HIRES Instrument and Data Format
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1. New software was developed and old software enhanced to handle the new electronics and higher data density In addition a new field flattener was created to accommodate the increased 7 April 2006 mosaic size and the flat focal plane characteristics of the new CCDs Table 1 0 below shows a comparison of the CCD characteristics between the two devices Other most up to date characteristics of the detector mosaic can be found at http www2 keck hawaii edu inst hires usernotes pdf Table 1 0 Comparison of CCD characteristics pC dD Upgraded CCDs CTE 999997 The figure below shows the layout of the new CCD mosaic compared to the old system and how it is situated in the dewar and oriented with respect to the spectral orientation The gaps between the CCD chips are about 100 um 6 7 pixels 2 1 REV OR CHRD DATE DESCRIPTION A Ge SVA 4103 _ NSTIAL RELEASE AFTER FIRST REVIEWS Lo crc sa 5903 CORRECTED DISPERSION DIRECTION EDITORIAL CORRECTIONS SIMULATOR X COMPASS ROSETTE AT ZENITH EE A r SIMULATOR Y COLD PINGER WO ROTATOR PREL 61444096 C ris 2048 1 FITS 2048 2048 A POCAL PLANE Y ECHELLE DISPERSION OLD TEKTRONIX DIRECTION 2048x2048 POSITION POSITION 2 POSITION 3 24ym PIXEL CCD SERAL READOUT D atsin FATS 41 2048 B BLUE CCO MIO CCD l e 3 45 CROSS DISFERSION DIRECTION 3 MIT LL 2048x4096 Syn PEL CCO S VIEW LOOKING INTO DEWAR BOTTOM Tor DUT IMAGE LABELLED2. A eee l tS iT pg Figure 3 2 HIRES spectrum of an extended object This is a portion of the green middle CCD of a comet with the reflected and absorbed sunlight from the earth s atmosphere The dark lines superimposed on the bright continuum bands are primarily Fraunhofer absorption from specific elements in the Sun s atmosphere 7 April 2006 Figure 3 3 HIRES spectrum of a bright star This is a portion of the blue CCD Each spectral order is narrow the width determined by the seeing and guiding of the telescope The diagonal streak meteor can be seen toward the lower left Wavelength increases from lower right to upper left The HIRES guider camera is used by the telescope observing assistant and the observer to identify objects and to point the telescope so that the proper point source or extended object appears on the spectrograph entrance slit An example guider image is shown in Figure 3 4 Guider images are stored at WMKO on a different computer than the HIRES control computer Frequently guider images are taken and stored only for observatory engineering purposes Observers have the option to choose and save selected guider images for their own use 7 April 2006 Figure 3 4 HIRES guider image of a star field The image scale is inverted black is bright The HIRES entrance slit is faintly evident as a brighter horizontal rectangle in the center of the image The signal from the bright star left of the slit has sat
3. BY ODSERVER LOOKING INTO MIRES NOTES TOLERANCES UNS OTHORVESE NOTED FRACTIONAL aae mae avn ORIENTATIONS BASED ON AND DERIVED FROM H7260 2 AMPLIFIER NAMES A B conan x aor poot wor 3 AMPLIFIER POSITIONS THRU G ena aes E comens tae Wax 4 TEKTRONIX DUAL AMP READOUT USED AMPS B 4 A AND USUALLY FLIPPED ROWS z Figure 1 0 Layout of the new HIRES upgraded CCD mosaic 7 April 2006 At the focus of the spectrograph camera the CCD detector is held at 130 C operating temperature continuously through the use of an automated liquid nitrogen filling system The CCD focus is highly stable and has required re calibration infrequently 2 0 HIRES Image Format The data produced by the new HIRES CCD mosaic are in multiple extension FITS file format This consists of a primary header which is the first header of the FITS file followed normally by three or more extensions called header data units HDUs Each HDU contains the two standard components of any FITS file a an ASCII text header holding a list of keywords that describe the data unit of that HDU and b the binary data following it For a description of the keywords in the primary header unit visit http www2 keck hawaii edu koa public keywords koa_keywords php The number of extensions is determined in part by the number of amplifiers used and can be controlled by the PANE and PANELIST keywords In normal operations single amp readout would produce thre
4. dispersers are changed out between blue and red blazed grating mosaics by observatory personnel for specific scheduled research programs Through an exacting calibration procedure the opto mechanical position of the cross dispersers is recovered ensuring the long term stability required of the spectrograph HIRES is highly user configurable through the remote operation of motorized stages to select spectral and spatial resolution filter bandpasses grating settings to position wavelength regions of interest precisely on the CCD and focus settings of optics and the CCD to achieve high data quality It is also supplied with internal calibration sources and supplemental instrumentation including the iodine cell velocity reference sky position image rotator and photon counting exposure meter 1 1 The Upgraded HIRES CCD Mosaic On 18 August 2004 HIRES underwent a major upgrade of its detector The CCD upgrade resulted in significant improvements in the HIRES detector dewar and CCD electronics The new detector consists of a mosaic of three 2048 x 4096 15 um pixel MIT Lincoln Labs CCDs compared to a single 2048 x 2048 24 um pixel Textronix CCD of the old detector The new device has dramatically 1 improved the blue UV response shortward of 3800 A by a factor of 8 2 increased the wavelength coverage for single instrument setting 3 provided finer sampling of the point spread function PSF and 4 reduced the CCD readout noise and readout time
