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UV-Visual Echelle Spectrograph (UVES) User manual

1. Instrument Features and Problems to be aware of 2 4 1 Spectral gaps in the Red Arm 66 ease 0 4 Hee OA RR 2 4 2 Optical Ghosts in the far red and UV spectra 2 4 3 Remnants of ThAr lamp spectra 4 44 4 444 pacs E Dad ad 2 4 4 Enhanced Dark Current after a FIERA start up 2 4 5 CCD Cosmetic Defects 2 4255 414 woe Ee EEN EES 2 4 6 Telluric features in flatfield exposures Preparing the Observations 3 1 3 2 3 3 3 4 3 9 Rea ser e DS BUD Re OA ee ee ea Se UVES instrument modes and basic choices UVES Standard settings EEN NEAR SME ew Ai RR Introducing Observation Blocks A EE daca ENA A 2444 Rapid Response Mode for UVES s ssc au veu es aus 06444 60 44 vil I On OO TO NO NY Fa 10 10 13 13 16 18 18 20 21 21 21 24 24 24 25 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 1825viii 3 6 The UVES Exposure Time and Spectral Format calculator 33 3 6 1 Definition ofthe target s ss s sse sos sida paia wie hate pa 33 3 6 2 Choice of instrument configuration and spectral format 33 3 6 3 Exposure time and predicted counts and S N ratios 34 3 7 Target Acquisition and Guiding 4 4 oe dau cesis carioca ricos 37 3 8 Computing time overheads for your program 38 Oe Ege so so ee BA ee he ee a a s E a a ee 39 4 The calibration of UVE
2. Date Section Parag affected Reason Initiation Documents Remarks Issue 76 01 06 05 2 2 1 3 3 amp Tab 3 1 update for P76 new setting with IS 3 and DIC2 760nm new standard setting RED600 w o iodine cell UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 1825vi This page was intentionally left blank Contents 1 Introduction 2 Li 12 1 3 1 4 1 5 1 6 1 7 1 8 19 On the contents of the UVES User Manual Information available outside this manual Capabilities of the Instrument A4 gg share res tee e UV ES within the VLT Observatory 4 spa aa at Lis at bee How to access UVES sample calibrations and observations High resolution spectrographs at ESO La Silla Pee e c A A RE ORR ERA OSS A RER RER KES RS ROO eat So ore eo BO he ee ee Se ee O 10e ae Abbreviations and Acronyms 244 Los mm be eu Ae NN ne EE RA Instrument Characteristics 2 1 A 2 3 2 4 Conseil layout A Ar ASE SUMMER E e D ES Lesen BUD cc st he whee palin a mL Elta meer 2 2 1 The preslit system 2 sos die t died EA EA E AE ER 2 2 2 Lhe wo specteograph MMS o se dd ae hb Ee niaire du 2 2 9 The Slit Viewer CODS oa cosce ed na ERE eee DE REE H ER 2 2 4 The Scientific CCDs and the associated shutters Spectral Resolution and Overall Efficiency
3. The Depolarizer slide can be used to insert a rotating 2 plate in the beam to cancel any intrinsic or telescope induced polarization that might affect the detected signal level since UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182516 also some UVES components notably the cross dispersers have a polarization dependent efficiency No strong instrumental polarization effects have been measured so far The Pupil Stop slide is used to insert a stop at the position of the image of M2 that is produced by the derotator This is required because apart from the sky baffle ring around M2 the telescope is not baffled so that the instrument may see the sky around M2 beyond this ring Three stop positions are available 1 regular stop a slightly oversized 2 stray light mask to stop any sky radiation bypassing M2 2 undersized stop a 6 undersized mask that provides a very stable pupil entering the instrument 3 unused The regular stop is the default one The undersized stop results in a light loss of 13 but has the advantage that the telescope and calibration light beams are perfectly stable and identical It is offered for high accuracy radial velocity measurements with the iodine cell only The Arm Selector unit has four positions Free direct feed to the red arm Mirror 1 to feed the blue arm Dichroic 1 and Dichroic 2 to feed both arms When the UVES main beam is stopped by the shutter the backside of M
4. The light from the lamps is fed into the instrument beam by 45 mirrors mounted on a slide Table 4 2 lists the lamps and exposure times with 1 arcsec slit to be used for four of the standard settings the ones with central wavelengths 346 437 580 and 860 nm respectively The exposure time of ThAr frames is to a first order independent of slit width The exposure time of flatfields is inversely proportional to the width In the corresponding dichroic modes the exposure times should be increased by 10 All exposure times have to be scaled with respect to gain and binning factors When using image slicers the exposure times have to be scaled according to the exit slit width of the slicer and the efficiency of the slicer 4 3 Calibration in wavelength The ThAr lamp provides accurate wavelength calibrations over the complete spectral range when the UVES matched line table available from usd help eso org is used The rms of the wavelength fit is typically better than 0 0002 nm ThAr exposures can be taken immediately after the science exposures to minimize the effects 40 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182541 Table 4 1 UVES Science Data Calibration Plan per instrument and detector setting Calibration number frequency 1 days purpose Flatfields 5 1 3 creation of master flats attached Flatfields n oT high precision flatfielding Wavelength 1 1 1 dispersion solution resolving powe
5. case of UVES two gratings One is the echelle grating the other one is called the cross disperser grating UVES hosts two cross dispersers each with two different gratings The cross disperser grating determines the distance between the echelle orders Decker Reflecting movable blades placed in front of the slit and determining its length Derotator This element not to be confused with the telescope adapter rotator unit is placed in the diverging beam coming from the telescope and compensates for field rota tion which is inherent to the Nasmyth focus Dichroic This element in the UVES mode selector reflects all the light below a certain wavelength and is transparent for longer wavelengths This allows the operation of the spectrograph using both spectrograph arms simultaneously Grating The main light dispersing elements of UVES are two echelle gratings one blue one red optimized Flatfield Spectrum obtained from light source with a flat i e without spectral features energy distribution e g a tungsten lamp The registered signal provides information about the response of the detector allowing a determination of the variation in sensitivity from pixel to pixel the echelle order shape the presence of bad columns on the detector etc Guide star A point source used for accurate tracking and active control of the telescope mirrors Image slicer This device converts a two dimensional image e g of a star in the foc
6. gt 500 nm 3 1 5 x 2 0 30 10 0 5 110 000 73 400 1000 nm The Image Slicer slide can be used to insert one out of three image slicers IS which reformat the 2D image of a rectangular area in the F 15 focal plane of the telescope into a narrow slit which is imaged on the spectrograph entrance slits The IS is inserted in the beam before the field derotator and thus no spatial resolution is possible Their entrance dimensions and output format are given in Table 2 1 The efficiencies given there are the optical transmission of the slicers The users can acquire the target through an image slicer to obtain spectra at the highest spectral resolution slit projection 2 pixels on detector or intermediate resolution R 60 000 without the strong losses of a narrow slit lt 1 during periods of mediocre seeing The spectrograph entrance slit will be automatically adjusted to the width of the virtual slit produced by the image slicer The actual gain with respect to a standard observation through a narrow slit depends on the value of the seeing and is shown in Fig 2 3 The turnover points where the use of a slicer is giving a better efficiency than the use of a narrow slit are at a seeing of gt 0 7 for IS 1 gt 0 5 for IS 2 and gt 0 3 for IS 3 slightly depending on the actual wavelength of the observation The length 7 9 of the 1 and 2 image slicer slits is smaller than the minimum
7. in service mode With this setting the 500 600 nm spectral range in which the iodine cell provides the highest density of absorption lines is placed completely on the EEV chip of the red CCD mosaic This allows the best possible reconstruction of the instrument profile IP in the subsequent data modeling because the EEV does not suffer from charge diffusion as the MIT chip which leads to an apparent degradation of the spectrograph resolution Finally the free Observation Templates can be used when the offered standard settings are not appropriate for a given program however in visitor mode only UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182531 346mn 390mn 437mn 520mn S80mn 860mn order separation arcsec 60 80 100 120 140 160 order Figure 3 1 Measured separations in arcsecs of the spectral orders in crossdispersion direction for the 4 crossdispersers at standard wavelength settings On the abscissa the physical order numbers of the red and blue echelle gratings are given UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182532 3 4 Introducing Observation Blocks An Observation Block OB is a logical unit specifying the telescope instrument and detector parameters and actions needed to obta
8. service mode SM observations 27 28 38 43 data package 49 data processing 2 sky baffle ring 16 Skycat 37 slit lengths 30 slit viewer SV CCDs 16 18 standard setting 8 27 30 39 43 47 48 standard stars 43 flux table 43 list 51 telluric features 25 template 8 32 acquisition template 32 37 46 attached calibration template 41 free template 30 33 39 observation template 28 32 reference guide 2 6 signature file 9 std observing template 43 tilt tables 17 18 user manual webpage 1 visitor mode VM observations 2 27 45 general 45 wavelength calibration 9 24 27 28 32 40 ThAr lamp 38 40 42 ThAr lines table 51 UVES User Manual VLT MAN ESO 13200 1825 This page was intentionally left blank 59 UVES User Manual VLT MAN ESO 13200 1825 000 96
9. the shutter open only and it is due to a glowing of the camera optics The CCD parameters are periodically remeasured as part of the UVES calibration plan 2 The updated values are entered in the instrument database and are recorded in the FITS headers for use in the data reduction The cosmetic quality of the three scientific CCDs is very good Details are given in Chapter 2 6 5 The CCD cryostats are attached to the blue and red dioptric cameras with the last optical element acting as window The Blue and Red CCDs are operated at a temperature of 153 K and 135 K respectively Two liquid nitrogen tanks ensure continuous operation without man ual intervention for 2 weeks The shutters are located between the cryostat windows and the cameras They are actuated by solenoids with an open close time of 50 ms The illu mination of the detectors is homogeneous within 50 ms but a minimum exposure time of 0 5 sec is recommended The reader is referred to the CCD webpages of the ESO Opti cal Detector Team for additional general information on the CCDs and the Control System FIERA http www eso org odt 2 3 Spectral Resolution and Overall Efficiency The user can only affect the spectral resolution by the choice of the slit width and to some extent by binning the CCD The factors outside his her control which affect the resolving power are the image quality of the optics including the focus and the alignment CCD effects chip tilt diffusio
10. 2 3 Measured resolving power Fig 2 3 32 R600 standard setting added 3 3 Tab 3 2 recommended slit lengths updated 4 1 Calibration Plan added Tab 4 1 4 6 section Quality Control added 4 7 1 iodine cell info added 6 2 qc pipeline web links added 6 4 1 iodine cell reductions info added Issue 1 3 1 01 10 01 minor corrections Issue 1 4 21 12 01 update for P69 3 6 acquisition moving targets 33 amp T CUSO4 filter replaced by HER_5 3 3 final CD 1 installed added Index prepared by T S Kim Issue 1 5 29 06 02 update for P70 Tab 2 1 IS efficiencies updated Fig 2 3 IS vs Slit added Fig 2 5 replaced by 2002 measurements 6 2 dark frame policy source types 4 4 6 2 master response curves added 522 filenaming scheme updated Issue 1 6 19 02 03 update for P71 4 5 calibration plan info added Issue 1 7 07 07 03 update for P72 224 MIT CCD info updated Tab 4 2 exp times for calibration lamps updated Issue 1 8 10 01 04 update for P73 3 1 link to the Garching QC webpage added 3 5 new section about RRM observations 7 3 references for ThAr line table added Issue 1 9 04 06 04 update for P74 6 3 red CCD image format change vs pipeline Issue 75 22 11 04 update for P75 2 2 4 amp Tab 2 3 3 3 amp Tab 3 1 information about new Blue CCD added standard Dichroic settings with 760nm added VLT MAN ESO 13200 1825iv UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 1825v Issue Rev
11. 7 11 16 17 guide star 7 37 45 46 guiding 37 46 secondary guiding 8 18 37 46 image slicer IS 7 10 13 15 28 37 40 46 48 49 instrument capabilities 2 3 data quality 2 efficiency 20 21 23 general layout 10 modes 27 schematic overview 12 iodine cell 8 10 13 30 43 49 ISAAC 5 mirror collimators 17 moving targets 37 observation block OB 8 26 introducing OBs 32 OB preparation 27 32 45 UVES User Manual VLT MAN ESO 13200 1825 94 webpage 2 observing 45 47 check list 39 general information on the site 45 Phase I and IT 26 webpage Phase I and IT 26 order definition 41 order separation 10 28 31 overhead times 38 39 P2PP 6 8 webpage 2 27 32 pre slit filter 13 15 50 Johnson broad band filter 15 50 neutral density filter 15 50 pupil stop slide 16 quality control 2 27 43 rapid response mode RRM 32 webpage 33 real time display RTD panel 47 48 reference stars 44 resolving power 2 3 14 17 20 22 28 39 webpage 21 rotator 10 14 scientific CCDs 3 18 19 binning 20 38 blue arm CCD 3 13 18 19 cosmetic defects 24 cryostat 20 efficiency 13 enhanced dark current 24 gain 19 ghosts 21 linearity 20 read out mode 20 33 38 read out noise 19 read out time 19 38 red arm CCDs 3 13 18 remnant of ThAr lamp 24 saturation 19 spectral gaps 21 28 table with the CCD properties 19 webpage 20 sequencer 8
12. C EEV up to 40 MIT up to 20 gt 0 99995 in disp dir MIT pix 40 50 2098 3008 EEV pix 1 50 2098 2148 lt 60um peak to peak UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182520 fringing at far red wavelengths The gap between the two CCDs is 0 96mm This and the non perfect alignment of the two chips require that the spectra on the two chips of the mosaic are extracted separately The CCD control system the ESO standard system FIERA reads the mosaic as a single image with nominally 100 pixels between the two sensitive areas The file has to be splitted before applying a standard echelle reduction package Windowing of the CCDs is not allowed Five read out modes of the CCDs can be selected 1 Low gain fast read out 1x1 binning VM SM 2 Low gain ultrafast read out 1x1 binning VM only 3 Low gain fast read out 1x2 binning VM only 4 High gain slow read out 2x2 binning VM SM 5 High gain slow read out 2x3 binning VM only The second digit in binning applies to the direction of the spectral dispersion The charac teristics of these modes are given in Tab 2 3 The linearity of the CCDs is measured to be better than 1 over the range from 200 e to the saturation limit Note that counts per pixel above 40000 ADU should be avoided for the MIT CCD chip because of non linearity The relatively high value of the dark current of the CCD in the blue arm is measured with
