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Current EFOSC2 Manual

1. s AZA Point Souree soe ea o osp sho eo s a Eog EN SOURCE oae S e a A25 Extended SOHPOR 1 2 29e a wee Reo ER aa Bw WORD EE ed He Ar Exposure Times Observing Log Standard FITS Header Sidereal Time and Sun Tables General Instructions For Visiting Astronomers Helium Argon Atlas Spectral coverage with off center long slits vii 113 114 115 118 119 120 121 viii EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 List of Figures or WN FE 22 23 24 25 26 2T 28 29 30 31 32 33 34 Optical and Mechanical Layout of EFOSC2 o Overall Transmission of EFOSC2 2e rs Transmission curves of EFOSC2 filters oo oca oo RS Schematic representation of EFOSC2 grisms Response functions of grisms nr 7 black and 14 red on November 28 2006 For each grism two standard stars have been used to define the response function Hiltner 60 aud DIT QUIBAS so cso Res kon bees Cee RR Ux 0 Rom EO XC EE E XOU RE dd ADU sec vs wavelength for the two spectrophotometric standards Hiltner 600 top spectrum and LTT 2415 For each standard the two spectra have been taken with arising Me rand dd 22d ues Rowe o Rub A GR RONEGA Re EUR Rm er G Image taken with Focus Wedge e Coronographl e Mask 2 ose Roo eps URGE Ron eee ON OE Red Xo d Default EFOSC2 CCD Orientation Location of data and bias sections on COD Quant
2. EFOSC_img_obs_Coronography EFOSC_ImaCor EFOSC_img_obs_Image EFOSC_Image EFOSC_img_obs_ImageJit EFOSC_ImaJit EFOSC_img_obs_Polarimetry EFOSC_ImaPol OBSERVATION TEMPLATES SPECTROSCOPY EFOSC spec obs Polarimetry EFOSC_SpecPol EFOSC_spec_obs_Spectrum EFOSC_Spectrum EFOSC spec obs MOS EFOSC Spectrum CALIBRATION TEMPLATES EFOSC img cal Darks EFOSC Dark EFOSC img cal Flats EFOSC FlatIma EFOSC img cal FocusSequence EFOSC_FocSeq EFOSC_img_cal_FocusWithWedge EFOSC_FocWedge EFOSC_img_cal_FocusWithPrism EFOSC_FocPrism EFOSC_img_cal_IntImage EFOSC ImaInt EFOSC_img_cal_PolarFlats EFOSC FlatPolIma EFOSC img cal PolarSkyFlats EFOSC_FlatSkyPolIma EFOSC img cal SkyFlats EFOSC FlatSkyIma EFOSC spec cal Arcs EFOSC spec HeAr EFOSC spec cal Flats EFOSC FlatSpec EFOSC_spec_cal_IntFlats EFOSC_FlatIntSpec EFOSC_spec_cal_PolarFlats EFOSC_FlatPolSpec Table 9 File names produced by EFOSC2 Templates EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 71 explicitly for calibrations If an acquisition template is not included in an OB the error will be indicated by a coloured dot next to the OB name in the main P2PP panel For more details refer to the P2PP User s Manual 72 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 3 EFO0SC img acq Preset This acq
3. 5000 Ul NJ CH O ouyse Jaen EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 60000 S Q 2 40000 UI E Q E UI E Wu 2 20000 Q a O Image tmp Row 1 T T T T T T T T T T T T T T T j M mr geg d 4 d bd ll MI a as TR A A Una AS A aaa AAA i i m l l l l l l 6000 6500 7000 7500 Position Figure 54 Grism 20 d3SS0 uorIsJao sepiu osa bb 80 ZTOZ Dm EO J4 een oJ73se Jesf 135
4. CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of exposures 5 Number of exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 97 4 3 27 EFO0SC spec cal PolarFlats This template is designed for taking both Dome and Sky Flat Fields in spectropolarimetric mode and does not use the Tyson amp Gal algorithm The operator is requested to preset the Telescope and the Dome to the proper positions and to switch ON the Flat Field lamps for dome FF only There are several lamps available and their intensity levels can be adjusted remotely by the operator This calibration template acquires Number of exposures dome sky flat fields with a level approxi mately the Requested intensity level with the HWP inserted and in continuous rotation with a Wollaston Prism mounted on the filter wheel and with the desired Starplate and Grism Before the exposure the Calibration Unit position is checked and it is automatically removed if it is in the light path The exposure time is automatically computed as follows e The average bias level is retrieved from a database A windowed flat with exposure time 1 sec is acquired e The bias level is subtracted from the windowed flat and the mean intensity is comput
5. However the observer interested in measuring circular polarisation may want to take highly linearly polarised standard to take into account during the data reduction phase the possible residual cross talk between the two type of polarisation As already mentioned in 2 4 9 the asymmetric reflection at M3 seems to introduce instrument linear polarisation with value and angle dependent on the elevation of the telescope e g Li et al 2006 Proc of SPIE Vol 6275 62751H 1 Therefore the users are encouraged to include observations of unpolarised standard stars in their program in order to remove the instrument polarisation at the data reduction stage We finally remark that the zero point offset of the polarisation angle is somewhat wavelength depen dent because of the chromatism of the Q HWP Therefore all calibrations have to be taken in the different pass bands that will be used in the science exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 49 Note that there is also the possibility of inserting a Polaroid filter on top of a pinhole mounted in the aperture wheel The user may want to take advantage of this to perform some additional tests on a nearly 100 polarised source A list of highly polarised standard stars for imaging polarimetry can be found online at http www eso org instruments fors tools FORS_Std FORS1_Std html 3 3 6 Target Acquisition To allow for a proper positioning of the target under one of th
6. In total there are 8 free positions in the grism wheel 11 in the filter wheel and 5 7 in the aper ture starplate wheel A form describing the current setup of the instrument can be provided upon request by the Day Operation crew at the beginning of the run and also after any changes In the next sections we will describe in detail all components which can be mounted on EFOSC2 2 4 1 Slits The terms Star plates slits and masks are used interchangeably they all refer to elements which block light from some region of the field of view of EFOSC2 All these are mounted in the Aperture Wheel of EFOSC2 The Slit wheel contains 10 positions of which e 1 position should always be kept free EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 7 Table 2 Increased spectral coverage that can be obtained by using off center long slits wavelengths are given in A The blue cut due to atmospheric transmission is not accounted for Grism Amin max Gr 5 3493 10621 Gr 7 2650 5829 Gr 11 2705 8940 Gr 13 2344 11131 Gr 18 4119 7418 Gr 19 4233 5349 Gr 20 5692 7516 1 position is permanently occupied by the movable 1 5 slit e 1 position is needed for the pinhole mask for aligning other optical elements grisms 1 position should be reserved for the 5 slit which is needed for spectrophotometric calibration 1 position is occupied by the Holes Mask used for focusing the instrument during the set up night Thus bet
7. Move HWP IN T Insert the HWP T F Continuous rotation of HWP F Continuous rotation of the HWP T F List of HWP rotator positions 0 22 5 45 0 67 5 Space separated HWP position list deg Exposure time NODEFAULT Exposure time sec CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of Exposures 1 Number of exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 87 4 3 18 Calibration Templates Calibration Templates are used to perform standard calibrations They permit full control of the CCD parameters and the optical components allowing the instrument setup for the science observations to be duplicated Some of the parameters are actually hard coded within the templates in such a way that the observer cannot select them by mistake For instance the Grism is always set to Free when taking imaging flat fields Calibration OBs can be defined in the P2PP main panel under either the ObsBlock category or the CalBlock category OBs under the CalBlock category do not require an acquisition template and are usually carried out when the telescope is parked at the z
8. Table 8 EFOSC2 Templates Quick Reference EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 67 available templates will be presented in the View OB window therefore the user does not need to remember these names by heart When using the EFOSC2 templates in P2PP the user will automatically get the default values for the parameters unless s he actively changes them However some parameters have NODEFAULT as their default values These parameters must always be changed to something else or P2PP will report an error In the following sections we give the names of the files produced by the templates and descriptions of the user serviceable parameters that will appear in the part of the View OB window dedicated to the Observation Description see P2PP user s manual An example of the main P2PP panel and the View OB panel is displayed in Fig 32 Note that the software system is unable to distinguish between the Half and Quarter Wave Plate as they are mounted on the same physical location Therefore all the polarimetric templates can be used indifferently for linear or circular polarimetry However polarimetric templates are present in two flavors Templates meant to be used for circular polarimetry having the same name as the linear polarimetry ones but for the two letters QW added to the name The slightly different name of the template e g QWPolarimetry which will appear in the fits header might then be used as a si
9. The two Grisms were commissioned during February 2008 with EFOSC2 3P6 and a report is avail able at http www eso org sci facilities lasilla instruments efosc doc vph report pdf The system efficiencies of the VPHGs with EFOSC2 at the NT T are shown in Fig 7 together with the efficiencies given by other grisms The efficiency of the blue VPHG goes from 30 at the red end down to 2096 at the blue end The red VPHG has a more constant response with an efficiency around 3096 In general as Fig 2 shows the system efficiencies are comparable to those obtained with the existing EFOSC2 grisms EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 13 EFOSC2 grisms T T T T T T T T T T T T T 1 MM ee pb o EL i ie 13 x 16 e 16 11 BAS ay NG 5 le j eee 4 LJ 3 3 c Q o KL D Os zez X 8 18 10 T 0 Burro E gt F nO L J 00 00 19219 LS 1 L 1 L bel 4000 6000 8000 10 Figure 4 Schematic representation of EFOSC2 grisms 14 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 MIDA lO4SEP User astro Frame Gru7 slitr1 O respons Identification POLY FIT resp tbl COL Area X 1 to 974 Y 1 to 1 Pixel value Scales X 8 58891 Y 0 101499 Min O Max 11 1 1 1 1 1 1 1 fi fi fi 1 Date 02 Dec 2006 3500 4000 4500 5000 Time 22 10 46 Position
10. intrinsic to the instrument CCD combination The image quality on any single image could be worse due to improper focus telescope tracking effects telescope optics distortion due to stresses in primary and secondary mirrors etc 3 2 10 EFOSC Vignetting The pixel scale of EFOSC2 NTT is 0 12 px The maximum field of view i e free of vignetting is set by the field lens just before the detector and it is a circle of radius 18 mm The current detector has 2048 pixels of 15um so its size is 30 7 x 30 7 mm Therefore 8 of the detector area will be vignetted at the edges beyond a radius of 2 4 from the field centre as is graphically illustrated in Fig 21 and visible in the accompanying flat field image Variation in the flat field illumination with rotator angle are negligible see Fig 22 3 2 41 Target Acquisition Two different templates have been implemented for pointing the telescope in the imaging mode according to the positioning accuracy needed by the observer The first EFOSC_img_acq Preset performs a blind preset of the telescope without taking any ac quisition image This template should be used for example for photometric standards or in all cases where an accurate positioning is not required If the observer wants to place the object in an exact position on the CCD i e to avoid bad columns the template to be used is EFOSC_img_acq MoveToPixel which allows a positioning accuracy of the order of one pixel
11. 9350 2 06 16 64 6 300 5000 3860 8070 2 06 16 77 7 600 3800 3270 5240 0 96 8 06 8 600 5300 4320 6360 0 99 8 06 18 600 5600 4700 6770 1 00 8 19 10 600 6500 6280 8200 0 95 7 67 11 300 4000 3380 7520 2 04 17 16 16 300 7900 6015 10320 2 12 17 29 13 236 4400 3685 9315 2 77 23 01 14 600 4000 3095 5085 0 93 7 54 17 600 8300 6895 8765 0 86 7 02 19 1557 ATTT 4441 5114 0 34 1 5 20 1070 6597 6047 7147 0 55 2 0 prism 1 prism 2 Using Loral 2048 CCD with 154 0 12 pixels binning 1 x 1 Gr 10 suffered a major damage and is no longer offered Table 5 EFOSC2 grisms The quoted resolution are for a 170 slit for all Grisms but Gr 19 and 20 For these latter Grisms the resolution was measured using a 075 slit All grisms are mounted in such a way that red end will appear at the top of the Real Time Display RTD and in the FITS files To facilitate data reduction the dispersion is aligned to better than a few tenths of a pixel with the CCD columns It takes 10 20 minutes to align the grism and slits So observers should not request grism slit changes during the night The resolution of the spectra depends on the chosen slit width If the slit width is doubled the line FWHM will be doubled as well One may have to change the CCD binning in order to give enough sampling for the line width Contrary to grisms used in a converging beam there are no
12. able parameters are hard coded within the templates themselves For more details on the EFOSC2 templates refer to Sec 4 3 The templates that a typical science OB contains are e An Acquisition template describing how the target acquisition is to be performed for example which filter or slit is to be used in the acquisition observation which exposure time the acquisition image should have which position angle on the sky the slit should have e Oneor more Science templates describing the instrument setup and the exposure parameters for example which mask should be loaded in a MOS observation which grism should be used which jitter pattern should be followed what exposure time should each exposure have e In some cases the OB may end with an attached calibration template For example if precise wavelength calibration is required an arc lamp exposure can be taken immediately after the last scientific exposure with the instrument in the same configuration The set of science and possibly attached calibration templates in a given OB compose the Observa tion Description OD This represents the core of an Observation Block Once an OD has been defined it can be associated with different targets to create different OBs In addition to the templates a science OB contains other important instrument independent infor mation The terminology is unfortunately a bit confusing since they both generate what is called an OB or ob
13. be present Further polarimetric standards will be measured in good dark conditions in order to further assess these effects Users interested in using the EFOSC2 polarimetric modes are encouraged to include observations of unpolarised standard stars in their program in order to remove the instrument polarisation at the data reduction stage 2 4 10 Coronograph One coronograph is available for EFOSC2 It is called by the name Cor_mask in the P2PP templates The sizes for the large and small spots are 8 0 and 4 0 arcsec respectively Tests done using this unit on extremely bright stars give very little scattered light when the Lyot stop is in place and properly aligned The layout and sizes of the coronographic spots are shown in Fig 9 The alignment of the Lyot stop must be done using bright stars Therefore observers using the coronograph must allow 1 2 hours at the beginning of the first night to perform this alignment Alternatively you can inform lasilla eso org of your request well in advance and depending on other tests that need to be made the Lyot stop may possibly be aligned during technical calibration nights This is usually done by the opticians but it may be checked using the following procedure e Point the telescope to a bright star V 6 8 and defocus it by about 500 encoder units e Refocus guide probe and acquire a suitable guide star e Obtain an exposure of the de focused image Typical exposure times should be
14. curve upwards Both types of features do not affect the wavelength calibration as long as care is taken when identifying the lines It must be emphasised that the ghost lines are faint EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 31 Flat Field Lamps Control Q w3p6tcs File Std Options ONLINE Digital Lamps Halogen Lamp 1 mii OFF pones Intensity 0 00 v o V 100 OFF pa 0 3 OFF Li 4 OFF o 1000 S OFF ad Set Intensity J5 OFF E OFF EIE OFF Halogen Lamp 2 Was ON Intensity 0 00 v o v 100 0 3 0 1000 Set Intensity Command Feedback Window options 19 23 11 SETLAMP REPLY L OK 20 47 58 SETLAMP INVOKED 20 47 58 SETLAMP gt REPLY L OK gl Figure 16 The control panel for the dome flat lamps This is usually controlled by the telescope operator Different lamps of different wattages some variable can be selected Such a figure refers to the 3 6m telescope Different lamps are available at the NTT as well as a slightly different panel 32 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 3 Observing with EFOSC2 3 1 The New Technology Telescope Since April 2008 ESO Period 81 EFOSC2 is mounted at the New Technology Telescope NTT where it is offered together with SoFI The NTT has an alt azimuth mounting a 3 5m primary mirror diameter and a f 11 focal ratio A description of the NTT can be found for instance at the followi
15. fields at the position of the targets as well as dome flats A fringe pattern may also be generated from a series of science exposures with the telescoped nod ded between exposures so that the spectrum does not fall on the same x position all the time However currently there is no P2PP template implemented for this mode of observation 3 5 8 Spectroscopy close to bright objects We have made a few tests on how bright objects in the vicinity of a target influence the spectroscopy We used Sirius and placed it at the edge of the FOV about 2 arcmin away from the target in the Note however that the Helium Argon arc spectra will be pretty useless for wavelength calibration at these resolutions Since usually the y positions of the slits do not differ by a few pixels and the response function is a slowly variation function with wavelength one may chose to take Helium Argon arcs with narrower slits and used them for the wavelength calibration EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 55 Le T T T T 2 I 2 co Normalized Pixel Value 0 8 1 L L L L L L 1 L L L 0 500 1000 1500 2000 Position px Figure 28 Upper panel normalised flat field taken with grism 12 and CCD 40 Lower panel cross cut along the central column of the same frame 56 EFOSC2 US
16. mm a E E m e E Onn Ge ESO test vfastL win 1 1 500 280 wollmask fits isaviane Skycat Mar 05 2006 at 00 41 31 Figure 24 A window to reduce read out time for polarimetry the source must be centred at pixel 427 157 not that the RTD does not have the full FITS header so this px will correspond to another position in the RTD 46 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Figure 25 Comparison of a two beam image without left and with right Moon 3 3 1 Fast Polarimetry If you have a single point source you can reduce the read out time by taking a CCD window of dimensions 500x280 and starting at 1 1 see Fig 24 The read out time of this sub frame is 3 07 sec in vfastL mode not offered and 3 28 sec in fastL aka normal When including all overheads transfer to ws etc the total time is 12sec for the fastL normal mode So basically this is the fastest time offered for polarimetry For plain imaging of one object an even smaller window can be used is appropriate For comparison reading out the full frame in vfastLR mode aka fast takes 9 71sec and to this overheads must be added 3 3 2 Observing close to the Moon When observing close to the Moon the scattered and polarised light from the sky increases inducing the effect shown in Fig 25 The background of the ordinary and extraordinary beams are very different but this is not an instrumental problem 3 3 3 Linear Polarisati
17. the telescope building and the rotator have to rotate very fast in order to track the object The result will be a poor image quality less accurate pointing and problems with the positioning of the object in the slit for spectroscopy In the worst case scenario if we point too close to the Zenith the system can crash A software interlock will trigger at telescope elevations of 89 and 10 respectively while an hardware interlock will trigger at telescope elevations of 90 and 8 9 respectively Users should be aware of the fact that once the hardware interlock has been activated a considerable amount of time will be needed to recover the telescope In order to avoid such problem it is advisable to respect the following limitations e Never ever point within 5 degrees from Zenith 32 lt dec lt 26 HA lt 00 10 00 e Never ever observe within 5 degrees from Zenith 32 lt dec lt 26 HA lt 00 10 00 e In the 32 to 27 range do NOT observe within 15 minute from the meridian e In the 50 to 10 range be aware that you may get bad surprises within 15 degrees from the meridian In all cases AO should not be attempted at elevation lt 40 and no optics adjustment must be done at elevation below 20 not even M2 focus adjustment for temperature variations 3 1 3 The Adaptor EFOSC2 is mounted horizontally at the NTT Nasmyth B focal station and connected to the telescope via an adaptor which contains some calibration units It allows the
