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Very Large Telescope Paranal Science Operations VIRCAM

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1. 60 40 Transmission Reflectivity 76 20 Figure 8 Transmission curves for the filters colored solid lines labelled on the top detector quan tum efficiency short dashed line labeled QE reflectivity of the primary and the secondary mirrors dot dashed and long dashed lines labelled M1 and M2 respectively and atmospheric transmis sion curve solid black line labelled on the top with the precipitable water vapor PWV in mm and with the airmass sec z The right panel shows the long wavelength filter transmission leaks and the detector quantum efficiency Note that the atmospheric transmission on the left panel is poor while on the right
2. RMS is defined here as the Gaussian equivalent MAD i e 1 48xmedian of absolute deviation from median The RMS can later be compared with library values for darks of the same integration and exposure times The detected image intensity weighted second moments will be used to com pute the average ellipticity of suitable signal to noise stellar images Shot noise causes even perfectly circular stellar images to have non zero ellipticity but more significant values are indicative of one of optical tracking and auto guiding or detector hardware problems Measure the median of the ratio of a new mean flat frame and a library flat frame Measure the RMS of the ratio of a new mean flat frame and a library flat frame RMS is defined here as the Gaussian equivalent MAD i e 1 48xmedian of absolute deviation from unity after normalizing by median level i e measuring the RMS sensitivity variation The RMS can later be compared with library values for troubleshooting problems A robust estimate of the background noise is done before the first fringe fitting pass Once the last fringe fit is done a final background noise estimate is done This parameter is the ratio of the value before fringe fitting to the final value after defringing Determined from pairs of darks and flatfields of the same exposure integration time and illumination by comparing the measured noise properties with the expected photon noise contribution The gain of each detecto
3. OS CHEN TY Se E aa Kr AE E A d SS 1 t tis d for SONA iN S ek 5 1 H I Zi 5 5 sx DE oe nin pi 4 BU Si e taf T bela s PTT d dB et SE L i de Phat dou s S gek idi ee WE fta i H P 153 Te ie b t M T o a iva E x L E M E 5 EG ahs VE X47 kB EI CNT Me P e 29 z po Ae ids Too B he ae B og zt eet D e ef E T T T T T T T T TT T T T T T T T T T 20091015 20091215 20100215 20100315 20100415 20100601 20100701 20100801 20100901 20101001 Date yyyymmdd T T rT T T T T T T T TT T T T T T T 20091015 20091215 20100215 20100315 20100415 20100601 20100701 20100801 20100901 20101001 Date yyyymmdd 21 ZP VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 a 8 T 4 H i E P i y 8 i s T ay T GEI Ton T T T T T 1 TT SE T EECH 20091015 20091215 20100315 20100415 20100601 20100715 20100815 20100915 20101101 20110101 Date yyyymmad Figure 11 Zero point trends in 2010 201 1 Courtesy of CASU amp e amp a a i H DH D T z 3 r H H D j es i Ks sd 4 l sr H z D NB118 amp T T T T T T T 1 T T T T T 20110501 20110601 20110701 20110801 20110901 20111001 20111201 20120301 20120401 20120601 20120701 Date yyyymmdd Figure 12 Zero point trends in 2011 2012 Courtesy of CASU VIRCAM VIS TA User Manual VIS MAN ESO 06000 000
4. Temperature unit 289 010 Temperature K CCi1 2 i Temperature sensor 2nd Temperature Temperature unit Temperature K Temperature sensor 2nd Temperature Temperature unit Temperature K Temperature sensor 2nd Temperature Temperature unit 9999 000 Temperature K WFS1 2 Temperature sensor type WFS CCD assembly PY Temperature sensor name K Temperature unit 9999 000 Temperature K WFS2 Temperature sensor type WFS CCD assembly NY Temperature sensor name K Temperature unit 9999 000 Temperature K Dt1AB d Temperature sensor type Science detector 1AB Temperature sensor K Temperature unit 71 281 Temperature K Dt1CD 2 Temperature sensor type Science detector 1CD Temperature sensor K Temperature unit 70 829 Temperature K Dt2BA Temperature sensor type Science detector 2BA Temperature sensor K Temperature unit 72 188 Temperature K Temperature sensor type type Cryo cooler 1 sensor name K gt 9999 000 0022 type Cryo cooler 2 Sensor name K 3 9999 000 CC3_2 4 Cryo cooler 3 K 2 type sensor name name name name name K Temperature unit 289 840 Temperature K Dt2DC Temperature sensor type Science detector 2DC Temperature sensor K Temperature unit 71 884 Temperature K Dt3AB Temperature sensor type Science detector
5. ES A EUROPEAN SOUTHERN OBSERVATORY Organization Europ ene pour des Recherches Astronomiques dans l H misph re Austral O Europ ische Organization f r astronomische Forschung in der s dlichen Hemisphare ESO European Southern Observatory Karl Schwarzschild Str 2 D 85748 Garching bei M nchen Very Large Telescope Paranal Science Operations VIRCAM VISTA User Manual Doc No VIS MAN ESO 06000 0002 Issue 85 0 Date 18 12 2009 V D Ivanov T Szeifert Prepared ra u s s Suha dE ma m ape ERE e Date Signature A Kaufer ADDIOVOU EE Date Signature C Dumas Released EE Date Signature VIRCAM VIS TA User Manual This page was intentionally left blank VIS MAN ESO 06000 0002 VIRCAM VIS TA User Manual 09 09 2008 18 12 2009 01 07 2010 01 12 2010 11 03 2011 04 08 2011 13 06 2013 29 08 2013 VIS MAN ESO 06000 0002 iii Change Record Section affected Reason lnitiation Documents Remarks All All All Twilight overheads Minor updates Web links updated Template tile6sky info Minor updates Creation First public release for P85 Update for P86 Phase Il and P87 Phase Update P87 Phase ll Update P88 Phase Update P92 Phase ll Update P93 Phase l VIRCAM VIS TA User Manual This page was intentionally left blank VIS MAN ESO 06000 0002 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Contents 1 Introduction Applicable documents and other sources of information Abb
6. The high order wavefront curvature sensor HOWFS uses some of the science detectors to deter mine occasional adjustments to the primary mirror support system This is done perhaps once at the start of the night and once around midnight Processing the signals from the HOWFS is done within the Instrument Workstation and so the pipeline will not have to deal with the HOWFS related data HOWFS cannot to operate concurrently with science observations The telescope can be offset to illuminate directly the sensor with a bright star limiting the necessary FOV The sensor within the IR Camera software package allows a suitable star to be selected The estimates suggest that there is a 99 probability of finding a suitable star within 1deg of any telescope position The required integration time will be 180 sec in most cases lt 60 sec The HOWFS will generate at least 22 Zernike or quasi Zernike coefficients so that the root sum square error of all 22 coefficients is lt 50nm After adopting a curvature sensing solution a stepped filter at one or more of the intermediate filter positions on the filter wheel is used to illuminate one of the science detectors in e g J passband for verification The HOWFS data are stored in the same manner as science exposures VIRCAM VIS TA User Manual m ze Figure 10 Zero point trends during the first year of operation 2009 2010 Courtesy of CASU 21 24 22 21 VIS MAN ESO 06000 0002
7. VISTA Infra Red Camera 6 1 General features The infrared camera VIRCAM Figure 3 is a state of the art design the largest of its kind as of 2010 It has a very wide field of view with 1 65deg diameter The camera uses a long cryostat with seven nested cold baffles to block out of beam radiation instead of the usual re imaging optics or cold pupil stop design that has been most common so far In addition the baffles serve to reject the unwanted heat load from the window by means of a specialized coating which is highly absorbing at wavelengths shortward of 3 um and highly reflective longward of 3 um The baffling system still leaves a smooth gradient caused by scattered thermal radiation across the detectors in the Ks band the total intensity of this scattered background is expected to be 20 of the sky level and the gradient may be up to 10 of that i e 296 of total sky level including the real sky emission and the scattered light This effect must be addressed during the data processing On the positive side the absence of a cold stop means that there is no intermediate focus so there should be no issue with nearly in focus warm dust particles The aluminum cryostat housing the camera consists of four main sections and includes over 10 m of O ring seals The nominal vacuum level is 1076 milibar and it is achieved in two stages an initial pump down with an external pump followed by pumping with a pair of He closed cycle cr
8. 46 and the pedestal assembly 23 The primary mirror weights 5520 kg the VIRCAM 2900 kg the secondary mirror 1000 kg The telescope has three Power Drive Units PDU enabling movement of the azimuth and altitude axis and the Cassegrain rotator Unlike most other telescopes VISTA lies on a ball bearing with a pitch diameter of 3658 mm instead on a oil bed The Altitude limit is 220 deg above the horizon which implies a mechanical pointing limit to the North at 6 lt 45 deg at the meridian The VISTA theoretical pointing error over the entire sky is 0 5 arcsec The open loop tracking error over 5min of observation is 0 22 0 24 arcsec The telescope can operate under humidity of up to 80 when the temperature is within the operational temperature range of T20 15 C VISTA can not observe within 2 deg from the zenith because of a rotator speed limitation The jitter movements are accomplished by moving the entire telescope unlike the UKIRT for ex ample where this can be done via the tip tilt mechanism of the secondary mirror The overheads due to moving the telescope are 8 sec for a jitter 15 sec for a pawprint on average The optical layout of the telescope is shown in Figure2 The telescope and the instrument should be treated as one integral design i e the telescope is just foreoptics to the VIRCAM The design is intertwined to the point that the telescope guider is part of the camera i e it is within the camera dewar
9. HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH COMMENT COMMENT HISTORY HISTORY HISTORY HISTORY HISTORY HISTORY ROOTEND COMMENT END ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO OCs OCs OCs OCs OCs OCs OCs OCs OCs OCs OCs OCs OCs OCS OCs OCs OCs OCs VISTA IR FTU 2_5_2 2009 08 11T04 54 38 fitsTranslateTable RAW ht FTU 2_5_2 2009 08 11 ADD FTU 2_5_2 2009 08 11 ADD FTU 2_5_2 2009 08 11 ADD FTU 2_5_2 2009 08 11 ADD FTU 2_5_2 2009 08 11 ADD FTU 2_5_2 2009 08 11 ADD VIRCAM VISTA User Manual REQTIME SADT AOSA1 ID SADT AOSA2 ID SADT AOSA3 ID SADT AOSA4 ID SADT AOSA5 ID SADT AOSB1 ID SADT AOSB2 ID SADT AOSB3 ID SADT AOSB4 ID SADT AOSB5 ID SADT CAT ID SADT GS1 ID SADT IP ID TARG ALPHAOBJ TARG DELTAOBJ TARG X TARG Y Camera OS Revi T 9 blank lines 10 000 Requested 83303221272 AO 83303221280 AO 83303221277 AO 83303221279 AO star star star star VIS MAN ESO 06000 0002 integration time s A A A A ID ID ID ID 330322113566 AO star A ID 330322191 AO star B ID 83303231321 AO 83303231319 AD 83303231320 AO 83303231364 AD star star star star B B B B ID ID ID ID GSC 2 at ESO Guide star catalogue used 8330322158 Guide star ID SADT v3 04 VIRCAM 1 25 Creator software vers 225055 896 RA of targ
10. SEQ TILE NAME SEQ TILE OFFSETX SEQ TILE OFFSETY VIS MAN ESO 06000 0002 Table 17 Fixed tile patterns N cw 6 patterns 6 step n pattern 0 475 0 475 0 475 0 475 0 475 0 475 0 475 0 0 0 475 0 475 0 0 0 475 Tile6u default for VIRCAM img obs tile6 SEQ TILE NAME SEQ TILE OFFSETX SEQ TILE OFFSETY Tile6z SEQ TILE NAME SEQ TILE OFFSETX SEQ TILE OFFSETY Tile6s SEQ TILE NAME SEQ TILE OFFSETX SEQ TILE DOFFSETY Tile6zz SEQ TILE NAME SEQ TILE OFFSETX SEQ TILE OFFSETY Tile6ss SEQ TILE NAME SEQ TILE OFFSETX SEQ TILE OFFSETY Tile3nx SEQ TILE NAME SEQ TILE OFFSETX SEQ TILE OFFSETY Tile3px SEQ TILE NAME SEQ TILE OFFSETX SEQ TILE OFFSETY Tile1_00 SEQ TILE NAME SEQ TILE OFFSETX SEQ TILE OFFSETY 6 step u pattern 0 475 0 475 0 475 0 475 0 475 0 475 0 475 0 0 0 475 0 475 0 0 0 475 6 step large Z pattern 0 475 0 475 0 475 0 475 0 475 0 475 0 475 0 475 0 0 0 0 0 475 0 475 6 step large S pattern 475 0 475 0 475 0 475 0 475 0 475 0 475 0 475 0 0 0 0 0 475 0 475 o 6 step zz zig zag pattern 475 0 475 0 475 0 475 0 475 0 475 0 475 0 475 0 0 0 0 0 475 0 475 o 6 step ss zig zag pattern 0 475 0 475 0 475 0 475 0 475 0 475 0 475 0 475 0 0 0 0 0 475 0 475 N cw 3 patterns 3 step nx negative x pattern 0 475 0 475 0 475 0 475 0 0 0 475 3 step px positive x pattern 0 475 0 475 0 475 0 475 0 0 0 475 Npaw 1 pattern 1 pawprint pattern 0 0 0 0 VIRC
11. The primary mirror is manufactured from zerodur Axial support is provided by 81 Force Control Assemblies FCAs mounted on the M1 cell lateral support is carried out by four FCAs The M2 position is controlled in 5 axis by a precision hexapod VIRCAM is connected to the telescope via a rotator on the back of the primary mirror cell and has a wide field corrector lens system with three infrasil lenses The camera is described in the next section The enclosure rotates at nominal speed of 2 deg per second and is able to stop rotation within 5 sec It can survive wind speed of up to 36 ms closed The nominal wind speed observing restrictions are closing the dome at gt 18 m s and observing at least 90 deg away from the wind direction for gt 12ms The mirror coating is a major operation requiring dismounting of VIRCAM and the mirrors and it implies interrupting the telescope operations for 10 days 8 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 mm NI 2 651 TELESCOPE CG IR CAMERA CG TELESCOPE Filters amp Detector plane Figure 2 Optical layout of the telescope M1 and M2 are the telescope primary and secondary mirrors The camera s entrance window the three lenses L1 L2 and L3 the filter and the detector planes are also marked VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 9 6 The VIRCAM
12. at VISTA s nominal pixel size Finally the 3 steps in Y described above are repeated at the next position in X So after 3x2 6 steps an area of 5 275x7 65 40 354 detector areas corresponding to 1 017deg x1 475deg 1 501 deg sky is exposed on a minimum of 2 separate pixels as shown in light green in the exposure time map below for a filled tile no jitter Some sky areas are exposed on more separate pixels i e in the overlapping regions and some areas are exposed on only one pixels along the top and the bottom edge of the tile but the SADT makes sure that this is compensated by the neighboring tiles providing another exposure for these areas This issue is discussed below Figure 19 demonstrates how the 6 offset pattern is combined into a tile The telescope movements used to assemble a tile out of six pawprints are made with respect to the X Y coordinates in the camera focal plane not with respect to the celestial coordinates Therefore pawprints are not tilted with respect to their neighbors unless such a tilt is specifically introduced by the observer during the survey definition with the SADT this is not straightforward but it can be achieved by defining individual tiles a separate survey areas each with an individual position VIRCAM VISTA User Manual VIS MAN ESO 06000 0002 TY Det 1 Det 13 X to centre of filter wheel Det 4 Det 16 Observe 3 pawprints 0 1 2 separated by AY 47 5 of a detector Figure 17 Complet
13. lakeshore ctrllr simulated If T controller is operational If T lakeshore monitor simulated If T controller is operational If T lakeshore monitor simulated If T controller is operational If T lakeshore monitor simulated Pressure sensor type Vacuum gauge 1 Pressure sensor name HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS I
14. 1 42 Version of the template ESO DPR CATG SCIENCE Observation category ESO DPR TECH IMAGE JITTER Observation technique ESO DPR TYPE OBJECT Observation type ESO TEL ABSROT END 29 156065 Abs rotator angle at end ESO TEL ABSROT START 28 715680 Abs rotator angle at start ESO TEL AG REFX 1666 741 Autoguider reference pixel X ESO TEL AG REFY 465 686 Autoguider reference pixel Y ESO TEL AIRM END 1 084 Airmass at end ESO TEL AIRM START 1 085 Airmass at start ESO TEL ALT 67 096 Alt angle at start deg ESO TEL AMBI FWHM END 0 79 Observatory Seeing queried from AS ESO TEL AMBI FWHM START 0 73 Observatory Seeing queried from AS ESO TEL AMBI PRES END 738 43 Observatory ambient air pressure q ESO TEL AMBI PRES START 738 43 Observatory ambient air pressure q ESO TEL AMBI RHUM 4 Observatory ambient relative humi ESO TEL AMBI TAUO 0 004422 Average coherence time ESO TEL AMBI TEMP 14 34 Observatory ambient temperature qu ESO TEL AMBI WINDDIR 336 Observatory ambient wind directio ESO TEL AMBI WINDSP 3 59 Observatory ambient wind speed que ESO TEL A0 ALT 67 206236 Altitude of last closed loop a0 ESO TEL AO DATE 2009 08 11T04 54 00 Last closed loop a0 ESO TEL AO M1 DATE 2009 08 11T04 54 00 Last M1 update ESO TEL AO M2 DATE 2009 08 11T04 54 05 Last M2 update ESO TEL AO MODES 15 Which a0 modes corrected closed lo ESO TEL AZ 317 336 Az angle at star
15. 2 5 0 21 0 54 2874 1 9 Table 4 VIRCAM VISTA sensitivities for 0 8 arcsec seeing in 2arcsec diameter apertures sat uration levels and other related parameters for individual filters minimum detector integration time DIT 1 0011 sec adopted Atmospheric extinction color terms listed are the coefficients in front of J H except for Ks where it is J Ks All values in the table are approximate For the most recent measurements use the VIRCAM web page and ETC Band Z y J H Ks NB980 NB990 NB1 18 Star Magnitude yielding peak image 11 3 108 11 1 11 0 102 TBD TBD TBD value of 30000 ADU Aver sky brightness mag arcsec 18 2 172 160 141 13 0 TBD TBD 163 Average background level ADU 41 64 254 1376 1925 TBD TBD TBD DIT at which the background alone 1207 787 197 36 26 TBD TBD TBD saturates an average detector sec Recommended maximum DIT sec 60 60 30 10 10 TBD TBD TBD Atm Ext coeff mag airmass TBD TBD 0 1 0 08 0 08 TBD TBD TBD 5o in 1 min limiting mag Vega 0 21 3 20 6 20 2 193 183 TBD TBD 17 9 Measured on sky Zero Points mag 23 82 23 45 23 78 23 87 23 03 20 95 TBD 20 83 yielding flux of 1 ADU sec J H color term with resp to 2MASS 41 025 40 610 0 077 40 082 TBD 0 680 TBD 240 100 J Ks color term with resp to 2MASS TBD TBD 0 065 TBD 40 010 TBD TBD TBD VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Table 5 Daytime dark current counts in ADU averaged over the individual detectors for number of d
16. 5 Three types of scheduling containers have been defined Concatenations Time Links and Groups They are described in more details in the User s Manual of P2PP for Surveys Table 14 VIRCAM VISTA templates Template Name Functionality to be used together with SADT VIRCAM img acq tile preset instrument set up and acquisition of guide stars VIRCAM img obs tile1 take a jitter and microstep sequence on one pawprint VIRCAM img obs tile3 take a jitter and microstep sequence on three vertical pawprint VIRCAM img obs tile6 take a jitter and microstep sequence on a full set of 6 pawprints VIRCAM_img_obs tile6sky like VIRCAM img obs tile6 but take sky images interleaved with the pawprints to be used without SADT support VIRCAM img acq quick preset to be used only with cal std and cal illumination templates VIRCAM img obs paw take a jitter and microstep sequence on one pawprint without se lecting guide stars VIRCAM img cal illumination take an illumination correction VIRCAM img cal std take a standard star observation VIRCAM img obs offsets make a sequence of exposures at a user defined set of telescope offsets for technical tests it does not offer AO and AG The design of VIRCAM VISTA requires only a small number of observation templates Table 14 Most surveys will use only two templates VIRCAM img acq tile and VIRCAM img obs tile6 In addi tion two calibration templates VIRCAM_img_cal_std and VIRCAM img cal illumination
17. A Hit T T T T T T UT _ H T F 0 1 2 3 4 5 5 4 3 2 1 0 Time after sunset hour Figure 14 Evening left and morning right sky brightness variation Only data from photometric nights have been used to make the plots No constraints have been applied on the moon distance and the fractional lunar illumination although the moon was always at least 30 deg away from the Time before sunrise hour observed area The dashed lines indicate the astronomical twilights Courtesy of CASU Table 10 Recommended value ranges for the twilight constraints for deep exposures The values are in minutes after the end of the evening astronomical twilight Negative values indicate that the observations can start within the evening twilight Filter Ks H J NB118 Y Z N B980 N B990 Minimum Maximum min 60 30 30 0 15 min 30 0 60 30 15 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Microsteps Interleaved Image 1 Figure 15 Combining exposures with microstepping left and jittering right Each numbered square corresponds to one pixel 7 4 Pawprints Tiles Jitters Microsteps 7 4 1 Definitions This section describes a number of basic actions that are used during the near infrared observations in general and during the VIRCAM VISTA operations in particular Integration a simple snapshot within the Data Acquisition System DAS of a specified elapsed time This elapsed time is kno
18. Reset Frames Daytime Daily 2 min VIRCAM img cal reset vircam reset combine Dark Current Daytime Weakly 10 min 2hr VIRCAM img cal darkcurrent vircam dark current Frames Dark Frames Daytime Weakly 10 min 2hr VIRCAM img cal dark vircam dark combine Detector Noise Daytime Monthly 1 min VIRCAM img cal noisegain vircam detector noise Linearity Daytime Monthly 1 hr filter VIRCAM img cal linearity vircam linearity analyse Readout or cloudy noise gain night Dome Flats Daytime Weekly 0 3 hr filter VIRCAM img cal domeflat vircam domeflat combine Twilight Flats Twilight Weakly 15min filter VIRCAM img cal twiflat vircam twilight combine Calibrations for photometric standard star observations Standard star Night Nightly 3min filter VIRCAM img cal std vircam standard process 1 per nigth Calibrations for astrometric distortions Astrometric Night Nightly in parallel all science templates vircam jitter microstep process Correction Calibrations derived from the science data Night Sky Maps Night Contin in parallel N A vircam jitter microstep process Sky Subtraction Night Contin in parallel NA vircam jitter microstep process amp Defringing Jittering Offsets Night As in parallel VIRCAM img obs paw vircam jitter microstep process needed VIRCAM img obs tile Microstepping Night As in parallel VIRCAM img obs paw vircam_jitter_microstep_process needed Opt Distortion Night Contin in parallel WCS Fit Night Contin in paralle
19. The authors thank Drs M Rejkuba M Hilker and M Arnaboldi for their effort to review this manual and for their valuable comments and suggestions VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 A VISTA VIRCAM Template Reference Please note that there were a few changes in the definition of parameters and their functionality in recent observation periods with respect to the dry run which used the first generation of templates A 1 Historic P86 Modifications of the Templates Oct 2010 VIRCAM img obs tile6sky Introduced a new template that allows to obtain images of a sky field interleaved with the pawprints Jitter 2ua Jitter 2da New asymmetric jitter patterns introduced to avoid the execution of the first offset in a jitter pattern the first offset is set to 0 0 A 2 Historic P85 Modifications of the Templates Feb 2010 Randomized Jitter at the First Exposures The first exposure will as well be taken at a ran domized position in the jitter box In the past version the 1st exposure was taken at x y position 0 0 0 0 Flags for SKY Fields and EXTENDED objects There are three options for parameter OCS EXTENDED DEFAULT EXTENDED and SKY which are used to flag the data as normal pawprint jitter se quences DEFAULT or as extended object EXTENDED or as sky fields SKY The parameter doesn t change the sequence of observations on the sky but will allow to properly flag the obtained data sets for the later data reduct