5. functional Amplifier modes SINGLE A or DUAL A 4B are not usable at this time An image recorded with these parameters would be 52 761 600 bytes in size assuming a fixed size for the image header Table 2 0 Default HIRES CCD readout parameters Number of postscan columns POSTPIX BO In order to increase the signal to noise ratio in the data the astronomer frequently bins the image in the spatial horizontal in Figure 2 0 direction An example bias image e g zero second no light exposed on the image taken with single amplifier readout and binned by 2 in the spatial direction 2x1 binning is shown in Figure 2 1 corresponding to the same layout displayed in Figure 2 0 This image is 26 461 440 bytes long and has a smaller postscan region 40 columns per chip An example of a flat field image taken with an internal quartz lamp is shown in Figure 2 2 Note the roughly vertical orientation of the spectral orders and the increasingly wider separations between them with wavelength The spectrum is recorded from an internal halogen light source directed into the entrance slit of the spectrograph It is used by dividing out of the science object spectra to correct for instrumental response The diagonal streak most clearly seen in the middle green chip is light that is dispersed twice by the spectrograph and is a scattered light defect Sometimes called the meteor such scattered light is not present in all HIRES spectra but mainly sho
6. taken on the same night as the science files or if they re not available those closest in time Currently the archive user interface is constraint to automatically look for associated calibrations within 3 days of the date of observations of the science targets All calibration files that match with the science files according to the above prescription within the specified date range will be returned An ascii file containing a listing of all the calibration files associated with each science file is also provided In future upgrades the calibration association algorithm will look for matching calibration files taken only on the same night as the science files moving out to neighboring nights only if a minimum number of files for each of the calibration file types has not been reached If users 7 April 2006 desire to search for calibration files over more extended time periods this option will also be implemented References HIRES User s Manual http www2 keck hawaii edu inst hires manual 1 pdf Vogt et al 1994 HIRES the High Resolution Echelle spectrometer on the Keck 10 m Telescope S P LE 2198 362
7. used to wavelength calibrate the science object spectra An example a Th Ar spectrum is shown in Figure 3 1 Table 3 2 lists keyword values that can be used to identify images as internal calibration spectra of certain types Table 3 2 HIRES internal calibration keywords Flatfield spectrum LAMPNAME quartz quartz1 or quartz2 ascii DECKNAME Same as program object DECKNAME LAMPNAME quartz quartz 1 or quartz2 ascii Focus DECKNAME D5 LAMPNAME hAr1 or ThAr2 ascii 7 April 2006 ILAMPNAME hArl or ThAr2 ascii ATCURI or 5 0 real nominal mA h Ar spectrum h Ar spectrum ON ATCUR2 Comparison mirror in beam ___ LMIRRIN in light path ascii Note that LAMPNAME is a configurable keyword so there is no guarantee that the values will match those in Table 3 2 For ThAr spectra the lamp current must also be turned on for the spectrum to be valid PrE er i hawt t 1 C8 Seay Bieta lati ERIH Figure 3 1 HIRES Th Ar comparison spectrum binned 2x1 Orientation as in Figs 1 0 and 2 0 Other images used for data calibration include spectra taken of standard stars or the sky background Standard stars fall into several categories including flux standards flat continuum stars for atmospheric telluric line removal radial velocity standards and other types Bright stars are also used to provide a trace spectrum for echelle order extraction Sky background or direct reflectance spectra are often taken in p
8. 7 April 2006 HIRES Instrument and Data Format 1 0 HIRES Instrument HIRES the High Resolution Echelle Spectrograph is installed permanently at the right Nasmyth focus of the Keck 1 telescope and was commissioned in the summer fall of 1993 The capabilities and functionality of the instrument are well described in Vogt et al 1994 and the HIRES User s Manual The instrument has arguably been the most powerful high resolution optical spectrograph ever built It has been used in a wide range of astronomical studies These include investigations into the large scale structure and history of the universe through absorption of high Z quasar spectra the structure and chemical evolution of stars and the related evolution of galaxies the chemistry and dynamics of solar system bodies and the discovery of hundreds of extra solar planets through precise time series analysis of small doppler motions of such planets around their parent stars The instrument has achieved outstanding results partly through its high opto mechanical stability and long well serviced continuity of operation HIRES was designed to be versatile through the optical spectrum covering 300 1000 nm by use of interchangeable optical components optimized for either blue or red sides of the bandpass in conjunction with a wide degree of control of the imaged spectrum by the user The interchangeable large optics include the collimating mirrors and cross disperser grating mosaic The cross