18. 1 1 1 Perform combined off T First row of window 1 1 1 Focus flag E Number of columns 2048 2048 2048 Rotator offset angle 0 Number of rows 2048 2048 2048 Number of Exposures 1 1 1 f Target Constraint Set Time Intervals Calibration Requirements f Class EllipticalGal Name Galaxy 1 Right Ascension 12 34 00 000 proper motion RA 0 0 Declination 20 30 00 000 proper motion DEC 0 0 Equinox 2000 Diff RA 0 0 Epoch 2000 0 Diff DEC 0 0 Figure 32 Top An example of the main P2PP panel In this case there are 2 Science OBs prepared They both have the same Observing Description and only the targets are different Bottom An example of the View OB panel The top left area defines the name of the OB and OD The OD consists of an acquisition template followed by 3 exposures of 5 minutes each using the B V and R filters The bottom section defines the Target properties such as the name and position The top right section shows the available templates for EFOSC2 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 69 4 3 1 Files Produced By The Templates All the Templates except EFOSC_img_acq_ Preset produce one or more fits files These files are named indicating which Template created it On wg5off the images are stored in data raw lt imagename gt lt seqnumber gt fits where lt imagename gt is the name given by the Template and lt seqnumber gt is a sequential num ber give
19. 20 18 20 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A Dark 10 BIAS 20 18 56 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A spec_HeAr HeAr_spe 22 36 19 18 10 20 29 22 43 2 5 slit 1 0 Free Gr 4 2x2 normal 60 A 9013 A Spec HeAr 1 HeAr spe 22 40 10 18 14 11 29 22 44 2 0 slit 1 0 Free Gr 8 2x2 normal 60 A 9013 A FlatTest FLAT 23 10 24 19 04 11 37 16 48 1 0 Free g 782 Free 2x2 normal 60 A 9013 A FlatSkylma SKYFLAT 23 11 01 19 04 11 37 16 48 16 2 Free g 782 Free 2x2 normal 60 A 9013 A FlatSkyIma 1 SKYFLAT 23 11 53 19 04 11 37 16 47 19 7 Free g 782 Free 2x2 normal 60 A 9013 A FlatSkyIma 2 SKYFLAT 23 12 48 19 04 12 37 16 41 24 2 Free g 782 Free 2x2 normal 60 A 9013 A AcqSlit Pointing 00 33 10 18 36 26 44 18 33 20 0 Free R 642 Free 2x2 fast 60 A 9013 A AcqSlit 1 Pointing 00 39 28 18 36 27 44 18 27 20 0 Free R 642 Free 2x2 fast 60 A 9013 A Spectrum LTT7379 00 42 46 18 36 27 44 18 28 30 0 slit 5 0 Free Gr 4 2x2 normal 60 A 9013 A Spectrum 1 LTT7379 00 43 57 18 36 27 44 18 28 30 0 slit 5 0 Free Gr 6 2x2 normal 60 A 9013 A Spectrum 2 LTT7379 00 45 08 18 36 27 44 18 28 30 0 slit 5 0 Free Gr 7 2x2 normal 60 A 9013 A Spectrum 3 LTT7379 00 46 18 18 36 27 44 18 28 30 0 slit 5 0 Free Gr 8 2x2 normal 60 A 9013 A Spectrum 4 LTT7379 00 47 29 18 36 27 44 18 28 30 0 slit 5 0 Free Gr 9 2x2 normal 60 A 9013 A Spectrum 5 LTT7379 00 48 42 18 36 27 44 18 28 30 0 slit 5 0 Free Gr 10 2x2 normal 60 A 9013 A Spectrum 6 LTT7379 00 49
20. 20 degrees step The spectra were taken with grism 20 i e the red VPHG to have a large dispersion Figure 26 shows the shift of the spectra in the dispersion direction which is the y coordinate on the CCD Efforts are being made to reduce these flexures but it is recommended to users looking to measure radial velocities that they take arc lamp exposures after each science frame Note that the telescope flexures cause a rigid shift of the wavelength scale Therefore it is always a good idea to check the wavelength calibration using the night sky lines and get the average shift which can be as big as several Angstroms Correcting for this shift usually gives good wavelength calibration An atlas of the brightest night sky lines can be found in Osterbrock amp Martel 1992 3 5 4 Target Acquisition Two templates are available for placing a target on the slit namely EFOSC img acq Move ToSlit and EFOSC img acq RotateToSlit The former is to be used when the user wants to place a single object whose orientation is known a priori into the slit or to orient the slit at the parallactic angle see below The latter is for placing two objects in the slit or to align the slit itself along a direction to be measured interactively from the acquisition image The exact y pixel positions of the slits on the chip are measured by Day Operations and stored in a database For this reason the user must specify the name of the slit to be used in the acquis
21. Ar 7384 0 _ Ar 6965 4 Ar 4158 6 p He 4471 5 He 5015 7 a 2 En 4000 5000 6000 7000 Wavelength A Figure 38 Helium Argon Atlas for grisms 3 and 4 124 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Grism 05 CCD 40 60000 Ar 8115 3 8103 7 o N 40000 3 4 E z 2 3 ral m z A o 3 3l a 5 v N v 3 Es e EI m Fl T e 4 oo lt o La 20000 o 4 lt d all l F n 6000 7000 8000 9000 o Wavelength A Grism 06 CCD 40 He 5875 6 Ar 7635 1 40000 al w o 30000 e g E E 20000 10000 Q oo o o D b He 3888 6 He 4471 5 He 5015 7 t 4000 5000 6000 7000 8000 Wavelength A Figure 39 Helium Argon Atlas for grisms 5 and 6 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 125 Grism 07 CCD 40 o 3 e 30000 E vi 2 2 L m oo 20000 2 S 4 E 4 a Sl d a an 3 g E 10000 n M un x un en E A bL 0 3500 4000 4500 5000 o Wavelength A Grism 08 CCD 40 b en en 3 E uw 4 3 N o kd 3 S 5 eo 3 ka al os S a Pai 4 E D e e y n em E e m LA L Au LAU 4500 5000 5500 6000 Wavelength A Figure 40 Helium Argon Atlas for grisms 7 and 8 126 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Grism 09 CCD 40 Ar 64
22. ObsBlocks are the Science OBs which require the target position to be specified in an Acquisition template CalBlocks are the Calibration OBs which do not require an Acquisition template and have no provision for defining a target The former is designed for observations of an astronomical target while the latter is used to acquire reference data which do not require the observation of an astronomical object The two are catalogued separately and cannot be changed from one type to another The core of an OB is composed of a number of instrument specific Templates Practically all calibration and observing procedures possible with EFOSC2 have been coded into the templates and these allow the observer to perform a certain type of observation following a pre defined path For example there is a specific template to take images which sets automatically the grism wheel in the free position When using this template the user can choose the filter or the exposure time but s he is not allowed to insert a grism since the procedure is specifically designed for Imaging Very briefly a template is an entity containing a sequence of commands dealing with the setup and execution of one or more exposures It also contains a set of parameters whose specific values determine the exact behaviour of its execution i e exposure time CCD binning filter etc The values of these parameters are mostly set by the observer using P2PP while other non user service
23. Opties syst s o sos RR o Ron m Rem RR Rol o3 E Re Roe n 35 34 8 Practical Considerations 222 o RR RUE Roy mo Bae es 37 3 2 9 The EFOSC2 PSF and Image quality ln 38 3 210 EFOSC VigneUbiBEg o gon s nonc o Rok mon ey xe 3x sm e eom Ee Ro Rs 38 2 11 Target Acquisition 4 442 424 6442 085 s 204 ba eae RS RO Rod HRS 38 3 2 12 Science Exposures 2 2 54 55 ok o o ee ee a ea 43 A AMOI AP 43 2o Polarimetric Imaging o sa s c9 ee ho eS eA OR RO ee E a d 43 vi 3 4 3 5 3 6 3 7 3 8 4 The 4 1 4 2 4 3 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 23 Fast Polarimetry saa kun s ee Rok eR ook oh OR oA ES ux E rad dos 46 33 2 Observar close to the Mooi 2222393 ycou RUE We EE eee eS 46 So Linear Polaris ali Wa o5 Ges ee E 3 ae Paw Eee Ro ES 46 334 Circular Polarisation Lou ue RR UR o De a wo wo y deos 4T 3 3 5 Flats and Other Calibrations 2 20202 000000007 48 8 6 Target ACQuISIIOW o 2 eos rro x exo y Rose Sb oe hoe o ae XE Yos 49 Sa Science DxDOSUP B oo sso boo a We eee we dex R AC WOR Pod x 49 Cboronopraphie Imaging 22d crasas RORGEGM EUR EUR RO 4 do A A 49 DUM OD ace Meee aes ae Bee Boe es ee ae e rer ee 49 34 2 Target Acquisition siq ass pitta RR RR a 9 ee b G 49 24 3 Science EXpOSUPOS o poa s xo eo x mee o eR eRe Sos do ES Peg 50 DDeoODPOSOUD uo Lea PB ee Ae ee le Gok we da be ew ee Ro
24. Parameter Default Description Filter R 642 User specified filter Insert HWP T F T Insert Half Wave Plate T F Exposure time 20 Exposure time sec for the acquisition image CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD readout speed fast Read Out Mode for the acquisition image Preset flag T Preset the telescope Focus flag T Focus flag Rotator offset angle 0 Rotator Offset Angle deg see definition in 8 3 1 3 78 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 9 EFO0SC img acq MOS This template is used to align objects in an astronomical field with slits on MOS plate for Multi Object Spectroscopy During its execution and in order to align the 3 slits with the 3 reference stars the user will be prompted for the filename of image of the mask This means that the observer has to take an image of the MOS plate usually in the afternoon before running this Acquisition Template by means of EF0SC img cal IntImage This image has to be left in the default directory 1NS ROOT SYSTEM DETDATA otherwise EFOSC img acq MOS will not be able to find it This template has three parts 1 telescope and rotator preset 2 focus rotator offset and approxi mate telescope offset 3 final telescope offset First the template presets the telescope to the coordinates of the Target associated with the Obser vation Block and rotates the Adaptor to the requeste
25. The process may be repeated until the operator is satisfied with the focus When the template is executed the Grism HWP and Calibration Unit positions are first checked If they are in the light path these components are automatically removed The CCD parameters are hard coded in the software and are set to fast readout with 2 x 2 binning Parameter Default Description INS FILTI NAME R 642 User specified filter DET WIN1 UIT1 20 Exposure time EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 101 4 3 31 EFOSC img cal FocusSequence This calibration template acquires a through focus frame It takes Number of subexposures frames of Exposure time seconds through a Filter and optionally a Grism If the Number of subexposures is EVEN then Number of subexposures 1 exposures are taken Before each subexposure the tele scope is offset by Telescope offset arcseconds in the specified Direction of telescope offset ALPHA or DELTA The telescope focus will start from Telescope focus offsetx Number of subexposures 1 2 below the original value and will increase by Telescope focus offset encoder units until all the subexposures are taken Between subexposures the shutter is closed At the end of the sequence the CCD is read out and the telescope is sent back to the original position The operator will be prompted to identify from the image all the positions of ONE star in the focus sequence sticking to the order of the sequen
26. Unless differently specified in the template the acquisition images are taken in the fast mode with binning 2 x 2 to reduce overheads EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 39 ES T T T T T T T T 2000 V 4 TE y ME L N A it y j P a SC J b ow un a Z y TY A 7 L d ie AAs UN D D a 1500 L i Y ES S d L nt ES VE be p 7 3 rud ed i E a o e TY L E ER er S e d ME SE E J amp 1000 E DES NX 2 T eT put bui e 4 f E s E Dee m WD suy og a fete 2 AN a x i i Be NA J c TA oS N Pi Av e Si P s 2 vk Ge AC SEH 4 dos Pes A WM a F Ye 3 ce 4 27 AEN E 500 geo e i sch s N Se X L Z es TAE So SR f Ly ES 1 pr ode e x x Ss P Heyn A as A ST Xm 5 i Son of Al M J E N i ll i ll l ll ji 0 500 1000 1500 2000 Figure 19 The PSF shape variation across the CCD It is measured by determining the PSF ellipticities in an image of the loose globular cluster Pyxis stellar fields taken under good seeing lt 0 75 arcsec conditions The vectors indicate the orientation and magnitude of the PSF ellipse at that CCD location 40 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 1 8 o o o d O 9 SS e 00 o Sa S o o 9 o o 146 S gt o E o e E ea A Q 1 4 lt 1 2 1 7 m Figure 20 The ellipticity of stars measured in the same stellar field as
27. by grism 17 129 Helium Argon Atlas for grism 19 2222s 130 Helium Argon Atlas for grism 20 22s 130 Helium Argon Atlas for grism 20 thanks to E Breedt 131 toos E c r 132 GUS Y e corens gi e eo aa SUE REOR EDAD A SER Ge ow b EON REOR Ronde X dodo 132 Gris Il os eke kee Ree Roo RR Bod e Eee a E A ROG Eom BOR OR E Rom Wes 133 CAS Lou ums cede ee RAUS Bae RE RONDE Oe a Re OO a ue uod dex npud 133 reel A1 E Err RA 134 Grsm UG o ew e a WE hee ee a RUE ee E Mon ee a 134 CEDA a fh 3 4m dO E ok ee roh EO we a Se ee eee Pe ee E 135 of Tables EFOSC2 Observing Modes ee ee 6 Increased spectral coverage that can be obtained by using off center long slits wave lengths are given in A The blue cut due to atmospheric transmission is not accounted Of 2d beo HbR AE A Wow ee Eo de Roh RO P oe es 7 Punching Besa coca a a ee a RS xD Oe o A AA d 8 BEROSCS FGETS e nk a ee RS RR eS E Ree Go A UO Be i d ek a 10 BPOSOO ONSE cobarde ra Bek a ee ANE aa 11 Wollaston Maske 04 24 4 abo oe pa we Bae yy eae HG we eo eee els 18 Specifications Of GIAO A Dk os ek ee ORAE RU De ee Se es oes eee 22 EFOSC Templates List coords o we Re X Ros a 66 Image Names 2 222 BA RA OE ee ea E s E X v Yos 70 Instrumental zero points colour terms and extinction llle 103 Expected Count Rates 2 2 454 uo o m o ROSE RU OS RO UR 105 Overall Bolengy A soe oso oce bk a hoax Mb RUE ee a ws obo H 106
28. by the user The offset can be iterated until the desired pointing accuracy is achieved When observing 2 objects with wide separations a common mistake is to forget to change the X pixel coordinate to be closer to the edges so that when one object is placed at this coordinate the other is not out of the frame Note that this template does not accept 9999 for the Initial Rotator Offset Angle because it is supposed to be used to align the slit along a precise direction for instance defined by two objects rather than using the parallactic angle which is time and telescope coordinates dependent If a value of 9999 is entered P2PP shall complain and display the value in red If this acquisition template is used during service observing a finding chart must be supplied by the user indicating the two points that must fall within the slit and the object or point in the sky to be placed at the reference pixel By default the acquisition images are taken in fast mode and binning 2 x 2 If the observer wants to use these images for scientific purpose he she may change the parameters Parameter Default Description Filter R 642 User specified filter Slit for Reference NODEFAULT User specified slit Exposure time 20 Exposure time sec for the acquisition image CCD readout speed fast Read Out Mode for the acquisition image CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction X pixel coor
29. certain amount of internal reflection resulting in ghost images especially of bright objects Care must be taken to locate the object in the field such that the ghost image does not fall on the area of interest A description of the performance obtained with the QWP and EFOSC2 3P6 can be found in Saviane et al 2007 Msngr 129 14 As is well known and discussed in the literature the asymmetric reflection at M3 introduces instru ment linear polarisation up to a few percent with value and angle dependent on the elevation of the telescope e g Li et al 2006 Proc of SPIE Vol 6275 62751H 1 This is of course a problem when trying to detect modest amounts of polarisation During the re commissioning phase measurements of both polarised and unpolarised stars at many telescope positions were taken Unfortunately the commissioning period was mainly during bright time and some of these stan dards were taken relatively close to the Moon introducing a polarised component in the sky from reflected Moonlight T he preliminary results are not encouraging There seems to be a considerable instrument polarisation of 496 596 The polarisation degree being nearly constant with hour angle and strongly dependant on the colour Variations in the Q and U Stokes parameters seems important and not trivial to model Also circular polarimetry shows some lower instrument polarisation of the order of 0 496 However some still unclear systematic effects might
30. computed e Based on the mean intensity and the requested intensity an exposure time sequence is computed automatically using the Tyson amp Gal algorithm The sequence is started only if the exposure time of the first frame is greater than 3 sec The sequence terminates when the desired number of exposures have been taken or when the exposure time exceeds 300 sec The template also checks the exposure level which can range from 1200 to 60000 ADUs The exposure levels obtained by this template are within a few thousand ADUSs from the one specified by the user This is due to seasonal effects and sky conditions Note that in evening twilight flats should be taken for the most insensitive passbands first U B whereas during morning twilight the reverse is true In this template it is also possible to specify a Grism but the Slit for Reference parameter does not cause an insertion of the slit into the lightpath hence the template is not usable for spectroscopic sky flats They are usually done using the EF0SC spec cal Flats template Parameter Default Description Slit for reference NODEFAULT User specified slit for reference Filter NODEFAULT User specified filter Grism Free User specified grism Requested intensity level 40000 Requested intensity level in ADUs CCD readout speed normal CCD read out speed CCD X binning CCD binning factor in X direction 2 CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F n
31. e 2 U t E S Grism 20 x 0 8 F L N 0 6 F ccu oO N O L o o a Q 89 v L e N y Re D oO o N o o F E o o e 02 F i F n n y or m Kup t J ju Led aM mr I La 6000 6200 6400 6600 6800 7000 Wavelength no o o o c2 o o o 000 NAX E O Q NS Qm co Y 2 i o eo E O N Y x y Us Save o c o co L os SL et Qi e Ke x ow e e e o e Ko e MEIN E UE dq l MEN Ah l N UW NS AS SE y Yo NJ ZA AO vo SESS 6000 6100 6300 6400 6500 o Qo o E Dr o e c co j co D o st eo NO p Ww LO x O5 x c2 Re Re 01 b xX o O O o ow x ll f V 0 05 F A F I d I li v 1 1 LJ Vo JL rl q NA oa I pert E ARAN 6600 6700 6800 6900 7000 7100 Figure 47 Helium Argon Atlas for grism 20 thanks to E Breedt Wavelength A 132 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Image slitz1 0 Free rou Row x1 2 C T T T T T T T T T T T T n L 4 40000 4 Hu L 1 2 a g m v 30000 o g had m 0 3 8 z 20000 N 9 S o a a 8 10000 0 j g ui 4000 6000 8000 10000 i n Position PIXEL 8 Figure 48 Grism 5 m Image slitz1 0 Free Flat 8 E T T T T T T I T T 3 2 F a 50000 M a E o E o 40000 FP 3m A A 3 80000 E i le tJ 3 I 3 g L N 20000 7 8 M 7 8 10000 F L
32. frames or to take the necessary calibrations with the CCD in fast mode with 2 x 2 binning The default slit orientation is East West so an offset of PA 90 must be applied to position the slit along a given position angle see 17 Therefore users wishing to use the EFOSC img acq Move ToSlit procedure along with a specific position angle are advised to add 90 to the supplied rotator offset angle 3 5 5 Parallactic Angle Since differential refraction occurs in a direction perpendicular to the horizon it is strongly recom mend to align the slit along the so called parallactic angle to avoid significant flux losses especially when observing at large airmass es For instance when the airmass is 1 5 the differential refraction at 3500A is about 1 3 with respect to a wavelength of 5000 a more detailed description of the effect EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 53 EFOSC2 grism 20 red VPHG T T T T T T T T T T T T T T T T T 0r e L J 1 L 4 B L 4 2 8 E E J l 2 4 gt L 4 L o 3 e re e L l 1 1 L 1 1 1 L l 1 l 1 L l 1 1 L 50 0 50 100 150 ADA ABSROT START Figure 26 The shift in dispersion direction of spectra taken at different rotator angles H beta H gamma H delta I l 1 005 K mJ FI 187 3 Figure 27 Illustration of the effect of differential atmospheric refraction The three spectra of standard stars have been
33. in normal spectroscopy as well as an image of the mask illuminated by the internal lamp used to centre the mask 58 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 3 6 2 Target Acquisition Target acquisition for Multi Object Spectroscopy is a particularly delicate procedure and is achieved by means of the template EFOSC_img_acq_MOS After the telescope and the rotator are preset the template proceeds with focusing if required by the astronomer Then the same focus image or the first acquisition image is used to perform the first approximate offset which is meant only to centre the field Then the real iterative acquisition process commences The template will prompt the astronomer for the name of the mask image taken in the afternoon and ask to select 3 slits Immediately afterwards the astronomer will have to identify in the acquisition image the 3 alignment stars into which the 8 selected slits should fall An offset angle is calculated and the instrument rotated This process is iterated until the user is happy with the orientation Next the telescope offset is calculated by the displacement of the 3 stars and the process repeated until the user is satisfied with the slit alignment Note however that if the 3 stars are centred in the 3 slits no further improvement in the alignment is possible From experience if the images have been taken during the same EFOSC2 run at the same nominal rotator angle rotation corrections ar