20. are available They are used with VIRCAM_img_acq_quick acquisition template and do not require input files from the SADT Similarly there is an option to take science exposures without the use of SADT with the templates VIRCAM img acq quick and VIRCAM img obs paw which are identical in their function ality but provide a different list of user selected parameters The calibration observations like twilight flats darks and standard star observations as well as the maintenance templates are not prepared by the users They are not described in this user manual The observing strategy and the optimization of VISTA observations are discussed in Sec 7 6 Next we will describe the VIRCAM VISTA templates VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 AA The Acquisition Templates VIRCAM img acq tile and VIRCAM_img_acq_quick The acquisition templates will set up telescope the instrument and it will preset the telescope to the requested sky position If needed then the auto guiding and wave front sensing will be started at this position VIRCAM img acq tile is used in combination with VIRCAM img obs tilecN sur vey templates Sec A 5 1 and VIRCAM_img_acq_quick is used only with single pawprint snapshot template VIRCAM_img_obs_paw and with the standard star templates VIRCAM img cal std and VIRCAM img cal illumination seen within P2PP in the calibration template section The acquisition templates set the instrument into IMAGING mo
21. are implemented FPJME construct the tile from a series of pawprints repeating each pawprint with a different science filter Within each pawprint execute a jitter pattern if specified and within each jitter pattern execute a microstep pattern if specified PFJME construct the tile from a series of pawprints Within each pawprint execute a jitter pattern only this time repeat each jitter with a different science filter before moving on to the next pawprint Within each jitter execute a microstep pattern if specified FJPME construct the tile from a pawprint and jitter pattern such that one jitter observation is made from each pawprint in turn Within each pawprint position there can be a microstep pattern The whole sequence may be repeated with different science filters The letters in these sequences stand for the following actions F set a filter P execute a pawprint Offset J execute a jitter offset M execute a microstep pattern and E take an exposure If the user plans to observe with multiple filters within an OB it is strongly recommended to combine multiple science templates in the OB each with one filter rather than to alternate between many filters in one template via nesting Following this suggestion will minimize the time loss in case of OB abort and restart The VISTA telescope system does not make any distinction between large movements known at the VLT as presets and small mo
22. are stable on the time scale of the length of the exposures Usually for astronomical detectors they are stable on the time scale of days To minimize contamination from transient events the darks are combinations of many frames with appropriate rejection The total duration of the calibration depends on the number of DITxNDIT combinations that need to be calibrated one set of calibrations must be taken for each set of observations The pipeline Table 12 Summary of the calibrations The columns contain type of calibration phase of the observations when the calibration is obtained frequency of repetition approximate duration of the calibration templates used to obtain the calibration and the pipeline recipe used to process the calibration data The duration of flats for narrow band filters is longer than the given numbers because of the lower transmission The duration of the persistence and the cross talk depends on the presence of bright stars in the field and may be longer if there are not enough of them to cover all detectors The less frequent calibrations taken on weekly or monthly basis will also be taken upon request by the CASU if and when they are needed Some calibrations are determined continuously from the science data i e the 2MASS based illumination correction as opposed to others that are measured only as needed Calibration Phase Freq Duration Template Pipeline Recipe Calibrations for instrument signature removal
23. as calibration by the data flow system according to the parameters written in the fits header by the template The astrometric fields will be tagged as science data The pipeline will provide an astrometric solution for them as for all other science frames based on the 2MASS 7 9 1 Instrument signature removal The aim of these calibrations is to provide pawprints as though taken with a perfect camera which produces a photometrically linear evenly illuminated though sparsely sampled reproduction of the Sky free of any instrument and detector defects The calibration cascade is shown in Figure 22 and details of the individual calibrations are summarized in Table 12 Note that all calibrations must be repeated after an instrument intervention regardless of the age of the last calibrations They are processed by the corresponding pipeline recipes to produce either FITS file products or systems of calibration coefficients The raw output of all calibrations are one or more fits files or fits tables Summary of the calibration data 1 Reset Frames measure the variation of the reset calibration is a Reset Read sequence taken with the minimum DIT plus the 5 8 sec overheads during which the IRACE processes an integration and starts the next one A typical sequence might be 5x10 sec exposures Note that this is different from a dark frame which consists of a Reset Read Read sequence where the output is the differ ence of the two reads The aim her
24. component to the telescope name VIRCAM VISTA User Manual VIS MAN ESO 06000 0002 is subject of frequent changes This web page is updated regularly An external with respect to ESO source with history of the project and relevant information is the VISTA consortium web page at http www vista ac uk index html e Please read the latest User Manual It is located at http www eso org sci facilities paranal instruments vircam doc e Contact information for questions about VISTA and VIRCAM write to vista eso org for questions about the service mode observations write to usd help eso org VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 3 2 Applicable documents and other sources of information Documents VLT MAN ESO 00000 0000 OS Users Manual VLT MAN ESO 00000 0000 DCS Users Manual VLT MAN ESO 00000 0000 ICS Users Manual VLT MAN ESO 00000 0000 P2PP Users Manual VLT MAN ESO 00000 0000 SADT Cookbook Web sites ESO VIRCAM VISTA main page http www eso org sci facilities paranal instruments vircam VIRCAM VISTA operation team contact list http www eso org sci facilities paranal instruments vircam iot html ESO Public Surveys http www eso org sci observing policies PublicSurveys sciencePublicSurveys html ESO VIRCAM VISTA Quality Control http www eso org observing dfo quality index vircam html ESO Data Archive http archive eso org cms ESO P2PP3 http www eso org sci observing phase2 P2PP3 html h
25. exposures in H J and Ks filters built as 12 co adds not averages of 1 0 sec and List of integration time s DET1 DIT 2 0 3 0 1 0 List of number of integrations DET1 NDIT 6 4 12 List of science filters INS FILTER NAME H J Ks the exposures in H J and Ks filters will be built as 6 co adds of 2 0 sec 4 co adds of 3 0sec 12 co adds of 1 0 sec respectively Several identical observation templates can be attached after the acquisition template VIRCAM img acg tile Each template can have a different filter and the corresponding choice of DIT and or NDIT facilitat ing the requirement mentioned abve to have only one filter per template A brief description of some template parameters Is object extended OCS EXTENDED This parameter is used to identify fields with extended objects which requires special data reduction recipes for the sky subtraction Similarly the respective potential sky fields can be flagged to be later concatenated with the observation block which contains the extended object Jitter scale multiplier SEQ JITTER SCALE Scale factor SEQ TILE SCALE and Microstep scale multiplier SEQ USTEP SCALE define the scale factors to increase the dimensionless offset see below read from the set up files SEQ TILE SCALE must be left to the default to guaranty that the guide and wave front sensor stars do not fall off the respective detectors Name of tile pattern SEQ TILE ID selects offset patterns for the
26. for when selecting a DIT Table 4 It is the strongest in Ks band followed closely by the H band It depends strongly on the temperature and humidity The sky background can easily saturate the array by itself if the user selects a long DIT Thin clouds and moon light can elevate the sky background significantly in Z Y and even in J The recommended maximum DITs for the five broad band filters are listed in Table 4 These values will keep the detector potential wells below the linearity limit minimizing problems with the saturation persistence non linearity dynamic range and not saturating the entire dynamic range of the Two Micron All Sky Survey 2MASS Skrutskie et al 2006 AJ 131 1163 stars The values quoted in the tables may change with time check the VIRCAM web page for more up to date information Background limited observations The RON can be neglected for DITs gt 60 sec gt 60 sec gt 20 sec gt 5 sec and gt 1 5sec for the N B980 N B990 N B118 Z Y and J filters respectively The background variations on a time scale of a 1 3 minutes are a source of systematic uncer tainties To account for them the user must monitor these variations on the same time scale As mentioned above this is done by alternatively observing the target and a clear sky field next to the target every 1 3 minutes The exact frequency of the sky sampling is determined by the product DIT x NDIT plus the overhead if the DIT value is set by
27. m are given in Table 6 together with the counts for the extrapolated initial lamp flux f For the latest information about the persistence and other known detector issues visit http www eso org observing dfo quality VIRCAM pipeline problems html 6 3 Filters The filter exchange wheel 1 37 m diameter is the only moving part of the camera It has eight main slots seven for science filters and one for a dark The science filter positions actually contain trays each with a 4x4 array of square glass filters designed to match the 4x4 array of science Table 6 Fitting coefficients for the VIRCAM persitence for the individual detectors Detector f ADU a ADUsec 1 m Detector f ADU a ADUsec m 01 460260 30 0 77 09 359700 243 1 11 02 283510 27 0 74 10 376500 236 1 15 03 326020 100 0 87 11 351710 250 1 13 04 371620 60 0 90 12 384880 540 1 18 05 380410 112 1 02 13 282690 10902 1 70 06 430810 135 1 02 14 372010 129 1 09 07 413130 283 1 10 15 428480 203 1 13 08 346750 189 1 05 16 323570 46 1 10 16 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 02 excess in ADU sec 0 04 0 500 1000 1500 2000 2500 3000 3500 4000 time after first saturation seconds Figure 7 VIRCAM persitence for the individual detectors detectors The wheel is driven with a step motor and it is positioned by counting the number of motor steps from a reference switch The available science filters are listed in Table 7 and their p
28. of 4 3 e ADU 1 these correspond to 26000 and 42000 ADU The average saturation levels of the detectors are listed in Table 3 Note that these are averaged over each detector and the saturation levels of the pixels within the detector also vary This effect is particularly noticeable in detector No 5 Cosmetically the best detectors are No 5 and 10 and the worst are No 1 2 16 and 3 The parameters of individual detectors are summarized in Table3 for standard readout mode Table4 lists some parameters related to the saturation of the detectors Properties of the detector dark current are described in Table 5 The values given here may change with time check the VIRCAM web page for the most up to date information The flat fielding is exceptionally stable after the flat fielding correction the images show r m s of 0 004 0 005 which promisses photometry of nearly milimag quality taking into account that the stellar images will spread over 4 9 pixels or more depending on the seeing on an individual expo sure and that the jittering and the microstepping will allow averaging over even more pixels Note that currently the users are discouraged to use microstepping because is tends to produce artificial patterns on the reduced images The VIRGO detectors suffer from some persistence A measurement from May 12 2010 is shown in Fig 7 First five dome flats were taken with DIT 8 sec to measure the flux in ADUsec then 5 dome flats with D
29. of growth of a series of fixed size aper tures Alternative simple measure of image profile properties particularly the presence of extended PSF wings as such monitors optical properties of sys tem also required for limiting magnitude computations Determined from the statistics of the pixel distribution from the ratio of two flatfield sequences of significantly different average count levels The number of bad pixels per detector hot or cold should not change Determined from the statistics of the pixel distribution from the ratio of two flatfield sequences of significantly different average count levels The fraction of bad pixels per detector either hot or cold should not change Determined from presence of ve or ve ghost images on other chan nels detectors using exposures in bright star fields Potentially a fully popu lated 256x256 matrix but likely to be sparsely populated with a small number of non zero values of band diagonal form This QC summary parameter is the average value of the modulus of the off diagonal terms Values for the cross talk matrix should be very stable with time hardware modifications notwith standing Measured using the median of the pixel values can later be compared with older darks for trends Measure the median of the difference of a new mean dark frame and a library dark frame Measure the RMS of the difference of a new mean dark frame and a library dark frame Median counts in a dark frame
30. off the respective detectors Please note Copying the observation descriptions in P2PP from OB to OB may cause inconsistent OBs for the same reasons Each time a new pawprint is selected the telescope control system TCS is provided with a new set of guide and wave front sensor stars read from the PAF files which are provided with the template after importing the Survey Area Definition File The pawprint jitter and microstep patterns are exe cuted in the detector coordinate system using the camera position angle specified in the acquisition template VIRCAM img acq tile Multiple filters are not allowed in a single template but if this is justified the user can obtain a waiver from the USD If the science template observes in multiple filters specified in a list it may be necessary to use different DITs and NDITs for each of them because the filters have different transmissions and the targets may have different colors It is possible to do this by specifying the List of integration time s DET1 DIT and the List of number of integrations DET1 NDIT parameters as lists The lists must have exactly the same length as the list of science filters but if DET1 DIT and DET1 NDIT are given as single values these exposure parameters will be applied to all filters For example List of integration time s DET1 DIT 1 0 List of number of integrations DET1 NDIT 12 List of science filters INS FILTER NAME H J Ks will obtain
31. panel is good to demonstrate the worst case scenarios The left and the right panel have different X axis scales for clarity 18 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Table 8 Paramaters of the VIRCAM filters Parameters for the two types of filters located in the NB 980 slot are given Band Z y J H Ks NB980990 NB1 18 Nominal Central Wavelength um 0 88 1 02 1 25 1 65 2 15 0 978 0 991 1 185 Nominal Bandwidth FWHM um 0 12 0 10 0 18 0 30 0 30 0 009 0 010 0 01 Minimum Camera Throughput 0 67 0 57 0 60 0 72 0 70 TBD TBD TBD Filter position index T Intermediate filters In beam position She Load position Tray of filters Figure 9 Layout of the VIRCAM filter wheel efficient and gives better sky subtraction to complete a tile in one filter then change filter and repeat the tile A full wheel revolution corresponds to 210000 half steps of the step motor and requires 53 seconds at maximum speed A filter change is likely to cause a small warming of the detectors because of the non uniform temperature across the wheel This effect is corrected by the temperature servo system so the temperature rise should be 0 1 K for a few minutes after the change With a wheel temperature 110 K photon emission from the wheel itself should always be negligible The wedge shaped spaces in between the science filter trays can be populated with smaller in termediate filters that only cover a subs
32. target in DDMMSS TTT Equinox TEL TARG EQUINOX parameter J2000 Equinox expressed as year Proper motion in RA TEL TARG PMA number 500 500 0 0 Proper Motion Alpha in arcseconds year Proper motion in DEC TEL TARG PMD number 500 500 0 0 Proper Motion Delta in arcseconds year Epoch TEL TARG EPOCH parameter 2000 Epoch expressed as year Only 1950 or 2000 are valid values user selected in the acquisition templates Confirm guide star TEL AG CONFIRM boolean TF F If T then request operator confirmation other wise not Enable autoguiding TEL AG START boolean TF T If T then autoguiding is enabled otherwise not Confirm active optics TEL AO CONFIRM boolean TF F If T then request operator confirmation other wise not Active optics priority TEL AO PRIORITY parameter LOW NORMAL NORMAL LOW never wait NORMAL sometimes wait HIGH HIGH always wait Enable active optics TEL AO START boolean TF T If T then active optics is enabled otherwise not Rotator Angle on Sky deg TEL ROT OFFANGLE number 180 0 180 0 0 0 Camera sky position angle as DDD TTT Differential tracking in RA TEL TARG ADDVELALPHA number 15 15 0 0 Alpha additional tracking velocity in arcsec onds s Differential tracking in DEC TEL TARG ADDVELDELTA number 15 15 0 0 Delta additional tracking velocity in arcseconds s Epoch system default J Julian TEL TARG EPOCHSYSTEM parameter JB J Epoch system expressed as a X coord of pointing TEL TARG X number 500 0 500 0 0 0 Point
33. tile Unlike for other ESO instruments the VISTA offsets are absolute with respect to the initial position at the start of VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 ryn TIT L Tile n I Tile6u T Tile6z i P Pee pio Tena o eene mes pte EE eon HHHH Ld di t Cl HA L Tile6s Tile6zz 0 5 lt o 4 i a r 2 1 T 6 ist Offset Y relative units pe U GC u J 0 5 0 0 5 0 5 0 0 5 0 5 0 0 5 Offset X relative units Figure 25 Fixed tile patterns The negative X corresponds to west and positive X to east Y runs from south negative to north positive for the default tiling orientation in the SADT The numbers indicate the sequence of pointings and the arrows show the direction of the offsets the observing sequence The user has to select one of the predefine tile patterns listed in Table 17 and shown in Fig 25 The Name of tile pattern is set when the Survey Definition xml file is imported and MUST NOT be changed after that It can be left at the default value for VIRCAM img obs tile1 and VIRCAM_img_obs tile6 templates One of the functionalities that this parameter allows is to split a tile into two OBs for example if it is necessary to reduce the OB execution time below the service mode limit of 1 hr exceptionally a waiver allowing OB execution time of up to 1 5hr may be granted by the USD In this case instead of one OB with one VIRCAM_img_obs_tile6 template the
34. ty wS Data Flow Pipeline Quality Control References and Acknowledgments VISTA VIRCAM Template Reference A 1 Historic P86 Modifications of the Templates Oct 2010 A 2 Historic P85 Modifications of the Templates Feb 2010 sss vi VIRCAM VISTA User Manual VIS MAN ESO 06000 0002 A 3 Introduction to the Phase 2 Preparation for Public Surveys ne AA The Acquisition Templates VIRCAM img acq tile and VIRCAM img acq quick A 5 The Science Observation Templates lll A 5 1 VIRCAMimg obs tile lt N gt ues zeer ae Awake were We EEE EAS A 5 2 VIRGAMAMG ODS 1IIB6sky iecore REOR RR RE Eee s A 5 3 VIRCAMimg obs paw we ald Pe Bet A 6 The Calibration Templates VIRCAM_imo_cal_illumination and VIRCAM img cal std A 7 Template Parameter Tables B VISTA VIRCAM Observing Blocks Cookbook C VISTAGVIRCAM FITS Header Description 55 57 57 64 66 66 66 72 74 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 1 1 Introduction VISTA or Visible and Infrared Survey Telescope for Astronomy is a specialized 4 m class wide field survey telescope for the Southern hemisphere VISTA is located at ESO Cerro Paranal Observatory in Chile longitude 70 23 51 W latitude 24 36 57 S elevation 2500 m above sea level on its own peak about 1500 m N NE from the Very Large Telescope VLT The telescope has an alt azimuth mount and quasi Ritchey Chretien opti
35. user should create two OBs each with one VIRCAM img obs tile3 template but with different tile patterns one with the Tile3nx and the other with Tile3px still to be confirmed if the SADT can guaranty the lull field coverage with the two tile3 patterns as mentioned above Name of jitter pattern SEQ JITTER ID selects offset patterns for the jitter sequence These offsets are also absolute with respect to the initial position at the start of the sequence The user has to select one of the predefined jitter patterns listed in Table 18 and shown in Fig 26 A single pointing and a random jitter pattern are also available the parameter value must be set to SINGLE and RANDOM respectively The latter enables the jitter box size and the number of jitter offset parameters which are ignored for the fixed jitter patterns Random Jitter Maximum size of jitter Number of Jitters The respective parameters for the jitter box radius and the number of jitter exposures are only used for the random jitter The jitter sequence will start already the first exposure at a randomized position Name of microstep pattern SEQ USTEPID parameter can be set to Single default 1 expo sure or Ustep2x2 4 exposures taken with half pixel offsets in a squared pattern In summary the sequence would take for every filter of the list at every of typically 6 pawprints of a tile at every jitter VIRCAM VIS TA User Manual Tile6n
36. venient place on your computer VIRCAM VISTA User Manual VIS MAN ESO 06000 0002 C VISTAGVIRCAM FITS Header Description This section contains an example of VISTA VIRCAM FITS header generated from a science ob servation The VISTAGVIRCAM headers use the standard ESO hierarchical structure A suit of stand alone FITS Tools in ANSI C is available from the ESO website http archive eso org saft to facil itate display of the header content and convertion to other formats i e for IRAF use hierarch28 SIMPLE T IMAGE extension BITPIX 32 of bits per pix value NAXIS 2 of axes in data array NAXIS1 2048 of pixels in axisl NAXIS2 2048 of pixels in axis2 PCOUNT 0 number of random group parameters GCOUNT 1 number of random groups EXTNAME DET1 CHIP1 Extension name ORIGIN ESO S European Southern Observatory DATE 2009 08 11T04 54 19 8443 Date this file was written EXPTIME 50 0000000 Integration time MJD OBS 55054 20368050 Obs start DATE OBS 2009 08 11T04 53 17 9884 Observing date CTYPE1 RA ZPN Coordinate projection type CTYPE2 DEC ZPN Coordinate projection type CRVAL1 342 734299997361 Coordinate value at ref pixel CRVAL2 40 1412983319488 Coordinate value at ref pixel CRPIX1 5388 6 Pixel coordinate at ref point CRPIX2 6847 8 Pixel coordinate at ref point ORIGFILE VIRCAM IMG 0BS223 0016 DETO1 fits Original File