13. MAN ESO 13200 18254 Figure 1 1 The UVES spectrograph on the Nasmyth B platform of VLT Unit Telescope 2 3D CAD view UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 18255 1 4 UVES within the VLT Observatory A detailed overview of the different instruments on the VLT is shown on the ESO homepage under VLT Instrumentation http www eso org observing vlt instruments In the choice of the best instrument for a given observing program the following trade offs have to be taken into consideration Spectroscopy in the UV Visual Red regions 300 1100 nm e FORS1 at UT2 since June 2004 can be used for spectroscopy in the spectral range 360 1100 nm Its overall efficiency is on average 2 times higher than UVES one reflection less in the telescope and simpler instrument optics but the maximum resolving power to be obtained with a 0 5 arcsec slit is 2 500 only e FORS2 at UTI is a replica of FORS1 but it will eventually include two transmission echelle gratings which when used in conjunction with a grism cross disperser will provide a resolving power of up to 6 000 and a wider spectral coverage comparable to that of UVES e GIRAFFE which is part of the FLAMES instrument at the opposite Nasmyth platform of UT2 is the instrument which approaches UVES in resolution An automatic fibre positioning unit is installed at the Nasmyth focal plane It can use up to 132 fibers in the field of view of 25 arcminutes in
14. PS4 R 650 gt 75 Acquisition filter Ps5 I 800 gt 85 Acquisition filter lt 2 920 1100 nm PS6 UG5 2mm ADC test filter PS7 ND1 300 1100 1071 Neutral density filter 2 5 mag PS8 ND2 300 1100 107 Neutral density filter 5 0 mag PS9 ND3 300 1100 107 Neutral density filter 7 5 mag PS10 ND4 300 1100 1074 Neutral density filter 10 0 mag PS11 ND5 300 1100 1075 Neutral density filter 12 5 mag 50 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182551 7 1 2 Below slit filters Blue below slit filters BFIL Name Spectral range nm Transm Comment BBS1 not available CUSO4 decommissioned BBS2 BG24 350 420 gt 96 Stray light rejection filter BBS3 HER 5 Herasil 5mm 310 500 gt 98 Focus compensation plate BBS4 HER 10 Herasil 10mm 310 500 gt 98 Focus compensation plate BBS5 HER 15 Herasil 15mm 310 500 gt 98 Focus compensation plate Red below slit filters RFIL RBS1 BG40 420 570 gt 90 Stray light rejection filter RBS2 SHP700 hot mirror 420 700 gt 90 Red Stray light rejection RBS3 0G590 605 930 gt 90 Order sorting filter 300 560 lt 0 001 for use with CD 4 RBS4 BK7_5 5mm 420 850 gt 90 Focus compensation plate RBS5 BK7 10 10mm 420 850 gt 90 Focus compensation plate RBS6 BK7_15 15mm 420 850 gt 90 Focus compensation plate The filters in bold face are recommended to be used for science observations T
15. The predicted values for R are indicated by symbols The 10 reduced resolving power measured on the MIT LL chip is due to charge diffusion effects in this CCD cf text The 2 pixel sampling limit is indicated by dashed horizontal lines In the blue the CCD bin size in the center of an order is 1 193 000 of the wavelength or 0 215 arcsec in the spectral direction In the red these numbers are 1 250 000 and 0 155 arcsec UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182523 0 15 0 10 efficiency E 00 3000 4000 5000 6000 7000 8000 9000 10000 11000 wavelength A Figure 2 5 The measured overall detection efficiency of UVES detectors 3 mirrors of UT2 corrected for the contribution of the atmosphere The values are from measurements of different standard stars in the period July to September 2004 i e one year after recoating of the primary mirror The measurements used the standard wavelengths Dic 1 346 580 Dic 2 437 860nm with the four different crossdispersers CD 1 CD 2 CD 3 CD 4 respectively The average uncertainty on the individual points is estimated from the scatter of the results to be about 5 Note that the prototype CDs 4 and 1 have been replaced by the final more efficient gratings in November 2000 and October 2001 respectively UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182524 echelle orders depends on the shape of the target spectrum With fla
16. They are folded and cross each other to minimize the size of the table on the platform The two arm solution gives high efficiency because it permits to optimize the spectral response of coatings gratings and detectors The design of both arms is of the white pupil type Baranne 1972 ESO Cern Conference on Large Telescopes With a beam of 200 mm the off axis parabolic collimators illuminate the echelle gratings of 214 x 840 x 125 mm with a large blaze angle 76 The echelle R4 gratings are the largest ever made of this type They are operated in quasi Littrow mode that is with the angle of incidence and diffraction equal but in a different plane to maximize efficiency The grating cross dispersers provide an order separation larger than 10 arcsec at any wave length in the spectral range 300 1100 nm This separation allows to perform semi long slit spectroscopy of compact objects the use of image slicers a good sampling of sky emission at red wavelengths and the possibility of accurate interorder background estimates The cameras are dioptric no central obstruction and provide an external focal plane for easy detector interfacing and upgrading during the lifetime of the instrument together with a large field good image quality and high optical transmission 10 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182511 Figure 2 1 A three dimensional CAD view of the UVES instrument table with the mounted sp
17. an image of the slit plane is focussed with a scale of 0 15 arcsec pixel The unvignetted field has a diameter of 30 arcsec A filter is permanently mounted on the blue CCD objective to match the imaging bandpass with the wavelength range of the spectra The objective is focussed on the slit jaws and deckers It is used to identify the target to center it on the slit aperture and optionally for secondary guiding The limiting magnitudes of the SV cameras for target acquisition are a function of seeing color of the target and sky brightness As an example with a 5 sec integration 1 arcsec FWHM seeing and dark sky m B 19 4 and m R 21 are detected at S N 10 with the blue and red camera respectively SV cameras are essentially able to acquire all objects for which spectroscopic observations can be made If the target is too faint to be visible on the SVs blind offset procedures from a nearby star are provided cf Ref 1 The corresponding limiting magnitudes for secondary guiding of a point source centered on the slit are 18 9 and 20 3 in the blue and red respectively 1 arcsec seeing and slit 5 sec integration 2 2 4 The Scientific CCDs and the associated shutters A summary of the properties of the blue and red arm scientific CCDs is given in Tab 2 3 The detailed QE curves can be found in the UVES database available through the ETC The detector in the blue camera consists of one EEV CCD EEV 44 82 The detector in the red camera c
18. and of the CCDs as measured in the laboratory in advance of the installation 3 6 1 Definition of the target For the input flux distribution to the ETC four options can be selected 1 A blackbody energy distribution at a given temperature 2 a power law distribution 3 a template spectrum stellar spectra from spectral type O5 to M2 nebular spectra galaxy spectra or a quasar spectrum 4 a single line at a wavelength width and flux level to be specified In all cases but point 4 the object magnitude in a given broad band filter have to be entered For extended sources magnitudes are given per square arcsec In addition to the target it is needed to enter the sky conditions phase of the moon and FWHM of seeing disc 3 6 2 Choice of instrument configuration and spectral format Based on the properties of the optical components of the spectrograph the format of the echelle spectrum covered by the detector depends exclusively on the selected central wavelength order The instrument templates with standard settings can be selected from the pull down menu The corresponding spectral formats are given in Table 3 1 In case that these formats are not compatible with the scientific program a free template with a different central wavelength can be specified The resolution is determined by the choice of the slit width as shown by Figure 2 4 An other key choice in the ETC is the selection of the CCD read out mode The two options
19. are listed in Chapter 2 4 The slow read out binned mode is suited for the faintest objects and observations at low medium S N ratios the unbinned fast read out mode is best suited for high S N non read out noise limited observations The final entry is the exposure time The output for the spectral format consists of a table listing the wavelength at the order maximum the order separation in the direction perpendicular to the dispersion the start and end wavelength of each order and the start and end of the Free Spectral Range i e the non overlapping part of the consecutive orders UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182534 U band slit 7 R 54 000 k m 12 100 00 Dont m 14 m 16 E ETETETT m 18 E H D ee ee D H D H ee ee ee D H eee cce An m 19 a m 20 o m 21 10 00 read nse limit dke skoy limit 1 00 ip Ume h Figure 3 2 Predicted signal to noise ratio S N in the U band at a central wavelength of 400 nm per wavelength bin as a function of exposure time The slit width was set at 0 7 arcsec corresponding to a resolving power of 57 000 Other data 1 x 2 binning pixel size 0 019 x 0 43 arcsec dark sky slit loss 30 summation of 4 pixels along the slit CCD quantum efficiency 65 read noise 3 electrons rms dark noise 1 e pix h The S N is shot noise dominated in the region above the read noise and dark sky limit line
20. decker height typically 10 to 12 of the spectrograph slit so that the remaining part of the spectrograph slit can be used to monitor the sky background IS 2 and 3 are dedicated to the blue and red arm respectively Due to the unavailability of a red arm setting with central wavelength 760 nm the possibility of using the combination of IS 3 with DIC2 and the setting with a central wavelength of 760 nm has been implemented for use starting with Period 76 IS 1 is for general use If IS 1 is used in a dichroic mode it is important to avoid observations at airmasses higher than 1 3 Otherwise considerable light losses due to the atmospheric dispersion and therefore the displacement of the blue with respect to the red image have to be expected This is also true in case of observations with IS 2 in the very blue e g in the Blue 346nm standard setting The Derotator not to be confused with the telescope adapter rotator unit is an Abbe Koenig type silica prism that is placed in the diverging beam of the telescope and provides compensation for the field rotation It incorporates a lens to create a parallel beam It cannot be taken out of the beam and it introduces an average loss of 4 of the light The user has two options a of derotating the field fixed projected position angle on the sky of the spectrograph slit SKY mode with the position angle PA of the slit measured positive from North over East For PA 0 the slit is aligne
21. diameter The fibers feed the GIRAFFE long slit spectrograph mounted on the Nasmyth platform The data are collected by a 2048 x 4096 pixels CCD One CCD frame contains the linear spectra of up to 132 objects observed in parallel with a limiting resolving power of 20 000 and a spectral coverage in a single exposure of 26 60 nm depending on the wavelength GIRAFFE is on average 30 less efficient than UVES but the multiplexing gain can make it the best choice if the observing program includes many objects in a single field at intermediate spectral resolution Spectroscopy at infrared wavelengths 1 5 um Complementary spectroscopic observations at infrared wavelengths can be obtained with two other VLT instruments e The infrared imager spectrometer ISAAC can be used to obtain spectra in the 1 5 um spectral region Two separate cameras in the same cryogenic vacuum vessel are opti mized separately for the 1 2 5 um and 2 5 5 um spectral ranges with resolving power up to 10 000 if a 0 5 arcsec slit is used e A high resolution infrared spectrometer CRIRES is currently under study It is in tended to be the counterpart of UVES in the 1 5 micron spectral region providing a resolution up to 40 000 0 5 arcsec slit in a single order or cross dispersed format 1 5 How to access UVES sample calibrations and ob servations A large number of scientific observations of a variety of targets and the associated calibrations have been obtained during th
22. during observing time allocated to the program of the observer unless very high accuracy is required see Chapter 4 Furthermore for these standard settings an automatic data extraction procedure is available i e the pipeline reduction The standard settings for UVES are listed in Table 3 1 They are chosen such that together they cover the optical wavelength domain from 300 1100 nm The standard settings com prised in Table 3 1 correspond to Observation Templates which can be selected for the preparation of the Observing Blocks with P2PP The wavelength coverage is computed for a 4kx4k red mosaic and a 2kx3k blue CCD In each standard setting a decker height has been chosen such that sufficient space at least 8 pixels or gt 2arcsec is left between neigh boring orders to be able to accurately estimate the stray light background Table 3 2 lists the recommended slit lengths at different wavelengths with the current set of crossdispersers In addition Fig 3 1 shows the order separation as function of the order number for all four cross dispersers in the standard wavelength settings The below the slit filters are used to suppress the second order of the CD gratings or undesired light from entering the spectrograph Their transmission curves are given in the UVES database The spectrograph is focussed with a below slit filter of 5mm thickness Therefore a filter has always to be inserted to achieve the best possible image quality In config
23. fixed CCD window settings 2 2 Instrument subsystems This section describes the UVES subsystems in the order they are encountered along the optical path going from the telescope to the instrument detector cf Fig 2 2 It is intended to guide the users in the selection of the optimal instrument configuration for his her observing program The functionalities of the different subunits are explained and reference is made to their measured performance Efficiencies e g in the form of transmission curves of the main instrument components including the CCDs are available in the UVES database accessible through the UVES Exposure Time Calculator see Chapter 3 5 2 2 1 The preslit system The light path The light from the telescope or from the calibration unit enters from the top and passes through the calibration mirror unit the iodine cell and image slicer unit respectively before entering the derotator The next elements are the pre slit filter wheel the ADC the depolarizer and the pupil stop At the position of the mode selector which includes the dichroic filters the beam is split into a red going straight and blue path reflected to the right Fibers coming from FLAMES at the opposite Nasmyth platform can be inserted in the mode selector unit from the left to feed the red arm The slit view cameras are located in front of the spectrograph slits The preslit functions In the converging f 15 beam coming from the telescope th