34. instrument to rotate around its mechanical axis with a resolution of 0 1 Note this movement is not fast the time required to perform a complete rotation 360 with this precision is about 5 minutes The adaptor orientation and hence the slit orientation definition used by ESO telescopes is non standard in that it does not follow the usual Position Angle definition positive angle subtended from north through east in the range 0 180 degrees The Rotator Offset Angle is the offset from the default Rotator Angle 0 It is this offset which has to be defined in P2PP With a Rotator Angle 0 the CCD is oriented with North to the top and East to the right as shown in Fig 10 The spectroscopic slit is always aligned along the x axis of the CCD and the default slit orientation is East West So if one wants a different orientation usually for spectroscopy or MOS preimaging one has to define a rotator offset angle in the Observing Block As can be seen from fig 17 an offset of PA 90 must be applied to position the slit along a given position angle The slit can be aligned along the parallactic angle calculated at the start of the OB automatically see Sec 3 5 5 34 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Rotator offset angle PA 90 gt x Default orientation Rotated negative offset Rotated positive offset Rotator offset angle 0 Rotator offset angle 30 Rotator offset angle 30
35. is worth noting that neglecting the time delay correction at all Atma 30ms turns into a 3 error 0 03 mag for a 1 second exposure by taking the shutter delay into account the position dependent error is less than 1 Starting with an exposure time of 3 seconds the error becomes smaller than 1 0 01 mag For this reason if the observer does not want to apply any shutter delay correction avoid exposure times shorter than 3 seconds when accurate photometry is required The mechanism which keeps the shutter open absorbs about 3 Watts causing a chimney effect inside EFOSC2 For long exposure times this may cause a degradation of the focus stability although so far this has not been noticeable 2 6 EFOSC2 CCD 2 6 1 General specifications of CCD 40 The CCD presently mounted on EFOSC2 is ESO 40 a Loral Lesser Thinned AR coated UV flooded MPP 2048 x 2048 chip with a pixel size of 15um corresponding to 012 pixel The field of view is thus about 4 1 x 4 1 The default CCD orientation is North to the top and East to the right of the RTD display Fig 10 The spectral dispersion is aligned with the columns and the wavelength increases upwards 22 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 The full specifications of CCD 40 are given in Table 7 The array has one serial register and two output ports one port at each end of the register This thinned CCD achieves its high quantum efficiency in the blue and UV through UV
36. of one dome flat field lamp has been added to show the relative trend of sensitivity across the whole spectral range The absolute trend of sensitivity will be obtained in the future with spectrophotometric standard stars More grisms will also be added as more data will be collected during NTT technical time 122 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Grism 01 CCD 40 60000 He 5875 6 Zero h Order He 7065 2 Ar 7635 1 40000 a oo E o o v Counts 20000 Ar 7384 0 Wh n Ar 9123 0 Ar 10830 3 He 3888 6 L He 44715 f 2500 5000 7500 10000 Wavelength A x101 Grism 2 7 00 T T T T T I E On na 00 e L oN SOW mM oO D E 1 RO ay uo oi NM wo bei P wom Ho ga in O L 150 DoD o o o 6 00 3 gle E 5 00 H 4 00 B f l H 5 L O 300 2 00 F 1 00 0 00 n dart LG 1 1 1 1 l 1 L l 509 1000 1500 Position Figure 37 Helium Argon Atlas for grisms 1 and 2 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 123 Counts Counts Grism 03 CCD 40 15000 12500 2 oo p 10000 T 4 2 o e E 7500 EA 2 en D Ke m LI D x a x zi 5000 a v T 2500 ad AUI ul la wn LL Alar ab Mu 9n 3000 4000 5000 6000 Wavelength A Grism 04 CCD 40 60000 He 7065 2 40000 He 6678 2 20000 A
37. on the Moon phase as shown in Table 13 where the expected count rates for the sky background have also been reported Days from Msky mag arcsec Ssky ADU s arcsec new Moon U B V R I U B V R I 0 22 0 22 7 21 8 20 9 19 9 8 20 47 121 141 3 21 5 22 4 21 7 20 8 19 9 13 26 52 133 141 7 19 9 21 6 21 4 20 6 19 7 57 54 69 160 169 10 18 5 20 7 20 7 20 3 19 5 207 124 131 211 203 14 17 0 19 5 20 0 19 9 19 2 824 373 249 305 268 Table 13 Sky surface brightness and expected background count rates Walker 1987 NOAO Newslet ter It is very useful to estimate the integrated signal coming from the sky background in the area covered by the PSF This is simply given by Fa 5 12 FWHM say ADUs 20 while the expected background count rate in a single pixel is expressed by the following formula fa 2 6 x 107 b sy ADUs px 21 y y Now the main sources of noise in CCD images are the Photon Shot Noise of the source PSN the background noise Lost and the Read Out Noise RON Nevertheless most of the time the dominating source is the sky background In fact if g is the gain in e ADU 1 we have Osky RON when RON gx Fsky 22 Inserting the proper values for g and RON in Eq 22 we have that during the new Moon the noise starts to be sky dominated after about 40 seconds
38. pkey Brightness ge bE eR Roo e xt eud eee BP Re UR RUN ACE EAD m E 107 He Ar Exposure Times 32 p o RR RR ee REG RS E RS eos 113 Sidereal Time and Sun Tables for La Silla 2l 118 HeAr blei 45 44 ra aa ds 120 x EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 This page was intentionally left blank EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 1 1 Introduction 1 1 Purpose This manual describes the operation of the ESO Faint Object Spectrograph and Camera EFOSC2 currently mounted at the New Technology Telescope NTT It is intended to be a general guide for the observer who is going to use EFOSC2 for both the proposal preparation and the observing run itself 1 2 Scope This is a revised version of the previous operating manuals In particular it collects the new features implemented with the relocation of EFOSC2 from the 3 6m telescope to the NTT as of April 2008 The present version of the manual includes the instrument specifications as measured and checked during the re commissioning phase April 2008 First time users are advised to read this manual carefully and to familiarise themselves with the optical system and the observing procedures even if observation with P2PP makes it much simpler than it used to be For recent changes updates and news related to EFOSC2 the WEB page http www eso org sci facilities lasilla instruments efosc should be checked before an observing run Th
39. projected onto the CCD and the intensity ratio between these two spectra gives the component of the Stokes vector for linear circular polarisation in the direction of the split The components in other directions can be obtained by rotating the HWP QWP as for polarimetric imaging Refer to Sec 3 3 for more details on the calculation of the polarisation degree and the polarisation angle In order to avoid overlapping object and sky spectra the slit is transparent only in slots which are as long as the separation produced by the Wollaston prism and separated by opaque masks of equal length Therefore one obtains spectra only for half the sky area covered by the slit One of the sections may contain the object of interest the others are devoted to the sky and possibly to a field star which if unpolarised can be used to check the instrumental polarisation This configuration is well suited to objects which are not extended more than 20 arcsec For larger objects only sections can be observed in a single set of spectra As for all prisms the Wollaston has dispersive power and so acts as a cross disperser When using low dispersion grisms 1 2 this is especially visible as a slight inclination and curvature of the spectrum This affects one of the two spectra the extraordinary beam The same discussion about additional calibration for polarimetric imaging applies equally here A list of highly polarised standard stars for spectropolarimetry ca
40. r y L U 4 La T UE 1 1 1 1 1 1 1 1 1 1 1 y g 3000 4000 5000 7 Position PIXEL El Figure 49 Grism 7 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 133 Image subcenf T T 60000 d35S50 uolsJao sepiu osa 40000 F El Pixel value T L E b0 ztoz Bnu EO 44 een 20000 F A LA A LA c O 5 I co fi fi 1 1 3 8 4000 6000 8000 EN Position PIXEL 5 Figure 50 Grism 11 Image slitz1 0 Free Flat Rou t1 8 50000 m g T T T T T T T T T T T T T Con i L 8 I J 3 40000 5 30000 S 0 H gt g m 2 gt oa 8 20000 N a DH 10000 O l l l l l l O F 4000 6000 8000 10000 D Position PIXEL 3 Figure 51 Grism 13 134 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 60000 o o o PixelNualue none Given O 23 O O O 60000 ven 0000 gA value none N O o o O Pixel Image tmp T T T Rov x1 d n uo sJao sepiu osa S0 20 ztoz ny EO 44 een 6000 Position Figure 52 Grism 18 A Q Oo o oJ1se Jaen Image tmp T T T I Lem d d3SS0 uoIsJa sepiu osa 10 80 ZiOZ ny EO 44 3 ep eoim nere esser ues qeu 4600 4800 Position Figure 53 Grism 19
41. sci facilities lasilla instruments efosc inst bsMOS html for the various stages of preparation from pre imaging to defining and punching the masks as well as calibrations and science observations The observer should read these instructions The observer should also read the MOS Operation Manual http docs ls eso org 3P6 MAN ESO0 90100 0002 3P6 MAN ES0 90100 0002 pdf Because the MOS design and punching process takes time one should arrive two days before the scheduled night to allow enough time for the preparation In fact all the required procedures for the mask designation preparation are local As such the observer must be at the LSO The observer is warned against requesting installation of MOS plates during the night since this is a time consuming operation and requires opening EFOSC2 2 4 3 Filters Filters are located in the filter wheel which lies in the parallel beam after the collimator Up to 11 filters may be mounted in the filter wheel however if you are doing spectroscopy you need to leave LSO MAN ESO 36100 0004 9 EFOSC2 USER S MANUAL 4 0 ESO Elter 1639 B Besse ESO Filter 1641 VU Besse ESO Fijter 640 U Bessel 1 i Instrument SUS Instrumenti SUBI ev a y e oon i N a nd y EE E 3 7 D A Z S i A ES E M ESO Filter 1642 R Bessel ESO Filter 1782 Gunn g ESO Filter 786 Gunn r Ati SUSI Inst zeg
42. should be set to T if the telescope is to be positioned accurately by offsetting the guide probe in this iterative process Note that if the Rotator Offset Angle is set to 9999 the Rotator Angle will be set to the parallactic angle at the start of the exposure If this acquisition template is used during service observing a finding chart must be supplied by the user By default the acquisition images are taken in fast mode and binning 2 x 2 If the observer wants to use these images for scientific purpose he she may want to change these parameters Note also that if a particular position angle is required the a rotator offset angle equal to PA 4 90 must be supplied see 83 1 3 and fig 17 Parameter Default Description Filter R 642 User specified filter Slit for reference NODEFAULT User specified slit Exposure time 20 Exposure time for acquisition image sec CCD readout speed fast Read Out Mode for the acquisition image CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction X pixel coordinate 1100 User specified X coordinate Preset flag T Preset the telescope Perform combined offset T Perform accurate offset using guide probe Focus flag T Focus flag Rotator offset angle 0 Rotator Offset Angle deg see 3 1 3 76 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 7 EFOSC_img acq RotateToSlit This acquisition template is used for grism spectroscopy
43. taken with grism 7 at different airmasses as indicated and with the 5 slit aligned to the parallactic angle While the low airmass spectrum is almost horizontal the one at airmass 2 187 has an offset of 3 between the position at 520 nm and that at 330 nm 54 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 can be found in Filippenko 1982 This would turn into strong flux losses in the blue An illustration of this problem is given in Fig 27 where spectra taken with grism 7 at different airmasses are shown Note that when observing at the meridian the parallactic angle is 180 i e the slit should lie along the N S direction i e perpendicular to the usual E W orientation For acquisition templates which allow the user to specify the Rotator Offset Angle if a value of 9999 is specified the rotator will be preset to the parallactic angle at the start of the exposure When taking spectra of spectrophotometric standard stars instead of aligning the slit to the paral lactic angle the user can choose to observe with a wide slit 5 10 in order to minimise the flux losses This of course will reduce the resolution which generally is not a problem for measuring the response curve If one is interested in correcting for the atmospheric absorption bands redder than 6500A one may instead want to observe the standards with the same spectral resolution as the target frames 3 5 6 Science Exposures The template to be used is E
44. the CCD columns becames visible when averaging many BIAS frames The gradient have an amplitude of a few 73 5 ADU This is most likely caused by the so called spurious charge generation AKA clock induced charge generation which appears in most CCDs and is heavily dependent on the fine tuning of the vertical clock waveforms and voltage excursion Since this charge is generated during the readout process it should be constant in time and indepen dent of integration time but it can be different for each readout mode It is advisable however to collect a set of BIAS frames in correspondence of each observing night The effect shows as a vertical slope increasing gradually into the direction opposite of the vertical readout as the farther away the row the more transfers and clock cycles are needed before reaching the readout serial register see Fig 14 2 6 5 Fringing Fringing is caused by multiple reflections internal to the CCD substrate or between the silicon and the supporting substrate For imaging fringe patterns appear in R and especially I images Their amplitude is of the order of 596 of the background intensity Note that this effect appears only in the exposures taken during the night due to the sky lines In fact fringing arises from the optical interference caused by near monochromatic light and variations in the thickness of thinned CCDs Therefore it is not possible to remove it using dome flats the lamps have a black body sp
45. the Starplate wheel and a Lyot stop in the grism wheel the template automatically sets the aperture wheel to COR MASK and the grism wheel to LYOT The template takes Number of Exposures coronographic images with a duration of Exposure time seconds each through a Filter The CCD readout binning and windowing can be controlled For acquisition one has to use the EFOSC img acq MoveToPixel template since the object has to be accurately placed behind the coronographic mask Note that the mask is not in place during the acquisition Obviously the pixel specified in the Move To Pixel template should be at the centre of the coronographic mask Hence it must be measured before the observations are started and entered in EF0SC img acq MoveToPixel Note that typically Coronographic targets are extremely bright stars and hence one should use very small integration times in the acquisition template The bright targets and the consequent saturation may result in small deviation from the ideal position In such cases one may have to position the telescope using trial and error offsets We recommend the following procedure Include in the OB a very short duration Coronographic Imaging template between the acquisition template and the programme Coronographic imaging templates Execute the OB and terminate it after the acquisition template this will position the star close to the centre of the coronographic mask Execute the OB again but skip the acquisitio
46. the previous figure is plotted as a function of the radial distance from the CCD centre Only stars below the dashed curve were plotted in the previous figure EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 A1 Figure 21 Left The dark shaded area shows the regions of the detector that will be affected by some degree of vignetting after changing to the slower f 11 ratio of the NTT It corresponds to 8 of the active field of view Right a blue dome flat field after the installation of EFOSC2 at the NTT 42 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 ESO ratio 34 73 90 00 fits average frame astro Skycat Apr 18 2008 at 22 57 28 Figure 22 Ratio of dome flat fields taken at different rotator angle The px to px differences are less than 1 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 43 3 2 12 Science Exposures Imaging can be performed by two different templates EFOSC img obs Image allows one or more exposures to be taken without offsetting the telescope EFOSC img obs ImageJit allows for small telescope offsets between exposures according to a user defined offset pattern The latter is partic ularly suitable for accurate photometry or in cases when a deconvolution coaddition technique is to be applied in the data reduction phase It is also useful for fringe removal for i band and also R band exposures The colour equations the efficiency of the whole system and other relevant informatio
47. to a 1 Angstrom region in the final 1 dimensional star spectrum will be 2 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 111 EFOSC2 Grism Throughputs for a 15th magnitude star ow a Throughput e Ang s ka N N uy an ul 3000 400D 5000 6000 7000 8000 9000 10000 Wavelength Angstroms Figure 35 EFOSC2 Grism Throughputs in electrons per Angstrom per second for a 15th magnitude star These represent the averaged values of different observations of many spectrophotometric standard stars normalised to 15th magnitude at all wavelengths 112 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 1 0 x 12 x 0 038 0 045 e el S for below Assuming Poisson shot noise from the star and from the sky the final SNR per Angstrom can be expressed as Oxt SNR 27 VOxt Sxt R where O and S denote the flux per Angstroms per second of the Star and Sky respectively R is the readout noise and t is the exposure time in seconds Plug in the relevant numbers calculated above we see that at 5000A to achieve SNR 5 per Angstrom in the final extracted 1 dimensional spectrum an exposure time of 500 seconds is required A 2 5 Extended source The calculation for an extended source is similar to the case for a point source The difference is that we work with surface brightness As an example one wants to take a spectrum of a large galaxy at 5000 A for example to make different spatial extractio
48. 000 6000 8000 o Wavelength A Grism 14 CCD 40 40000 2 t 09 He 4471 5 vi S o LI 30000 m 2 Ka s S 20000 4 E He 4921 9 10000 e L Ml Hi la 3000 3500 4000 4500 5000 S 4 e du la He 3187 7 e pe Es Se v T Wavelength A Figure 43 Helium Argon Atlas for grisms 13 and 14 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 129 Grism 15 CCD 40 60000 He 7065 2 Ar 8115 3 ui on o Re u lt 40000 Counts 20000 Ar 8424 6 Ar 8521 4 I Ar 7384 0 rp Ar 8667 9 7000 7500 8000 8500 Wavelength A Figure 44 Helium Argon Atlas for grism 15 replaced by grism 17 130 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 EFOSC2 VPHG 19 5000 4000 9 3000 c 2 o 2000 1000 0 f T i i 4600 4800 5000 Figure 45 Helium Argon Atlas for grism 19 EFOSC2 VPHG 20 5000 T T T T T T T T T T T T T T T T T T d 4000F E 8223 8 R GAZ Z E s ZS ER Gg 2 7 o 3000 E J L 5 ki 4 o E 7 2000 1000 F ME Lii 7 E A 6000 6200 6400 6600 6800 7000 A Figure 46 Helium Argon Atlas for grism 20 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 L Q eo Inl ane e2 L NTT EFOSC2
49. 16 3 ul aes L lid d A d He 5015 7 Ar 6172 3 p ud 00 2 o D v 4 He 4921 9 4 G t al Jk lu tle UI 5000 5500 6000 6500 Wavelength A Grism 10 CCD 40 40000 aq uw yo ZS E v 30000 a m 00 e o 2 ES n 8 S 8 20000 gt og 2 zx f A n a a 4 wi ee 4 Kai u n S KEE 4 EI E 10000 MH t 6500 7000 7500 6000 Wavelength A Figure 41 Helium Argon Atlas for grisms 9 replaced by grisms 16 and 10 decommissioned EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 127 Grism 11 CCD 40 60000 He 5875 6 a uw o E vU 40000 37 a A 2 E 2 4 g 20000 e p vi ES a 2 e 2 2 0 Mou A RP EA La e d 4000 5000 6000 7000 o Wavelength A Grism 412 CCD 440 Ar 8115 3 8103 7 60000 a en eS a d 40000 S e A 3 i ii lt g 20000 Ar 6965 4 Ar 8521 4 P Ar 9657 8 e 6000 7000 8000 9000 10000 Wavelength A Figure 42 Helium Argon Atlas for grisms 11 and 12 replaced by grism 16 128 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Grism 13 CCD 40 Ar 8115 3 8103 7 60000 od S vU m 40000 z N Q 3 dle E 2 3 E els a S t 4 WIS 8 20000 E E 4 E a L m E E 0 y A Li UL dL A3 JU QU JO JUL 4
