific program user supplied filters can be installed in HAWK I within the operational constraints of the observatory Please make sure to contact paranal eso org WELL before buying your filters The detailed procedure is described in a document available upon request please email to hawki eso org 2 1 3 Limiting magnitudes Limiting magnitudes are of course very much dependent on the observing co
15. 1 1 Center of Rotation and Centre of Pointing 25 C 2 Vignetting of the field of view 0 00000 00 2 eee 26 The HAWK I calibration plan 27 D 1 Do you need special calibrations 0200002 eee 27 D 2 The HAWK I standard calibrations ina nutshell a aa a a 27 D3 Quality CA iere ee ne teen d cd R Ee Ree eee ieee dh meet 27 The HAWK I pipeline 29 HAWK I Burst and Fast Jitter Modes 30 Sch Description s A sts eR a OED Se EPS rn Os eebe oe 30 F2 implementation 2 446324 44454684544 45 44 4 4G e oe OOS 31 F 2 1 Detector Windowing EE 445 be Bek OOS 32 Fuge Data Products and Cube Sizes os sd Soy cau oa E ad eae ae GZ 33 F 2 3 Minimum DIT Overheads and Frame Losses 36 F 3 Preparation and Observation 2 4068462 ee Ree RR we BOR 38 KSE OB Naming Convention 4 4 lt 2684 he 28m ea a oe ee e H 38 F 3 2 OB Requirements and Finding Charts 0 38 F 3 3 Observing Modes 1 cc a wa YA PARE eke eee 38 Pacer Calibration Ian e eo we Pe OR ee RR SS eee Oe Bed 4 39 Pao FITS Files Names so 2 6d Ha SSeS SR SERRE RE SRE CE RRS RG 39 F4 Template Guide s s oa ces Re BES ERS eee SHS EEE Ee oe g 39 F 4 1 Acquisition HAWKILimg_acq_FastPhot 39 F 4 2 Science template HAWKI_img_obs_FastPhot 41 F 4 3 Calibration templates HAWKI_img_cal_DarksFastPhot 41 HAWK I User Manual Issue 96 1 1 Introduction 1 1 Scope of this document The HAWK I user manua
16. 11 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 NDITxDIT 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 7434 sec collect together 148 717 sec of integration leaving 33 sec in overheads up to the template execution time of 182 sec These 33 sec are build up as follows 2 sec 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 10 sec to set up the IRACE detector controller 2 3 sec to transfer every data cube and to merge the fits file and
17. 75 SC E e t 4 S a E S x Ze E KK a re f es ae di d e S i L L Ec ZE Figure 11 The field around the z 2 7 quasar B0002 422 as seen in the 4 HAWK I quadrants Radioactivity effects are clearly visible in Q2 chip 78 HAWK I User Manual Issue 96 24 16 CHIP 1 14 CHIP 2 x 1 CHIP 3 2 107 CHIP 4 oO 3 8 Coadded stack ap E B 6 zZ 03 14 15 le L 8 I9 MAG_APER D 1 8 ZP 25 Figure 12 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 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 Manual Issue 96 25 C The HAWK I Field of View C 1 Relative pos
18. 8x2048 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 Ks 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 User Manual Issue 96 Contents 1 Introduction ie 1 2 1 3 1 4 Scope of this document ssrt EE A a a a Ee e e Structure OF this glaten s e e e ee e e EEN e E er ET oe ed BG EE EOS EE eRe EE eed Be Abbreviations and Acronyms 0 a Observing with HAWK I from phase 1 to data reduction 2 PHASE 1 applying for observing time with HAWK I 21 2 2 23 2 4 25 SN 32 4 1 4 2 4 3 4 4 4 5 4 6 4 7 Is HAWK I the right instrument for your project o oaoa oaa eel r T 1 View se ie oe wae oe ey bo ES Soe Reed ge a Glee s BE oe Sd A ee e EE Boe eee a ee 21 3 Limiting magnitudes gt lt a EEN GRE RAR ewe ee ee 2 1 4 Adapter defocussing 2 1 5 Instruments performance 54564 54564 Photometry with HAWK 2 2 e 2 2 1 Two ways to get reasonable photometry 2 2 2 Consider the 2MASS ca
19. ITxNDIT gt 120 Twilight Flat fields 1 set filter daily broad band filters best effort basis 1 set filter as needed for narrow band filters Zero points 1 set broad band filter daily UKIRT MKO or Persson std Colour terms 1 set monthly broad band filters only best effort basis Extinction coefficients 1 set monthly broad band filters only best effort basis Detector characteritics 1 set monthly RON dark current linearity Please do not hesitate to contact us usd help eso org if you have any questions D 3 Quality Control All calibrations taken within the context of the calibration plan are pipeline processed and quality controlled by the Quality Control group at ESO Garching Calibration and science raw data are available through the ESO User Portal More information about the HAWK I quality control can be found under http www eso org observing dfo quality HAWKI qc qc html The time HAWK I User Manual Issue 96 28 evolution of the most important instrument parameters like DARK current detector characteris tics photometric zero points and others can be followed via the continuously updated trending plots available on the HAWK I QC webpages http www eso org observing dfo quality index _ hawki html HAWK I User Manual Issue 96 29 E The HAWK I pipeline We refer to the pipeline manual for a full description on the HAWK I pipeline This section provides only a very brief overview of what to ex