24. is available here in the extraction of extended or multiple single objects the spatial infomation along the slit is maintained 48 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182549 More information about the UVES pipeline and Service Mode data packages is available under http www eso org observing dfo quality index uves html 6 3 Off line data reduction Any echelle data reduction package under MIDAS IRAF or based on IDL can be eas ily adapted to extract and calibrate UVES data MIDAS has a dedicated context UVES which uses the instrument s physical model to speed up the order definition and wavelength calibration On the 1 of April 2004 the format of the raw files produced by the red arm of UVES has changed The new format is a FITS file with one extension per detector i e the two red CCD images are split As a consequence of this files produced in the new for mat cannot be processed by versions of the UVES pipeline 2 0 0 or older A new version of the pipeline 2 1 is able to handle both the new and the old formats and is available at http www eso org projects dfs dfs shared web vlt vlt instrument pipelines html On the other hand the format of the products produced by the new pipeline has not changed 6 4 Special reduction cases 6 4 1 Data taken with the iodine cell With the begin of Period 68 data taken with the iodine absorption cell in Service Mode will be pipeline proces
25. the use of the numerous night sky emission lines in this spectral region should be considered instead 2 4 4 Enhanced Dark Current after a FIERA start up When the CCD Control System FIERA has to be restarted e g due to a general power failure or for an update of the database the level of the dark current will be a few times higher than the value measured in the running system It is important to check the performance of the detectors by taking e g a dark exposures of a few minutes in binned mode An interval of 3 hours is normally sufficient to return to optimal performance of the CCD 2 4 5 CCD Cosmetic Defects The three CCDs of UVES are of excellent EEVs or good MIT LL cosmetic quality The number of hot or less sensitive pixels is limited lt 0 1 and has little effect on the quality of the data because of the large sampling The defects which depending on the signal to noise of the spectrum might be visible in the extracted data are listed below In the EEV CCD on the blue side of the red arm mosaic there are four trails of hot pixels which appear in long exposures X coordinates 3896 3963 4052 and 4140 in an unbinned fits file middle of the chip in y They each affect a single column longer dimension of the CCD and are almost parallel to the echelle orders They would appear as broadish emission in the bluer part of the extracted spectrum of a faint object In the MIT LL chip red side of the CCD mosaic of the red arm th
26. to the World Wide Web text file editing etc The visitors receive advice on the OB preparation by a staff astronomer of the Observatory 5 2 During the night Observations with the UVES instrument are carried out at the User Station of UT2 located in the VLT Control Building just below the Paranal summit From there all telescopes and instruments are remotely controlled The telescope and instrument operator carries out the observations and is responsible for the checking that the telescope and isntruments perform correctly the main area of responsibility of the visiting astronomers is the selection of the OBs to be executed based on the sky conditions and on the results of the first observations The main actions are outlined below 5 2 1 Target acquisition The OB to be executed is loaded to the BOB panel and started The Telescope Control Software TCS reads the target coordinates from the OB and the telescope is pointed It au tomatically searches with the guide probe in the adapter for a tracking star which is also used for the active optics correction computation Once the telescope has completed the pointing and has acquired the guide star with the Adapter Guiding Probe the UVES Slit Viewing Cameras which produce images of the target field 30 x 30 arcseconds as reflected by the slit jaws can be used for the final step of target acquisition In the dicroic modes the user 45 UV Visual Echelle Spectrograph UVES User manual VLT
27. user has to select one of the two as primary camera for acquisition and eventually secondary guiding Note if ELEV mode is used and one of the two slits in the red and blue arm is considerably shorter it is better to center the star on the arm with the shorter slit i e to select the guide camera of the corresponding arm Otherwise the atmospheric dispersion can displace the object close to the edge of the shorter slit The tracking of the telescope is corrected for errors of low frequency lt 1 Hz by an autoguiding facility The autoguider makes use of a guide star observed by the guide probe in the adapter rotator that is moved into the telescope beam The guide stars will be automatically selected from the VLT guide star catalogue The SV software allows automatic initial centering using a SV image as well as continu ous monitoring of the position during the exposure If systematic offsets are detected slow frequency corrections are sent to the telescope secondary guiding This ensures that any possible relative motions of the optical axis of the telescope with respect to the plane of the entrance slit of the instrument are corrected for During the commissioning the amplitude of these corrections has been observed to be very small if not negligible at all The exposure UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182538 meters can be used to monitor the centering of the target on the slit through the
28. 04 95 P Santin amp A Longinotti 8 P2PP User s Manual VLT MAN ESO 19200 1644 Issue 6 20 12 2004 F Comer n D Silva 9 UVES ICS Dictionary ESO VLT DIC UVES_ICS Version 1 20 23 12 1997 A Longinotti 10 CCD DCS Dictionary ESO VLT DIC CCDDCS Version 2 12 17 04 1998 11 FIERA DCS Dictionary ESO VLT DIC FCDDCS Version 2 25 02 04 1998 12 TCS Dictionary ESO VLT DIC TCS Version 1 66 14 04 1998 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 18257 1 8 Glossary Acquisition Accurate positioning of the telescope in order to center the target on the spectrograph slit Atmospheric Dispersion Correction ADC unit This unit can be inserted in the pre slit area of UVES to correct for atmospheric dispersion BIAS frame Read out of the CCD detector of zero integration time with shutter closed The registered number of electrons per pixel has to be subtracted from a science exposure because these were not created by photons from the source Calibration Procedures to remove the instrumental signature from the scientific data e g by subtracting BIAS frames and by dividing through the flatfield Camera UVES has two dioptric cameras red and blue arm imaging the dispersed parallel beams on two CCD detectors Charge Coupled Device Electronic 2D array detector converting photons into electrons Cross disperser grating An echelle spectrograph contains two dispersive elements in the
29. 200 182552 missioning and Science Verification publicly available through the ESO ftp server and the ESO VLT archive Index abbreviations and acronyms 9 acquisition target on slit 38 45 adapter guide probe 45 arm selector 16 atmospheric dispersion corrector ADC 7 10 14 15 below slit filter 17 28 51 bias frames 7 blaze angle 10 17 blind offset 18 46 calibration 40 44 Calibration Plan 6 40 41 deuterium flat lamp 13 41 exposure times for calibration lamps 42 overview table 41 quality control 43 calibration unit 11 13 40 commissioning data 5 52 CRIRES 5 cross disperser units 18 data samples 5 51 data reduction 48 49 data quality information 2 pipeline reduction 27 43 47 48 webpage 49 with the image slicer 49 with the iodine cell 49 decker 7 14 16 28 29 depolarizer 10 13 15 derotator 7 10 11 13 15 37 ELEV mode 14 37 SKY mode 14 37 dichroic 7 9 10 14 16 27 29 30 40 dithering 44 DSS 37 exposure meter EM 16 17 38 44 46 exposure time 33 34 93 exposure time calculator ETC 27 33 34 predicted S N 33 34 38 webpage 33 FIERA CCD controllers 20 24 47 48 webpage 20 finding chart 26 37 38 FITS naming convention 46 FLAMES 2 5 13 flatfield 7 24 25 40 41 44 48 format check 41 FORS1 5 FORS2 5 GIRAFFE 5 glossary 7 grating 7 cross disperser CD grating 7 10 11 17 18 echelle grating
30. 4 DICHROIC2 both arms are used cross over wavelength 550 nm wavelength ranges 400 500 and 600 1100 nm UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182528 Apart from the instrument mode a decision has to be made regarding the acquisition of the target Under normal conditions the target is centered directly on one of the spectrograph slits the spectral resolution will then be determined by the slit width the resolving power slit width in arcsec product Rs is 40 000 The resolution increases when the slit is narrowed see Fig 2 4 In case of a seeing profile significantly wider than the slit the slit losses become significant and it becomes attractive to acquire the target through one of the image slicers see Table 2 1 3 3 UVES Standard settings To facilitate the preparation of Observation Blocks Section 3 4 standard settings have been defined that allow the observer to select a pre programmed instrument setting for which most parameters are set to fixed optimal values and only a few have to be defined e g the slit width The users are encouraged to use these standard settings to the extent that they are compatible with their program In service mode observations only standard settings are accepted Another advantage is that the Observatory keeps an updated database of calibrations obtained at a standard setting i e flatfields bias frames and wavelength calibrations do not need to be taken
31. 705 T2 5 RED CD 4 OG590 660 860 1060 12 10 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182530 Table 3 2 Recommended slit lengths for different wavelengths and crossdisperser combina tions CD wavelength separation separation recommended nm pixels P slit length 1 330 42 0 10 8 8 0 1 346 48 5 12 4 10 0 1 370 56 6 14 5 12 0 1 395 65 6 16 8 14 0 2 370 38 6 9 5 7 0 2 395 38 9 9 6 7 0 2 437 49 9 12 3 10 0 2 470 59 2 14 6 12 0 3 460 48 0 8 7 6 0 3 490 48 4 8 8 6 0 3 520 57 2 10 4 8 0 3 550 66 9 12 2 10 0 3 580 77 4 14 1 12 0 3 640 98 8 18 0 16 0 4 610 29 6 5 1 3 0 4 660 38 7 6 7 4 5 4 710 48 6 8 4 6 0 4 760 58 6 10 1 8 0 4 810 70 3 12 1 10 0 4 860 81 9 14 1 12 0 4 910 96 3 16 6 14 5 however in the region where the dichroic behavior changes from reflection to transmission 430 465 nm the resulting spectrum will not be optimally exposed Photometric accuracy may be lower due to polarization effects Standard Dichroic 2 settings with 760nm central wavelength have been introduced to obtain simultaneous observations of all three Ca 11 near infrared triplet lines along with Ha and many other spectral lines used as important diagnostics in the spectra of hot and cool stars The RED 600 standard setting is defined for use with the iodine absorption cell Starting with Period 76 it can also be used without the iodine cell
32. E EL m 16 ST qm 18 metiers 19 SH per bir m 20 LA m 21 10 00 E Fee KA bm pen pm Deg ve E Gem read nse limit dk skylimit exp tne Ou Figure 3 3 Same as Fig 3 2 but now in the V band at a central wavelength of 550 nm The slit width was set at 0 7 arcsec corresponding to a resolving power of 60 000 Other data 2 x 2 binning superpixel size 0 044 x 0 34 arcsec dark sky slit loss 30 summation of 5 superpixels along the slit CCD quantum efficiency 85 read noise 3 electrons rms dark noise 1 e pix h UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182536 V band slicer R 100 000 a ee EE EE EES a IS E PS ER CEE DEN DEN EN FE ER SIE Sea Rp Wa PS 9 ER ee SS DR L a OA AA JT HI n E KLEK ee TT zt BBS TT MES 100 00 ae Be a Lun M 14 Ces pour m 16 e Se KEE eet E E E E 5 Lier eee eee ATT vas M 18 TL ET Mets peed 3 7 LL S ETU le 20 CLLOU AT aen 10 00 o RS Deg et Eat pe emm bm pm read nse limit pe n a Ek dk sky limit Edel S ET sky limi Bee A TT EE Ge id 1 00 id 0 10 ER 10 00 oo exp ti me h Figure 3 4 Same as Fig 3 3 but now using image slicer 3 The resulting slit width is 0 3 arcsec corresponding to a resolving power of 110 000 Other data 1 x 2 binning pixel size 0 022 x 0 18 arcsec dark sky slicer slit loss 50 simple summation of the signal over 25 superpixels alo
33. EUROPEAN SOUTHERN OBSERVATORY Organisation Europ ene pour des Recherches Astronomiques dans l H misph re Austral Europ ische Organisation f r astronomische Forschung in der stidlichen Hemisphare ESO European Southern Observatory Karl Schwarzschild Str 2 D 85748 Garching bei Miinchen Very Large Telescope Paranal Science Operations UV Visual Echelle Spectrograph UVES User manual Doc No VLT MAN ESO 13200 1825 Issue 76 0 Date 01 06 2005 A Kaufer S D Odorico L Kaper E VE ed s ep de wae ne EE EEN Date Signature A Kaufer e E 4 lt oan t enews Auk uns Se aii a ao ty a Date Signature O Hainaut EE EE DO ONE a aos O Sos Date Signature UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 1825ii This page was intentionally left blank UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 1825iii Change Record UV Visual Echelle Spectrograph UVES User manual Issue Rev Date Section Parag affected Reason Initiation Documents Remarks Draft 15 07 99 all Issue 1 0 26 01 00 all first release after commissioning Issue 1 1 02 08 00 all update for P66 after 4 m of operation Issue 1 2 21 12 00 update for P67 2 2 preslit filters new CD 4 2 5 Fig 2 6 added detection efficiency 3 3 Fig 3 1 added order separation Issue 1 3 01 07 01 update for P68 1 7 bibliography reduced and updated 2 schematic view added Fig 2 2 2D CAD drawings removed
34. For visitors observing with non standard settings the on line pipeline at Paranal can in most cases be prepared to handle their settings limited to 2 non standard settings per visitor run The science data are calibrated with calibration exposures obtained upon arrival of the visitor i e one or two days before the start of the observing run The UVES Calibration Plan cf 2 ensures that ESO maintains and provides bias spectro scopic flatfield and order definition frames calibration lamp spectra The CCD characteristics like read out noise and gain are measured on a monthly basis Dark current and parasitic light measurements are carried out with the same frequency and are available on request from the ESO archive The following corrections of the science echelle spectra are available bias subtraction in terorder background subtraction flatfield correction order extraction sky subtraction rebin ning to wavelength scale and order merging Response corrections are applied using predeter mined master response curves All three detectors 1 blue 2 in the red mosaic are processed independently The extraction of the science data is carried out according to the selection of the Source Type POINT or EXTENDED in the UVES observation templates For point sources an optimum extraction algorithm with sky subtraction and cosmic rejection is applied image slicer data are extracted as the sum over the slicer length no sky subtraction