9. ages include short exposure i e generally less than 2s or zero length exposure bias images and long exposure dark images Table 3 1 lists keywords that may be used to identify bias and dark images Keywords listed with more than a single possible value might only be used to verify an image type for instance if AUTOSHUT is F then the shutter did not open and the resulting image is a bias or dark a similar discussion holds for other keywords in Table 3 1 Dark images are not frequently taken since the CCD system has very low dark current that is inconsequential for all reasonable exposure times Still a dark image can be used as a system diagnostic at any time and should be part of a long term instrument trend analysis Table 3 1 Internal calibration keywords bias or dark image Internal calibration identifier AUTOSHUT Bote Bias image exposure length TIME_____ Bhort2 s AUTOSHUT Dark image exposure length _ ELAPTIME Bias or datk image HATCLOS CE ERE HIRES is equipped with internal calibration lamps that project halogen flat field and Thorium Argon comparison sources onto the entrance slit The flat field spectrum is used to correct scientific object spectra for pixel to pixel variation in CCD response and in some cases to correct for instrumental wavelength response An example of a flat field spectrum is shown in Figure 2 2 The Th Ar spectrum provides emission lines at precise wavelengths the positions of which are
10. e extentions HDUs one for each CCD in the mosaic In dual amp readout mode the number of HDUs would double to six A schematic of the data mosaic in the single amp mode is shown in Figure 2 0 PRECOL 12 pixels cSixvh gt T o D D S o D mM C rm W W NAXIS1 2048 pixels pee Lo POSTPIX 80 pixels Figure 2 0 Schematic layout of the three HIRES CCDs in their default single amplifier unbinned format 7 April 2006 In its current default single amp unbinned format of Figure 2 0 each of the blue green and red CCD chips has a separate prescan region 12 columns wide keyword PRECOL and a postscan region 80 columns wide keyword POSTPIX The available image area of each chip is 2048 pixels wide NAXIS1 and 4096 pixels high NAXIS2 The blue green and red chips are also referred to as CCD 1 2 or 3 respectively The spectral orders run roughly up and down in the vertical direction on the chips in this schematic Wavelength increases from bottom to top and from left to right on each chip as in Figure 1 0 The HIRES CCD electronics and software are capable of reading out the current 2048 x 4096 pixel three CCD mosaic in a number of different modes The most important readout parameters corresponding keywords and default values are listed in Table 2 0 These values correspond to single amplifier low gain readout with single pixel binning Currently only one amplifier SINGLE B is
11. ection LFIL2NAME 12 same Echelle position _ ECHRAW and ECHANGL _ integer and real Cross disperser type KDISPERS BLUE RED 7 April 2006 X HIRES version 9 0 Humidity Temperatures 10 8 2 Inside Outside Rack Coolant 0 770 Jin closed closed 1 Elosed t AET Susten Disable Switch Interior Lights Figure 3 0 HIRES user interface Each motorized stage of the instrument is controlled through a menu which pops up when the stage button is selected The current position of each stage and cover is broadcast to the interface every few seconds 3 1 HIRES Calibration Images Calibration images are defined as data taken with internal illumination or without any illumination Standard internal calibrations include e Bias zero second non illuminated image e Dark non illuminated images taken at longer exposure times to measure dark current in the CCD electronics e Flat field spectra taken with internal quartz halogen illumination for each HIRES configuration setting 7 April 2006 e Thorium Argon Th Ar spectra taken with the Th Ar lamp in each HIRES configuration setting e Trace spectra taken with the D5 pinhole with internal quartz illumination to provide a trace spectrum for echelle order extraction This purpose is often fulfilled with standard stars or the program stars if sufficiently bright e Focus Th Ar spectra taken with D5 pinhole for focusing purposes Non illuminated calibration im