20. T 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 Nato 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 F 2 Implementation The Fast Photometry templates are discussed in details further but for clarity we will point out here that 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
21. The calibration and technical templates are listed in Table 2 The only calibration template accessible to the SM user is the one to take standard stars The calibration templates are foreseen to acquire darks flat fields and simple standard star obser vations to calibrate the zero point The technical templates are used for the periodical 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 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 imaging of standard field available to the SM user technical templates HAWKI_img_tec_I1luFrame imaging of illumination field HAWKI_img_tec_Astrometry imaging of astrometric field HAWKI_img_tec_Flexure measuring instrument flexure center of rotation HAWKI_img_tec_DetLin detector test monitoring HAWKI_img_te
22. 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 restored images is NX 32 NY 2 NDIT 4 gt 512 x 1024 x 1024 536870912 3 The maximum acceptable NDIT is NDIT ax lt 536870912 NX 32 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 m
23. 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 1282048 px and each of the detectors spans 2048x2048 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 4x 16 64 because HAWK I 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 windows 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 o
24. at the observing wavelength and requested airmass calculated from the seeing V band at zenith input parameter e The integration time is given on source depending on your technique to obtain sky mea surements jitter or offsets and accounting for overheads the total observing time will be much larger e The S N is computed over various areas as a function of the source geometry point source extended source surface brightness Check carefully what was done in your case Most of the other ETC parameters should be self explaining and or well explained in the online help of the ETC 2 4 Proposal Form HAWK I allows only 1 mode direct Imaging Please indicate which filters in particular narrow band filters you intend to use This will allow us to optimise their calibration during the semester 4 INSconfig HAWK I Imaging provide HERE list of filters s Y J H K NB0984 NB1060 NB2090 H2 BrG CH4 T 2 5 Overheads and Calibration Plan When applying for HAWK I do not forget to take into account all the overheads when computing the required time e Make sure that you compute the exposure time including on sky time not only on source if your observing strategy requires it HAWK I User Manual Issue 96 7 e Verify in the call for proposal that you have taken into account all listed overheads which can also be found in Sect 4 6 To do so you can either refer to Sect 4 5 or simulate the detailed breakdown of your program
25. c_Focus telescope focus determination HAWKI_img_tec_FilterWheel filter wheel positioning accuracy 3 2 Finding Charts and README Files In addition to the general instructions on finding charts FC and README files that are available at HAWK I User Manual Issue 96 10 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 a clear indication of the field orientation 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 The FC should show the position of the target at the end of the acquisition template We encourage HAWK I observers to use the new unified Guide Cam Tool GUCT that allows to prepare FCs that are compliant with the ESO general and instrument specific requirements The tool and its manual are available for download at the following link http www eso org sci observing phase2 SMGuidelines GUCT HAWKI html HAWK I User Manual Issue 96 11 4 Observing Strategies with HAWK I 4 1 Overview As with all other ESO instruments users prepare their observations with the p2pp
26. cal 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 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 DE T 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 F 4 3 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 f
27. d that decays slowly over minutes about 5min for the maximum tolerated saturation level in SM This might leave artifacts reflecting the dither pattern around saturated stars 2 2 Photometry with HAWK I As you will have noticed acquiring a single star per night does not allow to carry out high precision photometry but rather to monitor the instrument performance and make a rough evaluation of the quality of the night 2 2 1 Two ways to get reasonable photometry If good photometry is your goal you should go for one of the following options e Ask for special calibrations Take into account as early as phase 1 i e in your proposal the fact that you want to observe more and other standard fields than the ones foreseen in the calibration plan In your README file you can then explain that you want your specified standard field observed e g before and after your science OB HAWK I User Manual Issue 96 5 You can also specify that you want illumination maps for your filters close in time to your observations and or specify as special calibrations your own illumination maps e f a photometric calibration to 0 05 0 1 magnitude is enough for your program consider that the HAWK I field is large and that by experience you will have 10 100 stars from the 2MASS catalog in your field These are typically cataloged with a photometry good to lt 0 1 mag and would allow to deter mine the zero point on your image to 0 05 mag using t