37. year Proper motion in DEC TEL TARG PMD number 500 500 0 0 Proper Motion Delta in arcseconds year Epoch TEL TARG EPOCH parameter 2000 Epoch expressed as year Only 1950 or 2000 are valid values user selected in the acquisition templates Rotator Angle on Sky from TEL ROT OFFANGLE number 180 0 180 0 0 0 Camera sky position angle as DDD TTT SADT Active optics priority TEL AO PRIORITY parameter LOW NORMAL NORMAL LOW never wait NORMAL sometimes wait HIGH HIGH always wait Differential tracking in RA TEL TARG ADDVELALPHA number 15 15 0 0 Alpha additional tracking velocity in arcsec onds s Differential tracking in DEC TEL TARG ADDVELDELTA number 15 15 0 0 Delta additional tracking velocity in arcseconds s Epoch system default J Julian TEL TARG EPOCHSYSTEM parameter JB J Epoch system expressed as a Filter name INS FILTER NAME parameter ISF FILTERS Name of the filter element to place in the beam checks switches jenueW 48st VLSIA NVOUIA 2000 00090 OS A3 NVIMI SIA 19 VIS MAN ESO 06000 0002 VIRCAM VIS TA User Manual 68 Table 20 VIRCAM VISTA acquisition template VIC AM img acq quick parameters Parameter which are typically updated by users are high lighted P2PP Label FITS header Parameter Type Range Default Description translated to the target section of P2PP RA TEL TARG ALPHA coord 000000 240000 Alpha for the target in HHMMSS TTT DEC TEL TARG DELTA coord 900000 900000 Delta for the
38. 2 23 RERUM TE oi sd e maii en Ej Ks NB118 T T T T T T T T T 20120301 20120401 20120501 20120701 20120801 20120901 20121001 20121201 20130301 20130401 Date yyyymmdd Figure 13 Zero point trends in 2012 2013 Courtesy of CASU VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 7 Observations with VI RCAMGVISTA This chapter summarizes the experience accumulated over many years of NIR observations at ESO It borrows from the similar discussions in ISAAC and Sofl user manuals 7 1 Observations in the Infrared 7 1 1 The Infrared Sky Observing in the IR is more complex than observing in the optical The difference arises from a higher and more variable background and from stronger atmospheric absorption and telluric emission throughout the 1 to 2 5 micron wavelength region Short ward of 2 3 microns the background is dominated by non thermal emission principally by aurora OH and O emission lines The vibrationally excited OH lines are highly variable on a time scale of a few minutes Pronounced diurnal variations also occur the lines are strongest just after sunset and weakest a few hours after midnight A complete description and atlas of the sky emission lines can be found in the paper of Rousselot et al 2000 A amp A 354 1134 Long ward of 2 3 microns the background is dominated by thermal emission from both the telescope and the sky and it is principally a func
39. 3 17 9884 Observing date 17596 000 04 53 16 000 UTC at start sec 77451 583 21 30 51 583 LST at start sec UNKNOWN PI COI name UNKNOWN Name of observer VIRCAM IMG 0BS223 0016 fits Original File Name 3 Sequence number of jitter 13 660 X offset in jitter pattern arcsec 3 660 Y offset in jitter pattern arcsec 3 Value of 1st OBSNUM in jitter seq Jitter5z Name of jitter pattern 5 Number of jitter positions 6 Number of offset positions 1 Number of microstep positions 16 Observation number 2 Sequence number of offset 329 779 X offset arcsec 0 000 Y offset arcsec 15 First OBSNUM in offset sequence Tile6n Name of offset pattern RECIPE REQTIME USTEPNUM USTEP_I USTEP ID USTEP X USTEP Y ARCFILE CHECKSUM DATASUM HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH VIRCAM VIS TA User Manual DEFAULT 10 000 16 1 Single 0 000 0 000 VIS MAN ESO 06000 0002 Data reduction recipe to be us
40. 3AB Temperature sensor K Temperature unit 72 235 Temperature K Dt3CD Temperature sensor type Science detector 3CD Temperature sensor K gt Temperature unit 72 957 Temperature K name name name VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 HIERARCH ESO INS TEMP23 ID Dt4BA Temperature sensor type HIERARCH ESO INS TEMP23 NAME Science detector 4BA Temperature sensor name HIERARCH ESO INS TEMP23 UNIT K Temperature unit HIERARCH ESO INS TEMP23 VAL 72 305 Temperature K HIERARCH ESO INS TEMP24 ID Dt4DC Temperature sensor type HIERARCH ESO INS TEMP24 NAME Science detector 4DC Temperature sensor name HIERARCH ESO INS TEMP24 UNIT K 2 Temperature unit HIERARCH ESO INS TEMP24 VAL 72 112 Temperature K HIERARCH ESO INS TEMP25 ID FPA Temperature sensor type HIERARCH ESO INS TEMP25 NAME FPA thermal plate Temperature sensor name HIERARCH ESO INS TEMP25 UNIT K Temperature unit HIERARCH ESO INS TEMP25 VAL 67 874 Temperature K HIERARCH ESO INS TEMP26 ID WFSpl 5 Temperature sensor type HIERARCH ESO INS TEMP26 NAME WFS plate Temperature sensor name HIERARCH ESO INS TEMP26 UNIT K Temperature unit HIERARCH ESO INS TEMP26 VAL 95 801 Temperature K HIERARCH ESO INS TEMP3 ID Tube d Temperature sensor type HIERARCH ESO INS TEMP3 NAME Cryostat tube Temperature sensor name HIERARC
41. 5x1 deg field of view can be obtained with a six point observing sequence called a tile For more details on the tile and achieving a full contiguous coverage see Section 7 4 The focal plane assembly in addition to the science detectors contains two autoguider CCDs and two active optics or Low Order Wave Front Sensor CCDs also shown in Figure 5 as blue rectangles and blue squares respectively They will be described in detail in Sec6 5 The telescope camera optics together produce an on axis plate scale on the camera focal plane of 17 0887 arcsec mm7 with a focal length of 12 07m Each detector pixel size is 20 um and the 2048x2048 pixel detectors cover an area of 40 96 mmx40 96 mm on the focal plane The pincushion distortion due to projection effects between the spherical sky and flat focal plane and due to residual distortions in the optical system causes the detectors further from the opti cal axis to cover a smaller area on the sky The mean pixel size across the entire focal plane is 12 VIRCAM VISTA User Manual VIS MAN ESO 06000 0002 40998390 Sutunjoo 10198300 lt L Science detectors controlled by IRACE Figure 5 VIRCAM detector plane looking down on it from above On the sky the detectors are placed in a mirror image with detector No 1 in the top right The numbers in brackets at each science detector indicate the number of the IRACE controller used to run the corresponding detector The wavefront sen
42. AM VISTA User Manual VIRCAM_Jitter2d SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM_Jitter2da SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM Jitter2u SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM_Jitter2ua SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM_Jitter3d SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM_Jitter3u SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM Jitter4u SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM Jitter5n SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM_Jitter5z SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM_Jitter9s SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM_Jitter25s SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIRCAM Jitter30r1 SEQ JITTER OFFSETX SEQ JITTER OFFSETY VIS MAN ESO 06000 0002 Table 18 Fixed jitter patterns 2 position pattern diagonal left to right down 10 0 10 0 10 0 10 0 tion pattern center to right up 0 0 OO ON posi 0 20 0 20 2 position pattern diagonal left to right up 10 0 10 0 10 0 10 0 2 position pattern center to right down 0 0 20 0 0 0 20 0 3 position pattern diagonal left to right down 0 10 0 10 0 0 10 0 10 0 oo 3 position pattern diagonal left to right up 0 0 10 0 10 0 0 0 10 0 10 0 4 position pattern U shape rotated 30deg ccw 3 66 13 66 3 66 13 66 13 66 3 66 13 66 3 66 5 position pattern n shape with cent re rotated 60deg cw 0 0 8 66 5 0 8 66 5 0 0 0 5 0 8 66 5 0 8 66 5 position pattern Z rotated 30
43. EL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS ECS VENT2 1 00 ECS VENT3 1 00 ECS WINDSCR 1 00 FOCU ID CA x ef FOCU VALUE 2 617 GEOELEV 2530 GEOLAT 24 6157 GEOLON 70 3976 GUID DEC 39 98310 GUID FWHM 1 09 GUID ID py ST deet GUID MAG 13 60 GUID PEAKINT 0 00 GUID RA 343 632454 GUID STATUS ON SE ID y 0 101 M2 ACENTRE 32 40 M2 ATILT 35 35 M2 BCENTRE 102 30 M2 BTILT 54 49 M2 Z 2 61723 MOON DEC 11 92595 MOON RA 14 421736 OPER Operator name PARANG END 53 191 PARANG START 53 624 POSANG 89 956000 TARG ALPHA 225056 232 TARG COORDTYPE M d TARG DELTA 400828 674 TARG EPOCH 2000 000 TARG EPOCHSYSTEM J TARG EQUINOX 2000 000 TARG PARALLAX 0 000 TARG PMA 0 000000 TARG PMD 0 000000 TARG RADVEL 0 000 TH Mi TEMP 14 13 TH STR TEMP 14 55 TRAK STATUS NORMAL DATE 2009 06 05 FILT1 DATE 2009 07 25T02 FILT1 ENC 105866 FILT1 ERROR 2 0 FILT1 FOCUS 0 000 FILT1 ID SLOT5 FILT1 NAME J SR FILT1 NO 17 FILT1 POSEDGE 106841 FILT1 TRAYID ESO J 0002 FILT1 WLEN 1250 000 HB1 SWSIM F ID VIRCAM 1 57 LSC1 OK T LSC1 SWSIM F LSM1 OK T LSM1 SWSIM F LSM2 OK F LSM2 SWS
44. FFSET_Y OFFSTNUM OFFST_ID ESO DET IRACE ADC16 DELAY 7 ADC Delay Adjustment ESO DET IRACE ADC16 ENABLE 1 Enable ADC Board 0 1 ESO DET IRACE ADC16 FILTER1 O ADC Filteri Adjustment ESO DET IRACE ADC16 FILTER2 O ADC Filter2 Adjustment ESO DET IRACE ADC16 HEADER 1 Header of ADC Board ESO DET IRACE ADC16 NAME VISTA AQ GRP Name for ADC Board ESO DET IRACE SEQCONT F Sequencer Continuous Mode ESO DET MINDIT 1 0011000 Minimum DIT ESO DET MODE NAME 3 DCS Detector Mode ESO DET NCORRS 3 Read Out Mode ESO DET NCORRS NAME Double Read Out Mode Name ESO DET NDIT 5 of Sub Integrations ESO DET NDITSKIP O DITs skipped at 1st INT ESO DET RSPEED 1 Read Speed Factor ESO DET RSPEEDADD 0 Read Speed Add ESO DET WIN NX 2048 of Pixels in X ESO DET WIN NY 2048 of Pixels in Y ESO DET WIN STARTX 1 Lower left X ref ESO DET WIN STARTY 1 Lower left Y ref ESO DET WIN TYPE O Win Type O SW 1 HW Information from Primary Header T Standard FITS NOST 100 2 0 ESO European Southern bservatory 2009 08 11T04 53 17 Date this file was written VISTA ESO Telescope Name VIRCAM Instrument used DS Original target 342 734300 22 50 56 2 RA J2000 pointing deg 40 14130 40 08 28 6 DEC J2000 pointing deg 2000 Standard FK5 years ERR gt Coordinate reference frame 50 0000000 Integration time 55054 20368050 Obs start 22009 08 11T04 5
45. H ESO INS TEMP3 UNIT K Temperature unit HIERARCH ESO INS TEMP3 VAL 287 910 Temperature K HIERARCH ESO INS TEMP4 ID OBtop Temperature sensor type HIERARCH ESO INS TEMP4 NAME Optical Bench Top Temperature sensor name HIERARCH ESO INS TEMP4 UNIT K k Temperature unit HIERARCH ESO INS TEMP4 VAL 92 781 Temperature K HIERARCH ESO INS TEMP5 ID Baff Temperature sensor type HIERARCH ESO INS TEMP5 NAME Battle Temperature sensor name HIERARCH ESO INS TEMP5 UNIT K i Temperature unit HIERARCH ESO INS TEMP5 VAL 148 360 Temperature K HIERARCH ESO INS TEMP6 ID Lens 2 Temperature sensor type HIERARCH ESO INS TEMP6 NAME Lens barrel Temperature sensor name HIERARCH ESO INS TEMP6 UNIT K Temperature unit HIERARCH ESO INS TEMP6 VAL 89 823 Temperature K HIERARCH ESO INS TEMP7 ID FwShd Temperature sensor type HIERARCH ESO INS TEMP7 NAME Filter wheel shield Temperature sensor name HIERARCH ESO INS TEMP7 UNIT K Temperature unit HIERARCH ESO INS TEMP7 VAL 109 230 Temperature K HIERARCH ESO INS TEMP8 ID FwHub 2 Temperature sensor type HIERARCH ESO INS TEMP8 NAME Filter wheel hub Temperature sensor name HIERARCH ESO INS TEMP8 UNIT K Temperature unit HIERARCH ESO INS TEMP8 VAL 96 258 Temperature K HIERARCH ESO INS THERMAL AMB MEAN 289 01 Ambient temperature K HIERARCH ESO INS THERMAL CLD MEAN 0 00 Cold hea
46. IM F LSM3 OK T LSM3 SWSIM F PRES1 ID Vaci gt PRES1 NAME VIS MAN ESO 06000 0002 State of vent i State of vent i Wind screen position Telescope focus station ID M2 setting mm Elevation above sea level m Tel geo latitute North deg Tel geo longitude East deg Guide star DEC J2000 Seeing measured by autoguider Guider ID Magnitude of guide star Peak intensity of guide star Guide star RA J2000 Status of autoguider TCS version number M2 M2 centring alpha tilt alpha M2 centring beta M2 tilt beta Focussing position of M2 in Z coor 11 55 33 4 DEC J2000 deg 00 57 41 2 RA J2000 deg not set Telescope Operator Parallactic angle at end deg Parallactic angle at start deg Rot position angle at start Alpha coordinate for the target Coordinate type M mean A apparent Delta coordinate for the target Epoch Epoch system default J Julian Equinox Parallax Proper Motion Alpha Proper motion Delta Radial velocity M1 superficial temperature Telescope structure temperature Tracking status Instrument release date yyyy mm d 31 14 Filter index time Filter wheel abs position Enc Filter home switch offset Enc Filter focus offset mm Filter slot name Filter Filter wheel position index In position switch edge Enc Filter tray ID Filter effective wavelength nm If T heart beat device simulated Instrument ID name If T controller is operational If T
47. ISF CCD POSITIONS X VISTA uses absolute offsets from the original tar get coordinates ISF CCD POSITIONS Y VISTA uses absolute offsets from the original tar 0 0 ISF FILTERS GC DEFAULT get coordinates VISTA uses absolute offsets from the original tar get coordinates List of science filters to be sequenced Is object extended Enue yu 49S VLSIA WVOHIA 2000 00090 OS A3 NVIMl SIA LL VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 B VISTA VIRCAM Observing Blocks Cookbook This section is primarily meant as a guideline for first time users or re refresh for the other users of P2PP and SADT Download SADT and P2PP from Phase 2 web pages http www eso org sci observing phase2 SMGuidelines SADT html http www eso org sci observing phase2 P2PPSurveys html Install P2PP and SADT in this order because you need to know the path to the instrument package which comes with the P2PP Make sure that SADT points to the instrument package downloaded with P2PP see instructions on the download page Look at the parameters like the tile pattern jitter pattern jitter scale multiplier and scale factor in the templates and decide on the X and Y overlap and maximum jitter amplitude in the SADT After selecting the tile pattern and jitter amplitude run SADT and define the tiles for the survey Switch on the Find AO AG stars in the SADT under Options menu and run SADT search for the AG AO stars Save the resulting survey file in
48. IT 80 sec were taken yielding a nominal flux of 400000 ADU and heavily saturating the detectors Next 12 more dark frames with DIT 300 sec were taken to measure the actual persistence effect and its decay The reference dark level that has been subtracted from the measured persistence was retrieved from a dark taken 8 hr later The log ADU versus log time 14 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Table 3 Properties of the VIRCAM science detectors Different types of bad pixels are measured by pipeline recipes and the adopted definitions slightly vary hence the inconsistency The last two lines give the average values and their r m s over all 16 detectors Saturation and non linearity measurements are based on data from 2009 06 08 Detector Gain Read out Hotpixels Bad pixels Saturation Non linearity No e noise fraction fraction ADU deviation at ADU CR 10000 ADU 1 3 7 23 9 0 45 1 93 33000 2 2 2 4 2 24 4 0 51 1 30 32000 3 3 3 4 0 22 8 0 93 0 91 33000 3 8 4 4 2 24 0 0 45 0 63 32000 3 5 5 4 2 24 4 0 32 0 14 24000 2 0 6 4 1 23 6 0 33 0 23 36000 3 0 7 3 9 23 1 0 38 0 22 35000 2 0 8 4 2 24 3 0 34 0 32 33000 3 4 9 4 6 19 0 0 35 0 27 35000 3 3 10 4 0 24 9 0 33 0 10 35000 4 4 11 4 6 24 1 0 35 0 24 37000 4 6 12 4 0 23 8 0 38 0 22 34000 2 6 13 5 8 26 6 0 94 0 90 33000 10 0 14 4 8 18 7 0 61 0 97 35000 2 7 15 4 0 17 7 0 32 0 53 34000 1 7 16 5 0 20 8 0 27 1 43 34000 3 3 Average 1 16 4 3 22 9 0 45 0 65 33438 3 5 r m s 0 5
49. NS INS INS INS INS INS INS INS INS INS INS INS INS INS VIRCAM VISTA User Manual PRES1 UNIT PRES1 VAL SW1 ID SW1 NAME SW1 STATUS SW2 ID SW2 NAME SW2 STATUS SW3 ID SW3 NAME SW3 STATUS TEMP1 ID TEMP1 NAME TEMP1 UNIT TEMP1 VAL TEMP10 ID TEMP10 TEMP10 TEMP10 TEMP12 TEMP12 TEMP12 TEMP12 TEMP14 TEMP14 TEMP14 TEMP14 TEMP15 TEMP15 TEMP15 TEMP15 TEMP16 TEMP16 TEMP16 TEMP16 TEMP17 TEMP17 TEMP17 TEMP17 TEMP18 TEMP18 TEMP18 TEMP18 TEMP19 TEMP19 TEMP19 TEMP19 VAL TEMP2 ID TEMP2 NAME TEMP2 UNIT TEMP2 VAL TEMP20 ID TEMP20 TEMP20 TEMP20 TEMP21 TEMP21 TEMP21 TEMP21 TEMP22 TEMP22 TEMP22 TEMP22 VAL ID VAL ID VAL ID VAL ID VAL ID VAL ID NAME VAL ID VAL ID VAL ID VAL NAME UNIT NAME UNIT NAME UNIT NAME UNIT NAME UNIT NAME UNIT UNIT NAME UNIT NAME UNIT NAME UNIT NAME UNIT Win Cryostat window cell Temperature sensor VIS MAN ESO 06000 0002 mbar Pressure unit 9999 000 Pressure mbar INPOS S Switch ID Filter In position Switch Switch name ACTIVE Switch status REFSW Switch ID Filter Reference Select Switch name PRIMARY Switch status gt HOME Switch ID Filter Reference Switch Switch name gt INACTIVE Switch status Amb 2 Temperature sensor type Ambient temperature Temperature sensor name K
50. Name CDI 1 9 47983053801822E 05 WCS transform matrix element CDI 2 7 27998866955548E 08 WCS transform matrix element CD2_1 7 27998866955548E 08 WCS transform matrix element CD2_2 9 47983053801822E 05 WCS transform matrix element PV2_1 1 WCS parameter value term PV2_2 0 WCS parameter value term PV2_3 42 WCS parameter value term PV2_4 0 WCS parameter value term PV2_5 10000 WCS parameter value term CHECKSUM UJpiaHoOWHoOaHo0 ASCII 1 s complement checksum DATASUM 1704464255 data unit checksum updated 2009 08 11T HIERARCH ESO DET CHIP ID ESO Virgo35 Detector ID HIERARCH ESO DET CHIP LIVE T Detector live or broken HIERARCH ESO DET CHIP NAME Virgo i Detector name HIERARCH ESO DET CHIP NO 1 Unique Detector Number HIERARCH ESO DET CHIP NX 2048 Pixels in X HIERARCH ESO DET CHIP NY 2048 Pixels in Y HIERARCH ESO DET CHIP PXSPACE 2 000e 05 Pixel Pixel Spacing HIERARCH ESO DET CHIP TYPE IR g The Type of Det Chip HIERARCH ESO DET CHIP VIGNETD F Detector chip vignetted HIERARCH ESO DET CHIP X 1 Detector position x axis HIERARCH ESO DET CHIP Y 4 Detector position y axis HIERARCH ESO DET CHOP FREQ 0 Chopping Frequency HIERARCH ESO DET CON OPMODE NORMAL Operational Mode HIERARCH ESO DET DID ESOU VLT DIC IRACE 1 47 Dictionary Name and Re HIERARCH ESO DET DIT 10 0000000 Integration Time HIERARCH ESO DET DITDELAY 0 000 Pause Bet
51. X top and Y bottom axis Based on data from 2009 01 26 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 8 Data Flow Pipeline Quality Control The mean VISTA data volumes per night are exceptionally high estimated 150 300 GByte on a typical night because of the multiple short exposures usual for IR observations This makes it challenging to reduce the data at the telescope or even to carry out fully just the primary data reduction sky subtraction flat fielding Only partial processing is carried out at the telescope for preliminary quality control purposes The data are transferred first to the ESO archive in Garching where a copy is made and sent to CASU The nominal delivery time is a few hours Calibration data are processed at ESO by the ESO pipeline to create master calibrations and uses them for higher level quality control and trend analysis These reductions are limited Further data reduction is carried out by the users outside of ESO either at CASU or by the efforts of the survey teams themselves Immediately after the data pass quality control the raw frames become publicly available either via the ESO Archive or via the WFAU Finally after reducing and analyzing the data the users can upload high level data products into the ESO Archive to make them available to the community via dedicated tools The object extraction is vital for astrometric and photometric calibrations of the data and it is rigor ously monitored
52. ad function is under sampled for seeing better than 0 68 arcsec It improves the flat fielding same as jittering Unlike the jittering the pipeline interleaves the microstepped ex posures without rejection There is a number of predefined microstepping patterns i e 2x2 pattern with 0 5 pixel spacing Microstep patterns can be nested within each jitter position The pipeline combines the microstepped frames and produces confidence maps Note that using microsteps is currently discouraged due to data reduction difficulties VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 VIRCAM VIRCAM calibration cascade cascade NONE J FILTER FILTER FILTER CHANNEL TABLE BADPIXEL MAP MASTER DARK CONFIDENCE MAP raw types cxcluding technical calibrations ll static calibrations STD STAR PRODUCTS reference calibration op oual L master calibration grouping rule for raw frames ETE PRODL CIS match rule mone ESO QC 2010 Figure 22 VIRCAM cascade diagram for producing calibration frames VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 6 90 Figure 23 Distribution of the 2MASS touchstone fields on the sky VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 i35 0 337 0 338 0 333 0 34 0 341 0 3 i38 0 337 0 338 0 339 0 34 0 341 0 3 Figure 24 Maps of the pixel sizes across the focal plane along the
53. anges in values may indicate a hardware fault i e filter misplacement The number of detected hot pixels on an image Measured using an object catalog combined with a morphological classifier The number of objects classified as noise from frame to frame should be rea sonably constant excessive numbers indicate a problem Average number of pixels rejected during combination of dark frames used to give an estimate of the rate of cosmic ray hits for each detector This can later be compared with previous estimates and monitored The decay rate of the persistence of bright images on subsequent exposures will be modelled using an exponential decay function with time constant decay rate Requires an exposure on a bright star field followed a series of darks Determined from the persistence decay behavior from exponential model fit ting Requires an exposure on a bright star field followed a series of darks as above Measured from the noise properties of the difference in two consecutive dark frames using a MAD estimator as above for robustness against spurions The noise properties of each detector should remain stable so long as the electronics micro code have not been modified Measure the median of the difference of a new mean reset frame and a library reset frame VIRCAM VISTA User Manual Parameter units QC RESETDIFF RMS ADU RMS new library reset frame QC RESETMED ADU Median reset level QC RESETRMS ADU RMS noise in
54. anual Analog Digital Units Autoguider Adaptive Optics Broker of Observing Blocks Correlated Double Sample IR detector readout mode Cryo pump Data Flow System Detector Acquisition System Double Correlated Read Detector Control System Declination Detector Integration Time European Southern Observatory Exposure Time Calculator Force Control Assembly Flexible Image Transport System Field Of View Focal Plane Assembly Full Width at Half Maximum Glass Fibre Reinforced Plastic HOWFS High Order Wave Front curvature Sensor ICRF ICRS ICS IR ISAAC LOCS International Coordinate Reference Frame International Celestial Reference System Instrument Control System Infra Red IR Spectrograph And Array Camera Low Order Curvature Sensors LOWFS Low Order Wave Front curvature Sensor same as LOCS Local Control Unit Primary Mirror Secondary Mirror Median of Absolute Deviation MINDIT Minimum DIT 1 0011 sec NDIT NDR NINT NTT TSF UKIRT VDFS Number of DITs Non Destructive Read Number of NDITs New Technology Telescope Observing Blocks Observing Software Observing Tool Phase 2 Proposal Preparation Phase 2 Proposal Preparation version 3 Point Source Catalog Power Drive Unit Point Spread Function Right Ascension Quality Control Read Out Noise Survey Area Definition Tool Service Mode Son Of ISAAC To Be Confirmed Telescope Control System Template Signature File United Kingdom Infrared Telescop
55. ap that are part of the final science level data products These confidence maps are in effect combined weight maps where the mean level is normalized to 10096 and bad pixels are set to zero an important pre requisite for the deep stacking and tiling of the individual pawprints and for calculating the statistical significance of detected objects Twilight sky flats have a good but not perfect colour match to the night sky observations we wish to correct and can be taken under conditions where the contribution from night sky fringing emission from dust particles on the optical surfaces and other spatial effects are mostly negligible or match best the conditions for the science data The slightly imperfect colour match between the twilight and night sky will cause a very small residual error in the gain correction The sky level must be low enough to avoid saturating a MINDIT exposure but high enough so the emission from fringing or dust on the optical surfaces will be negligible in comparison with the sky level leaving only a short interval in which to acquire the twilight flats Therefore it will not always be possible to get a complete set of twilight flats every night especially during service observations using many filters or on cloudy nights Pre selected empty twilight fields will be observed on clear nights and offsets between the individual exposures will be executed to cancel the effect of bright stars in the field The pipeli