50. 24 1 Focus Wedge Prism a nouos oe dog Read a ee we ee ea Geh E 16 2 4 8 Wollaston Prisms and Masks 0 0 0000 les 18 248 Hal Quarter Wave Plate a4 hi va de eee be wea se ea Paroda 18 2 1 10 COFOROST D usse oso oU exec ERY Se on ae EL e x ne Se 19 203 ANUE eo 4 kw BA sh d de hae eel euh dE No Xov aes pA we to Ros 21 2 6 EFOSC COD so sos unirse ridad edo sm er EC DRE EEA GOES 21 2 6 1 General specifications of CCD 40 e e 21 202 Windowing and Binning o s sacio e eaa xoxo ko xo m RO e EO XS E 25 2 6 3 Bad Pixels and Columns ss ss d ok ER RR A Rm a e ROSE RES 25 2 6 4 Bias Darks and Cosmic Ray Events cacy 2 soet Eon rn 27 2D TAPERNE G one E ee Ba eh ae ee re ee Bei ee RE Ble dd 27 24 Calbraton Gamps uou sno ae ee fee OE ee Se BO oe ee Ge 29 3 Observing with EFOSC2 32 3 1 The New Technology Telescope 32 30 1 Telescope Focusing Lio ao a s EE go ee Ra Be RR XD e e o Fe d 32 ala Pointing LIrnddgssand Guiding e sc eroe E ee yu ee ook Ne NN e 32 Oda E ee ee ee X ee vus 33 Oe MOCNE co wa aS A A a wee ee Re Eee RS 34 8 2 1 World Coordinate System enemies eee 9 Roy wo ee 34 223 Flat Fields oo anat 9o x eoe eh Pao ae REOS ao Be oa ES 34 2 2 9 Dome Fl cross cero x eae ae Se A 34 2 24 Sky Plate 2 04 yeh ew e ond ox oe de OP po RR RE US Pe OUR v s 35 4 2 5 Sky C ncentraHion u Ln S Ron eu RO RU Re ee E RON ADR BOE 35 22 6 IMA QUES lt aeuo go hoe RO oin RERO ee oe UE GA UR oC Gd 35 S2 f The active
51. 33 0 R 0 64 0 17 1 76 45 7 I 0 79 0 13 1 20 32 7 Table 12 Overall computed efficiency for 3 6m EFOSC2 CCD 40 Clearly the system reaches its maximum efficiency in the R band Note that these are crude estimates since we assume here that the filters have a box car profile and the standard star spectrum is flat across the pass band A different approach can be used to estimate the overall efficiency i e by directly using the trans mission reflectance and quantum efficiency factors in the optical configuration When used in Imaging mode the system is made up of 2 mirrors M1 M2 5 lenses 2 in the Collimator and 3 in the Camera 1 filter and the CCD Typical values for mirror reflectance and lens transmission are 0 95 and 0 90 respectively The peak transmission for the V filter is 0 87 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 107 and the quantum efficiency of CCD 40 at this wavelength is 0 80 Using these numbers we have e V 0 95 x 0 90 x 0 87 x 0 80 i e e V c 37 which is in good agreement with the value reported in Table 12 A 1 4 Signal to Noise ratio and Detection Limits The expected count rate per square arcsecond and per unit time for the sky background is given by the following formula Ssky 1004x mo mas ADU s7 arcsec 19 where mo is the zero point and may is the sky brightness in the given band expressed in mag arcsec This value depends of course
52. 37 6 14 1 35 06 32 15 10 Mar 15 10 50 19 00 20 20 5 24 6 44 07 09 16 15 Apr 01 11 57 18 40 19 59 5 35 6 54 07 56 17 33 Apr 15 12 52 18 24 19 44 5 42 7 02 08 36 18 36 May 01 13 55 18 09 19 30 5 51 7 11 09 25 19 47 May 15 14 50 17 59 19 21 5 57 7 20 10 11 20 49 Jun 01 15 57 17 52 19 16 6 05 7 29 11 13 22 04 Jun 15 16 53 17 52 19 17 6 10 7 35 12 09 23 04 Jul 01 17 56 17 56 19 20 6 13 7 38 13 16 00 10 Jul 15 18 51 18 02 19 26 6 12 7 35 14 16 01 04 Aug 01 19 58 18 11 19 33 6 05 7 27 15 31 02 04 Aug 15 20 53 18 19 19 40 5 55 7 15 16 32 02 49 Sep 01 22 00 18 28 19 47 5 38 6 57 17 47 03 39 Sep 15 22 55 18 35 19 54 5 21 6 40 18 49 04 18 Oct 01 23 58 18 44 20 04 5 01 6 21 20 02 05 01 Oct 15 23 53 19 52 21 14 5 43 1 05 21 07 05 38 Nov 01 01 00 20 04 21 29 5 23 6 49 22 30 06 25 Nov 15 01 56 20 15 21 44 5 11 6 40 23 40 07 08 Dec 01 02 59 20 28 22 01 5 03 6 36 01 00 08 03 Dec 15 03 54 20 38 22 13 5 03 6 38 02 07 08 58 Table 15 Sidereal Time and Sun Tables for La Silla All times are EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 119 F General Instructions For Visiting Astronomers There are detailed instructions available online at the EFOSC2 web pages Below we briefly list a few instructions e Successful EFOSC2 applicants should book their trip to Chile in such a way to reach La Silla two days before starting the observations to get the proper introduction to P2PP and prepare their Observing Blocks
53. 56 18 36 27 44 18 29 30 0 slit 5 0 Free Gr 11 2x2 normal 60 A 9013 A Spectrum 7 LTT7379 00 51 07 18 36 27 44 18 29 30 0 slit 5 0 Free Gr 14 2x2 normal 60 A 9013 A FocWedge 8 Focus 01 44 56 22 16 26 00 21 44 20 0 Free R 642 Foc Wedg 2x2 fast 60 A 9013 A FocWedge 9 Focus 01 46 53 22 16 26 00 21 44 20 0 Free R 642 Foc Wedg 2x2 fast 60 A 9013 A AcqPix Pointing 01 49 41 22 16 26 00 21 43 20 0 Free R 642 Free 2x2 fast 60 A 9013 A ImaJit PG2213 0 01 51 09 22 16 27 00 21 38 45 0 Free U 640 Free 2x2 normal 60 A 9013 A ImaJit 1 PG2213 0 01 52 34 22 16 27 00 21 33 15 0 Free U 640 Free 2x2 normal 60 A 9013 A ImaJit 2 PG2213 0 01 53 36 22 16 27 00 21 38 30 0 Free B4639 Free 2x2 normal 60 A 9013 A Figure 36 Example of automatic EFOSC2 logfile C Observing Log An ASCII log file of all your observations is automatically updated each time a new image is produced Its name is EFOSC_YYYY MM DD log where YYYY MM DD is the date of the observations This file can be found under data raw on wgboff We suggest that the VA saves a copy of this log file A useful command for printing is a2ps c132 2 f7 land EFOSC YYYY MM DD log As well as this automatic log file the VA is encouraged to make his or her own handwritten log file especially for noting down comments which are relevant for the observations An example of the automatically generated file is given in the following A report containing the night weather conditions and details of the per
54. 6100 0004 4 3 11 EFOSC_img_obs_Image This template is used for the Simple imaging mode and takes Number of exposures normal images through a Filter with a duration of Exposure time seconds each The CCD readout binning and windowing can be controlled Note that it is possible to insert a slit even if this is usually and by default set to Free This option is used when an image of a field through a slit a MOS plate or the Coronographic Mask is needed When executed the template warns the user that the slit is in the beam Parameter Default Description Filter NODEFAULT User specified filter Starplate Free User specified slit Exposure time NODEFAULT Exposure time sec CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of exposures 1 Number of exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 81 4 3 12 EFOSC_img_obs_ImageJit This template is for the Jittered Imaging mode and takes Number of Exposures normal images through Filter according to a List of Exposure times Between exposures the telescope is offset in RA an
55. 623 z Gunn gt 840 98 692 Ha 657 7 6 2 56 lt 0 01 709 Ha red 664 5 7 1 88 742 H Beta 486 1 7 2 83 743 Hbe Cont 477 1 7 2 81 687 ONI 500 3 5 3 74 700 SII 673 0 6 2 56 lt 0 01 724 Tyson B 444 5 183 8 82 Table 4 EFOSC2 filters Basic set one position Free As for EFOSC1 EFOSC2 filters are 60mm in diameter with a maximum thickness of 10mm Since the filter and the grism wheels are located very close to each other there is very little possibility of squeezing in larger filters Also since the filter wheel is located at a relatively large distance from the focal plane the quality of images obtained through filters mounted in this wheel is extremely sensitive to filter defects These may appear in the form of image blurs or ghosts due to multiple reflections inside the filter These ghosts can be a nuisance for observations of satellite features near bright objects Table 4 lists the EFOSC2 standard set of filters the basic set Their laboratory transmission curves are plotted in Fig 3 note although the labels say SUSI they are instrument independent For a complete list of filters available on La Silla consult the online ESO La Silla Filters Catalogue http filters ls eso org efs index htm or invoke the MIDAS context filters create gui filters which provides utilities for searching for filters and extracting and plotting their transmission curves The ful
56. 65 4 2 1 Abort Stop Pause Continue and Change Exp Time It is possible to Abort Stop Pause and Continue an exposure by asking the TIO One can also change the exposure time of an observation once the template has started running in this manner These commands and changes are entered on the EFOSC2 Control Panel also known as the OS Panel 4 2 2 Telescope logs location of data data reduction and backup A log of all the data files taken by EFOSC2 is automatically displayed on a screen of wg5off This displays the filename the object name the start U T the object position and other instrument related parameters n example of the telescope log is displayed in Fig 36 in the Appendix Note that the data is saved at the telescope under the convention EFOSC_X fits where X denotes the type of observation Thus the first long slit spectrum of the day will be named EFOSC_Spectrum fits and the second will be EFOSC_Spectrum 1 fits An important point to note is that this filename convention is restricted to the data at the telescope only Once the file is transferred to the archive it will be named under the standard ESO convention EFOSC YYYY MM DDTHH MM SS SSS fits Once the file is read from the instrument it is distributed by the Data Subscriber program whose task is among others to deliver a copy of the data to the offline data reduction machines wg5off and to the ESO data archive On wg5off the data is put into a directory data r
57. Angstrom Figure 5 Response functions of grisms nr 7 black and 14 red on November 28 2006 For each grism two standard stars have been used to define the response function Hiltner 60 and LTT 2415 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 15 3000 pn l M n 4 M DA d UI y OSSEP 1 User isaviane o o o Frame gr7_7 Identification HILT600 i Area M p J x 1 to 974 Y 1 to 1 Pixel value py o o o _ Scales X 8 61707 4 Y 31 689 A Min 122 Max 3 318403 Date 03 Dec 2006 Time OO 41 08 3500 4000 4500 5000 Position PIXEL Figure 6 ADU sec vs wavelength for the two spectrophotometric standards Hiltner 600 top spectrum and LTT 2415 For each standard the two spectra have been taken with grisms nr 7 and 14 16 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 e photon 400 600 600 1000 nm Figure 7 System efficiency given by VPHGs 19 blue curve and 20 red curve compared to that of other EFOSC2 grisms To make the best use of these grisms users must be aware of the following issues The flat fields of both grisms show gradients in the cross dispersion direction These gradients are also wavelength dependent which means that the response functions depend on the position along the slit For point sources an accurate flux calibration then requires to obtain the spectrum of spe
58. C img cal SEYELACS x ee nica eee one ee E ES ee 4 9 22 EFUSC imp cal PalarFlate lt uo ncn hex daa ture bh Se hoe Das 43 20 BFOSG ime cal PolarSkyPlate seem x 4 ped waa ee ea ne es 23 24 EFOSC imge cal EC HEEN 4 3 25 EFOSC spec cal Flats 4 2404544 y ee wea Ew y e eos 43 26 EF SC Spec cal IntEl tS 2 cay m x a Sw aS ee ee we 4 3 21 EEUSO spec cal PolarElabe i233 ok oat eae he a bao Bas 4 328 EPUSU spec cal Eege oss ace nee m Oe Ron ee AH meh E xod E Sek ee 0 290 EFOSC special d OU ovo zu GR A OG ic E yeh 43 90 EFOSC img cal FocusWithWedge lt e sa c q Rok mc oc e E E Us 43 91 EF SC img cal FoctisSequence 2 s s RR xor RR Ro Ro o Ro E 4 3 32 EFO0SC img cal FocusWithPrism io s edea cred iende ee EFOSC2 Efficiency Pol A x oh epee Ae gs ee Ee doe Bt oe Oe we we e ATI Colour EquatloHS s 2 6 6 sb poe A a a OP X 4 WO Po R eyes AJ2 lxpected Count Rates 4 6 so Re Se ee ie RE we OX RR eo AUS Overall EHIGIeD y ess ir qoe RS EU OS s des e S ow Ea A 1 4 Signal to Noise ratio and Detection Limits A2 Spectroscopy so ssi sy sabi E Oo BR E A E OX E CR ORO OR REOR hes A 2 1 Relative Grism sensitivities 22s ee A 2 2 Grism throughputs 222 ls sss ee A 2 3 Signal to Noise ratio and Expected Count Rates
59. C2 CCD The right diagram shows the bleeding effect when a flat is taken the prescan and overscan sections are affected and do not give the correct bias value The user should taken bias frames before and after the observations LSO MAN ESO 36100 0004 EFOSC2 USER S MANUAL 4 0 24 00 1 80 DT A D 1 4 D 1 D D D D D D J H 1 H 1 H 1 H H q 1 1 1 H D D H 1 D D D 4 D D H 1 D 1 D 1 1 D 60 x zo DEET iii SE Rg eg ci E ee EE C ca 40 ee eee eee Serre a rrr rrr EE 20 A nm Figure 12 Quantum Efficiency of CCD 40 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 25 L and R and hence produces images with two different bias levels During the target acquisition this is not a problem However the user can select the normal read out mode also for the target acquisition images in such a way that he she can use them also for scientific purposes Alternatively the user can take flats biases and standards in the fast mode for calibrating the data The web site http www eso org sci facilities lasilla instruments efosc inst Ccd40 html gives more information about the CCD 40 Additionally the user can have a look at the weekly tests there to check the latest CCD performance 2 6 2 Windowing and Binning All three Read Out modes offer the possibility to window the CCD Th
60. DUs When binning 2 x 2 it is possible to take 3 frames for each of the U B V R and i broad band filters during a single twilight 3 2 5 Sky Concentration As with most focal reducers EFOSC2 is affected by the so called sky concentration a diffuse spot of light a few percent above the background in the centre of the image This effect is caused by light from the sky background and from stars reflected by the CCD back onto the camera and returned by some optical surfaces with the main contribution from the field lens see Fig 18 Sky concentration causes a distortion of the flat field which will lead to an underestimation of the counts in the central part of the field However this is comparable to the accuracy with which normal flat fields can be obtained If higher accuracy is needed a more sophisticated procedure has to be adopted See for example Andersen et al 1995 or Valdes 1998 3 2 6 Image Quality The excellent image quality of the NTT is the result of several factors i its New Technology enclosure which ensures a very good airflow through the telescope ii its active and passive temper ature control which guarantee that no heat source is near the optical path and that the mirror is always cool and iii its revolutionary active optics indeed the NTT was the first telescope featuring a flexible controlled mirror 3 2 7 The active optics system The good image quality of the NTT is in part due to the a
61. EFOSC with the principle broad band filters is constantly monitored Usually during setup nights photometric standards are taken and a full photometric solution is obtained according to the following equations U u ZPy CTy x U B ky xz 9 B b ZPg CTe x U B kpxz 10 V v ZPy CTy x B V ky xz 11 R r ZPnc CIRx V HR knxz 12 I i ZPr OTrx R I amp gxz 13 In these equations U B V R and J are the catalogue magnitudes of the standard stars and u b v r i are their instrumental magnitudes 2 5 x logfApu computed from the counts fapy in ADUs per second z is the airmass The quantities ZP CT and are the instrumental zeropoint colour term the atmospheric extinction coefficient respectively and their values are obtained by solving the above equations for a number of stars with different magnitudes and colour at different airmasses Normal readout is used for the CCD Notice that on EFOSC2 a Gunn i filter is used instead of the Bessel J and equation 13 shows how the J magnitude can be obtained from 7 Filter ZP K CT mag mag 24 39 0 53 0 04 26 16 0 25 0 03 26 28 0 17 0 04 26 36 0 11 0 01 25 48 0 05 0 01 o D DC Table 10 The instrumental zero points atmospheric extinction and colour terms ZP k and CT for different filters These values were obtained using data data from photometric nights obtained during the re commissioning of
62. EFOSC2 NTT April 2008 The mean values for ZP CT and x for different filters measured during the re commissioning of EFOSC2 NTT April 2008 are listed in table 10 Up to date values will be posted at http www eso org sci facilities lasilla instruments efosc inst zp index html In obtaining table 10 only data from photometric nights have been used A comparison of the UBVRI zero points for EFOSC2Q NTT and EFOSC2 3P6 is shown in Fig 33 Clearly the sensitivity is improved across all wavelengths Equations 9 to 13 and table 10 can be used for on line magnitude determinations or to compute expected count rates exposure times and signal to noise ratio Note that the overall efficiency of the system changes with time due to factors such as changes in the electronics and washing of the M1 mirror The extinction coefficients can change due to site conditions volcano eruptions for example Hence the values in table 10 are for reference only and users should obtain their own photometric solutions for calibrating their science data 104 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 EFOSC2 ZPs z L V B o d i S S n A N T L A O o o F A t L o ul N A E Ap Is d EI l a N L L 1 1 1 1 L 1 1 1 1 L L L L 1 1 400 500 600 700 800 Wavelength nm Figure 33 Zero points for the UBVRi broad band filters circles compared with the mean values for the same filters at t
63. ER S MANUAL 4 0 LSO MAN ESO 36100 0004 MACS IRAF V2 1EXFORT ghsudvis43ph ls esc org Tos H3 38 32 4 Jul 200 PEH A008 46d E awh A Ab J ago Bot KOU 110400 Column pixels NUAD IRAF VS A1ENPORT gheudris43SpB ls esc org Tos 9 93 15 f4 Jul ROd PEB 8005 460 E A u gn RED Bat ni 11444 Column pixels Figure 29 Upper panel normalised and sky subtracted spectrum of an astronomical object taken with grism 10 170 slit and CCD 40 The spectrum has been flat fielded by a spectroscopic dome flat taken in the afternoon Residual ripples of about 2 of the continuum level can be seen in the continuum especially towards the red Pixel 1 and 2048 correspond to wavelengths of 6285 and 8210 respectively Note that the 2 prominent absorption features are caused by the atmosphere and not fringing Lower panel the same spectrum but flat fielded by an internal flat taken at the target position instead of a dome flat T he ripples in the continuum are not at a significant level EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 57 direction of the slit It heavily shines into the slit and even placing it 5 arcmin away still results in an enhanced brightness of the background At 10 arcmin distance the effect is negligible We repeated this sequence 2 5 10 but moving perpendicular to the slit In this way the light of the bright object gets blocked by the mask and already at 2 arcmin distance
64. ESO ESO ESO ESO TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL TEL ADA ADA ADA ADA INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS INS DET DET DID ESO VLT DIC ID v 5 37 DATE not set ALT 81 035 AZ 334 696 GEOELEV 2400 GEOLAT 29 2584 GEOLON 70 7345 OPER I Condor FOCU ID CA d FOCU LEN 108 827 FOCU SCALE 1 894 FOCU VALUE 19 500 PARANG START 27 937 AIRM START 1 012 AMBI FWHM START 1 00 AMBI PRES START 773 50 AMBI WINDSP 0 55 AMBI WINDDIR 346 AMBI RHUM 38 AMBI TEMP 14 40 MOON RA 235 692618 MOON DEC 20 29768 TH M1 TEMP 1 00 TRAK STATUS NORMAL DOME STATUS FULLY OPEN CHOP ST F TARG ALPHA 190048 000 TARG DELTA 372118 000 TARG EPOCH 1950 000 TARG EPOCHSYSTEM J TARG EQUINOX 1950 000 TARG PMA 0 000000 TARG PMD 0 000000 TARG RADVEL 0 000 TARG PARALLAX 0 000 TARG COORDTYPE M 2 PARANG END 27 513 AIRM END 1 012 AMBI FWHM END 1 00 AMBI PRES END 773 40 ABSROT START 270 02238 POSANG 0 00000 GUID STATUS OFF d ABSROT END 270 02238 SWSIM NORMAL ID EFOSC 2 4 GRIS1 ID 9 7 GRIS1 NAME Gr 1i1 GRIS1 NO 9 FILT1 ID 1 i FILT1 NAME Free d FILT1 NO 1 SLIT1 ID E 2 SLIT1 NAME slit 1 0 SLIT1 NO 5
65. EUROPEAN SOUTHERN OBSERVATORY Organisation Europ enne pour des Recherches Astronomiques dans l H misph re Austral Europ ische Organisation f r astronomische Forschung in der s dlichen Hemisph re LA SILLA OBSERVATORY Science Operations EFOSC2 USER S MANUAL Doc No LSO MAN ESO 36100 0004 Issue 4 0 Date 11 2013 Ls El prepare EE Ce o te EE EA Name Date Signature Approved DR INE EET Name Date Signature Released DOREM idea ee Name Date Signature ii EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 This page was intentionally left blank EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 ili Change Record Issue Rev Date Section Parag affected Reason Initiation Documents Remarks 1 1 30 05 99 All First Release 2 0 16 09 03 All Major Rewrite 3 0 03 08 All EFOSC2 to be relocated to NTT User Requirements added New Grisms and Quarter Wave Plate available 3 1 06 08 All EFOSC2 re commissioned at NTT during April 2008 New instrument specifications implemented 3 2 03 11 2 4 1 Comment added about the width of the offcentred slits 3 3 12 11 ALL Re write of several parts description for Narrow_Slit acquisition template added 4 3 6 HeAr added for G20 Fig 44 45 3 4 02 12 HeAr atlas added for G19 Fig 43 New Op Model 3 4 04 12 3 5 3 5 8 Spectroscopy close to bright objects added 3 6 08 12 2 4 1 H new Spectral coverage with red