28. des 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 96 31 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 occultations 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 DI
29. e FITS file name F 4 Template Guide F 4 1 Acquisition HAWKI_img_acq_FastPhot 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 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 O
30. e 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 12 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 11 do result in an elevated number of spurious detections dashed lines in Fig 12 at faint magnitudes reaching 20 at the limiting magnitude for this chip The number of spurious detections in the other chips is negligible see Fig 12 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 z e ees lt weng S ENL SEN EE oe WC Sc E CHIP 4 SE EHIR 3 gt H E Se S ie s E E Se D H D We CH e EE SN E 7 S er ch L 9 ite 9 le WE ax x C ue S EE A ra oes es Tae r zg S H Ges d x e dE G te a e CHIP 17 v CHIP 2 r A o E KC E SCH SE e i d S e SE A E X
31. ed 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 B 2 Detectors structures and features We present some of HAWK I s detector features in two examples Figure 8 is a typical long gt 60s exposure Some features have been highlighted 1 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 8 HAWK I User Manual Issue 96 21 Figure 8 Typical raw HAWK I dark frame DIT 300sec 1 85 1 Figure 9 Typical raw HAWK I twilight flat field Y Band HAWK I User Manual Issue 96 22 2 On the left chip 88 there is an artefact on the detector s surface layer On the right chip 79 these are sort of doughnut shaped features More of these can be seen in Fig 9 on chip 88 Both features are stable and removed completely by simple data reduction no extra step needed 3 Detector glow which is visible for long DITs but is removed by e g sky subtraction 4 The darker area visible in Fig 8 corresponds to the shadow of the baffling between the detectors 5 Emitting structure whose intensity grows with the integration time It is however fully removed by classical data reduction 6 Q4 chip 88 dark median has been fo
32. hat this is not the telescope focus 2 1 5 Instrument s performance We expect HAWK I to be used for plain imaging fast photometry and astrometry The image quality of HAWK I is excellent across the entire field of view Distortions are below 2 over the full 10 diagonal and the image quality has always been limited by the seeing our best recorded images had FWHM below 2 2 pix i e lt 0 23 in the Ks band The photometric accuracy and homogeneity that we measured across one quadrant is lt 5 as monitored on 2MASS calibration fields We expect that with an even more careful illumination correction and flat fielding about 3 absolute accuracy across the entire field will be achieved routinely when the calibration database is filled and stable Of course differential photometry can be pushed to a higher accuracy Note in particular that given the HAWK I field size between 10 and 100 useful 2MASS stars calibrated to 0 05 0 10 mag are usually present in the field Finally the relative astrometry across the entire field 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 A note of caution as all current infrared arrays the HAWK I detectors suffer of persistence at the level of 107 1074 depending on how badly the pixels were saturate
33. he 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 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 is smaller than 30 deg 4 4 Twilight Because HAWK I is an infrared imager observations of bright objects 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 time difference from the HAWK I User Manual Issue 96 12 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
34. hese 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 2 2 2 Consider the 2MASS calibration fields The 2MASS mission used a number of calibration fields for the survey Details are given at http www ipac caltech edu 2mass releases allsky doc seca4_1 html In particular the sect II 2 http www ipac caltech edu 2mass releases allsky doc sec3_2d html provides a list of fields touch stone fields that you could use as photometric fields in order to calibrate your observations 2 2 3 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 Ks 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 2 3 The Exposure Time Calculator The HAWK I ETC can be found at http www eso org observing etc it returns a good estimation of the integration time on source needed in order to achieve a given S N as a function of atmospheric condit