35. Information on the current instrument performance and on the Service Mode pipeline data processing can be found on the UVES Quality Control pages at http www eso org observing dfo quality index uves html 1 3 Capabilities of the Instrument UVES the Ultraviolet and Visual Echelle Spectrograph located at Nasmyth platform B of the second Unit Telescope Kueyen of the VLT Fig 1 1 is a cross dispersed echelle spectrograph designed to operate with high efficiency from the atmospheric cut off at 300 nm to the long wavelength limit of the CCD detectors 1100 nm To this purpose the light beam coming from the telescope is split into two arms UV Blue and Visual Red within the instrument The two arms can be operated separately or in parallel with a dichroic beam splitter The resolving power is 40 000 when a 1 arcsec slit is used The two pixel resolution to be obtained with a narrower slit or with the use of an image slicer is 80 000 or 110 000 in the Blue and the Red Arm respectively The instrument is built for maximum mechanical stability and for accurate calibration of the wavelength scale down to an accuracy of at least 50 m s An iodine cell can be inserted in the light beam for observations requiring higher accuracy The main capabilities of the two UVES arms are summarized in Table 1 1 In 2003 a new mode of operation involving multi object spectroscopy was implemented Eight fibers input diameter 1 arcsec coming from the fibre p
36. MAN ESO 13200 182546 has to identify one of the two cameras as the primary one for acquisition and guiding The SV images are properly oriented in the sky and the coordinates which can be read with the cursor are converted to sky coordinates The target coordinates entered in the OBs have to be accurate to better than lt 1 to avoid unnecessary waste of telescope time in the identification process The image of the SV field is automatically archived at the start of the exposure The telescope pointing rms accuracy is of the order of 1 arcsec so that the target does appear close to the center of the SV images displayed on the WS panel The visiting astronomer has to validate the target identification on the image This is particularly important if the field has other close by objects of similar magnitude Note that if the target is invisible to the limit of the SV camera e g an emission line neb ula it is possible to define in the OB a blind offset from a nearby visible star The coordinates of the science target have to be entered in the target description In the acquisition template of the OB the offsets to the guidestar have to be entered in arcseconds target coordinates offsets acquisition star coordinates Whatever the acquisition procedure once the instrument operator signals that the target is centered on the slit the exposure is started The tracking of the telescope is corrected for errors of low frequency lt 1 Hz by
37. S data 40 a The UVES Calbration Plan ec s sx pe OS eg esse 40 a2 The UVES calibration mk Le i saie BUS sas SAD pra E Da 40 A3 Calibration m Wavelength su 2 2 580 drum Dos e ds E ace e E SE EC 40 AA Plat felding caseira de pu Ed E GAMES REE RR amp 8 41 4 5 Flux standard star observations 43 At Quality Contool ss s eme LME SHS OOS Ewe DER oe Bee LENS E 43 AT Peq CANGNORS se ca 4 24 giga pi Oe we SRA we eR Ee ets 43 4 7 1 Use of the iodine cell for accurate radial velocity measurements 48 4 7 2 Use of exposure meter for flux weighted exposures 44 Bite Detector MMS cece d usa ew eRe eae REY EB oS 44 4 7 4 Use of reference stars to correct for fringing or atmospheric lines 44 4 7 5 Use of camera tilt for spectral dithering very high signal to noise ratios 44 5 Observing 45 5 1 Before the observing nights preparation of OBs 45 Oe DGE LED La A ee eee dg ed ee ed HE ANR E gs 45 S21 Tarket Ge cg ee ee eee ee e BRE ee ees 45 ne Montorme the Integral e so 46 La dau he OL eee OEE ES 46 5 2 3 Evaluation of the results off line data analysis 47 6 The reduction of UVES data 48 6 1 Real Time Display and quick look 44 2 45 44454 var au eee e 48 6 2 Pipeline reduction of UVES data 2 4 6 4 4 8 ewe RE ERR RE SEA a 48 do line data reductil co oe Bk c das OEE RARE BREE E 49 64 Special reduction Gases s sac sa See rain ea des ed rue
38. ailable through the instrument ETC can be combined to compute the predicted global instrument efficiency which is higher than 0 2 from 400 to 800 nm Making appropriate assumptions on the reflectivity of the three telescope mirrors the overall telescope instrument detector efficiency has been computed and compared with measurements of the standard stars observed during the commissioning corrected for atmo spheric absorption The efficiency curve available in the UVES database cf the instrument ETC has been verified with the standard star observations during the instrument commis sioning runs Ref 3 An overview of the measured overall detection efficiency of instrument telescope is shown in Fig 2 5 and recent measurements of the efficiency can be found under the same link as above 2 4 Instrument Features and Problems to be aware of 2 4 1 Spectral gaps in the Red Arm The CCD detector in the red arm see Section 2 4 consists of a mosaic of two chips separated by a gap of approximately 0 96 mm This results in the loss of one echelle order in the recorded spectrum around the central wavelength selected by the observer At 580 nm the gap spans around 5 nm at 860 nm the gap is 10 nm The extension of the gap at any value of the central wavelength can be predicted with high accuracy lt 0 5 nm using the instrument ETC 2 4 2 Optical Ghosts in the far red and UV spectra Spectra imaged on the CCD mosaic in the red arm are part
39. al plane of the telescope into a one dimensional slit In this way the light that normally would fall outside the slit especially when using a narrow slit for high spectral resolution is fed to the spectrograph UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 18258 Iodine cell A glass cell filled with heated Ip gas can be inserted in the light beam to superimpose a molecular absorption spectrum containing many lines on the observed astronomical spectrum This enables very accurate wavelength calibration in the spectral range 500 600 nm Maintenance Technical procedures developed to control and maintain the quality of tele scope instrument and detector Mode Selector Unit in the pre slit area of UVES which directs the light to one of the two spectrograph arms or to both arms simultaneously with help of a dichroic Observation Block A logical unit of exposures needed to obtain a coherent set of data Encompasses all relevant information for a successful data acquisition on a target It consists of target information a set of templates parameter files for the templates con ditions requirements and comments concerning the specified observations It represents the entity the short term scheduler deals with Constructing Observation Blocks is part of the Phase II Proposal Preparation Process Phase II Proposal Preparation P2PP During this phase the successful applicant whose Phase I proposal has been acce
40. and not yet described in the UVES User Manual A UVES data reduction pipeline is also running at the Observatory It enables automatic extraction and wavelength calibration of all spectra of stellar objects taken in standard UVES settings It permits an on line check of the quality of the observations resolution S N in the extracted spectra For visitors observing with non standard settings the on line pipeline at Paranal can be prepared to handle in most cases their settings limited to 2 non standard settings per visitor run The science data are calibrated with calibration exposures obtained upon arrival of the visitor i e two days before the start of the observing run Note that the Paranal on line pipeline is intended as a quick look and quality control tool and was designed for robustness of the reduction and not for best possible reductions 3 2 UVES instrument modes and basic choices After the detailed description of the UVES spectrograph its subsystems and functions Chap ter 2 we provide an overview of the different UVES observing modes The UVES spec trograph has two arms one optimized for the blue and one for the red wavelength domain resulting in four different modes of operation 1 BLUE only the blue arm is used wavelength range 300 500 nm 2 RED only the red arm is used wavelength range 420 1100 nm 3 DICHROIC1 both arms are used cross over wavelength 450 nm wavelength ranges 300 400 and 500 800 nm
41. andard Settings of the instrument Template A set of instructions for the performance of a standard operation on an instru ment typically an instrument and detector setups The templates represent specially devised sequences for all instrument operations and calibrations UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 18259 Template Signature File This is a description of a Template and its parameters It contains information about the type and allowed ranges of the parameters some of the parameters have to be set by the observer Wavelength calibration Spectrum obtained from a reference emission line lamp The wavelengths of the many emission lines are accurately known and are used to transform pixel space into wavelength space 1 9 Abbreviations and Acronyms AT Acquisition Template BLUE Blue arm of the spectrograph BOB Broker for Observations Blocks CAL Calibration exposure CCD Charge Coupled Device CD Crossdisperser DIC Dichroic beam splitter feed to red and blue arm ESO European Southern Observatory ETC Exposure Time Calculator EM Exposure Meter IS Image Slicer OB Observation Block OS Observation Software OBS Observation Template for a scientific target P2PP Phase II Proposal Preparation RED Red arm of the spectrograph RTD Real Time Display STD Standard star SM Service Mode SV Slit Viewer TSF Template Signature File UVES Ultraviolet and Visual Echelle Spectrograph VLT Very La
42. behaviour of the count rate as a function of time The SV image is automatically saved and stored in the archive at the start of each exposure 3 8 Computing time overheads for your program By using the UVES Exposure Time Calculator the user obtains estimates of the observing time needed to reach the desired S N ratio depending on the object magnitude and observing configuration In order to arrive to the total observing time in hours or nights required for the program it is needed to add the time for the various actions related to the scientific observa tion When applying for service mode observations the computation of the overheads is required and has to be included in the application The current date of this issue of the UM estimate of the overheads is provided below e Telescope pointing guiding star acquisition start active optics Assuming that the telescope is moving to a new object at 180 degree the whole sequence can be completed in 6 minutes If the new target requires just a small motion of the telescope and the re acquisition of the guiding star 4 min e Target acquisition and centering on slit The target has to be identified from the slit viewer image and a finding chart When pointed with the cursor it is moved automatically to the slit In the case of image slicers it is moved to the position in the slit viewer which corresponds to the entrance of the IS direct slit or IS point source average brightness 2 mi
43. bservations Any problems which might occur during the exposure due to clouds or a telescope failure will show up in the exposuremeters counts and can be brought to the attention of the telescope operator Exposure can be paused and if necessary the exposure time modified The plots also show the variation of the flux entering the spectrograph as a function of seeing The panel showing the instrument status during the integration does also include the assigned archive name of the upcoming files This would typically be UVES_mode_OBSnnn_mmmm fits where the mode can be BLUE RED DIC1R DIC1B DIC2R or DIC2B nnn is a progressive number for that date the day of the year and mmmm indicates the number of files that have already been created in this mode mmmm starting with 0001 for the first frame In case of a flux standard star the suffix OBS is replaced by STD in case of calibrations by the type of calibration UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182547 e g BIAS FLAT WAVE 5 2 3 Evaluation of the results off line data analysis At the end of each integration the CCD frames are read out by the FIERA controller and transferred to the IW and subsequently to the archive At the same time the frames are displayed automatically on two Real Time Display RTD panels They can be analysed using the standard RTD tools Previous exposures can be re loaded when necessary Data obtained with templates in standard se
44. bsorption cell 4 7 2 Use of exposure meter for flux weighted exposures During each exposure the exposure meters monitor and plot counts as a function of time The minimum and maximum count rates the average value with its rms and the flux weighted mean of the exposure are stored as FITS keywords in the header of the spectrum file 4 7 3 Detector flats Detector flats with direct undispersed illumination of the CCD through the camera are taken at regular intervals according to the UVES Calibration Plan cf 2 to monitor the CCD per formance They are available on request with a valid justification from usd help eso org 4 7 4 Use of reference stars to correct for fringing or atmospheric lines Stars with featureless spectra typically white dwarfs or fast rotating hot stars can be used to provide a good template to correct for fringing as an alternative to the use of internal flatfield lamps These spectra can also be used to identify and estimate the depth of atmospheric H O and Os absorption lines Stars of magnitudes between 5 and 9 are best suited for this type of observations because they require short exposures but do not saturate the detector at the shortest shutter opening times The OBs for these stars should be prepared in Phase II by the observers who require them for their program A bright subsample of the hot flux standards stars is well suited for these observations 4 7 5 Use of camera tilt for spectral dithering ver