66. FOSC_spec_obs_Spectrum which allows one or more frames to be taken at the same position It is recommended that the user re acquire the object every couple of hours if the object is near the meridian and every hour if the object is at large hour angles or close to the zenith The overall efficiency in spectroscopic mode is discussed in Appendix A 3 5 7 Fringing There is significant fringing for grisms which cover the near infrared part of the spectrum above about 7200 A For example the left panel of Fig 28 shows a normalised flat field obtained with grism 12 one of the grisms most affected by fringing A cross cut along the central column of this image shows that the amplitude of the fringes can be as much as 10 of the continuum level right panel Due to the instrument plus telescope flexure there may be a slight positional mismatch between the fringes in the dome flats and the science frame causing an imperfect flat fielding Fig 29 illustrates this effect using a normalised and sky subtracted spectrum of an astronomical object observed with grism 10 The left panel shows the spectrum flat fielded using a dome flat Residual ripples of about 2 of the continuum level can be seen in the continuum However if an internal flat is taken at the same telescope position as the object and used to flat field the spectrum the residuals become negligible right panel Hence if fringing is an issue it is highly recommended to take internal flat
67. HIERARCH ESO DET EXP TYPE Normal Exposure type HIERARCH ESO DET EXP DUMDIT O of dummy readouts HIERARCH ESO DET EXP RDTTIME 22 381 image readout time HIERARCH ESO DET EXP XFERTIM 22 751 image transfer time HIERARCH ESO DET READ MODE normal Readout method HIERARCH ESO DET READ SPEED fast 4 Readout speed HIERARCH ESO DET READ CLOCK read R port Fas Readout clock pattern used HIERARCH ESO DET OUTPUTS 1 of outputs HIERARCH ESO DET OUTREF O reference output HIERARCH ESO DET OUT2 ID RB d Output ID as from manufacturer HIERARCH ESO DET OUT2 NAME R Description of output HIERARCH ESO DET OUT2 CHIP 1 Chip to which the output belongs HIERARCH ESO DET OUT2 X 1 X location of output HIERARCH ESO DET OUT2 Y 1 Y location of output HIERARCH ESO DET OUT2 NX 1024 valid pixels along X HIERARCH ESO DET OUT2 NY 1024 valid pixels along Y HIERARCH ESO DET OUT2 PRSCX 6 Prescan region in X HIERARCH ESO DET OUT2 OVSCX O Overscan region in X HIERARCH ESO DET OUT2 CONAD 1 30 Conversion from ADUs to electrons HIERARCH ESO DET OUT2 RON 0 00 Readout noise per output e HIERARCH ESO DET OUT2 GAIN 0 77 Conversion from electrons to ADU HIERARCH ESO DET FRAM ID 1 Image sequencial number HIERARCH ESO DET FRAM TYPE Normal Type of frame HIERARCH ESO DET WINDOWS 1 of windows readout HIERARCH ESO DET WIN1 STRX 1 Lower left pixel in X HIERARCH E
68. He Ar Grism He Ar 1 10 0 25 47 15 0 30 13 2 5 06 42 10 007 8 2 0 30 14 30 0 30 0 43 20 10 0 18 25 60 17 3 0 03 4 125 1 75 10 20 04 19 15 30 45 08 02 11 30 3 0 20 0 1 30 46 20 03 16 3 0 03 Table 14 He Ar comparison lamps exposure times in sec The values are suitable for CCD binning 2 x 2 and a slit of 1 0 Grism 10 is decommissioned Grisms 9 12 15 were replaced by Grisms 18 16 17 respectively 114 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 ESO 3 6m EFOSC OBSERVING LOG Thu Sep 25 19 52 47 UTC 2003 File Ident UTStart RA DEC Exp Slit Filter Gris BIN CCDSpeed Prog ID Dark BIAS 19 52 22 00 00 00 00 00 00 0 0 Free Free Free 2x2 normal 60 A 9013 A Dark 1 BIAS 20 13 36 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A Dark 2 BIAS 20 14 12 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A Dark 3 BIAS 20 14 48 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A Dark 4 BIAS 20 15 23 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A Dark 5 BIAS 20 15 58 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A Dark 6 BIAS 20 16 34 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A Dark 7 BIAS 20 17 09 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A Dark 8 BIAS 20 17 45 00 00 00 00 00 00 0 0 Free Free Free 1x1 fast 60 A 9013 A Dark 9 BIAS
69. ID ESO OBS PROG ID ESO OBS START ESO OBS TPLNO ESO OBS TARG NAME ESO TPL DID ESO TPL ID ESO TPL NAME ESO TPL PRESEQ ESO TPL START ESO TPL VERSION ESO TPL NEXP ESO TPL EXPNO ESO DPR CATG ESO DPR TECH Standard FITS format NOST 100 0 of bits storing pix values of axes in frame pixels axis pixels axis European Southern Observatory 961 UT date when this file was written value of ref pixel Ref pixel of center of rotation Binning factor Pixel coordinate system value of ref pixel Ref pixel of center of rotation Binning factor Pixel coordinate system pixel FITS BSCALE BZERO pixel FITS BSCALE BZERO MJD start 2003 09 29T22 55 08 920 Date of observation Total integration time Extension may be present Original target Instrument used 920 Name of observer Name s of proposer s ESO Telescope Name 19 04 10 8 RA J2000 pointing deg 87 16 48 1 DEC J2000 pointing deg Standard FK5 years Coordinate reference frame 18 45 12 831 LST at start sec 22 55 01 000 UTC at start sec ESO0 VLT DIC 0BS 1 7 OBS Dictionary UNKNOWN 179 UNKNOWN 2400 A NS ON NUUS OS PSS O SOON A I RUN RO RR RN RATS s bserver Name Expected execution time PI COI name ESO internal PI COI ID linked blocks 0B name bservation block ID ESO program identification 2003 09 29T22 54 50 OB start time 2 Template number within OB Sky Flat Grii OB targe
70. Instrument R ma p we A Lili oB i i aee i Ba EE E i A f po f H GE H Bo Noe x UNS Ze j j ee A ESO Filter 623 Gunn z ESO Filter 692 Hal RA E E Instrument SUSI i M j EM i Zi a pos vei J ier 2 1 d D j A A ak d Sd E Pe E eee E PP i H E CH Se a 156 wi ESO Filter 1709 HAl r ESO Filter 742 Hbeta ESO Filter 1743 Hbeta C Instrument Instrument SUSI Instrument SUSI IM 96x EN ar X i i Y j j 4 H A i j d R ji i 7 j V X X A i N Vs i i nn NS MM N ESO Filter ESO Filter 1700 S IJ EsO Filter 1724 Tus 8 Instr ment Instrument SUS Instrument SUSI sn Em i 3 S al A MEN Zl ATUM SE AX i i E a i T d X i 8 F 3 7 d 02 J i T Ji X N ra NE Pa X lea E S S 8 E i S Figure 3 Laboratory transmission curves of the EFOSC2 standard set of filters Note although they are labelled SUSI they are instrument independent 10 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 ESO filter Ac FWHM Peak Red leak H nm nm trans information 640 U Bessel 354 5 53 8 68 lt 0 005 1100nm 639 B Bessel 440 0 94 5 54 0 012 1150nm 641 V Bessel 547 6 113 2 87 0 055 1150nm 642 R Bessel 643 1 165 4 86 0 076 1150nm 782 g Gunn 516 9 77 6 81 0 01 1100nm 786 r Gunn 681 4 83 8 83 0 01 1100nm 705 i Gunn 793 1 125 6 83 0 01 1100nm
71. O Manual Szeifert T 1998 First Order Estimates of the systematic observation biases of FORS in polarimetric mode due to non Achromatism of the retarder plates VLT Instrument Consortium Issue 1 3 Tyson N D amp Gal R R 1993 AJ 105 1206 Valdes F 1998 Guide to the NOAO Mosaic Data Handling Software IRAF Package Abbreviations and acronyms The following abbreviations and acronyms are used in this document AG Autoguider BOB Broker for Observation Blocks EFOSC ESO Faint Object Spectrograph amp Camera EMMI ESO Multi Mode Instrument FITS Flexible Image Transport System GUI Graphical User Interface HWP Half Wave Plate QWP Quarter Wave Plate ICS LSO Instrument Control Software La Silla Observatory MIDAS Munich Image Data Analysis System MOS Multi Object Spectroscopy NTT New Technology Telescope OS P2P Observation Software P Phase 2 Proposal Preparation RID Real Time Display SA SE Support Astronomer System Engineer TBC To Be Checked TBD To Be Defined TBV To Be Verified TCS Telescope Control Software TIO Telescope amp Instrument Operator URL Uniform Resource Locator VLT Very Large Telescope VA Visiting Astronomer EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 3 2 EFOSC2 Overview 2 1 History of EFOSC2 Late in 1987 it became clear that before the implementation of EMMI the ESO Multi Mode Instru ment on the NTT an instrument with imaging and spectro
72. OPTI1 ID HWP d OPTI1 NAME hwp motor OPTI1 ST F OPTI2 ST F OPTI2 POS 0 089 ID CCD FIERA NAME TCS Data dictionary for TEL TCS version number TCS installation date Alt angle at start deg Az angle at start deg S 0 W 90 Elevation above sea level m Tel geo latitute North deg Tel geo longitude East deg Telescope Operator Telescope focus station ID Focal length m Focal scale arcsec mm M2 setting mm Parallactic angle at start deg Airmass at start Observatory Seeing queried from AS Observatory ambient air pressure q Observatory ambient wind speed que Observatory ambient wind directio Observatory ambient relative humi Observatory ambient temperature qu 15 42 46 2 RA J2000 deg 20 17 51 6 DEC J2000 deg M1 superficial temperature Tracking status Dome status True when chopping is active Alpha coordinate for the target Delta coordinate for the target Epoch Epoch system default J Julian Equinox Proper Motion Alpha Proper motion Delta Radial velocity Parallax So SOA SOS Ba ah Aa e e Coordinate type M mean A apparent Parallactic angle at end deg Airmass at end Observatory Seeing queried from AS Observatory ambient air pressure q Abs rot angle at exp start deg Position angle at start Status of autoguider Abs rot angle at exp end deg Software simulation Instrument ID GRIS1 GRIS1 GRI
73. Preset telescope and centre an object in slit with rotation EFO0SC img acq RotateToSlit IMAGING TEMPLATES Coronographic Imaging EFO0SC img obs Coronography Imaging without Jitter EFOSC img obs Image Imaging in Jittering mode EFO0SC img obs ImageJit Polarimetric Imaging EFOSC img obs Polarimetry SPECTROSCOPY TEMPLATES Spectropolarimetry EFOSC_spec_obs_Polarimetry Long slit Spectroscopy EFOSC_spec_obs_Spectrum MOS Spectroscopy EFOSC_spec_obs_MOS CALIBRATION TEMPLATES Darks EFOSC_img_cal_Darks Imaging Dome Flat Fields EFOSC_img_cal_Flats Telescope Focus using Focus Sequence EFO0SC img cal FocusSequence Telescope Focus using Focus Prism EFOSC_img_cal_FocusWithPrism Telescope Focus using Focus Wedge EFOSC_img_cal_FocusWithWedge Internal Lamp Imaging slits Cor Masks MOS plates EFOSC_img_cal_IntImage Polarimetric Imaging Dome Flat Fields EFOSC_img_cal_PolarFlats Polarimetric Imaging Sky Flat Fields EFOSC_img_cal_PolarSkyFlats Imaging Sky Flat Fields EFOSC_img_cal_SkyFlats Arcs spectroscopy EFOSC_spec_cal_Arcs Spectroscopy Dome Sky Flat Fields EFO0SC spec cal Flats Spectroscopy Internal lamp Flat Fields EFO0SC spec cal IntFlats Spectropolarimetry Dome Sky Flat Fields EFOSC spec cal PolarFlats Spectroscopy Arcs and Dome Flat Fields EFOSC_spec_cal_ArcFF
74. S1 FILT1 FILT1 FILT1 SLIT1 SLIT1 SLIT1 OPTI1 unique ID OPTI1 name Status depolarizer on off T F Position angle in deg Rev 2 87 Detector system Id unique ID name slot number unique ID name slot number unique ID name slot number TNS A SE SA ER SPR RTE ERAN EOIN A ERO efosc ccdefosc Name of detector system EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 117 HIERARCH ESO DET DATE 30 08 2000 Installation date HIERARCH ESO DET DID ESO VLT DIC CCDDCS ESO VLT DIC FCDDCS Diction HIERARCH ESO DET BITS 16 Bits per pixel readout HIERARCH ESO DET RA 0 00000000 Apparent 00 00 00 0 RA at start HIERARCH ESO DET DEC 0 00000000 Apparent 00 00 00 0 DEC at start HIERARCH ESO DET SOFW MODE Normal CCD sw operational mode HIERARCH ESO DET CHIPS 1 of chips in detector array HIERARCH ESO DET CHIP1 ID ccd40 Detector chip identification HIERARCH ESO DET CHIP1 NAME LORAL a Detector chip name HIERARCH ESO DET CHIP1 DATE 30 08 2000 Date of installation YYYY MM DD HIERARCH ESO DET CHIP1 X 1 X location in array HIERARCH ESO DET CHIP1 Y 1 Y location in array HIERARCH ESO DET CHIP1 NX 2048 of pixels along X HIERARCH ESO DET CHIP1 NY 2048 of pixels along Y HIERARCH ESO DET CHIP1 PSZX 15 0 Size of pixel in X HIERARCH ESO DET CHIP1 PSZY 15 0 Size of pixel in Y HIERARCH ESO DET EXP NO 1061 Unique exposure ID number
75. SO DET WIN1 STRY 1 Lower left pixel in Y HIERARCH ESO DET WIN1 NX 1030 of pixels along X HIERARCH ESO DET WIN1 NY 1030 of pixels along Y HIERARCH ESO DET WIN1 BINX 2 Binning factor along X HIERARCH ESO DET WIN1 BINY 2 Binning factor along Y HIERARCH ESO DET WIN1 NDIT 1 of subintegrations HIERARCH ESO DET WIN1 UIT1 10 000000 user defined subintegration time HIERARCH ESO DET WIN1 DIT1 9 999325 actual subintegration time HIERARCH ESO DET WIN1 DKTM 10 0244 Dark current time HIERARCH ESO DET SHUT TYPE Slit 2 type of shutter HIERARCH ESO DET SHUT ID ccd shutter Shutter unique identifier HIERARCH ESO DET SHUT TMOPEN 0 028 Time taken to open shutter HIERARCH ESO DET SHUT TMCLOS 0 027 Time taken to close shutter 118 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 E Sidereal Time and Sun Tables In the following table the Local Sidereal Time at midnight LST is reported together with the relevant times concerning the Sun for La Silla LST at evening and morning twilights are also tabulated to have a quick idea of the range of R A accessible during the night CST CDT Date LST Sun LST midnight set twilight twilight rise evening tw morning tw Jan 01 05 02 20 46 22 20 5 13 6 48 03 23 10 16 Jan 15 05 57 20 46 22 19 5 27 6 59 04 16 11 25 Feb 01 07 04 20 40 22 08 5 46 7 13 05 12 12 51 Feb 15 07 59 20 30 21 54 6 01 1 25 05 53 14 01 Mar 01 08 54 20 16 21
76. Slit position angle 90 Slit position angle 60 Slit position angle 120 Figure 17 EFOSC2 slit orientation 3 2 Imaging In this section the user will find some notes of specific interest when using EFOSC2 for Imaging In this and the following sections we will often refer to the Templates and Observation Blocks see Chap 4 3 2 1 World Coordinate System The rotation centre is near the centre of CCD at pixel 1016 990 The orientation at zero rotator angle to be North up and East right see 10 i e with the image reflected about the y axis relative to the view on the sky This information has been used to allow full World Coordinate System WCS information to be stored in the FITS headers of data taken with EFOSC2 which in test exposures of astrometric and standard star fields at various rotator angles to be accurate to within the typical pointing accuracy of the NTT a few arcseconds Note that the WCS information is correctly calculated for all binning modes 3 2 2 Flat Fields For an accurate flat field correction both dome and evening morning twilight exposures should be taken These will allow the pixel to pixel and low frequency variations to be taken into account 3 2 3 Dome Flats As part of the start up procedure every afternoon the telescope can be left in the flat field position by Day Operations The flat field screen can be illuminated using the quartz halogen lamps located in the dome which are controlled re
77. T T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window List of telescope RA offsets 5 Space separated RA offset list arcsec List of telescope DEC offsets 5 Space separated DEC offset list arcsec Return to origin T Return to origin T F Perform combined offset T Perform combined offset T F Number of Exposures 3 Number of exposures 82 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 13 EFOSC img obs Polarimetry This template is for the Polarimetric Imaging Mode and takes Number of Exposures images for Polarimetry through a Filter with a duration of Exposure time seconds for each of the positions in the List of HWP rotator positions specifled by the user If you ask for N exposures the template does N cycles where all HWP angles are repeated So the N exposures of angle say 22 5 are separated by those of the other three angles In algorithm e for every exposure for every angle take frame The Starplate is not free but contains a Wollaston Mask while the Grism wheel contains the cor responding Wollaston Grism The Move HWP IN flag should be set to T The Continuous rotation of HWP should be set to T to get depolarised radiation note in this case there has to be 1 and only 1 value any is fine entered against the List of HWP rotator positions and to F to have polar
78. a instruments efosc inst fringing html 3 3 Polarimetric Imaging As already mentioned see Sec 2 4 8 the Wollaston prism produces two images of the same object usually called ordinary and extraordinary with perpendicular polarisation on the output CCD image the separation of the two beams depends on the specific prism In order to avoid confusion and increased sky it is a common technique to insert in the aperture wheel a special mask with alternating transparent and opaque parallel strips with a width corresponding to the splitting Naturally this mask masks out half the viewing area Therefore a polarisation image of the whole field at one position angle requires two sets of exposures with the telescope moved by an amount equal to the beam split in order to recover the part of the field occulted by the mask Of course in case the object of interest is well contained in one strip one exposure for each position angle will be sufficient 44 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 1 02 F 0 98 Normalized Pixel Value de T L L 0 500 1000 1500 2000 Position px Figure 23 Upper panel Fringe pattern on a 10 minutes exposure in the I band CCD 40 Lower Panel A mesh of the central 100 columns from an I superflat obtained combining 14 exposures of 480s each courtesy of A Iovino EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 45 EHEHE BOGE HUANU Pm Ll E E Ll E
79. a slit or MOS mask and for taking an internal image of a coronographic mask This template means that the telescope does not need to be moved to the flat field screen This template takes Number of exposures images with the desired Internal lamp through the Filter and Slit with a desired Exposure time The CCD configuration may be controlled The Calibration Unit is automatically moved IN and OUT of the light path at the beginning and at the end of the execution respectively Currently Ne Ar He and Quartz lamps are available The mask images can be taken with any of the lamps The acquisition template for MOS spectroscopy EFOSC_img_acq_MOS requires the output from this template for identifying the 3 slits for alignment It will list only the files produced by EFOSC_img_cal_IntImage when requesting the MOS plate image Therefore the observer must always use EF0SC img cal IntImage when preparing the MOS plate images and these must be left in the default directory INS_ROOT SYSTEM DETDATA the user should take a note of the name of each file and which MOS mask it corresponds to in the afternoon Since all the files are moved in the morning into a subdirectory it may be necessary to copy them back to INS ROOT SYSTEM DETDATA before starting any acquisition Parameter Default Description Filter NODEFAULT User specified filter Slit Free User specified slit Internal lamp name Ar User specified internal lamp Exposure time 1 0 Exposure
80. and blue slits 3 7 12 12 2 4 4 Fig 4 with VPHG grisms and change 9 18 12 16 3 5 5 New Fig 26 illustrating atmospheric differential refraction with grism 7 and 14 3 8 05 13 All Several links updated 3 9 05 13 All Several links updated 4 0 11 13 2 6 4 CCD clock induced charge generation commented 2 7 Integration sphere Quartz halogen flat field lamp added iv EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 This page was intentionally left blank EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 M Contents 1 Introduction 1 LI PUO s echo bo o Ies Y uode A ee XQ BS E A ue e pem PD Re UA e 1 12 GBPS te ce lh nee Za ee xci OP S RUE Nu ek doe e ee o weg 1 LS Reference doc mients os ci Pee ee ee RR RONDE Bk XO EXE e 1 1 4 Abbreviations and actonyms 654464 o 9 oe x y Y s 2 2 EFOSC2 Overview 3 2 Beer EFOSCI e sua ace a3 e SI Hox o m Ko Re Rn E RES UE on DA RR d 3 2 2 General Description uo sa s sue kx ee bee RD UR RUE Rm OXON X a Rex A 3 20 EE ee Aur ea e A RARE ace wet des xo Be S 3 23 Instrument Detup co eov noc 4k ERO NIB a We Were ge ee Rex XOU ERE Ys 6 Pao OMe es a Ce eee oe SA ge ee eee oe Bae ee pee eee A 6 2412 MOS PISTES A uuo ee ke YORI a uiro eee vete e dos aes 8 DAS PITE 3509 x3 we we a ee eo ae Se ee ee ERROR 8 2 44 Grims and Prisms cec 4 oo kool a e Gn WO R3 Ga 4 Oe YS eR OS 11 2015 Grims ar amd ld x se eee hk oe hex a ew wee e 12 2 4 6 New VPH Grisms offered as of DR 12
81. asses as indicated and with the 5 slit aligned to the parallactic angle While the low airmass spectrum is almost horizontal the one at airmass 2 187 has an offset of 3 between the position at 590 35m and that ab 330 NM os oo eee ea xo Xx EUR ee om Fringe Pattern for grim BIZ x 222 x00 kl 9k e v 9 do Xe gu OUR Ee E a Fringe Removalforgrism 43010 oca oos as EE RR E L The BOB panel ce ia d oe hono Rs a p NR RR ER ERE EFOSC2StatusPanel esee es ExampleorP2PP pa al o og 243 dx a BR xx RR RR e A Zero points for the UBVRi broad band filters circles compared with the mean values for the same filters at the 3 6m triangles lt lt Relative Grism sensitivities a a EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 ix 35 36 37 38 39 40 Al 42 43 44 45 46 47 48 49 50 5l 52 53 54 List EFOSO2 Grist Throughputs s cso ek cR m ARR Rom GW XD A ee 111 BEOSUZ LOB Bile A eca eee a A e Gk ee aa ee A a ee ee 114 Helium Argon Atlas for grisms 1 and A7 122 Helium Argon Atlas for grisms 3 and A4 123 Helium Argon Atlas for grisms 5 and A0 124 Helium Argon Atlas for grisms 7 and A8 125 Helium Argon Atlas for grisms 9 replaced by grisms 16 and 10 decommissioned 126 Helium Argon Atlas for grisms 11 and 12 replaced by grism 16 127 Helium Argon Atlas for grisms 13 and 14 2 0200 128 Helium Argon Atlas for grism 15 replaced