35. 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 D 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 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 the total time requested HAWK I User Manual Issue 96 8 3 PHASE 2 Preparing your HAWK I observations This sections provides a preliminary guide for the observation preparation for HAWK I in phase 2 both for Service mode SM or Visitor mode VM We assume that you are familiar with the existing generic guidelines which can be found at e http www eso org observing observing html Proposal preparation e http www eso org sci observing phase2 SMGuidelines html Service mode informations e http www eso org paranal sciops VA_GeneralInfo html VM informations We know that they are not super thrilling but a quick browse over them might save you some time during phase
36. ions A few words about various input variables that might not be quite standard also read the online help provided on the ETC page HAWK I User Manual Issue 96 6 e As of P96 the seeing condition requested at Phase 1 no longer refers to the image quality at the observing wavelength but to the seeing in V band at zenith Such change has been reflected as well on the ETC for which the seeing in V band at zenith should be provided as seeing input parameter e the parameters to be provided for the input target are standard The input magnitude can be specified for a point source for an extended source in which case we compute an integration over the surface defined by the input diameter or as surface brightness in which case we compute values per pixel e g 106x106 mas e Results are given as exposure time to achieve a given S N or as S N achieved in a given exposure time In both cases you are requested to input a typical DIT which for broad band filters will be short 10 to 30s but for narrow band filters could be long exposures between 60 and 300s before being sky background limited e Do not hesitate to make use of the many graphical outputs In particular for checking your target line and the sky lines in the NB filters The screen output from the ETC will include the input parameters together with the calculated performance estimates Here some additional notes about the ETC output values e The expected image quality
37. ition of the four quadrants The four quadrants are very well aligned with respect to each other Yet small misalignments exist They are sketched below Q4 chip 88 chip 79 8 0 03 8 0 04 Q2 Q1 1 hip 78 chip 66 8 0 130 Quadrants 2 3 4 are tilted with respect to quadrant 1 by 0 13 0 04 0 03 degrees respectively Accordingly the size of the gaps changes along the quadrant edges The default orientation PA 0 deg is North along the Y axis East along the X axis for quadrant 1 For reference purposes we use the partly arbitrarily common meta system Quandrant offset in X pix offset in Y pix Ql 0 0 Q2 2048 153 0 3 Q3 2048 157 2048 144 Q4 0 5 2048 142 It is valid in its crude form to within a few pixels The distortion corrections for a proper astrometry will be added to all image headers Distortions including the obvious rotation component will be defined with respect to the above system First qualitative evaluations with respect to HST ACS astrometric calibration fields re covered the relative positions of objects to about 5 mas once the distortion model was applied a precision that should satisfy most purposes C 1 1 Center of Rotation and Centre of Pointing The center of rotation of the instrument is not exactly the centre of the detector array In the standard orientation North is Y East is X the center of the detector will be located 0 4
38. izes listed in the Table 5 practically disappear for DIT 0 5 1 0 sec F 3 Preparation and Observation F 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 F 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 larcsec However the simple preset HAWKI_img_acq_Preset can not define the correct detector windowing for the fast mode The windowing is defined only in the specialized acquisition template it HAWKI_img_acq_FastPhot Therefore HAWKIimg_acq_FastPhot must be executed at least once and the windowing parameters should be kept the same during the entire sequence Sec F 4 F 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 User Manual Issue 96 39 F 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 Ks flats and found no significant difference Fig 14 F 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 th
39. l 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 15sec 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 8 sec 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 the 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 mo