45. ccuracy and very high S N ratios The fifth Chapter provides information for the visiting astronomers who come to the Paranal Observatory to use UVES The sixth Chapter summarizes the properties of the pipeline reduction carried out for data obtained using the standard set ups of the instrument UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 18252 1 2 Information available outside this manual If you cannot find a specific piece of information in the UVES User Manual or in case you have remaining questions please contact http www eso org observing support html or more specifically e For information on the instrument performance and Phase I and Phase II proposal preparation please contact the User Support Department usd help eso org e For questions directly related to your granted observing run in Visitor Mode please contact Paranal Science Operations pso eso org e For Phase II preparation of Observation Blocks OBs follow the instructions given in the UVES Template Reference Guide http www eso org instruments uves templman UVES specific P2PP information is found in http www eso org observing p2pp UVES UVES P2PP html the P2PP instrument package is downloadable from http www eso org observing p2pp P2PP instr html e For checking on possible recent changes in the instrument not yet recorded in the current version of the UM consult the UVES web page at http www eso org instruments uves e
46. d North South b of maintaining the slit along the direction of atmospheric dispersion to reduce the losses due to atmospheric dispersion and to keep the target on both the blue and red entrance slit ELEV ation mode When retaining spatial information and a fixed slit orientation is important e g extended objects or multiple targets the derotator must be placed in SKY mode and the Atmospheric Dispersion Corrector see below should be used especially if observations cover the blue spectral range UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182515 0 8 0 6 0 4 0 2 EE he 0 8 0 6 0 4 0 2 ne mm IS 2 A gt 375nm Slit Transmission RO RE RE Co Se DN Cdi Es o el EF rtl 0 8 0 6 0 4 0 2 IS 1 A gt 375nm En Lx ll 0 2 0 4 0 6 0 8 1 1 2 1 4 1 6 1 8 Seeing arcsec Figure 2 3 Image Slicer vs Narrow Slit The pre slit filter wheel has 16 positions of which 15 are dedicated to filters of 40 mm diameter These are neutral density filters and a set of Johnson broad band filters The table listing the properties of the available filters is given in the Appendix The measured transmissions are available in the UVES database The color filters are used for instrument maintenance only the neutral density filters ND1 ND3 have to be used to acquire very bright objects lt 6mag on the slit viewer not to saturate the slit
47. e UVES Commissioning in October and December 1999 and in UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 18256 January 2000 They are available as public data from the ESO archive The list is accessible at http www eso org science uves_comm 1 6 High resolution spectrographs at ESO La Silla Other high dispersion echelle format spectrographs available at ESO La Silla are FEROS at the MPG ESO 2 2m telescope R 48 000 EMMI at the NTT R 7 700 60 500 and HARPS R 110 000 and CES R 220 000 at the ESO 3 6m telescope Information on these instruments can be found at http www 1s eso org lasilla sciops 1 7 Bibliography 1 UVES Templates Reference Guide VLT MAN ESO 13200 1567 Issue 76 0 01 06 2005 A Kaufer 2 UVES Calibration Plan VLT PLA ESO 13200 1123 Issue 76 0 01 06 2005 A Kaufer R Hanuschik 3 The performance of UVES and highlights of the first observations of stars and quasars S D Odorico et al 2000 SPIE 4005 Proceedings p 121 4 Design construction and performance of UVES H Dekker et al 2000 SPIE 4008 Pro ceedings p 534 5 UVES Pipeline User s Manual VLT MAN ESO 19500 2964 Issue 7 30 09 2004 P Ballester O Boitquin A Modigliani S Wolf 6 User Requirements on the UVES Software VLT SPE ES0 13200 0826 Issue 1 0 05 05 95 H Dekker amp S D Odorico 7 UVES Software Requirements and Functional Specifications VLT SPE AOT 13200 0001 Issue 1 0 18
48. e first element is the telescope entrance shutter which allows safe daytime use of UVES for tests and calibration without stray light entering the system from the telescope side Then follows the Calibration Unit It consists of a mechanical structure with calibration lamps an integrating sphere relay optics that simulate the F 15 telescope beam and a mirror slide with four positions that can be inserted in the telescope beam one free for a direct feed from the telescope three occupied by mirrors which reflect the light from the integrating sphere from a Thorium Argon or Deuterium lamp towards the instrument A description of the functionalities of the calibration system is given in Chapter 4 The Iodine Cell slide is used to insert a glass cell filled with L gas in the telescope beam Consequently when it is at the operating temperature of 70 C an absorption spectrum of that molecule is superposed on the object spectrum which can be used as a wavelength reference in the wavelength region 490 640 nm for high precision radial velocity studies see Chapter 4 for more details UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182514 Table 2 1 UVES image slicers Slicer Entrance Slit Slit Number of Resolving Efficiency number Opening width length slices power Kal 1 2 1 26 0 68 7 9 3 60 000 70 350 78 450 80 gt 650 nm 2 1 87 x 2 0 44 7 9 4 75 000 73 350 82 450 83
49. ectrograph elements The telescope beam enters the spectrograph from the left while we look at the pre slit area The cylindrical element at the left side of the table is the derotator The calibration unit is not included in this picture The mode selector splits the light in a red beam going straight and a blue beam reflected to the left The echelle gratings are mounted face down the red one in the rectangular unit at the front side of the table Each beam is reflected by a flat mirror first collimator echelle grating first collimator linear flat mirror second collimator and into the camera the red camera is visible at the right edge of the table via one of the two available cross disperser gratings For a schematic overview see Fig 2 2 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182512 Dic 2 Dic 1 Blue p mm _ ie Wen a Red Slitviewer Red Slit DN Hd ep p 8 p Figure 2 2 Schematic overview of the UVES spectrograph UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182513 The blue CCD detector format is 2048 x 4096 pixels windowed to 2048 x 3000 In the red a mosaic of two 4096 x 2048 pixels CCDs is offered separated by about 1 mm loss of one order in the gap The direction of the spectral dispersion echelle orders is along the larger dimension of the CCDs The instrument spectral formats wavelength coverage etc are always computed for these
50. ed to users who are not familiar with the UVES instrument and who are interested in a quick overview of its capabilities in comparison with similar VLT and La Silla instruments This should enable a potential user to select the best instrument for a given observing program It also includes information on how to access FITS files of reference UVES spectra and a glossary of terms used in the Manual The second Chapter provides the description of the instrument the instrument layout 2 1 its components 2 2 the properties of the two CCD slit viewers and of the two scientific CCD detectors 2 3 2 4 the resolving power and overall efficiency 2 5 and reference to instrument features to be kept in mind while planning the observations or reducing the data 82 6 It can be consulted by users who want to prepare an Observing Proposal Phase 1 but should definitely be read by those who have been granted observing time and have to prepare their observations Phase IT The third Chapter provides the basic information needed to prepare an observing pro gram the identification of the instrument observing modes 3 2 of the standard instrument wavelength settings 3 3 and a description of the Exposure Time Calculator 3 6 The fourth Chapter deals with calibration strategy wavelength flat fielding relative and abso lute calibrations of data obtained in standard operation It also outlines calibration techniques for high velocity a
51. eded iodine cell time critical observations etc 6 Define calibration needs exceeding the standard calibrations as defined in the calibration plan 7 Compute time to be requested including overheads Chapter 4 The calibration of UVES data 4 1 The UVES Calibration Plan The observatory s calibration strategy for the UVES instrument is described in detail in the UVES Calibration Plan cf 2 available from http www eso org instruments uves calplan Table 4 1 provides a summary of the current calibration plan for scientific UVES data All daily calibrations are defined and executed in a fully automatic procedure according to the science data obtained in the previous night This procedure is applied for the UVES standard configurations as well as for free settings If additional calibrations are needed the corresponding Observation Blocks have to be provided by the Visitor observer or the Service mode PI using the data and instructions provided in the following sections 4 2 The UVES calibration unit The UVES Calibration Unit is a mechanical structure mounted on the Nasmyth rotator flange which in the case of UVES is kept fixed during observations It hosts continuum lamps which in combination with various filters are used for flatfield calibration at the different wavelengths and one ThAr lamp for wavelength calibration The lamps are partly mounted on an integrating sphere and relay optics simulate the F 15 telescope beam
52. ere is a trap in the column X1609 which might show up as a slight depression over 130 pixels in the extracted spectrum of one order In long binned exposures this CCD shows also an emission band starting on the red side and extending over the rows 2790 2850 with decreasing intensity toward the blue UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182525 side of the CD spectrum format Since this band is perpendicular to the orders it is usually well subtracted in the sky subtraction step of the reduction process 2 4 6 Telluric features in flatfield exposures Due to the long optical path length inside the UVES spectrograph the flatfield exposures taken with the internal flatfield lamps display telluric absorption features of O and H20 The flatfielding performance in these spectral regions is reduced and possible wavelength shifts between calibration and science exposure will lead to spurious residual spectral features Chapter 3 Preparing the Observations 3 1 Introduction Before the actual execution of observations several steps have to be taken The prepara tion of an observing program is split in two parts Phase I and Phase IT In Phase I the emphasis in the application for VLT observing time is put on the scientific justification and on the technical feasibility of the proposed observations In Phase IT the successful appli cants prepare the detailed instrument set up and observing plan through the completio
53. erging F 10 beam and thus cause a defocus blur of 0 08 arcsec mm of thickness in the CCD plane this corresponds to a blur of 5 9 um in the blue and 8 3 um in the red The spectrograph is normally focused for a nominal filter thickness of 5 mm as of the filters used in the standard instrument setting for scattered light or second order suppression The blue and red mirror collimators each consist of two off axis parabolas and two flat mirrors They are of the white pupil type and so have two 200 mm pupils one for the echelle and one at the crossdisperser camera which leads to moderate size and simplified design of these components The blue and red echelle gratings are 84 cm long and 21 cm wide Because grating masters of this size cannot be ruled a new process has been developed in which a replica is made of two precisely aligned masters The result is a monolithic mosaic with a resolving power on the order of 2 000 000 and a stable Line Spread Function The groove density and hence the order length has been selected such that the order length is equal to the CCD width at 500 nm blue arm and 990 nm red arm Loss of the ends of the orders beyond these wavelengths can be recovered using the tilt tables see below Further information on the echelle and cross disperser gratings can be found in Table 2 2 The exposure meter pickup mirrors see below are permanently mounted before the echelles covering the 14 mm gaps between
54. esponds to an approved activation code and if this is the case the on going observations are ended and a new BOB starts an OB with the same name as the ftp file The telescope automatically presets to the coordinates specified in the ftp file and the requested observations are performed straight away PIs of approved UVES ToO programs requesting this mode need to prepare their OBs in the usual way However these RRM programs use specific acquisition templates described in the UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182533 UVES Template Reference Guide More information on the RRM can be found on the USD Phase II webpages http www eso org observing p2pp rrm html 3 6 The UVES Exposure Time and Spectral Format cal culator The UVES Exposure Time and Spectral Format Calculator ETC is accessible through the ESO world wide webpage at http www eso org observing etc The ETC models the instrument and detector in their different configurations It is the basic tool for an observer in the planning of an UVES observation It can be used to compute the detailed spectral for mat wavelength and order number as function of x y position on the detector and the S N to be expected for the specified target and atmospheric conditions and for a given instrument and detector setting as a function of exposure time The ETC can also be used to access the efficiency curves of the various optical components of the instrument
55. hange of 0 3 C induces the same change In a night the air pressure at Paranal can change by several hPa Temperature changes inside the enclosure are normally very slow a change of 0 3 C can take several hours The file header contains values of the airpressure and temperature at the beginning and end of the exposure 4 4 Flat fielding There are four standard flat fielding lamps combined with different filters to give well exposed flat continuum spectra at all wavelengths within a reasonably short exposure time see Ta ble 4 2 A deuterium lamp is recommended for the spectral region shortwards of 350 nm The flatfield spectra provide a good correction of the blaze function of the echelle They are also useful to correct for the pixel to pixel variation in CCD sensitivity as a function of the impinging wavelength of the light and to correct for the structures introduced by imperfections of the slit geometry slit function In the red part of the spectra gt 650 nm narrow fringes with peak to valley amplitudes up to 30 are present in the spectra on the EEV CCD of the UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182542 Table 4 2 Exposure times for Calibration Lamps for slit width of 1 arcsec unbinned low gain CCD read out mode CCD pixel saturation occurs at 65000 ADU 43000 ADU for the MIT LL with non linearity above 40000 ADU Exposure times have to be scaled down by a factor of 12 for the 2