82. ate P2PP only allows one acquisition template per Observing Block EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 33 that s he can select a guide star in a suitable region The acquisition is done by a technical CCD upgraded in November 2005 whose default orientation is North on the top and East to the left with a field of view of 1 7 x 1 7 and a scale of 072 pix The resolution of the guide probes is 0705 As the autoguider only corrects the altitude and azimuth motions tracking inaccuracies of the rotator may induce image displacements Note that in case of poor seeing or strong wind autoguiding may make the images worse since the corrections always lag behind actual conditions In such conditions it is better to lower the frequency of the corrections to average the effects It is also possible to observe moving targets with the NTT but this is not implemented in the autoguider Presently the best way is to use the tracking model and to supply differential tracking rates in arcsec sec The expected accuracy is the same as for simple tracking since the telescope is altazimutal it doesn t care if the tracking is sidereal or not Care should be taken in re acquiring the moving object in the slit on average each 10m depending on the telescope position and on the target speed The NTT has an Altitude Azimuthal mounting and as a consequence the singularity is in the Zenith and not in the pole When observing very close to the Zenith
83. atures of EFOSC2 is its flexibility in performing very different astro nomical observations In fact EFOSC2 offers seven different observing modes three for Imaging and four for Spectroscopy These modes are achieved using different combinations of the optical 4 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 EFOSC2 Calibr Lamps Aperture Wheel Tel F Plane Motor Encoder Collimator Half Wave Plate Filter Wheel Grism Wheel 10 Shutter 11 Camera 12 Thermal Comp 13 Focus Ring 14 CCD 15 Cryostat ONDARON Figure 1 Schematic optical and mechanical layout of EFOSC2 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 5 80 VA d Naa IS q v ww Jy 70 60 EFOSCZ ii EFOSC1 90 40 30 Transmission 20 10 300 400 500 600 700 800 900 ER o ce e Wavelength nm Figure 2 Overall transmission of the EFOSC2 optics compared to EFOSCI 6 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 components which can be inserted in the instrument All offered modes and their corresponding setups are presented in Table 1 MODE APERTURE FILTER GRISM HWP QWP WHEEL WHEEL WHEEL Imaging Free Filter Free Out Coronographic Imaging Cor Mask Filter Lyot Stop Out Polarimetric Imaging Woll Mask Filter Woll Prism In Spectroscopy Slit Free Grism Out Multi Object Spectroscopy MOS Plate Free Grism Out Slitless S
84. aw YYYY MM DD where YYYY MM DD denotes the date of the observation For example data collected from midday of today to midday of tomorrow will go into today s directory Each day a new directory will be created automatically The telescope log corresponding to the day can also be found in the directory Data reduction can be performed on the offline data reduction machine wg5off where IRAF and MIDAS are installed as part of the scisoft package There is also a quick look tool for long slit spectroscopy the software and detailed descriptions can be found at http www eso org sci facilities lasilla instruments efosc tools qlook index html On wgboff data shouldn t be reduced where the raw files are data raw YYYY MM DD but in a directory under data reduced Note that we do not keep backups of the user OBs and any OBs left in the system will be erased during regular software upgrades If the user would like to keep their OBs for example to be used in a future observing run then he she should export the OBs from the P2PP panel and make a backup Note however that the observing templates are modified from time to time for bug fixes or improvements hence it is recommended to make fresh OBs for each observing run using the latest version of P2PP and Instrument Package to ensure compatibility 4 3 EFOSC2 Templates a Reference Guide This section provides summaries of the currently supported EFOSC2 templates Table 8 contains a quick re
85. bes 50 3 5 1 Dome and Sky Spectroscopic Flats o 2l 50 9 5 2 Internal Spectroscopic flats 2302012 09e o9 a on RB SEU Ewe n 50 3 5 3 Wavelength Calibration es 51 S54 Target ACQuisition e o ex ooo pa eR Ga X 4o c RR REE AR EUR d 52 2 0 Pa allactio Angle soo ciedad ta nnay doeii oE eo XO CS ER s 52 3 5 6 Science Exposures a 54 ved ELIO pul gk Be a Be St ee a dye Po Pw ee poene 54 3 5 8 Sp ctroscopy close to bright objects lt s o sico cts o x RS 54 Multi Obel EEN uc iu eae we ee Ae ew AER UU E 57 C DAMM VD o E td Ria a AA REE a Se A oe eS 57 040 2 Target AGAUR uus e db whale a ES ROA RE Bw ae ee is 58 3 6 3 Science Exposures 2 42 3 44 aa RE Rh OO UR RO E A 58 plitless Spectrost6py lt lt 2644 5 484 ne eee ee a he Gee Pa as 58 3 7 1 Target Acquisition o s sca acs ee 59 dde EEN Expos reS zd lu kk ke taa ee BOE ERE DR ee Rx ROS RAS 59 Spectropolarimenry lt s osx eoo X ee ee eR RA ee d E Ped 59 SI Plaise ux 2 fb ee ee 6 eb ee se X25 9 WO wo ee Pub ee d bos 59 3 5 9 Target ACQUISII N e kee bse Rohde o GA odd Ed WS RE s 59 4 5 9 scence eege e cec aware 4 BAS a BS ae qo odo epo wes woo 60 EFOSC2 Observing Templates 61 Observing With PZPP sordas koe ook c9 a eet IR ROTE URS 61 What happens at the telescope 63 4 2 1 Abort Stop Pause Continue and Change Exp Time 65 4 2 2 Telescope logs location of data data reduction and backup 65 EFOSC2 T
86. ce A MIDAS routine will measure the Point Spread Function at each focus position and the result will be plotted in a graphics window where the operator can inspect the trend A best focus will be calculated and the operator can chose to apply the focus offset or not Note that a Grism can be inserted however for normal focus sequences this has to be set to Free The Focus Wedge prism Focw is selected only for calibration purposes Note also that only positive telescope focus offsets are allowed Since this procedure takes several minutes it is recommended to avoid using it for normal focusing which should be performed by means of the Focus Wedge This procedure is also not useful in very crowded fields Parameter Default Description Filter R 642 User specified filter Grism Free User specified grism Exposure time 20 Exposure time Telescope focus offset 10 Focus step encoder units Telescope offset 10 Telescope offset arcseconds Direction of telescope offset DELTA Direction of telescope offset Number of subexposures 9 Number of requested exposures 102 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 32 EFOSC_img_cal_FocusWithPrism This calibration template acquires an image with a specified Exposure time and Filter using the Focus Prism Pyramid This is a new addition to the focusing capabilities of EFOSC2 When the template is executed the Grism HWP and Calibration Unit positions are first checke
87. ch the requested intensity level is calculated Currently the lamp intensity is manually controlled using the Flat Field Lamp Control Panel Note that if the computed exposure time is less than 3 sec or greater than 5 min the template will be aborted automatically An identical template is available for circular polarimetry EFOSC img cal QWPolarFlats Parameter Default Description Filter NODEFAULT User specified Filter Starplate NODEFAULT User specified Wollaston Mask in Starplate Wheel Grism NODEFAULT User specified Wollaston Prism in Grism Wheel Requested intensity level 40000 Requested intensity level in ADUs CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of Exposures 5 Number of exposures 92 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 23 EFOSC_img_cal_PolarSkyFlats Before this template is executed the telescope must already be preset to an empty field either by an acquisition template or manually by the TIO This calibration template acquires Number of exposures sky twilight flats with an intensity of approximately the R
88. ching process and during the mounting in the Aperture Wheel Unfortunately if the bright reference objects are well centred there is no way to correct the centring in order to bring the other objects into the slit lets 3 7 Slitless Spectroscopy This mode of operation should be useful in a variety of survey programs due to the large number of available grisms and the overall efficiency The use of filters in combination with a grism can be useful to isolate the spectral region of interest and to reduce crowding and sky background intensity Note that the spectral coverage depends on the position of the objects EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 59 3 7 1 Target Acquisition Since here there is no need to place the objects in the slit the templates EFOSC_img_acq Preset or EFOSC_img_acq MoveToPixel can be used 3 7 2 Science Exposures The scientific frames are obtained with EFOSC spec obs Spectrum the same template used for normal spectroscopy The only difference is that the user must set the Aperture wheel to FREE and insert the desired grism and filter 3 8 Spectropolarimetry Spectropolarimetry can be performed by inserting the Wollaston Prism into the filter wheel to work in combination with a grism The Wollaston Prism splits the incoming radiation into two perpendicu larly polarised beams separated by a small angle which depends on the selected prism Therefore for each object in the slit two spectra are
89. close to 20s if a V filter is used e Obtain a similar exposure with the Lyot stop in position e Subtract the two images If the Lyot stop is properly aligned the difference image should be symmetrical and show the 4 quadrants of the telescope pupil not blocked by the Lyot stop If this is not the case please call the opticians as the alignment may require rotating the stop and offsetting the grism wheel 20 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Figure 9 Size and position of the spots in the EFOSC2 Coronographic Mask EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 21 Figure 10 Default EFOSC2 CCD orientation We remind you here that to use this EFOSC2 mode the coronograph must be mounted in the Aperture wheel while the Lyot stop has to be installed in the grism wheel The coronograph is very fragile Plenty of advance notice is required to ensure the coronograph is mounted safely before the observations start 2 5 Shutter The shutter of EFOSC2 is mounted at the Camera entrance see Fig 1 Since the shutter is of the iris type the effective exposure time in the central region is expected to be higher than in the outer region Nevertheless several tests have shown that the shutter delay is 24ms 5ms across the entire CCD with the position dependent time delay being smaller than 10ms This means that after adding 24ms to the exposure time a maximum position dependent error of 5ms is left It
90. ctive control of the primary and the secondary mirror The primary M1 mirror is supported by 75 actuators and three fixed points corresponding to actuators 7 29 and 50 The force applied to each of the 75 actuators can be adjusted and thus the shape of M1 can be modified The secondary mirror M2 can be moved in X Y Z where the X Y motion of M2 is used to correct for decentring coma and the motion in Z controls the focus The active supports are used to compensate for various deformation effects in the telescope structure and the mirrors and for effects due to inhomogeneities of the air temperature in the dome Some of these effects are elastic and can be empirically calibrated for each position Others have inelastic components and are more difficult to predict Confusion is sometimes found 36 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Figure 18 Normalised R dome flat field September 2003 The image cuts are 0 96 1 04 The scratches on the left side of the detector are due to the support of the Movable slit The spot in the centre is due to the Sky Concentration EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 37 about the difference between active optics and adaptive optics Adaptive optics can correct for turbulence in the atmosphere by means of very fast corrections to the optics whereas active optics only corrects for much slower variations Thus whereas adaptive optics can reach the diffraction limit of the tel
91. ctrophotometric standards in the same position as the targets For extended sources the spectrophotometric standards should be placed in different positions across the CCD or corrections to some fiducial response function should be obtained based on flat fields Second order contamination is apparent in the red grism for A gt 68004 so it is advisable to use order sorting filters to cut the blue flux if flux calibration is an issue for the science case Note also that the spectral range of the blue grism does not reach the Mg triplet at 5200 A or the G band at 4300 A However using the movable slit we verified that the two features can be reached with a slit offset of 15mm in either direction the displacement is 14 5 A mm Therefore the two sets of offcentred slit 15mm to the blue or to the red with respect to a central slit can be used to cover a more interesting blue spectral range by merging two spectra see also 82 4 1 2 4 7 Focus Wedge Prism At the NTT the telescope focus is done through an image analysis and applying a focus offset which is tabulated and proper to the different instruments However the telescopes focus can be checked quickly using a Focus Wedge prism which is permanently mounted in the EFOSC2 grism wheel The prism covers only one half of the beam and hence it acts as a transparent Hartmann mask Due to its geometry it also significantly enhances the distance between the baricenters of the two images produced by the tw
92. d 20 are reported in the commissioning report at the following address http www eso org sci facilities lasilla instruments efosc doc vph report pdf A Ion A Ion A A Ion 3888 646 He I 6172 278 ArII 8014 786 Ar I 3948 979 Ar I 6678 151 Hell 8115 311 Ar I 3964 729 He I 6752 833 Ar I 8264 522 Ar I 4044 420 Ar I 6871 289 Ar I 8408 210 Ar I 4158 590 Ar I 6965 430 Ar I 8424 647 Ar I 4200 674 Ar I 7030 25 Ar I 8521 442 Ar I 4300 101 Ar I 7065 190 He I 8667 944 Ar I 4333 561 Ar I 7147 04 Ar I 9122 967 Ar I 4471 479 He I 7272 93 Ar I 9194 638 Ar I 4510 733 Ar I 7383 980 Ar I 9224 499 Ar I 4713 146 He I 7503 869 Ar I 9354 22 He I 4921 931 ArII 7514 65 Ar I 9657 78 He I 5015 680 He I 7635 106 Ar I 9784 50 He I 5875 621 He I 7723 984 Ar I 10830 30 He I 6114 923 ArII 7948 176 Ar I Table 16 Recommended He Ar Lines for wavelength calibration EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 121 H Spectral coverage with off center long slits The figures in this section show the gain in spectral coverage that is obtained when off center blue and red long slits are used together with some of EFOSC2 grisms Each figure shows in the same plot the Helium Argon arcs obtained with the blue standard and red slits An increasing offset in counts has been added to the arcs from blue to red in order to clearly show the limits in spectral coverage defined by each slit A trace
93. d If they are in the light path these components are automatically removed The CCD parameters are hard coded in the software Note that Slit for Reference should always be set to free The Focus Pyramid splits each star into 5 in a cross shape The Pyramid is setup in such a way that the axes of the cross will be aligned with the X and Y axes of the CCD when the image is focused but the cross will be rotated if the focus is off T he telescope operator will be prompted to identify the centres of each cross in the image and the program will work out the angle of offset of each cross and hence the offset in focus The operator will be given the option to offset the focus or not This focusing procedure gives roughly the same performance as the Focus Sequence and the Focus Wedge comparison of their performances can be found online at http www 1s eso org sci facilities lasilla sciops team_only efosc2 tests Tests html This template is likely to fail in crowded fields Note that since this template is not frequently used please notify the astronomer or operations staff beforehand if you want to use it to ensure that the system is calibrated Parameter Default Description Slit for Reference Free Slit for reference Filter R 642 User specified filter Exposure time 20 Exposure time EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 103 A EFOSC2 Efficiency A 1 Imaging A 1 1 Colour Equations The photometric performance of
94. d DEC by user specified amounts in arcseconds These are relative offsets not absolute offsets from the original position Note that the first image will not be taken at the initial position unless the first value in the list is set to 0 If the offset list is shorter than the number of exposures the offset pattern is cycled until the end of the image sequence is reached The user can specify if he she wants to put the telescope back to the original position at the end of the sequence Return to origin and if accurate offsets by combining the guideprobe and the telescope offsets should be performed Perform combined offset The slit is automatically set to Free The CCD readout binning and windowing can be controlled Note that if the List of Exposure times has more than one entry and they are separated by spaces it is interpreted as its namesake If the List of Exposure times is shorter than the number of exposures then the list is cycled until the image sequence is reached Of course the exposure time list is effective only if Number of exposures is bigger than 1 Parameter Default Description Filter NODEFAULT User specified filter List of Exposure times NODEFAULT Space separated list of exposure times sec CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If S
95. d Rotator Offset Angle It then inserts a filter and takes a short exposure it can be a focus wedge image if the Focus flag is set to T which is displayed in a MIDAS window for inspection by the operator Following this an iterative acquisition loop is started to put the instrument into the correct orientation The user will be prompted for the name of the file containing the image of the slits He she will then be prompted to identify the 3 slits for the alignment from this image Afterwards an image of the sky is taken and displayed and the user is asked to identify the 3 stars corresponding to the 3 slits This process can be iterated until the desired rotator accuracy is reached When this is done the operator will be requested to find a guide star and to activate the autoguider An iterative acquisition loop is then started to refine the alignment In this loop a short image is taken and sent to the MIDAS display The operator selects the 3 alignment stars and a telescope offset is calculated and performed This process can be iterated until the desired positional accuracy is reached If the Focus flag is set to T after the rotator offset and before the alignment procedures an iterative focusing procedure using the focus wedge is initiated The last image produced during the focusing procedure will the be used to make the first approximate offset to centre the field If the Focus flag is set to F the focusing is simply skipped Note that i
96. dinate 1100 X coordinate in 1 x 1 binning of one of the objects Preset flag T Preset the telescope Focus flag T Focus flag Initial Rotator angle 0 Initial Rotator Offset angle deg EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 77 4 3 8 EFOSC_img_acq Polarimetry This template is used to place an object inside a Wollaston Mask for Polarimetric Imaging It has two parts First it presets the telescope to the coordinates of the Target associated with the Observation Block It then takes a short exposure it can a be a focus wedge image if the Focus flag is set to T which is displayed in a MIDAS window for inspection by the operator He she can then offset the telescope so that the target is placed in a suitable position within the Wollaston Mask The X and Y PIXEL coordinates in 1 x 1 binning system will be prompted from the user at this stage This means that he she has to measure them from an image of the Wollaston Mask taken beforehand usually in the afternoon using the template EFOSC_img_cal_IntImage The Insert HWP flag allows the Half Wave Plate to be inserted T or removed F before the acquisition is started Note that this template can also be used to place an object under one of the spots of the Coronographic Mask The pixel position of the spot has to be measured in advance as in the case of the Wollaston Mask An identical template is available for circular polarimetry EFOSC img acq QWPolarimetry
97. ditions Note that in evening twilight flats should be taken for the most insensitive passbands first whereas during morning twilight the reverse is true Also a polarimetric imaging sky flat requires an exposure twice as long as an equivalent simple Imaging sky flat Therefore one can take only 2 or 3 sets of flats during twilight An identical template is available for circular polarimetry EFOSC_img_cal_QWPolarSkyFlats EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 93 Parameter Default Description Filter NODEFAULT User specified filter Starplate NODEFAULT User specified Wollaston Mask Grism NODEFAULT User specified Wollaston Prism Requested intensity level 40000 Requested intensity level in ADUs CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of windows 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Telescope RA offset 10 Telescope offset in R A Telescope DEC offset 4 Telescope offset in DEC Number of exposures 5 Number of exposures 94 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 24 EFOSC img cal IntImage This template is mainly used for 2 purposes for taking an internal image of