40. l provides the information required for the proposal preparation phase 1 the phase 2 observation preparation and the observation phase The instrument has started regular operations in period 81 We welcome any comments and sug gestions on the manual these should be addressed to our user support group at usd help eso org 1 2 Structure of this document The document is structured in 2 parts Part 1 1 takes you step by step through the essentials writing your proposal in phase 1 preparing your observations in phase 2 conducting your obser vations at the telescope and reducing your data Part 2 II contains collected useful reference material 1 3 Glossary 1 4 Abbreviations and Acronyms DMO ESO ETC FC FoV FWHM HAWK I NIR OB P2PP PSF QC RTC RTD SM TIO USD VLT VM DIT NDIT Data Management and Operations Division European Southern Observatory Exposure Time Calculator Finding Chart Field of View Full Width at Half Maximum High Acuity Wide field K band Imager Near InfraRed Observing Block Phase II Proposal Preparation Point Spread Function Quality Control Real Time Computer Real Time Display Service Mode Telescope and Instrument Operator User Support Department Very Large Telescope Visitor Mode Detector Integration Time Number of Detector Integration Time HAWK I User Manual Issue 96 2 Part Observing with HAWK I from phase 1 to data reduction 2 PHASE 1 applying for obser
41. l windows such gap occur always because of the gaps between the detectors extra gaps occur if DE T 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 Ist DIT the first 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 Aslices 2 Frame l
42. libration fields 204 2 2 3 HAWK I extinction coefficients o ooo The Exposure Time Calculator EEN EE e445 bee be Proposal Formi 24 2 kone Sek eaa p ai ERE REO ee eee da e Overheads and Calibration Pla o c ec bd esoo idera doie guud ar PHASE 2 Preparing your HAWK I observations HAWK I specifics to templates OBs and p2pp o ooo a a a a a EN c 1 A E a ren ee eebe a A rege A er e er Bee oS 3 1 2 Observing Blocks OBs 2 446 624 64 55 be ache Peco A Slee Templates ov ea e oe ees eee oe Ue 4S boo ED ee ee heed a a Finding Charts and README Files co 26 5085 85 Ge ee eg la we ede a Observing Strategies with HAWK I OVP cx ke eh se RRS BEEK EOE E REE we See wee Ek Visitor Mode Op rations o 2 6 cs 468 dew PIS rb kiea bed wD Ys The influence of the Moon 2 2 a a a NONE 6 spoe he SR oe i ka Ae EKER CERES OE EE RES BY Orientation offset conventions and definitions Instrument and telescope overheads Recommended DIT NDIT and Object Sky pattern 2 2 KA KA KA Kad kad N Gn On Om Om Om A RA P A GO GO M M N WO CO o oo CO HAWK I User Manual Issue 96 v A Reference Material 16 The HAWK I filters 16 The HAWK I detectors 19 B 1 Threshold limited integration 20 B 2 Detectors structures and features 20 B 3 Detectors relative sensitivity e ENEE EE EE Gx 22 The HAWK I Field of View 25 C 1 Relative position of the four quadrants 25 C
43. lly feasible acceptable and if this is the case to ask for a waiver F 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 96 34 ae DET WIN STARTKI DET WIN STARTEX1 400 EI D D 3 z 4 300 E Z r N K KA Vi U J LU U ZB Z e 47 200 D H 100 S Ra ES G 0 G 100 200 300 400 X arcsec Figure 13 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 Note that the param eter DET WIN STARTX 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 96 35 between the individua
44. n 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 stripe For example if the user wants to define a window of 18x28 px on each stripe the corresponding values of DE T 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 18x 16x2 576 and the two detectors along the Y axis 28x2 56 The allowed values are 1 128 and 1 2048 for DET WIN NX a
45. nd 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 96 33 along each axis do not exceed the size of the stripe along that axis 128 or 2048 respectively for X and Y Figure 13 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 START Y 48 DET WIN NX 128 and DET WIN NY 32 corresponding to windows on the stripes with sizes of 128 x 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 x32 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
46. nditions The exposure time calculator ETC is reasonably well calibrated and we encourage you to use it In order to give you a rough idea of the performance to be expected we list here the limiting magnitudes S N 5 for a point source in 3600s integration on source under average conditions 0 8 seeing 1 2 airmass Filter Limiting mag Limiting mag Saturation limit Vega AB in 2 sec J 23 9 24 8 10 0 H 22 5 23 9 10 3 Ks 22 3 24 2 9 2 T assumed 0 8 seeing 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 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 HAWK I User Manual Issue 96 4 2 1 4 Adapter defocussing As of Period 96 it is possible to defocus the HAWK I adapter to aloo observations of bright stars avoiding saturation We expect this feature to be used mostly for transit occultation observations The defocussing is controlled by the keyword SEQ ADA FOCUS which allows to set different focus value in mm the default being 2 0 Please be aware t