56. he complete filter curves can be recovered from the UVES components database accessible through the ETC 7 2 List of standard stars Any flux standard star can be used for flux calibration and blaze correction The standards to be preferred should have measurements at a step of 2 nm or less to have a few points for each echelle order For the pipeline reduction it is necessary to use stars for which the flux Ta ble is available in MIDAS The UVES webpage http www eso org instruments uves contains a pointer to the lists of flux and radial velocity standards 7 3 Lists of arc lines Tables of the ThAr lines used in the pipeline reduction are available on request to usd help eso org A pointer to the UVES Atlas of the ThAr spectrum at resolution 100000 can be found in the UVES webpage http www eso org instruments uves The Thorium line list is based on Palmer B A Engleman R Jr 1983 Atlas of the Thorium Spectrum Sinoradzky H ed Los Alamos National Laboratory and lines are selected ac cording to R 100000 based on de Cuyper J P Hensberge H 1998 A amp AS 128 409 For the Argon lines the reference is Norl n G 1973 Phys Scripta 8 249 7 4 Pointers to UVES sample observations The UVES webpage http www eso org instruments uves contains a pointer to the list of scientific observations and calibrations from the instrument Garching test phase Com UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13
57. he effect of fringing is important A gt 650 nm The time required for dichroic calibrations should be computed assuming sequential FF calibration exposures different lamps have to be exposed one after the other As an example we consider a target where the ETC computes an exposure time of 180 minutes to reach the desired S N ratio in the red arm and it is required to obtain the highest accuracy in the wavelength calibration and in the FF correction We split the exposure time in three integrations of 1 hour to permit median filtering of the cosmic rays Additionally calibrations are attached for high radial velocity accuracy and a FF exposure We thus have telescope pointing 6m slit centering 2m UVES setup lm 1st exposure 60m read out time 1m ThAr 0 5m read out time 1m 1FF 0 5m read out time Im x three times This leads to a total time of 201m of which 183m of integration and 18m overhead 10 The overhead becomes relatively more important if many short exposures with different setups are required 3 9 Check list 1 Decide whether to use standard wavelength setting or free template 2 In case of standard setting decide for visitor justification needed or service mode In case of a free template the visitor mode is required 3 Use ETC to check spectral format and exposure time 4 If resolving power gt 40 000 is required decide whether to use narrow slits or image slicers 5 Any special constraints ne
58. he small fraction of light about 1 that hits the small gap in the center of the echelle mosaics is reflected to the exposure meters in front of the echelle gratings Via the intermediate spectrum mirrors and the transfer collimators the dispersed beams fall on the cross disperser units From here the echelle spectra enter the cameras and are recorded on the CCD detectors The spectrograph arm functions and components The slit units consist of two reflecting diamond machined Al blades whose separation slit width is continuously adjustable from 0 15 to a maximum of 20 arcsec The height of the slit is determined by continuously adjustable deckers of the same material which can open up to 30 arcsec UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182517 Table 2 2 UVES echelle and cross disperser gratings Echelle gratings g mm Resolving Spatial Blaze Blaze Power resolution angle Eff Blue 41 59 1 900 000 0 1 76 0 67 Red 31 6 2 100 000 0 09 75 04 63 Cross disperser gratings g mm Wav range Average Wav of Peak Blaze nm Ef Eff nm Eff CD1 prot 1000 300 390 gt 55 430 60 CD2 660 370 500 gt 60 460 65 CD3 600 420 680 gt 60 520 68 CD4 312 660 1100 gt 70 770 80 The below slit filter wheels have 23 positions each for 25 mm filters for order sorting or stray light rejection The filters are used in the div
59. in a single observation It is the smallest schedulable entity which means that the execution of an OB is normally not interrupted as soon as the target has been acquired and centered on the slit An OB is executed only once when identical observation sequences are required e g repeated observations using the same instrument setting but different targets a series of OBs must be constructed The detailed definition of UVES Observation Blocks and Templates is given in Ref 1 For example one would like to obtain a spectrum of a point source in the wavelength re gion 500 680nm with a resolving power of 60 000 First the instrument mode has to be chosen The wavelength region 500 680 nm is covered by the red arm of the spectrograph The instrument mode is set by chosing the corresponding sets of acquisition observation and calibration templates containing the mode red in their name Second it has to be decided if the observation should be carried out with a standard longslit or with an image slicer Accordingly one has either to select the red slit acquisition template UVES_red_acq_slit or the red image slicer acquisition template UVES_red_acq_ims1 and select slicer 1 which provides the required resolving power In addition the information on the target position has to be provided in the acquisition template For the observation itself the red observation template UVES_red_obs_exp can be used with the predefined wavelength
60. ing 1 and 4 The final gratings 4 and 1 have been installed in November 2000 and October 2001 respectively The performance is identical to that of the prototypes but with a higher efficiency The Cameras are both of the dioptric type with an external focus to facilitate detector exchange Focus is set manually and then maintained automatically by thermal expansion rods in the camera support structure The blue and red cameras have unvignetted entrance apertures of 210 and 230 mm focal lengths of 360 and 500 mm and fields of 43 5 and 87 mm diameter respectively Their image quality is 20 um on axis to 30 um in the corners diameter of circle containing 80 of the energy The transmission curves can be found in the UVES database available through the instrument ETC The camera CCD units are mounted on Tilt Tables that allow to tilt the optical axis by 0 48 degrees This allows a shift of the echellogram in the main dispersion direction of up to 200 pixels in the blue and 280 pixels in the red to recover spectral features that are lost at the order ends or fall on a bad column The setting accuracy and repeatability is better than 0 1 pixel 2 2 3 The Slit Viewer CCDs UVES includes four CCD systems two slit viewer technical CCDs and two scientific CCD detectors for the blue and the red echelle spectra The red and blue slit viewer units in corporate Peltier cooled 288 x 385 22um pixel frame transfer front illuminated CCDs on which
61. irror 1 will be used to feed the red arm of UVES with light from 8 fibres from the FLAMES positioner located on the other Nasmyth focus expected start of this mode beginning of 2003 Mirror 1 has a coating optimized for the wavelength range covered by the blue arm Dichroic 1 has a cross over wavelength at 450 nm Dichroic 2 at 550 nm The efficiencies of the two Dichroics can be found in the UVES database available through the ETC The working position of this unit is determined automatically by the instrument software once the instrument observing mode is selected Red and blue Slit viewer CCDs see Section 2 3 are available to view the field location of the spectrograph slit within the field The diameter of the unvignetted field at the slits is 30 arcsec while the useful field of the slit viewer CCDs extends up to 60 arcsec diameter Slit viewer images at the beginning of spectroscopic UVES exposures are automatically archived The operator can request the system to save or print additional slit viewer images 2 2 2 The two spectrograph arms The blue and red arms are functionally identical Differences in the properties of coatings cross dispersers and CCDs are addressed below where appropriate The light path In both arms the respective beams that enter the spectrograph are reflected by a folding mirror to the main collimators From here the collimated beams are dispersed by the echelle gratings and sent back to the main collimators T
62. lit the acquisition templates allow to enter additional velocities in right ascension and declination in units of arseconds per second The target is identified on the image of one of the Slit Viewers SVs by the visiting astronomer or in case of service observations by the ESO staff astronomer The target is identified by clicking on it with the mouse and automatically positioned on the slit The optical derotator can be used in SKY mode to orientate the slit according to a desired position angle PA by entering the value in the acquisition template During the exposure the derotator will keep the relative orientation sky slit constant If the ELEV mode is selected for the derotator the slit will be kept aligned with the directrion of the atmospheric dispersion during the exposure When the acquisition template for image slicers is used the target is moved automatically to the position on the SV CCD that corresponds to the entrance aperture of each slicer This has been calibrated in advance by the ESO operating staff When this operation is completed the IS is moved in blindly and the exposure started Note that no atmospheric dispersion compensation nor alignment with the parallactic angle is available with image slicers The atmospheric dispersion can be only compensated by the larger entrance apertures of the slicers cf Tab 2 1 In case of dichroic observations the target is visible on both the blue and red arm SV cam eras The
63. ly reflected back to the cross disperser grating through the camera lenses After a further reflection on the grating the second order spectrum is re imaged by the camera on the CCDs These ghosts appear as in focus echelle orders with a steeper inclination and approximately twice the order separation than the primary spectra The effect is relevant with the 4th CD at the far end of the spectrum central wavelength 860nm where the efficiency of the CCDs decreases and the importance of reflections is higher On the MIT chip upper CCD in the mosaic reflections from the EEV lower CCD of the mosaic are seen For reference see the flat field data available through the UVES webpage The relative intensity of the ghosts to the primary UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182522 dr Resolving power amp FWHM px blue EEV 1x1 100 1x1 2x2 2x2 under 50 pred sampling 0 red EEV 1x1 100 1x1 eo 2x2 S 2x2 E N pred E 50 E 0 red MIT 1x1 100 1x1 2x2 2x2 pred 50 0 0 0 5 1 1 5 2 0 0 5 1 1 5 2 slit width ares slit width ares Figure 2 4 Measured mean resolving power R in 1000 and FWHM in pixels as a function of the slit width The data have been measured as part of the pipeline processing of service mode data in the time between October 2000 and June 2001 Values for 2 x 2 binning modes are scaled and were added only for slit widths gt 1 0 arcsec where no 1 x 1 data was available
64. n of so called Observation Blocks Together with the Phase I and Phase IT documentation http www eso org observing proposals the information contained in this chapter and in Chapter 4 provides a guideline for the Phase I and Phase II preparation process for UVES observations In Chapter 5 information is given for astronomers who come to Paranal to observe with UVES The preparation process can be summarized as follows Phase I e Definition of scientific justification e Choice of instrument mode Estimate of exposure time to reach the needed S N ratio at the desired resolution Estimate of telescope and instrument overheads e Determination of scheduling constraints e g visibility time critical observations e Overview observation plan e g target list calibration needs Phase II for successful applicants e Identification of detailed instrument set ups e Identification of target acquisition requirements e g finding charts slit orientation offset star e Preparation of needed Observation and Calibration Blocks 26 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182527 Part of the VLT observing time is carried out in service mode by the Observatory Staff i e in absence of the applicant All information necessary to successfully execute the proposed observing program has to be provided in the form of Observation Blocks finding charts and other relevant information in advance of the ob
65. n of photoelectrons charge transfer as well as the echelle dispersion The instrument does not include a remotely controlled focus adjustment since the cameras automatically compensate for temperature variations of the complete optical train from slit to CCD The UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182521 image quality over the entire spectral range is expected to be better than 20 30 um over the full CCD 80 of the energy This allows to reach the maximum resolving power two pixel sampling using slits as narrow as 0 4 arcsec blue arm and 0 3 arcsec red arm The measured resolving power as a function of slitwidth is shown in Fig 2 4 The blue arm achieves a resolving power which is better than the predicted performance The resolving power as measured for the red arm with the EEV CCD chip is consistent with the predictions In the measurements with the MIT LL CCD a 5 10 reduction of the resolving power with respect to the predictions and to the EEV chip is measured for slit widths narrower than 0 8 arcsec Charge diffusion effects in the MIT LL chip lead to this apparent degradation in spectrograph resolution Recent measurements of the resolving power and other instrument characteristics are avail able under http www eso org observing dfo quality UVES qc qc1 html The transmission and reflection efficiency curves of the various optical components and of the CCDs cf UVES database av
66. ng the 7 5 arcsec slicer slit CCD quantum efficiency 85 read noise 3 electrons rms dark noise 1 e pix h UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182537 3 7 Target Acquisition and Guiding The pointing of the VLT is accurate to 1 arcsec rms this does however not guarantee that the target will be centered on the slit after telescope pointing In case of crowded fields the identification of the object is carried out by the astronomer or in case of service observations with help of a finding chart provided by the user Final coordinates and when required the finding chart in the format specified in the Proposal Instructions must be submitted during Phase II of the proposal preparation The target coordinates must be accurate to lt 1 to avoid an unnecessary waste of telescope time during the target acquisition phase In most cases the Digital Sky Survey DSS can be used to prepare finding charts and is accessible from the ESO world wide webpages http archive eso org dss dss or using Skycat For crowded fields or faint extended objects other well suited image sources have to be used The DSS and other tools can be accessed through the Proposal Preparation and Submission page http www eso org observing proposals which allow the calculation of site sky ephemerides the determination of object observability airmasses etc For the observation of moving targets or for drift scanning with the UVES s