56. arameters are given in Table 8 The filter transmission curves are plotted in Figure8 VIRCAM VISTA uses a Ks filter similar to 2MASS but unlike WFCAM UKIRT which uses a broader K filter Note that the NB 980 tray slot actually contains two different types of filters split equally between NB 980 and NB 990 To obtain homogeneous coverage of the sky with both of them the users should observe the survey area twice with position angles separated by 180 deg for example 0 and 180 90 and 270 etc The symmetry of the AG and AO CCD should allow to use the same reference sources for both observations The information which type of filter is located in each tray spot will be provided later on the VISTA web page Filter exchange time is expected to be 15 45sec depending on the required rotation angle The filter wheel rotates in both directions so the shortest path is chosen during nominal operation this is clearly longer than the time for a jitter or for a tiling telescope move so it is generally more Table 7 Location of the VIRCAM filters in the filter wheel slots INT 3 is the intermediate slot No 3 Slot Filter Slot X Filter Slot Filter 1 SUNBLIND INT3 HOWFS J beam splitter 6 y 2 NB 980 4 Ks 7 Z 3 H 5 J 8 NB 118 Two different types of filters NB 980 and NB 990 are located in the tray in this slot for their param eters see Table 8 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 100 80
57. ch detector Derived from the median flux in each of the monitor exposures if they are done This is the maximum percentage jump between adjacent exposures in the monitored sequence Derived from the median flux in each of the monitor exposures if they are done This is the percentage variation over the whole of the sequence of exposures Computed using a MAD estimator with respect to median sky after removing large scale gradients The sky noise should be a combination of readout noise photon noise and detector quirks Monitoring the ratio of expected noise to measured one provides a system diagnostic at the detector level The RMS of the stripe pattern removed from an image Measure of difference between dead reckoning pointing and true position of the detector on sky Derived from current polynomial distortion model and 6 parameter detector model offset Measure of difference between dead reckoning pointing and true position of the detector on sky Derived from current polynomial distortion model and 6 parameter detector model offset Measure of difference between dead reckoning PA and true position angle of the detector Derived from current polynomial distortion model and 6 parameter detector model effective rotation term Robust average of residuals from WCS solution for each detector Measure of integrity of WCS solution Measure of the average on sky pixel scale of a detector after correction using the current polynomial distor
58. combined reset frame QC SATURATION ADU Saturation level of bright stars QC SCREEN STEP Max imum percentage jump in monitor images QC SCREEN TOTAL To tal percentage variation in monitor images QC SKY NOISE ADU RMS sky noise QC STRIPERMS ADU RMS stripe pattern QC WCS_DCRVAL1 deg Actual WCS zero point X raw header value QC WCS_DCRVAL2 deg Actual WCS zero point Y raw header value QC WCS DTHETA deg Actual difference rotation PA raw PA header value QC WCS RMS arcsec Robust RMS of WCS solution for each detector QC WCS SCALE deg pixel Measured WCS plate scale per detector QC WCS SHEAR deg Power of cross terms in WCS solution deg QC ZPT 2MASS 1 pass zeropoint mag photometric QC ZPT_STDS 2nd_pass zeropoint mag photometric QC ZPT STDS CAT Standard catalog photometric zeropoint for VIS MAN ESO 06000 0002 Description Measure the RMS of the difference of a new mean reset frame and a library reset frame Median reset level Variation is defined here as the Gaussian equivalent MAD i e 1 48xmedian of absolute deviation from unity after normalizing by median level i e measur ing the RMS reset level variation The RMS can later be compared with library values for troubleshooting problems Determined from maximum peak flux of detected stars from exposures in a standard bright star field The saturation levelxgain is a check on the full well characteristics of ea
59. cs with a fast f 1 primary mirror giving an f 3 25 focus ratio at the Cassegrain focus It is equipped with a near infrared camera VIRCAM or VISTA InfraRed Camera with a 1 65 degree diameter field of view FOV at VISTA s nominal pixel size containing 67 million pixels of mean size 0 339 arcsec x 0 339arcsec The instrument is connected to a Cassegrain rotator on the back of the primary mirror cell and has a wide field corrector lens system with three infrasil lenses The available filters are broad band ZY JH Ks and narrow band filter at NB 980 NB 990 and 1 18 micron The point spread function PSF of the telescope camera system delivers images with a full width at half maximum FWHM of 0 51 arcsec without the seeing effects The weather characteristics and their statistics are similar to those for the VLT VISTA has one observing mode imaging and the telescope is used mostly in service mode to carry out surveys programs exceeding in size and scope the usual ESO Large Programs Typically the observations are carried out in a 6 step pattern called tile designed to cover the gaps between the individual detectors The high data rate on average 315 GB per night and the large size of the individual files 256 7 MB makes it a significant challenge for an individual user to cope with the data reduction challenges The VISTA raw data are available via the ESO archive High level data products i e photometry catalog with object classifica
60. d temperature K HIERARCH ESO INS THERMAL DET MEAN 71 98 Detector mean temperature K HIERARCH ESO INS THERMAL DET TARGET 72 00 Detector target temperature K HIERARCH ESO INS THERMAL ENABLE T If T thermal control enabled HIERARCH ESO INS THERMAL FPA MEAN 67 87 Focal plane array temperature K HIERARCH ESO INS THERMAL TUB MEAN 287 91 Tube temperature K HIERARCH ESO INS THERMAL WIN MEAN 289 85 Window temperature K HIERARCH ESO INS VAC1 OK F If T controller is operational HIERARCH ESO INS VAC1 SWSIM F If T vacuum sensor simulated HIERARCH ESO DET DIT 10 0000000 Integration Time HIERARCH ESO DET NCORRS NAME Double Read Out Mode Name HIERARCH ESO DET NDIT 5 of Sub Integrations HIERARCH ESO GEN MOON RA 14 43722 Moon Right Ascension HIERARCH ESO GEN MOON DEC 11 98059 Moon Declination HIERARCH ESO GEN MOON DIST 59 84113 Moon distance to target HIERARCH ESO GEN MOON ALT 27 67441 Moon altitude angle HIERARCH ESO GEN MOON AZ 60 12512 Moon azimuth angle HIERARCH ESO GEN MOON PHASE 0 68 Moon phase as fraction of period HIERARCH ESO OCS DET1 IMGNAME VIRCAM_IMG_OBS Data File Name HIERARCH ESO OCS EXPNO 1 Exposure number of dwell HIERARCH ESO OCS NEXP 1 Number of exposures per dwell HIERARCH ESO OCS RECIPE DEFAULT Data reduction recipe to be used HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH
61. de and select the science filter It also points the telescope to a new target using a preset The pointing center is the rotator center un less specified otherwise in the optional X Y parameters The default field of view orientation points the Y axis to the North and X axis to the West The position angle Camera sky position angle is defined at the pointing center note that the large field of view leads to some small deviations in the orientation away from the center If autoguiding and active optics correction are required to be set by the acquisition template Enable autoguidingz T and Enable active optics T one guide star and two AO stars are read from on line catalogs see below Most parameters are self explanatory A brief description of some of them is given below Rotator Angle on Sky Orientation on the sky opposite sign convention than the position angle on the sky This parameter is filled in automatically when the XLM file created by SADT is imported into P2PP and it SHOULD NOT be changed after this has been done because any change will lead to observing a wrong patch of the sky The rotator angle is however to be set by the user for single pawprint observations or standard star fields Differential tracking in RA and Differential tracking in DEC both these parameters MUST be set to 0 0 because the differential tracking has not been enabled or tested yet X Coord of Pointing and Y Coord of Pointing set an ini
62. ded to leave this parameter to F It is not selectable for the SADT based tile observations for which the guide stars are defined in each of the tiles independently VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Enable autoguiding and Enable active optics Select if the autoguiding and low order wave front sensing shall be started or not This should be kept as F for public surveys prepared with SADT where the guide and WEG stars are provided for all pawprints in the tile templates It should be left in T in the case that the OB is prepared without using the SADT with template VIRCAM img acq quick Filter name selects the filter to be used during the acquisition It is recommended to use the same filter as in the first science observing template to minimize the filter wheel movement Using many filters in one OB is only allowed for the science observation but it is discouraged for operational reasons Multiple filters can even be included in one template via the nesting Sec 7 6 However it is strongly recommended to separate the filters into individual templates in the same OB to minimize the time loss in case of OB abort and restart For now it is not allowed to select twice the same filter in the same template Template Sequence The steps through the execution of the template can be summarized like below To save time the instrument will be set up in parallel to the telescope preset With the default parameter setti
63. deg ccw 0 3 66 13 66 13 66 3 66 0 13 66 3 66 3 66 13 66 oo 9 position pattern square shape rotated 30 deg ccw 0 0 13 66 8 66 3 66 5 0 13 66 8 66 3 66 5 0 0 0 3 66 5 0 13 66 8 66 3 66 5 0 13 66 8 66 25 position pattern square spiral rotated 30 deg ccw 0 0 4 33 1 83 2 5 6 83 4 33 1 83 2 5 6 83 11 16 8 66 6 16 3 66 0 67 5 0 9 33 13 66 11 16 8 66 6 16 3 66 0 67 5 0 9 33 13 66 0 0 2 5 6 83 4 33 1 83 2 5 6 83 4 33 1 83 0 67 5 0 9 33 13 66 11 16 8 66 6 16 3 66 0 67 5 0 9 33 13 66 11 16 8 66 6 16 3 66 30 position pattern random numbers 5 66 9 10 9 37 2 73 4 77 6 63 9 56 7 53 3 14 5 63 8 22 4 91 2 24 3 61 6 70 2 66 5 65 6 16 3 59 0 88 2 24 1 16 3 11 7 61 9 96 7 85 4 86 5 02 6 66 2 49 9 89 4 65 4 11 3 19 4 87 6 68 4 35 5 17 1 83 0 94 4 27 8 02 7 95 8 11 4 76 5 40 8 78 2 31 8 16 7 51 8 55 9 94 5 19 2 57 8 39 5 64 9 29 4 03 0 84 4 00 61 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 JEjtterad ELAN DOTTY Tjittersu E We dades GBE bod diu a FJitteron jJitter5z F Jitter9s E 20 100 10 20 20 10 0 10 20 T EL S S T Jitter30r1 Offset Y relative units 1 Lol plume 1 10 10 0 10 Offset X relative units Figure 26 Fixed jitter patterns The orientation is the same as in Fig 25 The numbers indicate the sequence of pointings and the arrows show the direction of the off
64. detector array for the VIR CAM img acq quick template The corresponding offsets on the sky in arcsec are listed in brackets X Coord of Pointing 87 9 mm 29 3mm 29 3mm 87 9 mm 1484arcsec 494arcsec 494arcsec 1484arcsec Y coord of pointing 117 mm 1978 arcsec 13 14 15 16 39mm 659 arcsec 9 10 11 12 39 mm 659arcsec 5 6 7 8 117mm 1978 arcsec 1 2 3 4 of a given detector is given in Table 15 The corresponding offsets on the sky in arcsec are listed in brackets A 5 The Science Observation Templates A 5 1 VIRCAM_img_obs_tile lt N gt The tile templates will take jitter sequences over the full field of view of the camera using a selection of pawprints jitter and microstep telescope offset implemented with the different nesting strategies as described in Sec 7 6 The templates will set up the telescope the instrument and the detector controller according to the user selected parameters There are three template versions depending on the number of pawprints in the tile pattern VIRCAM img obs tile1 VIRCAM img obs tile3 and VIRCAM_img_obs _tile6 The template parameters are listed in Table21 The sizes of geodesic rectangles representing the field of view covered by these templates are listed in Table 16 Only the tile6 template would guarantee the full coverage of the field of view of the telescope In case of the tile3 templates the full field coverage would be only guarantied in case that observatio
65. ding standards at high airmasses The 2MASS Touchstone Fields will be observed if the UKIRT standards are not available i e due to wind pointing restriction These data will provide important information on the stability of VIRCAM and will be used to measure any intra detector spatial systematics i e illumination correction For any standard star i in any filter b m mi ZP ky x Xi 1 e where m is the calibrated instrumental magnitude in the system of the standard star mij 2 5 x logio counts sec is the measured instrumental magnitude ZP is the Zero Point k is the atmospheric extinction coefficient and X 2sec z is the airmass of the standard star during the ob servation It is assumed here that the second order atmospheric extinction term and the colour dependency of k are both negligible Typically ZPs are stable throughout a night if photometric but over months the ZPs decrease i e the sensitivity of the instrument is reduced for example due to accumulation of dust on the primary mirror The extinction coefficients k are usually stable over periods of months but they will be monitored through each night assuming fixed ZPs and making measurements over a range of airmasses The 2MASS found that their extinction coefficients vary seasonally but such an effect should be smaller for VISTA because of the drier site and narrower filter profiles especially at J A network of secondary photometric standard
66. djacent tiles for many surveys Assigning only one of the two 0 092 deg overlap top amp bottom to each of the two tiles involved in an overlap the result is that each tile when part of a filled larger area would cover 1 017 0 092 x 1 475 1 636 deg which will be covered at least twice 7 5 Scheduling Containers The survey nature of the VISTA operation implies executing a large number of similar or even identi cal OBs except for the target coordinates necessary to obtain uniform coverage of wide sky areas This complicates enormously the short term scheduling of observations because of the number of sometimes conflicting requirements timing and weather condition constraints uniformity and last but not least the requirement to complete a certain self containing set of observations before start ing a new one A good strategic planning of a survey may ensure early science output long before the survey is completed A new P2PP3 has been developed by ESO that enables implementing a survey strategy called VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 scheduling containers They are high level tools with respect to the jittering microstepping etc described in the previous Sec 7 4 The containers allow to streamline the operations giving at the same time enough flexibility to achieve the scientific goals of the surveys Three types of scheduling containers are available Concatenations the member OBs are executed sequentiall
67. during the quality control process The pipeline extracts objects from each frame and classifies them as stellar non stellar or noise A number of QC parameters are associated with every object mean sky background mean sky noise number of noise objects mean seeing mean stellar ellipticity etc The quality control QC adds no overhead to the observations A number of QC parameters are written in the fits headers of the files by the CASU pipeline A list of QC parameters is given in Table 13 ESO does not distribute a dedicated pipeline for VIRCAM data reduction to the user community All VISTA data available from the archive immediately following observations are raw The Public Sur vey teams have the obligation to return to ESO the reduced images and catalogues of the detected sources reduced images and other survey specific high level data products This is done as part of the Phase 3 which is mandatory for the public surveys but not for the the normal programmes ESO does not reduce the VIRCAM science data The users should therefore either develop their own data reduction procedures or get in touch with CASU CASU receives all VISTA data and they typically process all with the standard VISTA pipeline via processing that is roughly described in this manual However CASU has no obligation to deliver the reduced data to the general ESO telescope users this can be done but it is not guaranteed CASU reduces the data upon agreement with
68. e VISTA Data Flow System VIRCAM VISTA InfraRed Camera VISTA VLT VM VST VPO WCS Visual and IR Survey Telescope for Astronomy Very Large Telescope Visitor Mode VLT Survey Telescope VISTA Project Office World Coordinate System WFCAM Wide Field Camera IR camera at UKIRT ZP ZPN Zero Point Zenithal Polynomial Projection 6 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 4 VISTA and VIRCAM in a nut shell A summary of basic VISTA and VIRCAM related terms and concepts is given in Table 2 Table 2 Short telescope and instrument description Item Telescope VISTA Instrument VIRCAM Location Focus Observing mode Detectors Total number of pixels Pixel size Image quality Filters Integration Exposure Pawprint Tile FOV of a single pawprint FOV of a tile Intradetector gaps Image file size Nightly data rate Description a specialized 4 m telescope for surveys wide field 16 detector near infrared camera VISTA peak at ESO Paranal Observatory Latitude S24 37 5 Longitude W70 24 2 Altitude above sea level 2635 43 m f 1 primary giving a f 3 25 focus at the Cassegrain imaging 16 Raytheon VIRGO 2048 px x 2048 px HgCdTe on CdZnTe substrate arrays 64 megapixels square average 0 339 arcsec on the side for more details on the variation see Sec 7 9 3 FWHM 0 51 arcsec ZY JH Ks NB 980 NB 990 and NB 118 a simple snapshot within the Data Acquisition System of a specified Detector Integ
69. e is to map the effect of the reset and to trace any drift of the pixel level after a reset so each new reset frame is compared with a historical one from a database to detect changes The pipeline output is a variance with respect to the standard frame a QC parameter 2 Dark Current Frames are dark frames taken with increasing DITs used to measure the detector dark current by fitting a median slope to dark values versus DIT for each pixel to produce a dark current map The range of DITs starts at MINDIT currently 1 0011 sec and finishing at a large value depending only on the available time for this calibration The pipeline outputs calculates an array of detector dark currents for each individual pixel a QC parameter 3 Dark Frames are exposures with cold blank filters completely blocking the detectors from in coming radiation They are used to calibrate out and measure two separate additive effects i the thermal dark current and ii the reset anomaly a residual structure left in the image after the reset is removed in the DAS when it does a correlated double sample Reset Read Read VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 They are additive and can be removed together using dark frames taken with the same DIT x NDIT as the observation that need to be calibrated note that the NDIT also must be the same because the final frame is the sum not the average of the individual DITs assuming that the two effects
70. e jitter pattern for the first pawprint only middle column five sequential from top to bottom jittered pawprints right column five sequential from top to bottom randomly jittered sky sequences The template parameters in this example are listed in Sec A 5 2 Note that the number of jitters at each pawprint and the number of sky jitters can be different but they should be equal in order to have the same S N on the sky and on the object if the number of jitters on the sky is smaller the sky subtraction will introduce extra noise into the data because the noise of the sky will dominate the overall noise budget The number of sky jitters can be reduced only if the time between the sky sequences is small 1 3 min and one can combine all sky images from them together to create a common sky that will be used to remove the sky contributeion for the individual pawprints VIRCAM VISTA User Manual VIS MAN ESO 06000 0002 A 5 3 VIRCAM img obs paw The paw print template takes a jitter sequence around only one of the six payprints that would comprise a tile The definition of the parameters and the template sequence are both identical to the VIRCAM img obs tile templates See for details Sec 7 4 and Figures 17 18 and 19 Ap The Calibration Templates VIRCAM img cal illumination and VIRCAM img cal std The illumination correction template VIRCAM img cal illumination obtains a sequence of images with different XY offsets which allows
71. eb pages selecting VIRCAM in the Instrument Selector on the upper right http www eso org sci observing phase2 SMGuidelines html The actual observations are in effect executions of semi automatic scripts with minimal human intervention restricted usually to quality control of the data and real time decisions about the short term service mode scheduling The care and attention during the preparation stage is critical for optimizing the observations First the user defines the survey area and the observing strategy more details are provided in the VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 next sections Second the SADT is used to determine the coordinates of the tiles and the suitable guide star and active optics reference star candidates http www eso org sci observing phase2 SMGuidelines SADT html Third the OBs are prepared with P2PP3 http www eso org sci observing phase2 P2PPS3 html This new version of P2PP3 enables the definition of more complex survey strategy through the use of scheduling containers see Sec 7 5 The user should remember that the maximum total duration of an imaging OB in Service Mode can not exceed 1 hr the maximum duration of a concatenation is also 1 hr Longer OBs may be acceptable but ESO can not guarantee that the weather conditions will remain within the requested specification after the first hour i e even if the conditions deteriorate after 1 hr of observation the OB will still be co
72. ed Requested integration time s Value of 1st OBSNUM in ustep seq Sequence number of ustep Name of ustep pattern X offset in ustep pattern arcsec Y offset in ustep pattern arcsec VCAM 2009 08 11T04 53 17 995 fits Archive File Name gt JASpL35mJA5mJ35m ASCII 1 s complement checksum 0 3 data unit checksum updated 2009 08 11T ESO OBS DID ESO VLT DIC OBS 1 11 OBS Dictionary ESO OBS EXECTIME O Expected execution time ESO OBS GRP 0 j linked blocks ESO OBS ID 378057 Observation block ID ESO OBS NAME EN D I 1 1 1 J OB name ESO OBS OBSERVER UNKNOWN Observer Name ESO OBS PI COI ID 70033 ESO internal PI COI ID ESO OBS PI COI NAME UNKNOWN PI COI name ESO OBS PROG ID 60 A 9292 A ESO program identification ESO OBS START 2009 08 11T04 37 23 OB start time ESO OBS TARG NAME DS OB target name ESO OBS TPLNO 2 Template number within DB ESO TPL DID gt ESO VLT DIC TPL 1 9 Data dictionary for TPL ESO TPL EXPNO 14 Exposure number within template ESO TPL FILE DIRNAME INS_ROOT INS_USER MISC VISTA Storage filena ESO TPL ID VIRCAM img obs tile6 Template signature ID ESO TPL NAME VIRCAM tile 6 observation Template name ESO TPL NEXP 30 Number of exposures within templat ESO TPL PRESEQ VIRCAM_img_obs_tile seq Sequencer script ESO TPL START 2009 08 11T04 37 33 TPL start time ESO TPL VERSION Revision