47. ode Therefore in Burst mode the maximum NDIT is half of that for the FastJitt mode E 33 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 Table 5 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 instrument 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
48. oothed enhanced images of the optical ghosts visible in the four quadrants for the NB1060 left amp NB1190 right filters HAWK I User Manual Issue 96 18 100 80 60 40 efficiency 20 1000 1500 2000 2000 wavelength nm Figure 6 HAWK I Filters Black broad band filters Y J H Ks Green cosmological filters NB1060 NB1190 NB2090 Red CH4 H2 Blue Bry magenta visitor filter NB0984 HAWK I User Manual Issue 96 19 B The HAWK I detectors The naming convention for the four detectors is the following 2000 PTT 2000 BT 1500 F 4 1500 E 4 L Q4 b L Q3 1000 8 chip 88 E 0094 chip 79 500 H J 500 E 1 ay L j o bee Lala DIEN 0 500 1000 1500 2000 0 500 1000 1500 2000 X 2000 PITT 2000 PTT 1500 L 4 1500 L 4 L oi J L Q2 1000F chip 66 E 1000 f chip 78 500 F 4 500 E 4 posi tir tisiitiiii I nl 0 500 1000 1500 2000 0 500 1000 1500 2000 Note that quadrant 1 2 3 4 are usually but not necessarily stored in extensions 1 2 4 3 of the HAWK I FITS file Indeed FITS convention forbids to identify extensions by their location in the file Instead look for the FITS keyword EXTNAME in each extension and verify that you are handling the quadrant that you expect eg EXTNAME CHIP1 INT1 The characteristics of the four detectors are listed below Detector Parameter Ql
49. or 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 data in cubes The parameters for filter DIT and NDIT are lists allowing to obtain multiple darks in one go Specific details HAWK I User Manual Issue 96 42 e 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 e 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 e 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 e The hardware windowing is set to True e The store in cube option is set to True
50. oss 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 the 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 96 36 variations
51. pect from the pipeline The full link to the pipeline page is http www eso org sci software pipelines The planned data reduction recipes included in the last delivery will be e hawki_img_dark The dark recipe produces master dark and bad pixel map e hawki_img_flat The flat field recipe produces a master flat a bad pixel map a statistics table the fit error image e hawki_img_zpoint This recipe provides the zero points for the UKIRT selected standards e hawki_img_detlin This recipe determines the detector linearity polynomial coefficients com putation as well as the error on the fit e hawki_img_illum The illumination map of the detectors is obtained by observing a bright photometric standard consecutively at all predefined positions over a grid e hawki_img_jitter All science data resulting from the jitter and generic offset templates The four quadrants are combined separately The four combined products are eventually stitched together However these stitched images are not meant for scientific usage The online reduction pipeline working on Paranal will not provide this stitched image if min offset lt 1500 or max offset gt 1500 Besides utilities will be provided to make it easier for the users to reduce the data by hand step by step This utilities list is not finalised yet but will contain among others e hawki_util_distortion Apply the distortion correction e hawki_util_stitch Stiches 4 quadrant images
52. 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 During acquisition se quences the RTD can be used as well as for the interactive centring of the targets in the field Calibrations including DARKs sky flats photometric standard stars illumination maps etc are acquired by the Observatory staff according to the calibration plan and monitored by the Quality Control group of ESO Garching 4 2 Visitor Mode Operations Information policy on the Visitor Mode operations at the VLT are described at http www eso org paranal sciops VA_GeneralInfo 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 although the newly implemented adapter defocussing offered both in Visitor and Service mode see 2 1 4 should be the preferred strategy to avoid the saturation of very bright target Telescope defocussing is however not permitted 4 3 The influence of the Moon Moonlight does not noticeably increase t