98. e Upon arrival in La Silla they should contact as soon as possible their System Engineer e The Visiting Astronomer should discuss the EFOSC2 setup he she needs with the SE The online instrument setup form available from the EFOSC2 homepage should be filled in and sent to the telescope team at least the night before the start of the run and earlier if a non standard setup is required e Access to the NTT telescope and the Common Control Room is restricted Any visit to the telescope must be authorised by the Team Coordinator beeper 13 The telescope is available for calibrations from 16 00 onwards e Incase of Multi Object Spectroscopy successful applicants can ask the SciOps Team lasilla eso org to obtain images of some of their fields up to a total exposure time of 20 minutes per allocated observing night during the setup night In this case the request must be submitted at least two months before the observing run Clear finding charts scale orientation must be pro vided together with all precise coordinates and any other relevant detail centring position angle exp time filters etc 120 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 G Helium Argon Atlas The following He Ar lines are recommended for on line wavelength calibrations Particularly bright lines are marked in bold face Line identification charts are provided for all grisms in the next pages Lines identified in the arcs for the new VPH Grisms 19 an
99. e WEB page is updated constantly and may contain information not covered by this manual The present EFOSC2 User s Manual is based on previous versions of the same manual by G K T Hau and F Patat Santiago June 2008 1 3 Reference documents The following documents are referenced in this document 1 Andersen et al 1995 Calibrating and understanding HST and ESO instruments ESO Confer ence and Workshop Proceedings n 53 p 87 2 Augusteijn T amp Storm J 1996 Commissioning of new CCD 40 for EFOSC2 ESO Memo randum 3 Filippenko A V 1982 PASP 94 715 4 Lamy H amp Hutsemekers D 1999 The Messenger No 96 p 25 5 McLean L 1997 Electronic Imaging in Astronomy I McLean WILEY PRAXIS Series in Astronomy and Astrophysics John Wiley and Sons 6 Melnick J Dekker H D Odorico S 1989 EFOSC ESO Faint Object Spectrograph and Camera ESO Operating Manual n 4 7 Melnick J 1993 EFOSC1 Update to the Operating Manual Version n 1 8 Melnick J 1993 EFOSC2 Operating Manual Version n 2 2 10 11 12 13 14 15 1 4 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Melnick J amp Mendes de Oliveira C 1995 EFOSC2 Operating Manual Version n 2 1 Osterbrock D E amp Martel A 1992 PASP 104 76 Savaglio S Benetti S Pasquini L 1996 EFOSC1 Operating Manual Version n 3 Storm J amp Brewer J 1997 Observing at the Danish 1 54m Telescope ES
100. e at the start of the exposure If this acquisition template is used during service observing a finding chart must be supplied by the user By default the acquisition images are taken in fast mode and binning 2 x 2 If the observer wants to use these images for scientific purpose he she may want to change these parameters Note also that if a particular position angle is required the a rotator offset angle equal to PA 90 must be supplied see 3 1 3 and fig 17 Parameter Default Description Filter R 642 User specified filter Slit for reference NODEFAULT User specified slit Exposure time 20 Exposure time for acquisition image sec CCD readout speed fast Read Out Mode for the acquisition image CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction X pixel coordinate 1100 User specified X coordinate Preset flag T Preset the telescope Perform combined offset T Perform accurate offset using guide probe Focus flag T Focus flag Rotator offset angle 0 Rotator Offset Angle deg see 3 1 3 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 75 4 3 6 EFOSC_img acq NarrowSlit This acquisition template is similar to EFOSC_img_acq_MoveToSlit and also used for grism spec troscopy where the position angle of the object is known or is the parallactic angle It was designed to deal with the flexure problems that have aroused since EFOSC was mounted on the NTT Due to th
101. e first approximate pointing to the desired object Note that the exposure time for the focus image in all acquisition templates is hard coded to 20 seconds because no matter what the field is with this exposure time it is always possible to find suitable stars for focusing Note that it is possible to skip the focusing by setting the Focus flag to F When this is completed the template takes an exposure of Exposure time seconds which is displayed in a MIDAS window for inspection by the operator He she can then perform a combined offset so that the desired object e g as marked on a finding chart is placed on the CCD pixel coordinates specified by X pixel coordinate and Y pixel coordinate It is important to note that these coordinates are in the 1 x 1 binning system This process can be iterated until the desired pointing accuracy is achieved The Perform combined offset flag should be set to T if the telescope is to be positioned accurately by offsetting the guide probe in this iterative process Note that if the Rotator Offset Angle is set to 9999 the Rotator Angle will be set to the parallactic angle corresponding to the start of the exposure If this acquisition template is used during service observing a finding chart must be supplied by the user By default the acquisition images are taken in fast mode and binning 2 x 2 If the observer wants to use these images for scientific purpose he she may want to change these parameters When t
102. e of the order of 0 1 which is the resolution of the rotator adaptor For this reason in most cases no adaptor rotation is necessary The typical time needed for focusing and accurate centring is about 10 minutes 3 6 3 Science Exposures Once the acquisition phase is over the spectrum can be taken using the EFOSC_spec_obs_ Spectrum template by specifying the desired mask and grism However some observers find it useful to take a through slit image at this point to check that indeed all the objects are visible through the slits by inserting the same template with the same mask but without the grism i e using template EFOSC_img_obs_Image with Grism Free This may be worthwhile for long exposures of faint objects It is also worthwhile to take a through slit image between long exposures to check the alignment Due to autoguider drifts and telescope flexures cfr Sec 3 1 2 it is always a good idea to re acquire the field from time to time especially when observing at large hour angles or close to the zenith see also Sec 3 5 6 It may also be worthwhile to re acquire the field if the seeing has improved substantially It takes only a few minutes Caution The visiting astronomer is reminded that from time to time it may not be possible to have all the targets perfectly centred in the slit lets after the acquisition especially when using the narrowest Punch Head This problem seems to be related to MOS plate bending both during the pun
103. e transparent strips of the Wollaston mask it is necessary to measure the position of the transparent strip The template EFOSC_img_obs_Image can be used for this purpose while pointing the telescope towards the flat field screen Note that some tuning of the dome flat field lamp may be necessary to obtain the correct exposure level Alternatively EFOSC_img_cal_IntImage may be used with the advantage that there is no need to move the telescope It might be necessary to insert a narrow band filter i e Ha to avoid saturation Once such image has been produced the coordinates of the suitable position must be measured X and Y pixel coordinates in 1 x 1 binning and noted down since it will serve as an input for the acquisition template EFOSC_img_acq Polarimetry Caution The images of the mask have to be taken without the Wollaston Prism 3 3 7 Science Exposures The template EFOSC_img obs Polarimetry allows one or more sequences of images to be obtained The default sequence takes four images at 0 0 22 5 45 0 and 67 5 respectively for linear polari sation and two images at 45 and 135 respectively for circular polarisation For more details refer to Chap 4 and check the web for additional information 3 4 Coronographic Imaging 3 4 1 Flats For the coronography flat fields the discussion concerning Imaging flats applies Remember that the flats both dome and sky have to be taken with the Coronographic mask and the Lyot stop in
104. ections are still relative to EFOSC2 3P6 A 2 3 Signal to Noise ratio and Expected Count Rates Using the throughput values one can calculate the expected flux and hence the signal to noise ratio for a spectrum The example below demonstrates the cases for a point source and for an extended source A 2 4 Point Source As an example one wants to take a spectrum of a star which is 20th magnitude at 5000A The observer wants to know how much time is needed to achieve a SNR ratio of 5 per Angstrom at 5000Ausing Grism 8 and the 170 slit From Fig 35 a 15th magnitude star at 5000 observed with Grism 8 gives 26 0 e A el hence a 20th mag star will give 0 260 e AT sl Only a fraction of this flux arrives at the detector As the star image is smeared out spatially by the seeing some of the flux is obscured by the slit For example assume the seeing FWHM is 1720 and the slit is 1 00 wide Assuming that the atmospheric scattering is not correlated in directions perpendicular and parallel to the slit the probability of a photon falling into the slit will be given by a one dimensional normal distribution The seeing is 1 2 2 35 0 51 and the slit width is therefore 1 0 0 51 1 960 Reading off from a table of standard normal distribution gives 67 296 probability Thus the flux at the detector will be 0 260 x 0 672 0 175 e A sl In the spatial direction the flux will be spread out with a profile equivalent to the seeing convolved with t
105. ectrum or twilight flats the solar continuum is dominating The only way of correcting for this effect is the use of a super sky which is obtained by making a median of all the images taken during the night with the given filter see also Sec 3 2 13 Note that the effect of fringing is additive and the fringe pattern should be scaled and subtracted from the image Fringing in imaging mode is further discussed in 3 2 13 For spectroscopy fringes can be satisfactorily removed by taking internal flats at the position of the science observations and using these to construct the normalised flat field image to be divided from each frame Dome flats taken during the day are not suitable due to flexure of the tele scope instrument Fringing in spectroscopic mode is further discussed in 3 5 7 It is also discussed on the EFOSC2 web page http www ls eso org sci facilities lasilla sciops team only efosc2 tests Tests html 28 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Image col Row 11 T T T T T T T T T T T T I T T T T I T 198 F A dasso uOIsJan sepiu osa 196 be Pixel value 2v ZZ ETOZ Dm pt am a1ep 194 4 O 500 1000 1500 2000 Position PIXEL ouyse Jesfi Figure 14 Clock induced charge generation in the EFOSC2 CCD EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 29 2 7 Calibration Lamps Note that EFOSC2 now makes use of the old EMMI Calibration lamps which are avai
106. ed from the spectrum From this intensity the exposure time needed to reach the Requested intensity level is calculated Note that since this template is designed for a stable light source the computed exposure time is fixed Hence when taking sky flats the levels will change in successive exposures due to darkening or brightening of the sky For evening sky flats the Requested intensity level should be set to about 40000 whereas for morning sky flats it should be set to about 10000 An identical template is available for circular polarimetry EFOSC spec cal QWPolarFlats Parameter Default Description Wollaston Prism NODEFAULT User specified Wollaston Prism Starplate NODEFAULT User specified slit Grism NODEFAULT User specified grism Requested intensity level 40000 Requested intensity level in ADUs CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of Exposures 5 Number of exposures 98 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 28 EFOSC_spec_cal_Arcs This template is used for taking arc line spectra for wavelength calibration in spectr
107. el in ADUs CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of exposures 5 Number of exposures 90 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 21 EFOSC img cal SkyFlats Before this template is executed the telescope must already be preset to an empty field either by an acquisition template or manually by the TIO This calibration template acquires Number of exposures sky twilight flats for normal imaging with an intensity of approximately the Requested intensity level through the specified Filter Before the start of each each exposure the telescope position is offset by Telescope RA offset and Telescope DEC offset The HWP and Calibration Unit positions are checked If they are in the light path these components are automatically removed The Guide probe is parked to avoid possible vignetting The exposure time is computed automatically as follows e The average bias level is retrieved from a database e A windowed flat field with exposure time 3 sec is acquired e The bias level is subtracted from the windowed flat and the mean intensity is
108. emplates a Reference Guide 00020 eee eee 65 4 3 1 Files Produced By The Templates e 69 4 3 2 EFOSC2 Acquisition Templates oe stia s aad eaa ee oa 69 2 49 EE me aca Preset lt poca A Ao ok dk ew oe Bde a hes 72 4 3 4 EF0SC_img acq MoveToPixel cerrarse o erwe 73 4 3 5 EFOSC imp acg Mov Toglit sca 2222 om adog X Ro ERO RR ae RR RSS 74 4 3 6 EFDSC img acq NarrowSlit gt 5 29 refa dda yo 9 EN T5 Ax EF SC img acqg RotateToSlit ecb ek ck ok d 4 y y RU Y RS 76 14 3 EFOSC ime acg Polarimetry 44 24 4344 00 03 om ERR RR R3 77 40 0 EF SC ime acg MUS ees Ro B RE rn eee oq RES oe qe 78 4 8 10 EFOSC Observation Templates o e 2224493 Ps 644 es 79 4 3 11 EFOSC img obs Image s serea e Oe EE ee s 80 43 12 CRU img obs Image Jit s s aiea saphi e oe A ROS 81 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 A m pg m E o S9 4 34 13 EF SC img obs Polarimetry sce ok x c E 903 90k a UR Ro Rx 4 3 14 EFOSC img obs Coronography 4 4 daona s daoi es 4 3 15 EFUSC epec obs SpecLrum oues md a Ge Sh a a he Eon 9 oos 4 3 16 EPRDUSO SpecoBs M S oo soc m mo lm p Ron moe x OR ESR RUE o3 X Rok es 43 17 EFOSC spec obs Polarimetry s 12 cedo Rm OR OR RR SCR Ey 4 3 18 Calibration Templates 2 ba Eep Eb garp aa 4 3 19 BROSC img cal Darks icem ac oo mode ex be we ee ae ens 2320 EFOSC tmp cal Flats o cor pos sane ek ede EG eee POE xe 2321 BPOS
109. enith or at the Flat field position e g darks internal lamp flats dome flats and comparison lamps Note that automatic preset to the Flat Field Screen is NOT YET implemented This means that the operator has to issue the command from the TCS panel before the calibrations are carried out Calibration template s may also form part of an OB under the ObsBlock category These calibrations are done usually with the telescope pointing to the sky e g Sky flats and often for on source calibration of science data e g Helium Argon arc lamp internal flat field and for focusing These OBs usually include an acquisition template as well as the science and calibration templates For example when the observer wants to take sky flats on a particular region of the sky e g empty field he she should attach an acquisition template to preset the telescope to the desired position Since no accurate position is needed EFOSC_img_acq Preset will serve the purpose Alternatively and this is the way that is usually done one can ask the TIO to preset the telescope to one of the empty fields selected from the catalogue on the TCS machine and then execute an OB which contains just the Sky Flat field template 88 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 19 EFOSC img cal Darks This Template acquires bias or dark exposures specified by Number of exposures Bias frames are acquired if the Exposure time is set to O Conversely dar
110. equested intensity level through a desired Filter with the Half Wave Plate inserted and in continuous rotation The user can insert the desired Wollaston Mask and Wollaston Prism into the Starplate and Grism wheel positions respectively Before the start of each exposure the telescope position is offset by Telescope RA offset and Telescope DEC offset The Calibration Unit position is checked If it is in the light path this component is automatically removed The Guide probe is parked to avoid possible vignetting The exposure time is computed automatically as follows e The average bias level is retrieved from a database e A windowed flat field with exposure time 1 sec is acquired e The bias level is subtracted from the windowed flat and the mean intensity is computed e Based on the mean intensity and the requested intensity an exposure time sequence is computed automatically using the Tyson amp Gal algorithm The sequence is started only if the exposure time of the first frame is greater than 10 sec to allow for a complete de polarisation of the incoming light by the rotating HWP The sequence terminates when Number of exposures frames have been acquired or when the expo sure time exceeds 300 sec The template also checks the exposure level which can range from 1200 to 60000 ADUs The exposure levels obtained by this template are within a few thousand ADUs from the one specified by the user This is due to seasonal effects and sky con
111. eral frames to be combined later on Note that for some grisms the strong red lines of Argon produce ring like ghosts in the blue part of the spectrum To reduce this effect the template automatically inserts a diaphragm in the beam This component is permanently mounted in the filter wheel An atlas of the He Ar lines can be found in Appendix G There are 2 features of the wavelength calibration which should be noted see Fig 15 Firstly for several grisms the Argon lamp has a very bright reflection in the red part of the spectrum which may seem alarming on first sight However this reflection has a broad profile and as long as the superimposed individual arc lines are not saturated a satisfactory wavelength calibration can be obtained Secondly the instrument suffers from internal reflection and this produces very faint but visible ghost images of very bright lines These ghost lines are not second order lines since in the two dimensional spectrum they have a curvature different to the first order lines Care must be taken when performing wavelength calibration that these ghosts lines are not misidentified as faint lines in the arc spectrum 52 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 The instrument suffers from considerably large flexures Arcs with grism 20 were taken at several rotator positions The spectrum taken with rotator angle 174 9 corresponding to 0 position angle on sky was cross correlated with other spectra at
112. escope active optics as on the NTT only allows the telescope to reach the ambient seeing There are two different procedures to set the NTT Active Optics System AOS The first is to use a default setting correcting for gravitationally induced deformations using predefined look up tables at different values of the telescope altitude These tables include corrections for astigmatism and defocus but not for higher order effects The second method is to do a full wavefront analysis the so called image analysis and to calculate the mirror settings from this The image analysis systems there is one at each Nasmyth station located inside the instrument adaptor rotators consist of a Shack Hartmann grid and a CCD to record the image The pupil image corresponding to a particular star is transformed by the grid into a regular pattern of dots The position of each dot has been calibrated with an internal light source The wavefront distortions can be obtained from the displacement of each dot from its calibrated position From this a software determines the telescope aberrations Wilson et al 1991 Journal of Modern Optics 38 219 it solves for defocus r spherical aberration r coma r cos astigmatism r cos 29 triangular coma r cos 3 and quadratic astigmatism r cos 4 where r is the radial and the azimuth mirror coordinate A low order Zernike polynomial is fitted to the map of the displacement vectors The accuracy or valid
113. f the observer does not need to rotate the adaptor the second step can be skipped The operator is requested to make this choice just after the telescope terminates presetting Parameter Default Description Filter R 642 User specified filter MOS Plate NODEFAULT User specified MOS plate Exposure time 20 Exposure time sec for the acquisition image Preset flag T Preset the telescope Focus flag T Focus flag 0 Rotator offset angle Rotator Offset Angle deg 8 3 1 3 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 79 4 3 10 EFOSC2 Observation Templates Observation Templates are used to perform the actual scientific observations They allow full control of the CCD parameters and optical components required for each kind of observation Some of them are hard coded within the templates so that the observer cannot select them by mistake For instance the grism is always set to Free when taking Images When executed all templates make an automatic check to assess if there are undesired components in the light path For example the Calibration Unit and the Half Wave Plate positions are always checked if they are in the way they will be removed The various observing modes and associated templates are described in detail under the section Observing Modes in the EFOSC2 main web page http www eso org sci facilities lasilla instruments efosc where examples for typical uses are given 80 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 3