73. ed twilight constraints for deep exposures are listed in Table 10 The users are free to optimize these parameters for their science cases The twilight constraints reduce the observability period of a target and the effect can be important at the end of the observation period when the target is setting already at the beginning of the night Eventually the target could even be missed during the current observation period From http casu ast cam ac uk surveys projects vista technical sky brightness variation VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 o e em eegen e 5 1 E zi IT egies fat xw 23 5 PAN h a ZE 4 vesi M Laag es mie WE Ry a W eet ak cot mt Wer Z a ss a H e ap A ow Rene T V AKT v A AD FA LAC een M Ki x Y A Z CN d afer oe lt X x a Check S Fe Sg df fr Kt e sw d Ww ei el 7 e E e 9 A 9 a Ze D o e ss S ANEN ear ae S TE METTE o er A wd gt oe en OS G ER OR e Lei Z G se ef gt ee DA 11 t ee o ek EE di ee g Ju T d Ce SE s Sch A S e 3 A Q8 4 E EE a j I b R VS e E E o WAT o e SCT Met E T EA E Wij 24 ART t t ee th amu DA Pod s M S Tn t e NEEDS gt DUE E as ready e En e We l oo Xx o Id e t n j H b lt E Di Tee e one ge S i tue ie eo e Wi ef Ks V v DE e H L e J te SC Z obt NB118 fb o nn
74. ejection The pipeline also produces fringe and dust maps 2 Dark Sky Flats may be constructed from the dark sky maps Their advantage over twilight flats is the better colour match to the average astronomical object minimizing the sensitivity of the gain and flat field correction to differential colour terms with respect to astronomical objects However fringing and thermal emission from dust particles on the optical surfaces need to be removed because they can be high enough to affect the background significantly in some passbands leading to systematic errors in photometry 3 Jittering removes detector cosmetic defects and cosmic ray hits and allows to create sky maps while accumulating sufficient signal to achieve the required S N The flat fielding is also improved because the flux coming from a given point on the sky is averaged over the response of many different pixels For jittering the total requested exposure is split into several shorter exposures at least 5 to obtain good sky maps with random or predefined telescope offsets between them It is similar to microstepping but with coarser sampling and the pipeline combines the jitterred exposures with a rejection algorithm The pipeline combines the jitterred frames after removing the other instrument signatures and produces a combined frame and confidence maps 4 Microstepping improves the sampling by non integer sub pixel offsets It can make a difference when the point spre
75. eline in some pixel rejection algorithms i e during the combination of individual jittering science frames 6 Linearity curve of each detector can be determined through a series of 20 dome flats taken under constant illumination at varying exposures starting at MINDIT up to just into saturation for all chips The illumination is set to produce 1000 ADU at MINDIT The constant screen illumination requirement implies that the dome flats cannot be taken in condi tions of variable or excessive ambient light i e no work in the dome is allowed during the linearity calibration Check frames of constant exposure are intertwined with the ramp exposures to mon itor the screen illumination The dome lights are typically stable within 196 level Alternate runs of this procedure should use increasing and decreasing sets of exposure times or take exposures with different exposure times in a randomized non monotonic order The pipeline calculates lin earization curves and polynomial coefficients bad pixel maps and various QC parameters such as measurement of non linearity and bad pixel statistics 7 Twilight Flats remove pixel to pixel gain variations and the instrumental vignetting profile for a given filter They also provide a global gain correction between the 16 detectors and between the 16 individual read out channels within each detector giving a total of 256 channels The mean flat fields and bad pixel maps are sources for the confidence m
76. ervations aim to add signal from several individual OBs of the same field the best strategy to minimize the persistence effects is to use random jitters or to use a different jitter pattern for every visit of te field This strategy will assure accumulating many relatively short exposures at different offset positions Note that the pattern can be modified either by selecting a different jitter pattern or by small modifications in the jitter scale multiplier parameter see the Apendix 7 4 2 Filling in a tile with multiple pawprints To fill in the gaps between the detectors or in other words to produce a single filled Tile with reasonably uniform sky coverage requires a minimum of six pointed observations with fixed off sets This is achieved first by observing at three positions offset in Y Figure 17 i e so that after them an area with a vertical side 5 275 detector widths 24 3x 0 425 is covered at least twice This corresponds to 1 017 deg 61 arcmin at VISTA s mean pixel size There is also a strip at the top and another at the bottom which is only covered once by this tiling pattern These strips are each 0 475 of a detector height corresponding to 0 092 deg 5 5 arcmin at VISTA s mean pixel size Then a position shift is made in X direction Figure 18 so that the 2 positions in X cover a horizontal side of 7 65 detector widths 4 3 x0 90 0 95 with no strips at the X edges This corresponds to 1 475 deg 88 5 arcmin
77. ery visit of the target as mentioned in Sec 7 4 1 7 9 2 Photometric Calibration The IR window between 1 and 2 5 microns contains several large absorption features that are pri marily due to water vapor and carbon dioxide in the atmosphere The edges of the atmospheric windows are highly variable Although the infrared filters are designed to exclude the regions af fected most for some filters in particular Ks the edges of the useful passbands are defined by these absorption features rather than the transmission curves of the filters themselves Thus when the column density of water vapor is variable accurate photometry can be difficult to achieve On good nights generally when the humidity is low and it is cold it should be possible to achieve better than 196 absolute photometry however on most nights this should be considered as the best limit and the typical accuracy is 3 596 Of course the relative photometry can be much more accurate Good planing of the observations and sophisticated data reduction i e image subtraction instead of aperture photometry and PSF fitting has allowed some users to achieve on a 4 m class telescope relative photometry of a few milimagnitudes The camera will be on the telescope semi permanently providing a stable configuration that enables us to take a long term approach for the photometric calibration The strategy is to define robust routine calibration procedures so that the accuracy and hence the scie
78. et object HHMMSS TTT 401344 760 Dec of target object DDMMSS TTT 0 00 Pointing origin X coord mm 0 00 Pointing origin Y coord mm sion 1 13 GEN MOON RA GEN MOON DEC GEN MOON DIST GEN MOON ALT GEN MOON AZ GEN MOON PHASE
79. et of the science detectors and are designed for specific unique calibration observations and engineering tests These filters don t cover the entire focal FPA but they can be shifted to cover a few different detectors by rotating the filter wheel slightly The beam splitters for the high order wavefront sensor HOWFS fit into these intermediate positions The VISTA filter wheel control software knows the approximate transparency of each filter and it is designed to protect the detectors from being flashed unnecessarily with ambient light by selecting a wheel movement path which passes the least number of bright filters through the beam VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 6 4 Sensitivity The VISTA sensitivities for different filters the average sky brightness on the site and other relevant items are listed in Table 4 These values change with time For example the zero points gradually degrade over time between the mirror re coatings The degradation can reach up to 7 for the bluest bands and up to 2 3 for Ks as seen from the plots in Fig 10 13 Mirror coatings are evident in Sept 2009 and Apr 2011 as well as the silver coating degradation in late 2010 early 2011 Please check the VIRCAM web page for the most up to date information 6 5 Low Order Wavefront Sensors and Autoguiders The camera incorporates six CCD detectors grouped into two units Y and Y that provide auto guiding and wavefront sensing infor
80. f observing periods and the list of their parameters might undergo modifications Therefore the users should use the latest version of this Manual for the preparation of their observations Sometimes the template parameters are referred to as template keywords VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 For the ESO survey telescopes VISTA and VST a survey area definition tool SADT was devel oped to allow the preparation of large number of similar or identical OBs necessary for covering large survey areas with tiles a mosaic of six pawprints offset that covers twice nearly uniformly the otherwise sparsely populated VIRCAM field of view see Sec 7 4 The SADT also selects auto guider and wave front sensor stars from astronomical catalogs The result of the survey area defini tion is written at the end into an xml format file to be imported later into P2PP The user is required to prepare only one initial OB or a few if the survey is not entirely uniform and the P2PP tool will clone OBs with the same parameter sets for every tile of the survey The SADT is described in detail in a separate user manual and in the SADT Cookbook See also http www eso org sci observing phase2 SMGuidelines SADT html Both P2PP and OT were heavily modified with respect to the previous versions to handle the large number of public survey OBs The most prominent modification is the new functionality to group the OBs in scheduling containers Sec 7
81. fields is set up allowing routine photometric standard observations The standard fields are selected among the UKIRT faint standard fields and 2MASS Touchstone Fields Figure 23 Many of them have already been observed and calibrated by WFCAM at the UKIRT Note that the UKIRT standards do have Y and Z band measurements In the interest of time we only observe them on detector No 11 The secondary fields meet the following criteria 1 cover the camera pawprint area 2 span RA 0 24 hr with an approximate spacing of 2 hrs 8 enable observations over a range of airmass i e some fields pass close to the VISTA zenith and others are available to the North to allow for WFCAM cross coverage and South to optimize telescope azimuth slewing and to allow observations during strong wind from different directions 4 contain 100 stars per detector to allow characterizing the systematic position dependent photometric effects but avoiding crowding problems with J 18 and Ks lt 16mag for short expo sures 5 encompass stars with broad ranges of colours to allow derivation of extinction colour terms and to facilitate transformations from to other filter systems VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Photometric Standard Field Calibration is obtained with a template Table 12 that sets the header DPR parameters so the pipeline can identify the raw fits files as standard star observations and to process them accordingly The pipe
82. ften than 45 sec the user must choose between extra overheads to wait for the LOWFS or operation with somewhat degraded image quality This choice is implemented with the AO priority parameter see Sec A 4 The filter change time depends on the wheel rotation angle from the last position The time neces sary to move between two neighboring filters is 21 sec filters separated by one position is 27 sec filters separated by two positions is 33 sec filters separated by three positions is 40 sec Larger offsets are not needed because they can be accomplished by a shorter movement of the wheel in the opposite direction The filter changes can be done in parallel with the position change to save time The filter positions are listed in Table 7 The science observations accumulate overheads for pawprint and jitter offsets microstepping de tector readout and storing the FITS files Filter changes during the science observations after the initial instrument set up for the OB will add extra overheads All these must be taken into account and they are listed in Table 11 7 9 Calibration Plan There are four types of VIRCAM calibrations related to e properties of the transfer function of the end to end system telescope camera IR detector system including associated controllers etc so that instrumental signature can be re moved from the data As VISTA has a wide field of view particular attention must be paid to
83. g self sky subtraction impossible It obtains a number SEQ SKYJITTER NJITTER of randomly jittered images within a box with a given size SEQ SKYJITTER MAX centered at a user defined sky position SEQ SKYOFFSET ALPHA SEQ SKYOFFSET DELTA The sky fields are only executed if the option FIXEDSKYOFFSET is selected in the is object extended field in P2PP This was introduced to simplify the survey preparation in case that the sky field is only required for a few tiles on a larger survey area In case that other options DEFAULT EXTENDED or SKY they were meant to provide instructions to the pipeline what recipe to use for the data reduction a feature that is not implemented are selected the template sequence would follow exactly the one of the VIRCAM_img_obs_tile6 template The template operate as follows first it takes images at the six pawprints that form the tile at the first jitter positions in each pawprint the jitter pattern is identical for all pawprints Next it goes to the offset sky field and takes images jittering there within a user defined jitter box following a user defined jitter pattern Then the template returns to the second jitter position of the first pawprint of the tile end begins to circle through all pawprints in the tile After the tile is completed the next sequence of jandom jittered sky images is taken and so on The template ends with a sky sequence An example is shown in Fig 27 for the following
84. gnal to noise ratio because the noise will be dominated by the sky 7 1 2 Selecting the best DIT and NDIT Selecting the best DIT and NDIT is a complex optimization problem and it depends on the nature of the program type of the targets necessary signal to noise frequency of sky sampling etc Therefore it is hard to give general suggestions and the users should exercise their judgment and discuss their choices with the support astronomer The first constraint is to keep the signal from the target within the linear part of the detector array dy namic range below 25000ADU Tables 3 and 4 for a discussion on the detector non linearity see Sec 6 2 Considering the large VIRCAM field of view it is likely that a number of bright stars will fall into the field of view and they will illuminate the detectors with signal well above the non linearity limits The data reduction pipeline is designed to correct at least partially the effects of non linearity and cross talk caused by these sources However the requirement to keep the signal from the science target below the non linearity limit is paramount The only way to do that is to reduce the detector integration time Unfortunately small DIT values of 1 2 sec increase greatly the overheads to gt 50 100 because the overhead associated with every DIT is 2sec For comparison obser vations with DIT210 20 sec have an overhead of 10 The sky background is another factor that has to be accounted
85. h Order Wavefront Sensor HOWFS and the light reaches them via corresponding beamsplitters to provide two out of focus images used in the analysis The VIRCAM field distortion can be noticeable it is expected that the difference between the pixel scale averaged over the entire field of view and the on axis pixel scale may reach 0 89 with up to three times larger radial variations for more details on the pixel scale variation accross the field of view see Sec 7 9 3 Therefore pixels can be combined without re binning only for small jitters up to 10 px and if no microsteps are used because they by default are fractions of the pixel size However in most cases the sky background removal will dictate the usage of larger jitters and the data reduction will require re binning of pixels when co adding frames at different jitter positions VIS MAN ESO 06000 0002 VIRCAM VIS TA User Manual 10 u3ea sjaxid grog X 8p0Z sim3al p Cell u su es p X p d 5 aouald eure euetd e904 ag uals 129 LAL U Suojerqae pp U IH ZAL ID JUSWAADW PIO MOT sando a nav Q papauoo saunxay suoneuage gawe ado3saja stosuag WO 1 9AU AX y Jepms omy EX SO 31249 pasor samdo 105095 ppio u IH Sa Aman SABLE Gm 2303135 01 df O igawa uit PALA ZET 1003 aud 404 N T UIM pay OLUO Stay 3 SAIR 404 404 amps p oo UIEN JULI wedonin pmbr T SEO pioa paBeun ar uou 10 aqry Duo Eeay mopu 13934 ing wnz uf Aeme Bu
86. ifferent DITs columns 2 11 The last column contains the average dark current rate for each detector calculated from the measurements with DIT gt 50 sec Based on data from 2009 05 21 Detec Detector Integration Time DIT seconds Dark current tor 10 50 75 100 125 150 200 250 275 300 ADUsec 1 146 20 2 22 7 25 1 27 1 29 2 32 9 36 2 37 9 39 4 17 2 0 4 2 33 55 67 83 95 11 3 141 16 9 18 1 19 7 2 5 0 1 3 6 4 17 2 17 7 27 3 25 0 35 0 41 0 45 7 44 8 49 7 11 2 2 3 4 6 8 16 5 21 0 25 3 29 5 33 2 40 6 47 7 51 2 54 4 10 0 0 5 5 40 55 62 69 75 81 392 10 2 10 7 112 4 6 0 1 6 41 65 75 85 93 10 1 11 5 12 9 13 6 14 2 5 30 1 7 4 6 79 9 7 11 2 12 7 14 2 16 8 19 3 20 5 21 6 5 70 2 8 8 0 15 6 18 4 20 4 22 4 23 9 26 7 29 1 30 3 31 3 14 1 0 6 9 6 3 13 4 16 7 19 3 21 6 23 7 27 4 30 7 32 3 33 8 11 0 0 6 10 40 43 43 45 45 47 48 50 50 5 1 4 1 0 0 11 5 3 11 0 13 8 16 3 18 5 20 4 24 1 27 6 29 3 30 9 8 2 0 4 12 56 98 11 5 12 8 14 0 15 0 16 6 18 1 18 7 19 3 8 90 4 13 18 4 50 8 67 6 82 2 97 9 110 5 136 8 161 4 174 2 185 3 28 4 1 9 14 49 3 144 6 185 8 221 5 254 1 283 7 339 8 389 3 413 2 436 0 103 1 6 9 15 35 45 50 55 58 62 69 75 78 8 4 0 0 1 16 17 7 40 1 47 0 52 3 56 8 60 6 67 3 73 1 76 0 78 4 36 5 1 5 diagram shows the decay as a straight line so the persistence was fit by a power law where the time after the saturation t is in seconds and the coefficient a is in ADUsec P t a x t ADU sec giving the excess in the count rate The best fit parameters a and
87. ing a tile with six pawprints the three vertical steps along the Y axis Gen d Det 1 Det 13 Move across by AX 95 _ and observe X I 3 aHa to centre of PAN POI mi filter wheel with AY 47 5 I I again Det 4 Det 16 Figure 18 Completing a tile with six pawprints the two horizontal steps along the X axis VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 0 95 detector widths E L lm O O H E L1 BEER GOOG C RES 4 SHEER BEER BEE ESE E A Pawprint 3 Pawprint 4 Sa 8 l sn BENBNUDUDUUU mm Si WU Ufsfbstets 3 e GE gm IDD giu Pawprint 2 PawprintS I z Tile EEENOO0E m m m DOOD 1 6 E U E i z E Ei HENEN UL Et Pawprint 1 Pawprint 6 a o c Figure 19 Contiguous tile formed by combination of six overlapping pawprints Figure 20 Exposure time coverage for a contiguous coverage tile of 6 pawprints dark green 1 light green 2 magenta 3 red 4 yellow 6 in units of the single pawprint exposure time angle Relative tilts among neighboring tiles in a multi tile survey will be present especially near the celestial poles Sec 7 6 A map showing the integration times accross the entire field of view provided that the integration at each pointing is the same is shown in Figure 20 The dark green areas at top and bottom of the plot are each 1 475 deg x0 092 deg 0 135 sq deg and can be overlapped by corresponding areas from a
88. ing origin X in focal plane mm Y coord of pointing TEL TARG Y number 500 0 500 0 0 0 Pointing origin Y in focal plane mm Filter name INS FILTER NAME parameter ISF FILTERS Name of the filter element to place in the beam checks switches Table 21 VIRCAM VISTA science template VIRCAM img obs tile N parameters Parameter which are typically updated by users are high lighted P2PP Label List of DET DIT List of DET NDIT Name of jitter pattern Maximum size of jitter Number of jitters Jitter scale multiplier Nesting FITS header Parameter Type DET1 DIT DET 1 NDIT SEQ JITTER ID SEQ JITTER MAX SEQ JITTER NJITTER SEQ JITTER SCALE SEQ NESTING Guide star setup file for pawprint SEQ REF FILE1 1 6 from SADT Name of tile pattern SADT Scale factor Name of microstep pattern List of science filters Is object extended from SEQ TILE ID SEQ TILE SCALE SEQ USTEP ID INS FILTER NAME OCS EXTENDED numlist intlist parameter number number number parameter paramfile parameter number parameter Range 0 0 3600 0 ISF IR NDIT RANGE ISF JIT TER_RANGE RANDOM 0 0 150 0 1 100 0 0 10 0 FPJME FJPME PFJME ISF TILE RANGE1 ISF TILE _DEFAULT1 0 0 10 0 ISF USTEP_RANGE parameterlist ISF FILTERS_SCI parameter DEFAULT EX TENDED SKY Default 20 0 5 1 0 FPJME 1 0 Single DEFAULT Description Single integration time in seconds or li
89. ion Users should use these flags to prepare their OBJECT SKY sequences within concatenations Modified Labels and More Hidden Parameters The parameter labels were changed to be more clear in some cases like in case of the TEL ROT OFFANGLE for which we have included a mini help to make clear that this is the opposite of the position angle Some parameters which are not supposed to be changed were hidden in this release A 3 Introduction to the Phase 2 Preparation for Public Surveys All scientific and calibration observations with ESO instruments are prepared as observing blocks OBs with the Phase 2 Proposal Preparation P2PP tool The scheduling of these OBs is then done on site with the broker of observing blocks BOB tool and the P2PP in visitor mode or with the Observation Tool OT during the Service Mode SM observations The P2PP has been heavily modified with respect to the previous versions to handle the survey operations Observing blocks contain the target information a small number of user selected templates con straints sets and the scheduling timing information The parameters of the templates define the configuration and set up to be used for the respective observations Some parameters are selectable by users others are hidden from the users to simplify the templates The hidden parameters can not be changed by the users but only by the telescope and instrument operators The templates are reviewed usually at change o
90. jitter pattern as listed in instrument TER RANGE package RANDOM SEQ JITTER MAX number 0 0 150 0 20 0 Maximum size of a randomized jitter in arcsec onds SEQ JITTER NJITTER number 1 100 5 Number of points in a randomized jitter SEQ JITTER SCALE number 0 0 10 0 1 0 Multiplier for each jitter step 1 normal SEQ NESTING parameter FPJME PFJME FPJME Filter Pawprint Jitter Microstep Exposure nesting FJPME FPJME PFJME FJPME SEQ USTEP ID parameter ISF Single Name of microstep pattern USTEP_RANGE INS FILTER NAME parameterlist ISF FILTERS_SCI List of science filters to be sequenced OCS EXTENDED boolean DEFAULT EX DEFAULT Is object extended TENDED SKY Table 23 VIRCAM VISTA illumination correction template VIRCAM_img cal_illumination parameters P2PP Label Parameter Type List of integration time s DET1 DIT numlist List of number of integrations DET1 NDIT intlist List of tel RA offsets arcsec SEQ OFFSETALPHA numlist List of tel DEL offsets arcsec SEQ OFFSETDELTA numlist List of tel rotator offsets de SEQ OFFSETROT numlist 180 0 180 0 grees List of science filters INS FILTER NAME parameterlist ISF FILTERS SCI Is object extended OCS EXTENDED boolean Range 0 0 3600 0 ISF IR NDIT RANGE 6000 0 6000 0 6000 0 6000 0 DEFAULT EX TENDED SKY Default 10 0 1 Description Single integration time in seconds or list of times for each filter Single NDIT or list of NDITs for each filter
91. l obviously vary over the night with time wave length filter and as airmass 9 This variation should be predictable given local site seeing measurements A comparison with the expected value can be used as an indication of poor guiding poor focus or instrument malfunction Estimate of 5 sigma limiting mag for stellar like objects for each science ob servation derived from QCs ZPT 2MASS SKY NOISE APERTURE CORR Can later be compared with a target value to see if main survey requirements i e usually depth are met Derived from measured non linearity curves for each detector interpolated to 10 000 counts ADUs level Although all IR systems are non linear to some degree the shape and scale of the linearity curve for each detector should remain constant A single measure at 10 000 counts can be used to monitor this although the full linearity curves will need to be examined quarterly TBC to look for more subtle changes Derived from the RMS of the line fit to linearized fluxes versus exposure time and applied to a nominal level of 10 000 counts The number of stars on this image used to calculate the photometric zeropoint A measure of the RMS photometric zero point error using an aperture of 1 4 x TBC the core radius A measure of the photometric zero point using an aperture of 1 x the core radius Computed using a clipped median for each detector sky levels perhaps not at Ks it should vary smoothly over the night Strange ch