12. ed to be matched for the rest of the calibration file types both the instrument and CCD configurations are matched see Table 4 2 7 April 2006 Table 4 1 Instrument and CCD Configuration Keywords INSTRUMENT DESCRIPTION UNIT FORMAT EXAMPLES TOLERANCE CONFIGURATION KEYWORDS SLITWID Slit width mm float 10 21383190 0 005 SLITWIDT Slit width projected on sky arcsec F10 8 0 861 0 005 FILINAME Filter 1 A8 KV370 FIL2NAME Filter 2 A8 clear COLLRED Red collimator in Al T F COLLBLUE Blue collimator in Al T F ECHANGL Echelle angle deg F9 8 0 01441866 0 001 XDISPERS Cross disperser type A4 RED XDANGL Cross disperser angle deg F9 8 0 32800001 0 001 CCD CONFIGURATION KEYWORDS AMPMODE Amplifier mode char SINGLE B AMPLIST Amplifier list char 3 1 0 0 BINNING Binning pix ILII 2 1 MOSMODE Mosaic readout mode char B G R NVIDINP No of video inputs Il 3 PRECOL Pre column pixels pix 13 12 0 POSTPIX Post column pixels pix 13 80 0 CCDGAIN CCD gain setting char low WINDOW CCD window A25 0 0 0 2048 2048 CCDSPEED CCD readout speed char fast Table 4 2 Keywords Comparison for Association IMAGETYP Science Files Calibration Files CCD Comparison Only Both Instrument and CCD Comparison Object Bias Flatlamp Dark Trace Arclamp Focus The best set of calibrations is defined to be those
13. lanetary programs to provide a solar spectrum for subtraction from the scientific object spectrum 3 2 Program Object Images The scientific versatility of HIRES means that the instrument is used to observe a number of classes of objects by astronomers These include but are not limited to the following e Point source spectroscopy of faint objects e g quasars and faint stars 7 April 2006 Point source spectroscopy of bright stars Extended source spectroscopy of faint objects e g galaxies some planetary objects Extended source spectroscopy of bright objects e g planetary objects comets Point source velocity calibrated spectroscopy of bright stars e g planet hunting with the use of the iodine cell Each observing program will be conducted in the manner determined by the PI The resulting data will therefore be organized and calibrated in different ways Two example program object spectra are shown in Figure 3 2 extended object spectrum with a superimposed sky background and Figure 3 3 point source spectrum of a star ee ENEN 2 SSE T SSE u FE 2 NSS SS A I E E EE E k 2a EE GS E BE 2 N S SS sae AN meee ee Ei EIE i iE i ai FEIFEEN I TIE nE nifi PIREN EM OS RE 2 212 i EFL es pim Se EE e e E ar j JERE E WE i eed a pIE AES paip TEER t l y aire pE eee SRT Bs pi GBS b 239 roger omc o menee aea S EEA i ee eRe t 5 Re SE SS EENEN AE Ar a A E FRE E
14. urated the CCD causing the charge to bleed in the vertical direction 4 0 HIRES Data Set Definition for the Keck Observatory Archive The HIRES dataset consists of a set of image files of several types As discussed above these image categories can be further subdivided as follows 1 Calibration images 2 Scientific program object images For the purposes of the archive a HIRES dataset is defined as all spectra taken with the same instrument and CCD configurations A simple method of linking science targets with the appropriate calibration files is to say that all calibrations taken on the same night as the science target and with the same configuration is part of that objects dataset The basic set of calibration files consist of a number of flats ThAr arc lamp bias and or darks A trace or focus spectrum taken through a pinhole may also be present The calibration files can be distinguished from each other and from the science files by their IMAGETYP header keyword Association of a science object with calibration files is made in near real time as an archive query is sent A calibration can be associated with a target by comparing certain keywords that define both the instrument and CCD configurations see Table 4 1 A pair of science and calibration files is said to be associated if these keyword values are identical or matched within the specified tolerances For bias and darks only the CCD configuration keywords ne
15. ws up in bright flat field and star images at certain HIRES spectral settings More details on internal calibration images are found in section 3 1 7 April 2006 Figure 2 2 HIRES flat field image in its 2x1 binning format Orientation as in Figs 1 0 and 2 0 7 April 2006 3 HIRES Configurations and Image Types The HIRES is very broadly configurable through its user interface which controls the selection and positions of instrumental components through remote operation of motorized stages The HIRES user interface is shown in Figure 3 0 The user interface provides a schematic of the instrument light path a status display with broadcasts of the current position of each motorized stage and individual and compound control of the motorized stages through pop up menus and a multitasking utility called GO Components which form a basic HIRES instrumental configuration include e Slit or decker size e Wheels behind the slit filter 2 each 12 position e Collimator selection including focus which is accomplished through a look up table e Echelle grating position e Cross disperser type e Cross disperser grating position Table 3 0 lists keywords which describe the above configuration parameters Table 3 0 HIRES Instrumental Configuration Parameters Configuration Keyword Possible values parameter Slit decker IDECKNAME 30 ascii configurable but generally fixed Filter wheel 1 selection LFILINAME 12 same Filter wheel 2 sel
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