53. t Photometry included Issue 86 0 30 Jun 2010 Several correction in the Appendix F Issue 87 0 02 Aug 2010 No changes from P86 to P87 Issue 88 0 05 Feb 2011 Many different small changes Issue 88 1 10 June 2011 Many different small changes once again Issue 90 0 18 Feb 2012 No changes from P88 to P90 Issue 90 1 17 Jun 2012 Updates for P90 Phase II Issue 91 0 06 Sep 2012 Updates for P91 Phase and Il Issue 91 1 04 Oct 2012 Fast Photometry section heavily updated Issue 91 2 04 Dec 2012 Update of several broken links Issue 92 0 01 Mar 2013 No news Issue 93 0 06 Jan 2014 Fast Photometry update Issue 94 0 28 Jan 2014 USD comments implemented Issue 94 1 07 Jun 2014 Corrected several typos Added a figure Issue 95 27 Aug 2014 No news Issue 96 22 Jan 2015 Add a description of Adapter defocusing Issue 96 10 Jun 2015 Add reference to the GUCT to the ETC seeing IQ USD comments implemented fix broken links HAWK I User Manual Issue 96 HAWK I as a CAD drawing attached to the VLT and in the integration hall in Garching HAWK I in a Nutshell Online information on HAWK I can be found on the instrument web pages and in Kissler Patig et al 2008 A amp A 491 941 HAWK I is a near infrared 0 85 2 5 um wide field imager The instrument is cryogenic 120 K detectors at 75 K and has a full reflective design The light passes four mirrors and two filter wheels before hitting a mosaic of four Hawaii 2RG 204
54. 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 96 32 afterwards If an OB is aborted for some reason before this step the IRACE remains in hardware windowing mode with the window size defined during the OB and with the store in data cube mode ON F 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
55. therwise 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 96 40 T T T T T T T T FF Win FF NonWin1 FF Win FF NonWin2 FF NonWin1 FF NonWin2 Gaussian mean 1 sigma 0 02 log N i VI i 1 AN M d 1 1 2 1 4 Ratio of different flat fields Figure 14 Histograms of the ratios between a windowed and two non windowed Ks twilight flats For comparison the ratio of the two non windowed flats and a Gaussian function is also shown HAWK I User Manual Issue 96 41 F 4 2 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 NDITxDIT 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 identi
56. ting 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 Fig 2 In the above example Fig 2 7 offsets are requested and the way the are performed is shown in Fig 3 The sequence of offset will be 10 10 90 10 100 200 100 200 300 420 and 580 10 HAWK I User Manual Issue 96 13 Telescope offsets 1 i 3 p 200 1 300 220 6 110 I 100 4 1 1 10 19 2 100 01 dnn egen SR Aen i i Delta CH fi Figure 2 Pop up window at the start of an example template it provides a quick check of your offset pattern 4 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 E HAWK Initial instrument setup for ACQ only 1 HAWK I Telescope Offset small 0 15 HAWK I Telescope Offset large gt 90
57. together e hawki_util_stdstars Generates the standard stars catalog from ascii files e hawki_util_gendist Generates the distortion map used for the distortion correction HAWK I User Manual Issue 96 30 F HAWK I Burst and Fast Jitter Modes F 1 Description This section describes a mode for high cadence and high time resolution observations with HAWK l 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 1 sec 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 the 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 observationa
58. und to be larger than the other detectors and to increase with NDIT see Fig 10 Thanks to Sylvain Guieu for detecting this 7 Q2 chip 78 suffers from radioactive effects see Fig 11 below CHIP 2 mo peer pot Kb 4 8 C S L E a E L xX A bal Q L 4 A A LA A A A A A a L F aa tr LLL Ligal 5 10 NDIT CHIP 4 DT FT CT T LA A A d 0 6 S 5 L x 5 a o L E F A A 08 L a a Q S A N A A A A A L A 1 0 L A GE Eat Ld 5 10 NDIT Figure 10 Trend of dark with NDIT in the 4 detectors B 3 Detectors 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 HAWK I User Manual Issue 96 23 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 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 apertur
59. ving time with HAWK I This section will help you to decide whether HAWK I is the right instrument for your scientific projects take you through a quick evaluation of the observing time needed and guide you through the particularities of HAWK I in the proposal form 2 1 Is HAWK I the right instrument for your project HAWK I does only one thing but does it well direct imaging in the NIR 0 97 to 2 31 jum over a large field 7 5 x7 5 So far HAWK I has been successfully used to study the properties of medium redshift galaxy clusters see e g Lidman et al 2008 A amp A 489 981 outer solar system bodies Snodgrass et al 2010 A amp A 511 72 the very high redshift universe Castellano et al 2010 A amp A 511 20 and exo planets Gillon et al 2009 A amp A 506 359 The recent implementation of Fast Photometry see Appendix F is probably going to boost more activity in the exo planets field The basic characteristics FoV pixel scale can be found in the nutshell at the beginning of this document 2 1 1 Field of View The Fo 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 Thus the FoV looks like this 15 217 lt gt 1y 1657 _ HAWK I User Manual Issue 96 3 Note that it is very tempting to point right onto your favourite target and to loose it in the gap since this is where the telescope

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