92. l vircam jitter microstep process VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 outputs are a mean dark fits frame and some QC parameters dark current signal plus reset anomaly stability measurement detector dark current and detector particle event rate 4 Dome flats are used for instrument performance monitoring and evaluation of the image struc ture They are not used for gain correction flat fielding due to non uniform illumination of the screen and the different colour of the illumination compared with the night sky The dome flats are a series of timed exposures of the dome screen taken through a given filter in conditions that exclude variable or excessive ambient light i e no working in the dome during the dome flats The illumination exposure times are adjusted to yield 8 000 ADU i e a fraction of the potential well depth of 36 000 ADU The pipeline outputs are a master dome flat for the given filter bad pixel mask and a number of QC parameters number of saturated pixels lamp efficiency etc 5 Detector Noise calibration measures the readout noise and the gain of each chip for purpose of detector health monitoring The measurement uses a pair of dome flats and a pair of darks matching the DIT x NDIT of the flats The flats must be exposed to give 8 000 counts The pipeline calculates readout noise and gain for each read out channel of each detector QC parameters Later on these values are used by the pip
93. lance between the area the depth and the filter coverage Once this decision is made the user should run the Survey Area Definition Tool SADT to determine the number of tiles necessary to cover the survey area Note that the tile pattern selected in the SADT must not be changed in P2PP3 because the AO AG reference stars selected in the SADT are suitable only for that tile pattern they will not be valid for another tile pattern and the change will cause the OB to fail during execution Next comes the question of how to split the total integration time for each filter into different exposures i e to select DITs NDITs microstepping and jitter patterns see the discussion in Sec 7 1 2 Finally the user has to decide on the sequence in which the various observations will be obtained For example the filter rotation is relatively slow 21 40 sec for a filter exchange see Sec 7 8 and it might be more efficient to combine the observations of a few nearby tiles in the same filter in one scheduling container group that will likely lead to their consecutive execution rather than to change the filter and to re observe the same tile multiple times However this strategy may leave the user waiting for some time before the observations in all filters of each tile are collected and it will not ensure nearly simultaneous multi band photometry The order in which various filters are observed in a tile should be optimized to shorten the filter wheel mo
94. line output is ZP atmospheric extinction coefficient extinction color term illumination correction and a global gain correction 7 9 3 Astrometric Calibration The astrometric calibration provides the transformation between pixels coordinates of instrument signature free pawprints and celestial coordinates for all 16 sub images leaving the pawprints on the appropriate photometric scale The transformations are saved in a Flexible Image Transport System FITS World Coordinate System WCS header parameters Zenithal Polynomial Projection ZPN is used Calabretta amp Greisen 2002 A amp A 395 1077 There is a measurable variation of the pixel scale accross the field of view from 0 3363 to 0 3413 arcsec px along the X axis and from 0 3351 to 0 3413 arcsec px along the Y axis based on data from 2009 01 26 Fig 24 Given the physical pixel size of 204m these translate into physical scale variations 58 60 59 47 um arcsec and 58 60 59 68 jum arcsec 1 respectively As can be seen from the plot the strongest term in the optical distortion model is the cubic radial one The true on sky radial distance r from the optical axis is related to the measured radial distance in the focal plane r as r ki x r ka x r ks x r 3 where k 0 34 arcsec px 1 k 42x ki ba 10000 xk and higher order terms seem to be neg ligible The rms of the residuals from individual detector linear fits to the 2MASS RA and Dec af
95. ltaneous readout channels so each detector is read into 16 stripes of 2048x128 pixels The minimum detector integration time is 1 0011 sec All detectors but one are linear to 4 696 for illumination levels below 10000 ADU and for the worst one the non linearity at this level is 10 Table 3 There is also a small non linearity of 1 296 at low illumination levels 1000 ADU that affects all detectors It can not be measured with the calibration plan linearity monitoring but the effect is neglegible These values may change with time check the VIRCAM web page for more up to date information The linearity is correctable for up to 25000 ADU the number varies for the different detectors The stability of the non linearity VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 100 60 QE 40 Figure 6 Quantum efficiency of the VIRCAM Virgo detectors Note the long wavelength tail at A22 5 um corrections will be studied and reported later The detectors are read in the standard Double Correlated mode which means an image of length DIT seconds is effectively the difference of an exposures of DIT 1 0011 sec and 1 0011 sec Well depths for the arrays defined as the point at which the non linearity of the response exceeds 5 range between 110000 and 180000 e for a bias voltage set at 0 7 V For a typical gain
96. mation to the VISTA telescope control system for the purpose of active control of the telescope optics to correct the flexure and various opto mechanical effects arising from both the telescope and camera parts of the system There are two Low Order Curvature Sensors Autoguiders LOWFS AGs units self contained sub systems mounted between the third camera lens and the filter wheel assembly next to the in frared detectors Figure 5 They can sample the beam as close as possible to the science field of view Each unit contains three e2v Technologies type CCD 42 40 2048 x 2048 CCDs with pixel scale 0 23 arcsec px The first of them uses only half of the field of view 8x4 arcmin for speed and it provides auto guiding capability for the telescope at up to 10 Hz frame rate for a 100x100 pixel window The other two CCDs are mounted at the two outputs of a cuboid beamsplitter arrangement which provides pre and post focal images for wavefront curvature analysis They use the full field of view 8x8 arcmin From a software perspective the LOWFS AG units logically are part of the telescope control system TCS rather than the instrument control system ICS The guide sensor operates concurrently with the science observations It is expected that the guide sensor can start to operate within 30 min after sunset but this may require to choose the telescope pointing placing a suitably bright guide star in the LOWFS AG field of view The field of view
97. mpleted and considered executed In this case the user should request in advance a waiver from the User Support Department http www eso org sci observing phase2 SMGuidelines WaiverChanges VIRCAM html The SADT step of the preparations often must be repeated many times To save time and for a quick view of the survey area tiling the user can initially turn the autoguiding and wavefront reference stars search flags off in the SADT preferences but the AO AG reference sources are necessary for the surveys and the flags have to be turned back on before producing and exporting the final survey tiling configuration Once the AO AG reference star search is turned on and the SADT is re run the user will find that the number of tiles necessary to cover the survey area depends strongly on the available AO AG reference stars The area within which the SADT searches for such stars for each offset position in turn depends on the SADT parameter Maximum Jitter Amplitude listed in Table 9 it is discussed in detail in the SADT Cookbook If the maximum jitter value is very large it would be difficult to find reference stars especially away from the Galactic plane A maximum jitter value smaller than the one used in the templates of the OBs later would cause loss of reference stars during some of the jitter offsets and image quality degradation The large field of view of VIRCAM VISTA implies that closer to the celestial poles the rectangles representing the
98. ne output includes mean twilight flats confidence maps and ratios with respect to a reference flat for all detectors and channels QC parameters 8 Image Persistence or remanence memory is a detector feature causing residual traces of images from a preceding exposure on the current image It is measured observing a fairly empty VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 41 field to avoid confusion with the cross talk effects with a close to saturated star followed by a sequence of dark frames to measure the characteristic decay time of the remnant from the star This must be done for each detector or even for each readout channel The pipeline product is a set of persistence constants It was thought until mid 2010 that the persistence of VIRGO detectors is negligible but the data reduction eventually demonstrated that this is not the case The persistence is nearly impossible to correct if it is caused by saturated objects Therefore the faux sources caused by this effect will eventually be flagged but there will be no attempt to correct it Please check the VISTA web page for updates The users are strongly adviced to take their data via as many different jitter offsets as possible especially if they plan to accumulate signal during multiple visits of the target in other words split ting the observation between many OBs This is easiest to achieve with random jitter offsets or alternating the jitter pattern for ev
99. ng They depend on the adopted observing strategy The overheads have to be taken into account when requesting time with VIRCAM and the total allocated time includes both the exposure time on sky and the overheads To estimate the total execution time for an OB one has to add to the total on sky observing time the overheads for filter changes microstepping jittering tiling read out overheads as well as the overheads associated with the preset the active optics and instrument set up A summary of the VISTA and VIRCAM overheads is given in Table 11 and a more detailed description is given further These numbers will be updated to reflect the real behavior of the system For recent updates check the ESO VISTA web page An easy way to estimate the overheads associated with a typical OB is to use the P2PP3 tutorial account username 52052 passwd tutorial A full preset includes for a stand alone non concatenated OB or for the first OB in a concatenation the overhead is 120s For the second and subsequent OBs in a concatenation the overhead is equal to the altitude and azimuth slewing time of 20sec target distance slew speed where the slew speed is 1 degs rotator offset is fast and it is usually completed during the telescope motion so it adds no extra overhead acquiring a guide star includes 3 s for guide star identification and 5 s for AG start LOWFS observation to update the M2 position takes 45 s instr
100. ng there will be no step which requires manual interaction Acquisition Template Execution Sequence If pointing origin is not 0 0 then Adjust telescope coordinates to bring target to pointing origin End if Set instrument mode to IMAGING If science filter has been specified Select science filter End if Preset telescope to target if XY offset 0 0 If science filter has been specified Adjust telescope focus for science filter End if If autoguiding is enabled then If AG CONFIRM is TRUE then Prompt operator to confirm autoguiding End if Wait for autoguiding to start End if If the AO correction is invalid If active optics are enabled and AO0 PRIORITY HIGH then Wait for active optics to start End if End if VIRCAM img acq quick is functionally identical to VIRCAM img acq tile but with a different selec tion of user defined input parameters The only specifics for this template is related to the parameters X Coord of Pointing and Y coord of pointing that define the initial offsets on the focal plane in mm In most cases the initial offset parameters must be modified because the center of the focal plane is in the gap between detectors 6 7 10 and 11 Therefore the target will not be covered by any of the detectors A map of the focal plane with the offsets that would put the target at the center VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Table 15 Offset map placing a target at the center of a given
101. ns with two tile3 templates are taken with the alternating tile patterns the latter is still to be implemented with SADT to be confirmed later The tile pattern is selected early in the observing strategy selection process in the SADT This is necessary because the SADT must search and select AO and AG reference stars and to do that it needs to know the tile pattern NOTA BENE If the tile pattern is changed after importing the SADT produced xml file then wrong AO AG reference stars will be passed over to the TCS leading to the failure of the execution Table 16 Sizes of geodesic rectangles representing the field of view covered by different science templates at least once and twice The maps of the coverage is shown in Fig 19 and the details of filling in a tile are described in Sec 7 4 2 Science template Coverage at least once Coverage at least twice Width X deg Height Y deg Width X deg Height Y deg VIRCAM img obs tile1 pawprint 1 292117 1 017301 VIRCAM img obs tile3 half tile 1 292117 1 201 1 292117 1 017301 VIRCAM img obs tile6 tile 1 475 1 201 1 475 1 017301 VIRCAM img obs tile6sky 1 475 1 201 1 475 1 017301 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 The users MUST NOT CHANGE the Name of tile pattern after importing the SADT xml file Simi larly the jitter box size or the jitter scale multiplier can be only modified by small factors without risking that the guide and wave front sensor stars will fall
102. ntific value of the archived survey observations will be maximized The ultimate goal is to provide a photometric calibration accurate to 2 This value may change with time check the VIRCAM web page for more up to date information Zero points defined as magnitudes at airmass unity which yield flux of 1 count sec on the detector will be determined in the Vega system via two independent methods 1 Calibration from 2MASS The 2MASS will provide directly the initial photometric calibration for J H and Ks The Y and Z bands have no 2MASS counterparts but Hodgkin et al 2009 MNRAS 394 675 demonstrated that it is possible to calibrate them within the requirements of the calibration plan using the 2MASS J band and the J H color as long as E B V lt 0 2 and E B V 1 5 mag respectively for Z and J The 2MASS photometric system is globally consistent to within 196 Nikolaev et al 2000 AJ 120 3340 This approach will enable each detector image to be calibrated directly from the 2MASS stars that fall within the field of view The experience with WFCAM indicates that this approach will result in a photometric calibration to better than 296 for VIRCAM Note that the 2MASS based calibration can rely on a relatively narrow dynamic range because the 2MASS is shallower than the typical VISTA surveys and the 2MASS photometric errors are relatively large near the 2MASS limiting magnitude For example at Ks 15 mag the uncertainty is u
103. of the AG units covers sufficiently large area so there is a 9996 probability of finding a suitable guide star for a random telescope pointing in the region of Galactic Pole at Full Moon The start and end of exposure on the two wavefront analysis CCDs of one sensor are coincident within 1 sec and the estimated Zernike coefficients are sent to the TCS within 15 sec from the com pletion of the LOWFS AG exposures The autoguiding and the wavefront analysis add negligible overhead to the science observations less than 0 5sec per LOWFS frame In other words the LOWFS AGs are slaved to the science readouts and telescope dithers to make sure the autogu iding doesn t interfere with the observations The use of the LOWFSs imposes a minimum time between jitter moves of 45 sec since they have to complete an exposure with adequate S N in between consecutive jitter moves If it is essential to jitter more often than once per 45 sec then the observations will be taken in open loop AO In this case an initial AO correction will be performed before starting the sequence of jitter offsets and periodic AO corrections will performed between the exposures These AO corrections will be repeated periodically after the validity in time of last AO correction expires The validity is determined by the AO priority HIGH NORMAL or LOW A software enhancement may be added to enable co adding two or more 15 sec LOWFS exposures of the same star with relative jit
104. parameters SEQ TILE ID Tile6z INS FILTER NAME J SEQ TILE SCALE 1 0 OCS EXTENDED FIXEDSKYOFFSET SEQ TILE FROMPAW 1 SEQ SKYJITTER MAX 210 0 SEQ JITTER IDz Jitterbz SEQ SKYJITTER NJITTER 5 SEQ JITTER MAXz 15 0 SEQ SKYOFFSET ALPHA 160853 000 SEQ JITTER NJITTERz 1 SEQ SKYOFFSET DELTA 022847 000 SEQ USTEP ID Single SEQ SKYOFFSET ROT 0 0 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Eat TA F 2 T t Ta K e2 el Did a L J ep 2 45 ep ZS L jJ 2 EE EE EE E vo r 7 O g A 8 E ef 5 3 A 2 55 a T L H Kita opt 13 e12 J vlo 20 L 7 o0 2 45 242 240 238 Book cid 015 31 7 os RA deg d E j j bos Q wo SAP s16 j 255 Ett EL e24 23 2 795 y _ it au SC te 25 e26 SUUS 25 9 9 E J 9 2 See at 28 27 j 255 ritiiiitiiny zaa E e 35 e 34 E 238 175238 17 s E a 2 45 SE Toug 86 s T A 7 m Q E jJ 9 a Sp E 39 38 J 2 55 g OE tae e eee 36 o E 4 o ant 947 48 j V 25 9 E j 9 n E L 50 49 2 55 Ps L L L L L L i 238 4 238 2 238 RA deg Figure 27 Example of an offset pattern for the VIRCAM img obs tile6sky template The numbers indicated the sequence in which the images are taken Solid dots mark images in the tile open circles are images in the sky field Panels eft column top the entire pattern the sky filed is in the top left corner the tile proper in the bottom right eft column middle blow up of th
105. pensate this increase by decreasing correspondingly NDIT to keep the total integration time constant Still there will be some increase in the overheads Alternatively the sky may be constructed combining a few nearby pointings tiles Summarizing under average conditions for faint targets one can safely use DIT 40 60 20 40 5 30 1 10 and 1 10sec for Z Y J H and Ks filters respectively The narrow band filters can tolerate DITs of up to a few minutes Brighter targets require to reduce these times in some cases all the way down to the minimum DIT of 1 0011 sec for 13 18 mag stars see above The users may even have to consider splitting their observations into shallow and deep sequences optimized for different magnitude ranges High humidity can also affect the sky background in particular in H where it is dominated by OH and water emission lines and for some of the detectors note that the detectors have different gain and non linearity limits DIT 10 sec may be too much for this filter One more complication is caused by the nature of the target If it is point source like or a sparse field of point source like objects the simple dither or a tile will suffice to create a sky frame For objects that fill in a significant fraction of a chip or for very crowded fields it is necessary to image the sky and the object separately effectively adding 10096 overhead Unfortunately it is common that the sky frames will contain other object
106. r should remain stable so long as the electronics micro code have not been modified Parameter units QC GAIN CORRECTION Detector median flat field global median QC HOTFRAC Fraction of hot pixels QC IMAGE SIZE arc sec Mean stellar image FWHM QC LIMITING MAG mag Limiting mag i e depth of exposure QC LINEARITY Percent age average non linearity QC LINERROR RMS percentage error in non linearity measure QC MAGNZPT Number of stars in zero point calculation QC MAGZERR mag Photometric zero point error QC MAGZPT mag Pho tometric zero point QC MEAN SKY Mean sky level ADU QC NHOTPIX Number of hot pixels QC NOISE OBJ Number of classified noise objects per frame QC PARTICLE RATE count s detector Cosmic ray spurion rate QC PERSIST DECAY s Mean exponential time decay constant QC PERSIST_ZERO Fractional persistence at TO extrapolated QC READNOISE Readnoise e QC RESETDIFF_MED ADU Median new library reset frame VIRCAM VISTA User Manual VIS MAN ESO 06000 0002 Description The ratio of median counts in a mean flat exposure for a given detector relative to the ensemble defines the internal gain correction for the detector These internal relative detector gain corrections should be stable with time The fraction of the pixels on an image that are estimated to be hot Measured from the average FWHM of stellar classified images of suitable signal to noise The seeing wil
107. ration Time the stored product in a file a sum not an average of many individual detector integrations the 16 non contiguous images of the sky produced by VIRCAM with its 16 non contiguous chips a contiguous area of sky obtained by combining multiple offsetted pawprints filling in the gaps in a pawprint 0 6 deg with gaps 1 64 deg filled FOV obtained with a minimum of 6 exposures 9096 and 42 596 of the detector width 256 7 MB 250 GB peaking up to 600 GB VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 7 5 The VISTA Telescope Technical Description VISTA is a 4 m class wide field survey telescope Figure 1 It has an alt azimuth mount and quasi Ritchie Chretien optics with a 4 10 m fast f 1 primary mirror M1 giving an f 3 25 focus at the Cassegrain The f 3 hyperboloid shaped secondary M2 has a diameter of 1 24 m The unvi gnetted field of view is 2 deg but VIRCAM uses only 1 6 deg The entrance pupil has a diameter of 3 70 m The focal length is 12 072 m The mirrors were coated with silver at the start of the VIR CAM operations in 2008 because was optimal for near infrared performance However the silver coating suffered from fast aging so it was replaced with aluminum coating in 2011 and the current version of the VIRCAM ESO ETC reflects this change The total telescope mass above the foundation peer is 113 metric tons distributed among the optical support structure 44 the azimuth rotation structure
108. reviations and Acronyms VISTA and VIRCAM in a nut shell The VISTA Telescope Technical Description The VIRCAM VISTA Infra Red Camera 6 1 General feat res bris E ee ech OM SE eot RP de de e UG TRI ENT SEU se AEN 6 2 EECHER 0 93 LEE esent eb eret M e Mur Md EE E EE ncn A E uL PEL TITEL 6 5 Low Order Wavefront Sensors and Autoguiders 6 6 High Order Wavefront Sensor Operation e Observations with VIRCAM VISTA 7 1 Observations in the Infrared seii rw Cree UN RT RR en qr e ake BAAL Thelnfrared SKY Arnar rte PucnN dam m Aves qe Red que EIC 7 1 2 Selecting the best DIT and NDIT 7 2 Preparation for observations and general operation of VIRCAM VISTA 7 3 Twilight ConstrainiS __ _ EIE Sy eee Re E ehe ee eee EXE 7 4 Pawprints Tiles Jitters Microsteps pA Weien PLU m ET 7 4 2 Filling in a tile with multiple pawprints 7 5 Scheduling Containers eek d esa Soe e Popolo RUE Poe EE ME Sue Res 7 6 Observing Strategy Nesting aat RE ELE REB UE XS 7 7 Autoguiding and AO operation EE 750 EIER t e u ae QA u SEE Jeon ek been bel Ze 7 9 Galibratiori A uu ma sa fe h p EE E 7 9 1 Instrument signature removal 0 ee 7 9 2 Photometric Calibration 2 ee ae e E eee Ed re ee a 7 9 8 Astrometric Calibration 7 9 4 Additional Calibrations Derived from Science Data and Related Observing Strategies an d faci Ee ee Cae Geen