67. nutes direct slit faint point or extended source requiring two iterations 5 minutes e Instrument set up and CCD read out time A new instrument set up takes at most 1 minute The read out time for the CCD mosaic in the red arm 1 port chip is slow read out mode 50 Kpix sec 2x2 binning 45 seconds fast read out mode 225 Kpix sec unbinned 40 seconds and 10 sec shorter for the blue arm CCD In a dichroic exposure with identical exposure times in the two arms the CCDs are read out in parallel The shortest possible cycle time with the UVES instrument can be achieved by the use of the ultrafast read out mode 625 Kpix sec unbinned 2 ports per chip 10 seconds In this configuration the deadtime between closing and re opening of the CCD shutter is 25sec only if no other movements of the instrument functions are needed This read out mode is only available in Visitor Mode e Calibrations BIAS frames and FF and ThAr calibration lamp exposures are taken with the same instrument and detector set up as the science exposures during the day for details cf 2 If the wavelength accuracy is critical the ThAr calibration should be taken immediately after the science exposure This will take into account any significant change UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182539 in the air pressure or in the air temperature see Chapter 4 2 The same applies to the FF at wavelengths where t
68. onsists of a mosaic of one EEV EEV 44 82 and one MIT LL CCID 20 4kx2k CCD this is to optimize the detector response as a function of wavelength and to reduce UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182519 Table 2 3 Measured properties of UVES scientific CCDs Dec 99 values Blue EEV Red Mosaic Quantum efficiency Number of pixels Pixel size Gain MIT LL values in brackets Read out noise fast read out low gain slow read out high gain Saturation low gain MIT LL in brackets Full frame readout s at 50 kpix 2x2 bin at 225 kpix unbinned at 625 kpix unbinned Dark current levels Fringing amplitude at 850nm CTE Read out direction Prescan Overscan areas Flatness 49 at 320 nm 56 at 350 nm 82 at 400 nm 88 at 500 nm 2048 x 3000 2048 x 4096 used in windowed readout 15 um low 1 84 e7 ADU high 0 54 e ADU 3 9 2 1 e rms 65000 ADU 34 1 port 30 1 port 6 4 2 ports 0 4 e pix h at 120 C gt 0 99993 in disp dir Pix 1 50 and 2098 2148 lt 15um peak to peak 89 at 450 nm EEV 89 at 600 nm EEV 81 at 800 nm MIT LL 46 at 900 nm MIT LL 4096 x 4096 2048 x 4096 2 x 1 mosaic 15 um low 1 6 1 5 e ADU high 0 57 0 57 e ADU EEV 3 4 2 0 e rms MIT 3 8 3 4 e rms 65000 ADU 43000 ADU 45 2 ports 40 2 ports 10 4 ports EEV 0 5 MIT 1 1 e7 pix h at 120
69. ositioner of FLAMES the instrument mounted at the opposite Nasmyth platform can feed the red arm of the UVES spectrograph UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 18200 18253 Table 1 1 UVES characteristics and observing capabilities Blue Arm Red Arm Wavelength range 300 500 nm 420 1100 nm Resolving power slit product 41 400 38 700 nm pixel Max Resolving power 2 pixel sampling Throughput at blaze TEL UVES no slit no atm Limiting magnitude 90m exp time S N 10 0 7 arcsec slit seeing 0 7 CCDs Pixel 15um scale disp dir varying along order along slit dep on cross disp Echelle R4 mosaic Cross dispersers Blaze wavelength Blaze wavelength Typ wavel cov CD1 and CD3 CD2 and CD4 in parenthesis Min order separation standard setup 0 0019 nm at 450 nm 80 000 12 at 400 nm 18 R 58 000 at 360 nm 2048 x 4096 windowed to 2048 x 3000 0 215 20 0 25 CD1 and CD2 41 59 g mm CD1 1000 g mm 430 nm CD2 660 g mm 460 nm 85 126 nm in 33 31 orders 10 arcsec 40 pixels 0 0025 nm at 600 nm 110 000 14 at 600 nm 19 5 R 62 000 at 600 nm two 2048 x 4096 mosaic of different types 0 155 20 0 18 CD3 0 17 CD4 31 6 g mm CD3 600 g mm 560 nm CD4 312 g mm 770 nm 200 403 nm in 37 33 orders 9 arcsec 51 pixels UV Visual Echelle Spectrograph UVES User manual VLT
70. pted based on the scientific rationale and technical feasibility prepares the Observation Blocks to carry out the observing program Pre slit area UVES spectral elements located in front of the spectrograph slits Secondary Guiding The image of the target reflected by the slit jaws is used to correct for possible small displacements between the telescope optical axis and the instrument which is mounted on the Nasmyth platform Sequencer A sequence of exposures on different targets i e different OBs can be obtained using the Sequencer or Scheduler The Sequencer is capable of conditional branching and has knowledge of parameters not necessarily accessible to the observation software e g the seeing conditions Slit Viewers Simple optics which focus the light reflected by the slit jaws on two CCDs detector They are used to center the targets on the slit Spectrograph arm UVES consists of two separate spectrographs one optimized for the blue blue arm and one for the red wavelength region red arm Spectrograph slit Two parallel reflecting metal blades with an adjustable separation slit width form the entrance slit of the spectrograph The image of the astronomical source produced by the telescope is focussed on the slit plane Standard Setting A pre defined setting of the instrument facilitating the preparation of the observations The Observatory keeps an updated database of the relevant calibration files for all St
71. r attached Wavelength n oT high precision wavelength calibration Order Definition 1 1 3 pipeline calibration order definition Format Check 1 1 3 pipeline calibration physical model Bias 5 1 7 creation of master biases Dark 3 1 30 creation of master darks Flux Standard n or response correction flux calibration Telluric Standard n or removal of telluric spectrum Radial Velocity Std n or absolute radial velocity calibration Iodine Cell Flatfields 5 1 1 master flats for IP reconstruction if iodine cell was used o r on request only corresponding OBs to be provided by user n number to be defined by user of changing temperature and or pressure or of a small earthquake To this purpose the user can insert in the OB after the Observation Templates a so called attached calibration template where a lamp is selected and all instrument parameters except the exposure time are left unchanged The telescope will not lose the guide star during the lamp operation because the calibration unit is located after the adapter of the Nasmyth focus The instrument currently repositions the moving functions with great accuracy Taking different ThAr spectra after changing the instrument configuration leads to shifts which are less than 1 20 of pixel rms This corresponds to errors in radial velocities of less than 50 m sec As a guidance note that 1 hPa millibar change in the pressure corresponds to a shift of about 1 20 of a pixel A c
72. r http www eso org observing dfo quality index uves html The time evolution of the most important instrument parameters like resolving power spec tral stability detector characteristics and others can be followed with the help of continuously updated trending plots as available on the UVES QC webpages 4 7 Special calibrations 4 7 1 Use of the iodine cell for accurate radial velocity measure ments As indicated in Chapter 2 UVES is equipped with an iodine absorption cell which can be inserted in the beam and operated remotely to obtain a dense grid of iodine absoprtion html UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182544 lines superimposed on the target spectrum The iodine cell currently mounted on UVES has an operating temperature of 70 C and produces a rich absorption line spectrum in the range 490 640 nm Because of the operating temperature the iodine cell requires a warming time of at least one hour and can be used only during dedicated observing runs For the iodine cell observations the following R600 standard configuration is used RED mode free template CD 3 central wavelength 600 nm To make best use of the iodine absorption spectrum a slit width of 0 3 should be chosen and combined with the undersized pupil stop and possibly with 1543 to reduce slit losses ESO does currently not provide any support for the required modeling IP reconstruction of data obtained with the iodine a
73. rge telescope VM Visitor Mode Chapter 2 Instrument Characteristics 2 1 Opto mechanical layout Figure 2 1 is a 3D CAD view of the instrument table with the mounted spectrograph elements Fig 2 2 shows a schematic layout of the instrument The present configuration was selected in May 1994 after a trade off among the different concepts outlined in the initial feasibility study The instrument consists of two main parts the first part is mounted on the rotator which remains stationary while the telescope adapter rotates to follow the field rotation It includes the calibration system a removable iodine cell a slide with image slicers and an optical derotator which is permanently installed in the beam The second part the two arms cross dispersed echelle spectrograph is mounted on a steel table fixed to the floor of the Nasmyth platform and is covered by a light tight enclosure which also provides thermal insulation and protection from dust The light beam from the telescope is focussed on the red arm entrance slit or is directed to the blue arm slit by a mirror On the fixed table in the pre slit area additional optical components are available for insertion in the optical beam filters a depolarizer an Atmospheric Dispersion Compensator ADC and two pupil stops of different size Two dichroics are available to work in parallel with the two arms The blue arm AA 300 500 nm and the red arm AA 420 1100 nm have an identical layout
74. rum and the standard star spectrum have to be obtained under photometric conditions at similar airmasses and preferably with the same slit width In this case dedicated OBs have also to be provided by the observer or service mode PI Recently for QC purposes daily monitoring of spectrophotometric standard stars using three Dichroic settings 346 580 390 564 437 860 and 1 x 1 binning was introduced during twilight A table of flux standard stars suitable for observations with UVES is given in the Appendix For flux standards only the std Observing Templates have to be used The response curves of the UVES spectrograph are found to be very stable in time Therefore master response curves for all standard instrument settings are provided through the qual ity control webpages under http www eso org observing dfo quality UVES qc std_qcl which can be used to correct for the relative response of the instrument A correction of the science spectra by the master response curves does allow to recover to a certain extent the shape of the source continuum or to measure relative line strengths across the complete UVES spectral range 4 6 Quality Control All calibrations taken in one of the standard settings are pipeline processed and quality controlled by the Quality Control group at ESO Garching The calibration products are de livered with the corresponding Service Mode data More information about the UVES quality control can be found unde
75. s Breaking up a long exposure in N partial exposures will raise up the read out noise line by VN 3 6 3 Exposure time and predicted counts and S N ratios To be guided to a preliminary estimate of the exposure time the predicted S N at the blaze peak efficiency in the UV 360 nm and V 550 nm spectrograph arms are given as a function of magnitude for different exposure times and a resolving power of 55 000 0 7 arcsec slitwidth in Figs 3 2 3 3 and for an image slicer in Fig 3 4 These plots have been produced with a set of parameters which are not yet exactly matched to the current parameters of the instrument They can be used for a quick first overview of the capabilities only The UVES ETC includes the updated instrument parameters and should be used to estimate the exposure times in Phase I and II of the observing proposals The output of the ETC is a table listing the pixel size in wavelength for each order the computed efficiency the total expected electrons for the object and the sky the maximum pixel intensity to monitor saturation the predicted S N ratio the central wavelength of the order and the wavelength bin size The computation is repeated for the minimum and maximum wavelengths of the free range of each echelle order UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182535 YV band dit 0 7 R 55 000 binned 1000 00 L La m 12 100 00 sed Demi 4 I AE EE ER ER Led ER ER
76. sed in the same way as data obtained without the iodine cell But ESO does not plan to provide a package for the modeling IP reconstruction of the iodine cell data However ESO has quantified the instrument capabilities for high radial velocity accuracy measurements using IP reconstruction techniques on dedicated commissioning data cf K rster et al contact akaufer eso org a long term stability of lt 2m s rms has been achieved over the commissioning time span of one month 6 4 2 Image slicer data Standard echelle data reduction packages can be adapted to extract image slicer spectra taking into account the need to use an extended extraction slit which matches the length of the slicer Monitoring of the sky spectrum is possible if slit lengths longer than the slicer length are chosen The UVES pipeline extracts science data taken with image slicers in the average extraction mode i e by summing the signal over the slicer slit Chapter 7 Other useful information 7 1 List of available filters 7 1 1 Pre slit filters The available pre slit filters for maintenance and Observatory calibrations only neutral den sity filters in bold face for acquisition of bright stars and the Johnson U filter for image slicer acquisitions are Pre slit filters Name Peak nm Peak Transom Comment PS1 U 350 gt 60 Acquisition filter PS2 B 420 gt 60 Acquisition filter PS3 V 540 gt 80 Acquisition filter
77. servations to ESO following the instructions sent to the applicants The Observatory staff will combine the execution of different programs in the same night optimizing the time sequence and the seeing and moon requirements Obser vations carried out with the applicant present at the telescope are referred to as visitor mode observations In this mode the astronomer prepares or finalizes the OBs at the Observa tory in advance of his her nights He she decides about the sequence of observations during the night but their execution is however still performed by the telescope and instrument operator To facilitate the preparation of Phase I and Phase II proposals besides the information provided in this User Manual ESO has developed a sophisticated Exposure Time Calculator ETC see Section 3 5 The ETC permits to estimate the signal to noise ratio for a given configuration and exposure time taking into account specific atmospheric conditions and determines the spectral format resulting from the selected instrument set up The Observing Blocks are prepared using another ESO provided software tool called P2PP see 8 and http www eso org observing p2pp Before preparing the observations it is advisable to look at the UVES quality control webpage http www eso org observing dfo quality UVES qc problems html which gives infor mation on current problems and possible new instrument artifacts detected during the current observing period