109. ried back to back so there will be more images taken close in time but at different pointings on the sky suitable to con struct a sky image Further suggestions may be added as more experience of observing with VISTA is accumulated 7 7 Autoguiding and AO operation The autoguiding and the wavefront sensing are fully transparent to the user during the observations However earlier during the definition of the survey the user must define AG AO stars with the help of the Survey Area Definition Tool SADT The SADT finds the minimal number of tiles necessary to cover a user defined survey area For each tile the SADT verifies the presence of suitable stars in the LOWFS AG field of view and if this is not the case it modifies the position of the tiles to ensure that such stars are available The AG operation is not optional having suitable guiding stars is mandatory During normal operations usually once at the beginning of the night the HOWFS are used to imple ment initial corrections of the primary Then during the operation the LOWFS are used in parallel with the observations if the telescope stays at one position more than 45 sec This is the minimum time within which the LOWFS can provide correction For more details on the wavefront sensing see Section 6 5 and 6 6 7 8 Overheads VISTA is intended to survey quickly primarily through having a large field of view but as with any telescope there are overheads associated with observi
110. ruoaut quosae o Dugem JENSA aqu aed AO SPIM 10 101381103 PIAN BimgsusT J pumip w ADDITA 36 150A 1 Figure 3 VIRCAM general view VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 11 Bcam from Telescope M3 at elge of FOV l Window Telescope MI MI Cell region Mount flange Cable wrap region Warm electronics Services bundle Figure 4 VIRCAM optical layout During normal operation the camera is maintained at temperature T 72K The immediate camera cooling is achieved by circulating liquid nitrogen The total camera cooldown time is 3 days The IR Camera is designed with the intent that it will remain in continuous operation at cryogenic temperatures for a full year on the telescope with a minimum annual downtime scheduled for pre ventative maintenance and any filter changes baring any failures that might require emergency intervention 6 2 Detectors VIRCAM contains 16 Raytheon VIRGO 2048 px x2048 px HgCdTe science detectors 64 megapixels in total covering 0 59 deg per single pointing called a pawprint i e taken without moving the telescope The spacing between the arrays is 90 and 42 5 of the detector size along the X and Y axis respectively Figure 5 the science detectors are marked as green squares Therefore a single pointing provides only a partial coverage of the field of view A complete contiguous coverage of the entire 1
111. s and it is not uncommon that one of these objects will be in the same region of the array s as the science object To avoid this it is important to jitter the sky images as well The experience shows that a reasonable minimum number of the sky images and respectively the object sky pairs is 5 7 to ensure a good removal of the objects from the sky frames Note that this may lead to an extra overhead because in some cases the NDIT has to be reduced artificially contrary to the optimization strategy discussed above to a number below the optimal just to split the total integration into 5 7 images adding an extra overhead for the telescope offsets Considering the large field of view of VIRCAM the user may encounter these problems only for a handful of objects i e the Galactic Center the Magellanic Clouds 7 2 Preparation for observations and general operation of VIRCAM VISTA The VIRCAM VISTA observations are executed as for all ESO telescopes using Observing Blocks OBs that are prepared with the Phase 2 Proposal Preparation Tool version 3 P2PP3 However there is an extra preliminary step for the Public Surveys to define the survey area with the Survey Area Definition Tool SADT that determines the optimal tiling and finds guide star candidates and active optics reference star candidates for LOWFS Before preparing the observations the user should read the SADT manual the P2PP3 manual and the guidelines provided on the Phase 2 w
112. s from the RMS of the fit and the known systematics of the reference catalog The pipeline output includes refined WCS FITS header parameter values for all frames and some QC parameters i e pointing accuracy calculated from equatorial coordinates computed at the particular location using the fitted WCS and the initial WCS that was written to the raw header 7 9 4 Additional Calibrations Derived from Science Data and Related Observing Strategies The procedures described in this section and summarized in Table 12 are calibrations only in a broader sense they are rather data reduction steps related to the astrometric calibrations of the data They are derived from raw data FITS files during the regular data flow i e do not require VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 dedicated observations and extra overheads Their purpose is to remove the instrument signature i e the sparse sky coverage of the individual pawprints or the cosmetic defects of the detectors 1 Sky Subtraction and Defringing removes the well known sky background variations over large scale in the IR and the fringing and thermal emission from local dust particles on the optical sur faces The sky maps are formed either from the target frames if the target field is sparse or from any special offset sky frames for crowded fields or extended targets by combining frames over an appropriate time range determined by the sky flat stability with appropriate r
113. s selected Pawprint the 16 non contiguous images of the sky produced by the VISTA IR camera with its 16 non contiguous chips The name is from the similarity to the prints made by the padded paw of an animal the analogy fits earlier 4 chip cameras better Tile a filled area of sky fully sampled filling in the gaps in a pawprint by combining multiple pawprints Because of the detector spacing the minimum number of pointed observations with fixed offsets required for reasonably uniform coverage is 6 which would expose each piece of sky except for the edges of the tile on at least 2 camera pixels The VIRCAM focal plane is sparse i e there is significant space between the detectors Therefore a single integration of length DIT sec or a co added series of these known as an Exposure it doesn t include moving the telescope between the individual DITs produces a sparsely sampled image of the sky known as a Pawprint in red in the following Figures The area of sky covered by the pixels of a pawprint is 0 6 sq degrees For comparison the fields of view of NICMOS ISAAC VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 31 Figure 16 Comparison between the field of view of VIRCAM and other instruments HAWK I and WFCAM are shown below in Figure 16 together with a crescent moon NOTA BENE Recent tests as of P85 on ward indicated that the VIRGO detectors do suffer from persistence If your field contains bright stars and the obs
114. sands of times fainter than the sky Under these conditions it has become standard practice to observe the source together with the inevitable underlying sky and subtract from it an estimate of the sky obtained from images taken away from the target or moving the target on different locations in the detector also known as jittering Since the sky emission is generally variable the only way to obtain good sky cancellation is to do this frequently The frequency depends on the wavelength of observation and respectively on the nature of the sky background emission and on meteorological conditions Ideally one would like to estimate the sky more frequently than the time scale of the sky variations While this could VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 be done quickly with the traditional single and especially double channel photometers the over head in observing with array detectors and the necessity of integrating sufficient photons to achieve background limited performance are such that the frequency is of the order of once per minute In exceptionally stable conditions the sky can be sampled once every two or three minutes This sky subtraction technique has the additional advantage that it automatically removes fixed electronic patterns sometimes called bias and dark current NOTA BENE The sky and the object sky have to be sampled equally integrating more on the object sky than on the sky will not improve the overall si
115. sets The dashed arrows on the two left panels in the top row show the a designated patterns see Table 18 For clarity the maps of Jitter25s and Jitter30r1 are blown up and the numbering is omitted in the lower right side panel VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 position either 1 or 4 exposures offset by half pixel size microsteps The default value is Single and it doesn t use microstepping It is strongly recommended to keep this parameter with default Single value and not to use microstep From preliminary results from commissioning we expect a complicated PSF shape as the result of microstepping Therefore the Pls should discuss the microstep strategy with ESO and CASU The science observation sequence can be summarized in the following program listing in case of the default nesting Science Template Execution Sequence If SEQ NESTING is FPJME then For each science filter Select science filter Determine telescope focus for science filter For each pawprint If SEQ REF FILE pawprint is not a blank or null string then If SEQ REF FILE pawprint file exists then Define new guide star setup parameters from SEQ REF FILE pawprint Else Issue warning and define new guide star setup parameters to select stars on the fly from online cataloger Endif Else Keep previously defined stars Endif For each jitter offset For each microstep offset Convert X Y ROT offset into ALPA DELTA ROT offset Offset telescope
116. sors are also shown The gaps between the detectors are 10 4 and 4 9 arcmin along the X and Y axis respectively Each detector covers 11 6x11 6 arcmin on the sky North is up and East is to the right for rotator offset 0 0 0 339 arcsec px on the sky and each detector covers a 694 694 arcsec area of sky The 16 detectors cover 274 432 mm x216 064 mm on the focal plane which gives a nominal field of view of 1 292x1 017 deg on the sky To ensure the flatness of the focal plane assembly FPA all pixels are enclosed between two planes separated by 25 um measured along the optical axis of the camera In other words the distance between the most deviating pixels measured along the optical axis is 25 um The Nyquist sampling suggests an image quality of 0 68 arcsec but it is expected to gain a factor of 0 7 yielding FWHM 0 5 arcsec in resolution because of the sub pixel sampling The science detectors are sensitive over the wavelength range 0 85 2 4 um The detector readout time is 1 sec and the size of a single file is 256 7 MB The mean quantum efficiencies of all 16 detectors are Z Y J H Ks 70 80 90 96 92 A plot of the quantum efficiency as function of wavelength for this type of the detectors in shown in Figure 6 In addition the combined losses due to reflection off all VIRCAM lens surfaces are 3 596 The science detectors are read out simultaneously by four enhanced ESO IRACE IR controllers with a total of 256 simu
117. st of times for each filter Single NDIT or list of NDITs for each filter Name of jitter pattern as listed in instrument package Maximum size of a randomized jitter in arcsec onds Number of points in a randomized jitter Multiplier for each jitter step 1 normal Filter Pawprint Jitter Microstep Exposure nesting FPJME PFJME FJPME A TCS setup file defining new AG and AO stars for each pawprint Name of tile pattern as listed in instrument pack age Multiplication factor for each tile step 1 normal overlap Name of microstep pattern List of science filters to be sequenced Is object extended jenueW 49S VLSIA NVOUIA 2000 00090 OS A3 NVI SIA 69 VIS MAN ESO 06000 0002 P2PP Label List of integration time s List of number of integra DET1 NDIT tions Name of jitter pattern Maximum size of jitter Number of jitters Jitter scale multiplier Nesting Name of microstep pattern VIRCAM VISTA User Manual List of science filters Is object extended 70 Table 22 VIRCAM VISTA paw print template VIRCAM_img_obs_paw and photometric standard star template VIRCAM_img_cal_std parameters Parameter which are typically updated by users are highlighted Parameter Type Range Default Description DET1 DIT numlist 0 0 3600 0 Single integration time in seconds or list of times for each filter intlist ISF Single NDIT or list of NDITs for each filter IR NDIT RANGE SEQ JITTER ID parameter ISF JIT Name of
118. sually 0 15 0 2 mag At the same time the larger VISTA telescope size leads to saturation of the brighter stars so typically the useful magnitude range is limited to 12 14 mag in all bands VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 The photometric zero point is derived individually for each image from measurements of stars in the 2MASS Point Source Catalog PSC by solving the equation for each filter and detector ZPVIRCAM Minstr Momass CT J H auAss const 1 for all common stars above a threshold signal to noise in the PSC and unsaturated in VIRCAM Here Z Py rgcAM is the VIRCAM zero point minst 2 5xlogio counts sec is the VIRCAM instrumental magnitude moy Ass is the 2MASS PSC magnitude J H oy Ass is the 2MASS PSC star color and const is an offset which may be required to transfer some passband to the Vega system The 2MASS based photometric calibration is the primary calibration strategy for VISTA 2 Calibration from Standard Star Fields A small fraction of the VISTA observing time is devoted to observations of standard stars The evening and morning twilights will be used for taking pho tometric calibration data as a rule we will observe a faint UKIRT standard in ZY J in the evening useful also for measuring the sky brightness and if some time remains at the end of the night that can not be filled in with science observations we will observe additional standard s in all broad band filters inclu
119. t deg S 0 W 90 ESO TEL DATE not set TCS installation date ESO TEL DID ESO VLT DIC TCS 01 00 Data dictionary for TEL ESO TEL DID1 ESO VLT DIC VTCS 0 2 Additional data dict fo ESO TEL DOME STATUS FULLY OPEN Dome status ESO TEL ECS FLATFIELD 0 Flat field level ESO TEL ECS MOONSCR 0 58 Moon screen position ESO TEL ECS VENTI 1 00 State of vent i VIRCAM VIS TA User Manual HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL T
120. t jitter fixed pattern pre generated with a random number generator Random Use value set for amplitude of the This is not a fixed pattern but generated with random jitter pattern a given amplitude when the OBs are created new observing constraint that limits how close to the evening twilight the constraint is NOT applied to the morning twilight their observations can be carried out in addition to the usual ones seeing sky transparency airmass moon distance and fractional lunar illumination This section reviews the new twilight constraints and the operational consequences from its application The time scale on which the sky brightness varies after the evening sunset and before the morning sunrise can be estimated from the plot in Fig 14 Note that the time scale on the X axes is in hours after sunset and before sunrise while while in P2PP3 the constraints sets must be specified in minutes after the end of the astronomical evening twilight no constraint is applied to the morning twilight The following conclusions can be drawn from these plots e the Z Y NB118 and J bands suffer from the effect of the excitation of the OH sky lines until after 1 5 2 hr after the end of the twilight e the night to night variations are large and they are comparable to the amplitude of the overall trend even after one hour after sunset or before sunrise e the brightness of the sky is largely unaffected by the morning twilight Recommend
121. ter shifts this is not currently implemented but is under consideration as a software enhancement If it is implemented a simple co add of LOWFS images with a shift by the nearest integer number of pixels will be used There is only one case when a significant overhead from the LOWFSs may arise after a telescope slew giving a large gt 10 deg change in altitude and the AO priority is set to HIGH in this case From http casu ast cam ac uk surveys projects vista technical ohotometric properties VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 there will probably be a need for a 45 sec pause for one LOWFS cycle to be completed to update the M2 position at the new altitude before science observing can re start see Sec A 4 Given the LOWFS fields 8x8 arcmin of view generally a jitte move of 15arcsec will re use the same guide and wavefront sensor stars by simply offsetting the selected readout window in software whereas a tiling move of 5 10 arcmin nearly always will require different guide and AO reference stars to be selected after the move There are various graceful degradation modes in the event of hardware failure of one sensor unavailability of stars etc these include reducing the autoguider frame rate and or operating with one LOWFS and 3 axis M2 control There is no non sidereal guiding and no closed loop wavefront sensing during tracking of a non sidereal target 6 6 High Order Wavefront Sensor Operation
122. ter the distortion correction are 100 miliarcsec and they seem to be dominated by the 2MASS coordinate errors The distortions are wavelength i e filter dependent It is necessary to remove the distortion before combining images taken at different jittering positions by means of non linear pixel re sampling The radial scale variation due to the distortion has also an impact on photometric measurements inducing an error of up to 3 5 in the corners of the field compared with the center The WCS distortion terms are measured from on sky observations based on the 2MASS PSC as trometry in the system of the International Coordinate Reference Frame ICRF The astrometric calibration is carried out in parallel with the observations and doesn t require dedicated time Ta ble 12 The camera software writes initial WCS parameters values into the FITS headers of each raw data frame based on the guide star position The accuracy is better than 2 arcsec and it depends on the guide star coordinates accuracy and the accuracy with which the camera geometry is known After the instrumental signature removal the pipeline uses this initial approximation as a starting point for orientation of the data frames and location of astrometric stars for a full WCS solution that provides refined scientific quality astrometry The astrometric stars are centroided in the data frames to typically 0 1 pixel accuracy The uncertainty of the final astrometric solution come
123. the Survey Teams Instead the general users have free access to the Phase 3 products delivered by the Survey Teams to ESO via the ESO Science Archive A good source of technical information on the CASU data processing is http casu ast cam ac uk surveys projects vista technical Up to date information about the progress of the data processing can be found at http apm49 ast cam ac uk surveys projects vista data processing VIRCAM VISTA User Manual Parameter units QC APERTURE_CORR mag 2 arcsec diameter aperture flux correction QC BAD_PIXEL_NUM Number of bad pix els detector QC BAD_PIXEL_STAT Fraction of bad pix els detector QC CROSS TALK Aver age values for cross talk component matrix QC DARKCURRENT ADU sec Average dark current on frame QC DARKDIFF MED ADU Median new library dark frame QC DARKDIFF RMS ADU RMS new library dark frame QC DARKMED ADU Median dark counts QC DARKRMS ADU RMS noise of combined dark frame QC ELLIPTICITY Mean stellar ellipticity QC FLATRATIO_MED Median new library flat ratio QC FLATRATIO RMS RMS new library flat ratio QC FLATRMS RMS flat field pixel sensitivity per detector QC FRINGE RATIO Ratio of sky noise before after fringe fit QC GAIN e ADU Gain VIS MAN ESO 06000 0002 Table 13 Quality Control Parameters Description The aperture flux correction for stellar images due to flux falling outside the aperture Determined using a curve
124. the linearity constraint the frequency of the sky sampling determines the NDIT The observer can verify the choice of the sky sampling frequency by subtracting sequential images from one another and by monitoring how large is the average residual Ideally it should be smaller than or comparable to the expected Poisson noise but this is rarely the case Usually a few tens or a few hundred ADUs are considered acceptable by most users VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Finally the total integration time is accumulated by obtaining a certain number of images specified by the total number of exposures offsets the number of jitterred images at each position the number of microsteps and the location of the object in the field of view note the overlapping areas at the edges of the detectors in Figure 20 that get longer total exposure time If relatively long integrations are necessary it is simply a matter of increasing the number of exposures respectively the number of tiles or pawprints However in the cases when the total required time can be accumulated in less than 5 7 exposures it might become difficult to create a good sky for the sky subtraction especially if the field is crowded because the sky image may contain residuals from the stellar images that will produce holes in the sky subtracted data This situation will require to adopt a strategy with an increased number of exposures above 5 to 7 It might be possible to com
125. the user to estimate the sky concentration and the illumination corrections based on the phorometry of the same sourceses either a single photometric standard is used or a large number of field stars to avoid variability issues However the illumination correction can also be estimated from the spatial trends of photometric zero points derived from the 2MASS stars in each science field The standard star template VIRCAM img cal std is used to obtain a sequence of a standard star or standard star field for an additional photometric consistency check independent from the zeropoints measured in the science fields The parameters of these two templates are listed in Tables 22 and 23 A 7 Template Parameter Tables Tables 19 20 21 22 and 23 list the parameters of the available VIRCAM VISTA templates except for tile6sky wich is nearly identical Table 19 VIRCAM VISTA acquisition template VIRCAM img acq tile parameters Parameter which are typically updated by users are high lighted P2PP Label FITS header Parameter Type Range Default Description imported via xml file from SADT and translated to the target section of P2PP RA TEL TARG ALPHA coord 000000 240000 Alpha for the target in HHMMSS TTT DE TEL TARG DELTA coord 900000 900000 Delta for the target in DDMMSS TTT Equinox TEL TARG EQUINOX parameter J2000 Equinox expressed as year Proper motion in RA TEL TARG PMA number 500 500 0 0 Proper Motion Alpha in arcseconds
126. the users a better control over the conditions under which their observations will be executed we introduced a VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Table 9 Maximum Jitter Amplitudes for different jitter patterns The actual deviation from the central position during the jitter is Maximum Jitter Amplitude i e it is half of the total extension of the jitter pattern movement The different patterns are described in Sec A Table 18 and they are plotted in Fig 26 Jitter Pattern Maximum Jitter amplitude arcsec Short jitter pattern description Single 0 No jitter Jitter2d 10 xJitter Scale Multiplier 2 point jitter top left to bottom right Jitter2u 10 xJitter Scale Multiplier 2 point jitter bottom left to top right Jitter2da 20 x Jitter Scale Multiplier 2 point jitter bottom left to top right Jitter2ua 20 x Jitter Scale Multiplier 2 point jitter top left to bottom right Jitter3d 10 xJitter Scale Multiplier 3 point jitter top left to bottom right Jitter3u 10 xJitter Scale Multiplier 3 point jitter bottom left to top right Jitter4u 14 xJitter Scale Multiplier 4 point jitter rotated u shape Jitter5n 9x Jitter Scale Multiplier 5 point jitter rotated n shape Jitter5z 14x Jitter Scale Multiplier 5 point jitter rotated z shape Jitter9s 14x Jitter Scale Multiplier 9 point jitter rotated square shape Jitter25s 14x Jitter Scale Multiplier 25 point jitter spiral pattern Jitter30r1 10xJitter Scale Multiplier 30 poin