78. setting 580 which covers the requested wavelength region The other parameters to set are in case of a longslit exposure the slit width e g 0 7 to obtain a resolving powr of 60000 the read out mode of the detector see 82 4 and the exposure time If one likes to carry out a dedicated wave length calibration after the science exposure the attached wavelength calibration template UVES red cal waveatt has to be added Together the three selected templates form an Observation Block that is used to perform the required observation The preparation and editing of Observation Blocks is done with the Phase IT proposal prepa ration software P2PP 8 which successful applicants for observing time can obtain from ESO http www eso org observing p2pp for installation at the astronomer s home institute This software is also available at the observer s station at the VLT Observatory for preparation of the OBs in advance of the observations 3 5 Rapid Response Mode for UVES Starting in Period 73 a new mode the Rapid Response Mode RRM is offered for obser vations of transient phenomena such as gamma ray bursts or supernovae in semi automatic mode The user PI or Co I of an approved target of opportunity program submits an ftp file with the coordinates of the target to a specific ftp server on Paranal A special program at the telescope continuously monitors this ftp directory when it detects a file it checks if the filename corr
79. t fields at a central wavelength of 860 nm the intensity of the ghost orders is lt 1 of the real orders on the EEV chip and between 1 and 7 on the MIT chip The same effect is seen with CD 1 at the standard setting with central wavelength 346nm For a source with a flat spectrum over the range 300 400 nm the intensity of the ghosts is 1 of the primary spectrum The measurements of the ghost intensities were carried out with the prototype crossdisperser gratings 1 and 4 With the installation of the final 1 and 4 gratings in October 2001 and November 2000 respectively the intensities of the ghost orders have been reduced as expected from their higher efficiencies in the relavant wavelength regimes 2 4 3 Remnants of ThAr lamp spectra In the spectral region above 700 nm the ThAr lamp has some very bright Argon lines which saturates the CCDs even for the short exposures time needed for a wavelength calibration exposure The standard read out will not completely remove the electrons at the positions of the heavily saturated lines Faint remnants will then surface in any relatively long integra tion which follows the calibration exposure The effects vanishes after several CCD wipings or typically after 1 2 hours It is recommended not to take a ThAr calibration in the far red spectral region during the night if they are to be followed by a long integration on a faint object If highest wavelength calibration accuracy is required
80. tes 49 6 4 1 Data taken with the iodine cell 49 OAS Image SGA src rasa Sub esse ee e amp Eee 49 7 Other useful information 50 ZG Diep er pala o AV e ein AR Ak E MARGE ERY RM RES E 50 7 1 1 Pre slit filters eu Lux d au RE NASA EER Ew Le amp de 50 TL2 Delow sht Derm 4 4 8 s WEE PASE Man DE Ed E o e 8 51 Lo dist of standard stats Le 2 224088 28 D be eA RGR A E GA E A 51 UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 1825ix Co Ba E PDT RT ee Se ae Se ee OE ES OE e 51 7 4 Pointers to UVES sample observations 26 265 266 be bee ee ae rs 51 Index 53 Chapter 1 Introduction 1 1 On the contents of the UVES User Manual The current version of the UVES User Manual is available as a retrievable postscript file at the ESO home page on the World Wide Web http www eso org observing vlt instruments uves Before the observing proposal application deadlines the User Manual is normally updated any significant changes are announced on the UVES webpages If you have no access to the WWW a printed copy can be requested from ESO s Visiting Astronomers Section on Internet visas eso org in Garching Germany Paper copies of a new version of the UVES User Manual are printed out only after a major revision of the document The reader is referred to the web version of this document for the best quality of the included color figures The first Chapter of this manual is address
81. th The start and end points of the spectral ranges reported in the table are generally conservative as they do not include the echelle orders which are outside the sensitive area of the CCD by more than 50 of their length UVES standard settings Mode Cross Below Min Central Max Decker Gap Disp slit filter Wav Wav nm Wav Height nm Using dichroic DIC1 CD 1 HER_5 308 346 388 10 CD 3 SHP700 476 580 684 12 5 DIC1 CD 2 HER 5 326 390 445 8 CD 3 SHP700 458 564 668 11 2 DIC1 CD 1 HER 5 303 346 388 10 CD 3 SHP700 458 564 668 11 2 DIC1 CD 2 HER_5 326 390 445 8 CD 3 SHP700 476 580 684 12 5 DIC2 CD 2 HER 5 308 346 388 10 CD 4 BK7 5 565 760 946 8 7 DIC2 CD 2 HER_5 326 390 445 8 CD 4 BK7_5 565 760 946 8 T DIC2 CD 2 HER5 373 437 499 10 CD 4 BK7_5 565 760 946 8 7 DIC2 CD 2 HER5 373 437 499 10 CD 4 OG590 660 860 1060 12 10 DIC2 CD 1 HER5 303 346 388 10 CD 4 OG590 660 860 1060 12 10 DIC2 CD 2 HER 5 326 390 445 8 CD 4 OG590 660 860 1060 12 10 Using blue arm only BLUE CD 1 HER 5 308 346 388 10 BLUE CD 2 HER 5 373 437 499 10 Using red arm only RED CD 3 SHP700 414 520 621 8 9 1 RED CD 3 SHP700 476 580 684 12 5 RED CD 3 SHP700 500 600
82. the auto guiding This primary guiding is based on the tracking of the guide star detected with the guide probe in the telescope adapter UVES is installed on the Nasmyth platform To make sure that there are no displacements of the telescope optical axis with respect to the plane of the entrance slit of the spectrograph during long exposures due e g to flexures of the platform as the telescope moves in azimuth the primary guiding is complemented regularly at slow frequency typically every few minutes using information provided by the Slit Viewing Camera The reference object can be either the target itself or another object in the field This facility is called secondary guiding In case that the OB foresees target acquisition with an image slicer the identification pro cedure is initially identical Once the target has been identified the operator will move it automatically to the position in the field which corresponds to the entrance of the IS When this step is completed the IS is moved in the beam and the exposure is started Secondary guiding is not available for observations with image slicers 5 2 2 Monitoring the integration The visiting astronomers can monitor the development of the observation on one of the ter minals of the WS by following the continuously updated plots of the counts of the blue and red exposure meters see 2 2 2 The instrument operator will set up the plot intensity and time scale according to the running o
83. the two echelle segments and directing light that would otherwise be lost to blue and red optimized uncooled photomultipliers operating in photon counting mode The dark current rate is on the order of 1 blue to 10 counts per second red at a table temperature of 12 C The EMs are mostly useful to monitor the count rate during an exposure The actual signal is a function of the magnitude and color of the target of the spectrograph mode of the seeing and the slit width of the selected below slit filter but not of the CD set up The results are presented to the user in a strip chart like display which can be printed Counts statistics are stored in the image headers Note that the EM signal is proportional to the total flux entering through the slit including sky During commissioning at the telescope it was possible to monitor the flux of objects as faint as 19 magnitude object in both arms typically 20 cps above the background UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182518 The blue and red cross disperser units are grating turrets with two gratings mounted back to back on each unit Selection of the grating is done by rotation of the unit the angle of the grating is automatically set according to the required wavelength of the central echelle order The properties of the cross disperser gratings 1 4 can be found in Table 2 2 At start of the operation of UVES prototype gratings were installed for grat
84. ttings are also reduced on line by the UVES instrument pipeline using a pre populated calibration database Up to 2 non standard settings can be set up per visitor run The raw files and the products of the pipeline are FITS files cf Chapter 6 2 They can be accessed and inspected by the astronomer on the assigned off line WS which is also available for running the major image analysis systems like MIDAS IDL and IRAF This preliminary reduction extraction wavelength calibration flat fielding and sky subtraction provides advanced information on the quality of the obtained data but has to be regarded as a quick look reduction facility only Chapter 6 The reduction of UVES data 6 1 Real Time Display and quick look As soon as they are read out by the FIERA Controller and transferred to the instrument WS the CCD frames are automatically displayed on a Real Time Display RTD panel on a screen of the instrument WS on two windows in case of dichroic exposures The visiting astronomer can use the standard tools of the RTD on the astronomer s offline WS to visually display and inspect the spectra to produce intensity traces and to compute the statistics of pixels values in a subwindow Previous exposures can be reloaded 6 2 Pipeline reduction of UVES data ESO has developed a pipeline reduction for UVES which primarily supports the predefined standard central wavelength settings in 1x1 and 2x2 binning modes as available in Service Mode
85. urations where no order separation or straylight rejection filter can be used the 5mm clear filters i e HER_5 in the blue and BK7_5 in the red have to be inserted The HER_5 filter has replaced the CUSO4 straylight rejection filter in Decem ber 2001 as below slit filter in the blue settings The CUSO4 filter has been decommissioned because of degrading performance of its transmission By combining the standard settings DIC1 346 580 and DIC2 437 860 the full spectrum 300 1006 nm of a target can be covered with only two exposures of the instrument with the exception of the small gaps due to the CCD mosaic At wavelengths longer than 993 nm the orders do not overlap anymore and the wavelength coverage is incomplete A shift of up to 200 or 280 pixels of the blue respectively red echelle spectrum in the dispersion direction can be obtained by changing the tilt of the camera see 2 2 This might be useful in case an important spectral line falls outside the edge of the CCD With the standard setting DIC1 390 564 it is possible to cover the continuous wavelength region from 332 to 668 nm UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182529 Table 3 1 The UVES standard settings 2 in the blue 4 in the red and 7 in dichroic mode are listed below The two CCDs in the red camera are separated by approximately 0 96 mm this results in a gap in the wavelength coverage approximately centered on the central waveleng
86. viewer technical CCD which would lead to a degradation of the centering accuracy during the interactive acquisition procedure For filter NDn n 1 3 the brightness is lowered by n x 2 5 mag Make sure that the effective brightness of the target is between 7 11mag Note that the filter will be forced to FREE no filter for the science exposure The U filter must be used for acquisitions with an image slicer if the subsequent observations are carried out in the blue arm of UVES with CD 1 to minimize the effects of atmospheric dispersion the ADC cf below and the derotator mode ELEV cannot be used in combination with the image slicers The Atmospheric Dispersion Corrector ADC unit is a slide that can be used to insert two counter rotating prisms in the telescope beam which compensate for atmospheric dispersion up to zenith distances of 65 degrees The ADC is useful when the derotator cannot be used to align the average atmospheric dispersion direction with the long slit direction on the sky which may be the case for instance when observing extended objects or close pairs It helps to reduce slit losses and so provides a better absolute flux calibration in the blue and when observing with a dichroic at large zenith distances The ADC transmission is higher than 90 from 350 to 900nm Note that the ADC cannot be used in combination with the image slicers because the ADC is located in the optical path behind the slicers
87. x2 binning high gain case LAMP MAXIMUM EXPOSURE INTENSITY TIME REMARKS ADU sec Central wavelength 346 nm Deuterium 30000 140 D spectral lines above 350nm HELI 30000 12 use D lamp below 340nm ThAr 15 Central wavelengths 390 or 437 nm FFL2 30000 36 ThAr 15 Central wavelengths 520 564 580 or 600 nm FFL3 30000 8 ThAr 15 Central wavelength 760 nm FFL4 30000 16 ThAr 15 Central wavelength 860 nm FFL4 30000 16 ThAr 10 several strongly saturated lines UV Visual Echelle Spectrograph UVES User manual VLT MAN ESO 13200 182543 mosaic On the MIT LL CCD the fringes are less sharp and a smaller amplitude Flat Field frames have been proven to correct well for fringing up to S N ratios of at least 300 To the FF calibrations applies the same note of caution regarding stability depending on air pressure and temperature mentioned for the wavelength calibration in Chapter 4 2 FF exposures can also be attached to science OBs 4 5 Flux standard star observations Spectrophotometric standard stars can be used to obtain response curves of the instrument to allow a relative flux calibration of the spectra and at the same time to correct for the blaze function of the different orders before merging Such calibrations are only obtained on the request of Pls with usually a 10 arcsec wide slit i e with negligible slit losses For an absolute flux calibration both the science spect
88. y high signal to noise ratios The two camera units of UVES can be slightly moved with respect to the incoming beams In this way the spectrum is shifted in the direction of the dispersion rows of the CCDs up to 200 pixels The shift in pixels can be selected in the definition of a free observing template This option can be used to move an interesting spectral feature out of a bad region of the detector or to achieve very high S N ratios by obtaining multiple spectra on different pixels in a way similar to the dithering technique used when a very accurate subtraction of the sky background in deep imaging is needed It is important to obtain wavelength calibrations and flat field at each position of the camera Chapter 5 Observing This Chapter summarizes the instrument related information for the visiting astronomers coming to Paranal to observe with UVES 5 1 Before the observing nights preparation of OBs The visiting astronomers are normally asked to come to Paranal one night in advance of their observing run They should arrive already well documented on the instrument properties and on the preparation of the OBs for their observing run or ready to finalize them if they have been prepared in advance at the home institute These activities take place on an X terminal in an office at the Paranal base camp which can also be used for electronic mail correspondence with the outside world telnet connection to the home institute access

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