127. tial offset on the focal plane in mm This is set hard coded to zeros corresponding to the center for normal survey observations in the acq tile template but must be set correctly to non zero values for pawprint observations if it is required to center targets on the respective detectors The offsets that would center a target on individual detectors are listed in Table 15 Active optics priority Optional for the users to specify if the low order active optics corrections have HIGH NORMAL or LOW priority with respect to the science observations This parameter should be set to HIGH if the requested seeing is about 1 0 arcsec or better For now there is a more complex logic in place considering that the AO can be run in parallel to the science observations The AO priority defines an altitude and time difference within which a AO correction is considered as valid Only in the case of HIGH priority it will wait for a first valid correction For short exposures when the AO can not be done in parallel the template will however wait for one loop AO if there is no valid AO correction done Please note that the definition of the AO priority will be reviewed after the experience of science verification and dry runs Confirm guide star and Confirm active optics select if the operator will be asked to confirm starting the autoguiding and low order wave front sensing based on his evaluation of the AG and AO performance It is recommen
128. tiles with sizes listed in Table 16 do not follow well the lines of constant declination The users should keep this in mind when observing areas with Dec 60 deg where the effect is strongly pronounced The same effect is present near the Southern Galactic pole if the survey is defined in Galactic coordinates Refer to the SADT Cookbook for more detailed instructions how to address this problem These and other related issues are discussed in greater detail in the SADT Cookbook The observations are carried out in service mode by the ESO Paranal Science Operations During the VIRCAM VISTA nominal operating mode for science observations the camera and the tele scope are driven by the pre defined OBs The instrument is actively cooled the IR detector system is continuously taking exposures The images are only recorded upon command triggered by an executed OB In normal conditions the filter wheel moves periodically to exchange filters upon re quest the AG and LOWFS sensors are continuously recording images and passing data to the TCS for the active optics operation The raw data are subjected to quality control They are delivered via USB disks to the ESO Science Archive in Garching and are made available to the Pls upon request 7 3 Twilight Constraints Infrared instruments are commonly used for observations in twilight but the bluest VIRCAM VISTA filters can be severely affected by the the elevated sky background during twilight To give
129. tion and derived physical parameters etc are also available via the ESO archive for the ESO Public Surveys This manual is divided into several sections including a technical description of the telescope and the camera a section devoted to the observations with VISTA including general information about the nature of the infrared sky the operation of VISTA the sensitivity of the instrument and a prelimi nary calibration plan Next the manual summarizes the data flow the pipeline and the parameters that are used for the quality control Finally the Appendix contains a template reference guide This manual was based on many documents kindly provided by the VISTA consortium The authors hope that you find it useful in your VISTA observations The manual is continuously evolving with the maturing of the telescope and there will always be room for improvement Comments from the users are especially welcomed Please refer to the ESO VISTA web site for contact details Nota Bene e The web page dedicated to VIRCAM VISTA is accessible from the La Silla Paranal Observa tory home page at http www eso org sci facilities paranal instruments vircam You will find there the most up to date information about VIRCAM VISTA including recent news efficiency measurements and other useful data that do not easily fit into this manual or 1A wide field visible camera was considered during the early stages of VISTA development accounting for the visible
130. tion model Measure of WCS shear after normalizing by plate scale and rotation ex pressed as an equivalent distortion angle Gives a simple measure of dis tortion problems in WCS solution The magnitude of a star that gives 1 detected ADU s or e s for each de tector derived using 2MASS comparison stars for every science observation This is a first pass zero point to monitor gross changes in throughput Extinc tion will vary over a night but detector to detector variations are an indication of a fault The magnitude of a star that gives 1 detected ADU s or e s for each de tector derived from observations of VISTA standard star fields Combined with the trend in long term system zero point properties the ensemble average zero point directly monitors extinction variations faults mods in the system notwithstanding The photometric zeropoints will undoubtedly vary slowly over time as a result of the cleaning of optical surfaces etc This is a label for the standard star catalog used to calculate the photometric zeropoint 51 VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 9 References and Acknowledgments This manual was based on many VPO documents among which was the VISTA IR Camera Soft ware User and Maintenance Manual VIS MAN ATC 06080 0020 Version 2 8 from 29 April 2008 prepared by Steven Beard The introduction and the general IR imaging sections are partly based on the Sofl and SINFONI user manuals
131. tion of the temperature The background in Ks can vary by a factor of two between the winter and summer months but is more stable than the J or H band background on minute long time scale It also depends on the cleanliness of the primary mirror Imaging in broadband Ks can result in backgrounds of up to a couple of thousand ADU sec 1 depending strongly on the temperature and humidity The Moon has negligible influence on the sky background longward of 1 um However the back ground in Z and Y filters can be affected The IR window between 1 and 2 5 microns contains many absorption features that are primarily due to water vapor and carbon dioxide in the atmosphere These features are time varying and they depend non linearly on airmass The atmosphere between the J and H bands and between the H and Kg bands is almost completely opaque The atmospheric transmission between 0 5 and 2 5 microns is plotted in Figure8 middle panel As the amount of water vapor varies so will the amount of absorption The edges of the atmospheric windows are highly variable which is important for the stability of the photometry in J and Ks filters but to a lesser extent for Js These difficulties have led to the development of specific observing techniques for the IR These techniques are encapsulated in the templates see for details Appendix A that are used to control VIRCAM and the telescope It is not unusual for the objects of interest to be hundreds or even thou
132. to pawprint jitter and microstep offset If new guide stars are available then If TEL AG START is TRUE then If AG CONFIRM is TRUE then Prompt operator to confirm autoguiding End if Wait for autoguiding to start End if If TEL AO START is TRUE and AO PRIORITY O then Wait for active optics to start End if Endif Get WCS information from TCS Calculate dwell time NEXPO DIT NDIT and inform TCS For each exposure Define header parameters TILE ID TILE I TILENUM NJITTER JITTRNUM JITTR ID JITTER I JITTER X JITTER Y NUSTEP USTEPNUM USTEP ID USTEP I USTEP X USTEP_Y Set WCS parameters VIRCAM VISTA User Manual VIS MAN ESO 06000 0002 Make exposure Next exposure Next microstep Next jitter Next pawprint Next science filter Else if SEQ NESTING is PFJME then Else if SEQ NESTING is FJPME then End if Number of exposures taken with a science observation template For N filters in the list 6 pawprints taken within the tile6 template 5 jitter positions of the jitter5x pattern and 2 microstep ex posures one would obtain Nx6 x5 x2 N x60 exposures written on the disk in 60 different fits files Each exposure is the sum not the average as is the case with most other ESO IR instruments of NDIT individual detector integrations of DIT seconds A 5 2 VIRCAM img obs tile6sky This template is used to observe extremely crowded fields and or extended objects that cover large fraction of the VISTA field of view makin
133. ttp www eso org sci observing phase2 P2PP3 P2PP3Documentation html ESO SADT page http www eso org sci observing phase2 SMGuidelines SADT html http www eso org sci observing phase2 SMGuidelines SADT VIRCAM html VIRCAM VISTA Science Archive at ROE http horus roe ac uk vsa www vsa browser html VIRCAM VISTA Science Verification http www eso org sci activities vistasv html VIRCAM VISTA Consortium http www vista ac uk index html VIRCAM VISTA at UK Astronomy Technology Centre http www roe ac uk ukatc projects vista eso html Cambridge Astronomical Survey Unit CASU http casu ast cam ac uk http www ast cam ac uk mike casu index html VIRCAM VISTA Data Flow System VDFS at CASU http www ast cam ac uk vdfs www maths qmul ac uk jpe vdfs VIRCAM VISTA User Manual VIS MAN ESO 06000 0002 Wide Field Astronomy Unit WFAU http www roe ac uk ifa wfau Astronomical Wide field Imaging System for Europe Astro WISE http www astro wise org Deep Near Infrared Survey of the Southern Sky DENIS http cdsweb u strasbg fr denis html The Two Micron All Sky Survey 2MASS at IPAC http www ipac caltech edu 2mass UKIRT IR Deep Sky Survey http www ukidss org VIRCAM VISTA User Manual 3 Abbreviations and Acronyms VIS MAN ESO 06000 0002 5 The abbreviations and acronyms used in this manual are described in Table 1 FITS FOV FPA FWHM GFRP Table 1 Abbreviations and Acronyms used in this m
134. ument set up requires 0 40 sec depending on the length of the filter wheel movement VISTA is an alt azimuth telescope so that the sequential presets between objects on the North and the South take long time and should be avoided if possible Therefore the users should try to combine in a separate group OBs located North or South to optimize the short term OB scheduling The Low Order Wavefront Sensor LOWFS is used to update the position of the secondary mirror VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Table 11 VISTA and VIRCAM science observation overheads Current and historical values are shown for completness Action Overheads sec P84 P86 P87 Preset for a single 120 120 non concatenated OB 120 120 Preset 20 distance deg 1 degs 1 20 distance deg 1 degs GS handling 3 3 AG start 5 5 AO start 45 45 Filter change 21 40 21 40 Detector readout 2 per DIT 2 per DIT Writing FITS to disk 4 4 Pawprint change 10 15 Jitter offset 3 8 Micro step 4 4 during observations and needs data for a minimum time of 45 sec to smooth out seeing variations The initial AO set up requires about 45 sec Later on the LOWFS can operate in parallel with science observations It takes 45 sec for one closed loop LOWFS cycle to complete and update the M2 position before science observing re starts Therefore if the telescope stays in one position for gt 45 sec there is no extra LOWFS overhead but if the telescope moves more o
135. user defined position covering only a third part of the VIRCAM field of view VIRCAM img acq quick VIRCAM img obs paw or VIRCAM img cal std or VIRCAM_img cal_illumination VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 In the latter case it will be required to provide the xy offsets to center the target on one of the detectors if it is not intended to center the user provided field coordinates between the detectors in the center of the field of view of the camera After the relevant template parameters are set remember to set the User priority under sched ule tab on P2PP main window After all the parameters of the template OB are set selecting this OB run File Import Survey Definition to create final OBs but updating the coordinates and importing the relevant information about guide stars Revise the user priorities and if relevant define time delays for the time linked OBs and group contributions for the OBs combined in groups Finally prepare the README and submit OBs In addition to the above cookbook steps you can also look at the manuals tutorials on how to prepare the Survey Area and OBs available at http www eso org sci observing phase2 SMGuidelines SADT html http www eso org sci observing phase2 P2PPSurveys html Since it is not guaranteed that your preparation would survive all future changes at software and template level Export all OBs and containers and save the resulting ascii files at a con
136. variations of the transfer function across the field VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 e photometric zero points and extinction coefficients corresponding to the images The expected accuracy is a few percent e astrometric distortions of the images the nominal astrometric calibration is based on the 2MASS Point Source Catalog 2MASS astrometry is derived from direct calibration to TY CHO2 and it is in the ICRS system note that this requires RADECSYS ICRS in the FITS headers It is known to have average systematic errors smaller than 100mas and RMS errors smaller than 100 mas for all point sources with S N 10 e generating Quality Control measurements for monitoring the instrument health and perfor mance and the weather conditions for example the FWHM of the stellar images verifies the instrument alignment the quality of the AO correction and the seeing conditions Generally obtaining the necessary calibrations is a responsibility of the Science Operations De partment The users can only submit OBs for i extra photometric standard star observations ii observations of astrometric fields and iii illumination correction if they require additional calibration data i e obtained more frequently than envisioned by the calibration plan see Table 12 We list here the rest of the calibrations for completeness only The photometric standard star observations and the illumination correction images will be tagged
137. vements known at the VLT as offsets so the telescope move ments made by an acquisition template or by one of the observation templates are just as efficient The data acquisition efficiency would not have been improved for example by combining multiple tiles together in a single Observation Block a feature that is not forseen at the moment as long as the OBs are scheduled efficiently A number of measures can be undertaken to improve the survey efficiency use in the acquisition template the same filter as in the first science template so the filter wheel movement is carried out in parallel with the telescope movement minimize the filter movements in the science templates if possible use tile and jitter patterns which minimize the number of telescope movements if possible use the minimum total exposure time required for achieving the science goals of the survey pull together into groups OBs with nearby targets on the sky and with similar instrument set up to minimize telescope movements and instrument set ups the re prioritizing of the OBs in a started group will ensure that the telescope operator will execute first the rest of the OBs in the same group before switching to another group VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 The first and the last of the three nesting sequences might be the best suited for most VISTA pro grams because they ensure that all the observations in one filter will be car
138. vements see Sec 6 3 for the filter order The individual steps in this sequence of decisions are intertwined and often can not be separated as clearly as described in this example The tile is the basic unit of a survey being the smallest contiguous area of sky that the camera can image A contiguous survey covers the required sky regions by tessellating tiles together with a small amount of overlap The contiguous sky coverage can require some tiles to be tilted with respect to their neighbors especially near the celestial poles Figure 21 The overlaps between neighboring tiles is a user defined SADT parameter Minimizing the overlaps makes the survey more efficient but some overlaps are desirable because they provide repeated measurements that can be used to verify the internal astrometric and photometric self consistency of the survey The process of defining an observing strategy for a survey is intentionally streamlined here In fact VIRCAM VIS TA User Manual VIS MAN ESO 06000 0002 Tile 1 Tile 2 Tile 3 Figure 21 Example of a contiguous survey containing three partially overlapping tiles The curva ture of the pawprint edges is ignored many steps may have to be iterated i e the SADT re run many times modifying the survey area until an acceptable strategy is found The filter exchanges pawprint patterns jitter and microstep offsets can be executed in different order called nesting sequence Three nesting sequences
139. ween DITs HIERARCH ESO DET EXP NAME VIRCAM IMG 0BS223 0016 Exposure Name HIERARCH ESO DET EXP NO 640 Exposure number HIERARCH ESO DET EXP UTC 2009 08 11T04 54 19 8443 File Creation Time HIERARCH ESO DET FILE CUBE ST F Data Cube On Off HIERARCH ESO DET FRAM NO 1 Frame number HIERARCH ESO DET FRAM TYPE INT I Frame type VIRCAM VIS TA User Manual HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH ESO ESO ESO ESO ESO ESO ESO DET DET DET DET DET DET DET VIS MAN ESO 06000 0002 FRAM UTC 2009 08 11T04 54 19 5302 Time Recv Frame IRACE ADC1 DELAY 7 ADC Delay Adjustment IRACE ADC1 ENABLE 1 Enable ADC Board 0 1 IRACE ADC1 FILTER1 O ADC Filteri Adjustment IRACE ADC1 FILTER2 0 ADC Filter2 Adjustment IRACE ADC1 HEADER 1 Header of ADC Board IRACE ADC1 NAME VISTA AQ GRP Name for ADC Board similar entries for IRACE ADC2 to IRACE ADC15 are omitted HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH COMMENT COMMENT COMMENT ROOTHEAD ORIGIN DATE TELESCOP INSTRUME OBJECT RA DEC EQUINOX RADECSYS EXPTIME MJD OBS DATE OBS UTC LST PI COI OBSERVER ORIGFILE JITTER I JITTER X JITTER Y JITTRNUM JITTR_ID NJITTER NOFFSETS NUSTEP OBSNUM OFFSET_I OFFSET_X O
140. wn also as the Detector Integration Time DIT and it is measured in seconds Exposure the stored product in a file a sum not an average of many individual detector integrations that have been co added in the DAS Each exposure is associated with an exposure time equal to NDIT xDIT sec Microstep pattern a pattern of exposures Figure 15 left at positions each shifted by a very small movement 3 arcsec from the reference position Unlike the jitter see below the fractional i e non integral part of the shifts are specified as 0 5 pixel which allows the pixels in the series to be interleaved in an effort to increase resolution A microstep pattern can be contained within each position of a jitter pattern Note that using the microstep pattern is currently discouraged due to problems with the data reduction because the data obtained with microsteps exhibit an artificial hole pattern Jitter pattern a pattern of exposures Figure 15 right at positions each shifted by a small move ment 30 arcsec from the reference position Unlike a microstep see above the fractional i e non integral part of the shifts is any fractional number of pixels Each position of a jitter pattern can contain a microstep pattern The jitter pattern can be pre defined fixed or random In the latter case the user defines the jitter box width within which the offsets are made The jitter box width parameter is ignored if a fixed jitter pattern i
141. xml format Open P2PP select the VIRCAM observing run and create a container if needed then select container and create a new OB If containers are not needed then directly make a template OB under the current VIRCAM run folder In this template OB select templates to use and set the desired parameters i e filters in acquisition and in observing template DIT NDIT and jittering pattern and size There are two possible types of observation blocks The first type requires the preparation of a survey area before getting started In this case a large number of parameters will be properly set when importing the xml output file of SADT To get started it is required to prepare only a template OB with the proper settings in respect to filter jitter patterns exposure times constraints set and time intervals The OB for a typical wide field survey would look like the following tileN can be one of tile1 tile3 and tile6 only the tile6 one would provide a full coverage of the field of view VIRCAM img acq tile VIRCAM img obs tileN 1st filter VIRCAM img obs tileN 2nd filter optional VIRCAM img obs tileN 3rd filter optional For observations of crowded areas or object with extended sources comparable with the usual offsets it is possible to obtain clear sky images interleaved with the target images with the template VIRCAM_img_acq_tile6sky Finally it is also possible to define an OB which would take a jitter sequence on a
142. y without interruptions the order of execution is not specified if any of the OBs in a concatenation is not executed the entire con catenation must be repeated the total execution time of the OBs in a container of this type can not exceed 1 hr Time links the member OBs are scheduled whenever there is an upcoming time window defined by the users the time windows are relative but after the execution of the first OB in a time link they become absolute a time link OB will not be observed ata later time if it cannot be executed within the required time interval Groups the member OBs may be executed depending on the needs of the flexible scheduling of the observatory but the OBs in the respective groups are dynamically reassigned higher and higher priorities depending on the rate of completion of a group to increase the probability that a group that has been started is completed before other groups are started See the P2PP3 User Manual for a more detailed description of the scheduling containers 7 6 Observing Strategy Nesting The observing strategy is determined by the science goals of the program convolved with the limitations imposed by the technical characteristics and software features of the telescope and the camera VISTA is a purpose built survey telescope so VIRCAM s primary function is to produce a contiguous map of large sky areas using overlapping exposures The starting point in the survey design is to select a ba
143. yopumps The Cassegrain rotator has a full range of 540 deg so that the position angle of the focal plane with respect to the sky may be chosen freely The autoguiders are fully 180 deg symmetric so if desired one can observe a field at two camera angles 180 deg apart while re using the same guide star and Low Order Wavefront Sensors LOWFS stars but with proper paf files and re acquisition to re assign the guide stars to the opposite LOWFS The camera faces forward towards the secondary mirror The light after bouncing off the primary and the secondary enters the instrument through a 95 cm diameter entrance window and then it passes through three corrector lenses all made of IR grade fused silica and the filter wheel to reach the 16 detectors assembly at the focal plane The lenses remove the field curvature to allow a large grid of detectors to be used while controlling the off axis aberrations and chromatic effects The optical layout of the telescope camera system is shown in Figure 2 and camera cut offs are shown in Figures 3 and 4 Two fixed autoguiders and active optics wave front sensors are integral part of the camera They use CCDs operating at 800 nm roughly I band to control the telescope tracking and to achieve active optics control at the telescope to correct the flexure and other opto mechanical effects arising from both the telescope and camera parts of the system There are two Low Order Wavefront Sensors LOWFS a Hig

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