114. ference to the templates currently implemented and supported There are three types of templates for EFOSC2 that concern the observer Observation Templates obs for science observations Calibration Templates cal for calibration exposures and Acquisition Templates acq for target acquisition The names of the templates have been set according to the ESO official Data Interface specifications All the template names start with the word EFOSC followed by img or spec according to the type of observation imaging or spectroscopy Then comes the template type acq obs cal for acquisition observation and calibration respectively Finally the template name ends with a meaningful string like MoveToPixel or MoveToSlit which permits a quick understanding of the purpose of the template itself When P2PP is running a list of the 66 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Procedure Template to use ACQUISITION TEMPLATES Preset telescope and centre objects in slits for MOS EFO0SC img acq MOS Preset telescope and move object onto a pixel EFO0SC img acq MoveToPixel Preset telescope and centre an object in slit EFO0SC img acq MoveToSlit Preset telescope measure slit position and centre an object in slit EFOSC img acq NarrowSlit Preset telescope and position an object for polarimetry EFO0SC img acq Polarimetry Simple telescope preset without focus EFO0SC img acq Preset
115. flooding of the backside The quantum efficiency curve is plotted in Fig 12 Note that even though the CCD has 2048 x 2048 pixels the image size is 2060 x 2060 In fact during the read out process 12 rows and 12 columns are added see Fig 11 We remark that these additional pixels cannot be used as a real over scan since the region is too small and contaminated by the adjacent area during the charge transfer process The observer should therefore take bias images at the beginning and or end of the night Type Loral Lesser Thinned AR coated UV flooded MPP Image Size px 2060x2060 Pixel Size ul 15 x 15 Dark Current e pz hr lt 3 5 at 140 K Full Well Capacity e nr 104k Controller ESO FIERA Explored Range e7 2000 83000 Saturation ADU 65535 Mode Slow Normal Fast Transf Rate 27kpx s 60kpx s 178kpx s Bias ADU 219 219 239 R O N e7 rms 10 2 0 1 10 7 0 1 14 4 0 4 Linearity 0 24 0 24 0 19 Conv Factor e ADU 1 33 0 01 1 35 0 01 1 37 0 01 Full CCD R O Time s 160 70 24 Table 7 Specifications of CCD 40 All values correspond to a CCD binning 1x1 The Bias R O N Linearity and Conv Factor are average values from the first half of 2003 As the electronics may be changed or adjusted from time to time please check the latest results of the CCD tests which can be found on http www eso org sci facilities lasilla instruments efosc ins
116. for a given retarder plate angle 8 One could determine the circular polarisation observing at one retarder plate posi tion but two observations are required to eliminate the strongest observing biases in the first order approximation 8 45 d nun 6 mg e the improper flat field correction FF e the colour dependent offset to the nominal retarder plate zero angle e the incomplete and colour dependent retardation of 90 g A degree of the quarter wave plate These Q and U are normalised parameters sometimes indicated in the literature as Q T and U I As for the case of linear polarisation V is normalised parameters sometimes indicated in the literature as V I 48 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Observations at only one retarder plate angle would cause hardly correctable Stokes parameter cross talks in the case of objects with non negligible linear polarisation The colour dependence of the retarder angle eg would cause an additional polarisation of AV 2egU and the incomplete retar dation eg 490 degree quarter wave would cause the additional polarisation of AV 2egQ e amp eg in radians UVQ being the Stokes parameters One would get fe fe Ufo pelt V erp 2egU Q 7 plas V erp 2egU e4Q 8 The difference between the two observations yields V while the small deviations have the same sign in the two equations and are therefore eliminated
117. for interactively putting 2 objects into the slit when the position angle is not well known in advance It has three parts First it presets the telescope to the coordinates of the Target associated with the Observation Block and it rotates the Adaptor to the initial Rotator Offset Angle It then inserts a filter and takes a short image through the Focus Wedge to focus the telescope before acquiring the targets into the slit After the iterative focus process is finished the last focus image is used by the operator to perform the first approximate rotation to align the slit with the 2 objects The exposure time for the focus image is hardcoded to 20 seconds and it is possible to skip focusing by setting the Focus flag to F After completing these steps the template takes an exposure of Exposure time seconds which is displayed in a MIDAS window for inspection by the operator He she can then supply two user specified objects or points to be aligned with the Slit for Reference When this is done the adaptor is rotated to a new position angle and an acquisition image is taken and loaded in the MIDAS display This process iterated until the desired rotation accuracy is achieved Next the operator can perform a combined offset so that one of the 2 objects or a point in the sky is placed in the slit position specified by the X pixel coordinate in 1 x 1 binning system The Y position is automatically selected according to the Slit for Reference supplied
118. for small angles eg amp eg See also the FORS1 2 User s Manual http www eso org instruments forsi doc Note also that an instrumental circular polarisation up to 0 4 seems to present see 2 4 9 3 3 5 Flats and Other Calibrations The procedure to obtain polarimetric flats dome and sky is similar to the one described for normal Imaging The only relevant difference is that in this case the exposures are taken with the Wollaston mask Wollaston prism and HWP QWP in the beam Note that to achieve a complete de polarisation of the incoming light the HWP QWP is automatically set to a continuous rotation Since the rotation time is 2 3 4 seconds the templates EFOSC img cal PolarFlats and EFOSC img cal PolarSkyFlats and the equivalent for the QWP do not allow exposure times shorter than 105 Note that in addition to the usual bias dark and flat field other additional forms of calibration are needed for polarimetry e To determine the instrumental reference angle a known polarised star should be measured Note however that the only reliable polarimetric standards available are all very bright e These stars can also be used to determine the instrumental polarimetric efficiency e To determine the intrinsic instrumental polarisation one ore more known unpolarised standard stars should be measured e The cross talk between linear and circular polarisation is known to be small below 0 0596 see Saviane et al 2007 Msngr 129 14
119. formed observations is issued by the TIO at the end of every night using the NightLog 2 0 tool Such a report can also be e mailed to the VA EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 115 D Standard FITS Header The images produced by FIERA have the standard VLT FITS header IRAF users may encounter some problems when dealing with these headers as they are in the standard ESO Hierarchical Format To convert them to standard FITS headers the user can use the command hierarch28 which comes with the standard Scisoft distribution SIMPLE BITPIX NAXIS NAXIS1 NAXIS2 ORIGIN DATE CRVAL1 CRPIX1 CDELT1 CTYPE1 CRVAL2 CRPIX2 CDELT2 CTYPE2 BSCALE BZERO MJD OBS DATE OBS EXPTIME EXTEND OBJECT INSTRUME OBSERVER PI COI TELESCOP RA DEC EQUINOX RADECSYS LST UTC HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH T 16 2 1030 1030 ESO 2 2003 09 29T22 55 19 1 0 1 0 2 0 gt PIXEL 1 0 1 0 2 0 gt PIXEL S 1 0 32768 0 52911 95496435 2003 09 29T22 55 08 9 9993 F Sky Flat Grii1 EFOSC 2 4 UNKNOWN UNKNOWN ES0 3P6 286 045114 37 28004 2000 ERR 67512 831 82501 000 ESO OBS DID ESO OBS OBSERVER ESO OBS EXECTIME ESO OBS PI COI NAME ESO OBS PI COI ID ESO OBS GRP ESO OBS NAME ESO OBS
120. g the centring phase MOS design is done by a program xm and the observer will be taught how to do it during the introduction Once the slits are defined masks are punched using a special punch machine Observers are reminded that preparing a MOS plate including running the mask design software and punching may require up to 30 45 minutes Therefore the preparation of the MOS plates for the first night should be done the day before For the next night mask definition and punching can be done during the observations Delays in delivering the MOS plates to Day Operations may result in insufficient time to run all the required calibrations in the afternoon As soon as the MOS plates are mounted an image of the mask without the grism should be taken to check the position of the slits This image will also be required later in the target acquisition stage for centring the 3 alignment stars with their corresponding slits The observer is reminded that if for some reason the MOS plates are removed from the Aperture Wheel and re mounted again flat fielding and wavelength calibration must be performed again 3 6 1 Flats The discussion concerning flat fielding for normal spectroscopy applies to MOS as well In this case the procedure is not completely automatic and the Telescope Operator must select manually on the display a suitable region to be used to compute the correct exposure time Helium Argon arc exposures are also required for MOS as
121. gnature that the Quarter Wave Plate was used 68 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 File Edit Folder Reports Synchronise Ba R fall New Duplicate Verify View E No CCS AppServer Folders 7 60 a 9013 a Summaries Fobatiece uge Name Galaxy 1 BVR 5 min each 0 Galaxy 2 BVR 5 min each o _ P artially Galaxy 2 BVR Dbaseld Status Target OD Plartially Galaxy 1 BVR 5 min each No Name 5 min each cs Acquisition EFOSC img acq MoveToP No Name io Name File Edit Synchronise Name Galaxy 1 BVR 5 min each Template Type Template f Add acquisition EFOSC img obs Coronography 4 Status P artiallyDefined f Delete Col 4 calib EFOSC img obs ImageJit Execution Time 00 02 57 000 test EFOSC img obs Polarimetry Duplicate Col 4 7 EFOSC_spec_obs Polarimetry User Priority 1 E EFOSC spec obs Spectrum OD Name BVR 5 min each User Comments EFOSC img acq Mov 1 EFOSC img obs Image 1 2 3 Filter R 642 Filter B 639 V 641 R 642 Exposure time 20 Starplate Free Free Free CCD readout speed fast Exposure time 300 300 300 CCD X binning 2 CCD readout speed normal normal normal CCD Y binning 2 CCD X binning 2 2 X pixel coordinate 1100 CCD Y binning 2 2 2 Y pixel coordinate 1024 CCD windowing flag F F F Preset flag T First column of window
122. grisms however the counts in the blue end are of the order of 10 of the peak counts This may turn into somewhat noisy normalised flats in the extreme regions of the spectral range The effect can be reduced by taking a large number of flats Sky flats aka solar spectrum are obtained with the sky and the twilight spectrum is much bluer due to the Rayleigh scattering than dome flats and therefore provides significantly more photons in the blue region where the quartz lamp is faint The problem is that these flats are dominated by strong lines making them unsuitable for flat fielding in the spectral direction Sky flats are useful for constructing the so called slit function which traces the variations of the slit illumination in the spatial direction This is needed if one is doing spectroscopy on an extended object and very accurate sky subtraction is needed 3 5 2 Internal Spectroscopic flats Internal flats can be taken during the night at the same telescope position as the science target at the expense of increased overheads of about 40 seconds per flat field image This can be achieved by means of the template EFOSC_spec_cal_IntFlats which makes use of the internal quartz lamp We remark that this requires the calibration screen to be inserted in the beam and this means that the autoguider is automatically switched off This may turn into a drift of the object out of the slit Nevertheless internal flats are normally done before moving t
123. he seeing FWHM 2 35 x 0 and that all the flux is contained within a circle with a radius 30 the total number of pixels is given by 15 FWHM y b n 350 0 where is b 1 for binning 1 x 1 and b 2 for binning 2 x 2 With a seeing of 1 5 this implies that the star light is distributed over about 790 pixels using a binning 1 x 1 Of course under the same assumptions one can compute also the expected central intensity Jp After expressing c as a function of the FWHM converted to pixels we obtain L i Ta TITAN a 0 72x 10 WHEN ADUs 16 The last column of Table 11 reports the expected peak intensities for a seeing of 1 5 and binning 1 x 1 according to Eq 16 This formula can be used to estimate the time needed to reach a given peak intensity In particular it is useful to compute the maximum allowed exposure time to avoid saturation of bright stars If maz is the maximum permitted intensity we have 58 tmar 53 FWHM Imaz 10704 Mom y 17 106 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 As an example for a star with V 11 0 mag and B V 0 0 FWHM 175 Imax 65000 and b 2 we get tmar 6 6s Such result has to be kept in mind while trying to obtain images of photometric standards brighter than V 11 0 mag since this may require a de focusing of the telescope or binning in 1 x 1 in order to avoid saturation without reducing too much the exposure times cfr also Sec 2 5 A 1 3 Ove
124. he 3 6m triangles EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 105 Older reference values for the extinction coefficients are ky 0 55 kg 0 25 ky 0 14 amp g 0 11 and zr 0 09 mag A 1 2 Expected Count Rates Using the colour equations given in Sec A 1 1 it is possible to compute the expected count rate for a star of given magnitude and colour For sake of simplicity in the following we will neglect the colour dependence and any atmospheric extinction If mg is the zero point and m is the magnitude of the star in a given band then the expected count rate in ADU per second is simply given by py mo ADUS T 14 If g is the gain e ADUT the expected count rate in electrons per second is simply F gx Fs The expected count rates in both ADU s and e s7 for a star of magnitude U B V R i 15 are reported in Table 11 Filter Count Rate Count Rate Io ADU s7 e7 s71 ADU s px U 5 0 10 5 7 10 38 B 2 5 104 2 9 10 193 V 2 9 104 3 3 10 219 R 3 0 104 3 5 104 233 I 1 3 104 1 5 104 100 Table 11 Expected count rates for a star of U B V R i 15 The peak intensity o was calculated by assuming a seeing with FWHM 175 and binning 1 x 1 These count rates refer to the global flux integrated over the entire Point Spread Function PSF which distributes the star light over many pixels Assuming that the PSF is a Gaussian where t
125. he object profile a delta function for a star In this case the profile has a FWHM the same as the seeing For ease of calculation let s assume that we can extract all the flux from the profile to make the 1 dimensional spectrum In this case the flux per Angstrom of the final one dimensional star spectrum will be just 0 175 e7 T s71 O for below To estimate the readout noise assume that for extracting the 1 d spectrum a summation collapse over a spatial region corresponding to the seeing FWHM 1 20 is required We want to estimate the SNR which corresponds to a 1A bin at 5000A Hence the area under consideration is 1 20 x 1A For a CCD binning of 2 x 2 and Grism 8 the area covered by a pixel is 0 314 x 1 98A Hence our area of consideration is 1 93 times that of an image pixel The Read Out Noise for one image pixel is about 10 e thus the Read Out Noise for the area under consideration is 10 x v1 93 13 9 e R for below This is the Read Out Noise contribution to a 1 Angstrom region in the final 1 dimensional star spectrum Note that if the exposures are to be split into n sub exposures R should be multiplied by Jn To estimate the flux from the sky we assume that the sky brightness at 5000 is 22 1 mag per arcsec for a 3 day moon Using the throughput value from Fig 35 gives a sky surface brightness of 0 038 e Al sl arcsec Since the slit width is 1 0 and the spectrum is extracted over a region of 172 the sky contribution
126. he telescope to another position Internal flats taken at the position of the science object are useful for removing fringes in the near EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 51 infrared part of the spectrum A gt 7200A Due to telescope flexure there might be a spatial shift between the fringes in the dome flat field exposure and the fringes in the science exposure Since the fringe pattern is strong 15 of the continuum in a raw spectrum this shift up to a few pixels is enough to give ripples of about 2 or more of the continuum level in the flat fielded spectrum if the dome flat is used If instead of dividing by the normalised dome flat field the science spectrum is divided by the normalised internal flat field taken at the same position as the science object then the residual becomes negligible Thus internal flat fields are recommended for observers who need good flat fielding in the near infrared part of the spectrum There are several points to note Firstly as opposed to the fringes in the images which are additive fringes in the spectroscopic exposures seem to be multiplicative and can be satisfactorily removed by dividing the scientific exposure with the normalised internal flat Secondly the internal quartz lamp is rather red in colour which means the blue part of the spectrum is not well flat fielded unless a large number of flats are taken during the night at the expense of increased overheads Even in t
127. his case the result is not satisfactory since there seems to be a fair amount of internal reflection which is more pronounced in the blue than in the red Thus internal flats may be used for the red part of the spectrum whereas dome flats should be used for the blue part of the spectrum Thirdly there is a software limit of 1 second for the exposure time as short exposures will result in an uneven illumination of the slit For certain slit and grism combinations the calculated exposure times for a 2 x 2 CCD binning is shorter than 1 second and the template will exit with a warning message In this case the observer should specify a 1 x 1 CCD binning and rebin the flat field image during data reduction Fringing in spectroscopic mode is further described in 3 5 7 3 5 3 Wavelength Calibration The Helium and Argon lamps used for wavelength calibration of slit spectra are obtained by means of the template EFOSC_spec_cal_Arcs Exposures can be taken with one or both of the lamps In the former case just specify a non zero exposure time only for the lamp to be used and set the other to zero The recommended exposure times are shown in Table 14 and on http www eso org sci facilities lasilla instruments efosc inst Perf_HeAr html These values avoid line saturation however the observer may consider increasing the exposure times to obtain a better signal to noise ratio for the weaker lines Alternatively there is the possibility of taking sev
128. his template is used to put an object under one of the dark spots of the coronographic mask the user must take an image of the mask using the template EFOSC img obs IntImage before performing the acquisition in order to measure the pixel centre coordinates in the 1 x 1 binning system of the spot Alternatively the user can use EFOSC img acq Polarimetry to reach the same goal in a slightly different way Parameter Default Description Filter R 642 User specified filter Exposure time 20 Exposure time for the acquisition image sec CCD readout speed fast Read Out Mode for the acquisition image CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction X pixel coordinate 1100 User specified X coordinate Y pixel coordinate 1024 User specified Y coordinate Preset flag T Preset the telescope Perform combined offset T Perform accurate offset using the guide probe Focus flag T Focus flag Rotator offset angle 0 Rotator Offset Angle deg see definition in 3 1 3 74 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 5 EFOSC_img_acq MoveToSlit This acquisition template is used for grism spectroscopy where the position angle of the object is known or is the parallactic angle It has three parts First it presets the telescope to the coordinates of the Target associated with this Observation Block and rotates the Adaptor to the requested Rotator Offset Angle It then inser
129. imetry they are mounted in the filter wheel The corresponding separations of the ordinary and extraordinary beams are 10 and 20 for the two Wollaston prisms respectively Both prisms produce a symmetric throw Caution The 10 Wollaston prism can be used for imaging ONLY since its size does not allow it to be mounted in the filter wheel The orientation of the image separation can be changed by rotating the prisms in the wheels At EFOSC2 the prisms are aligned to split the images either along the x or the y axis of the CCD For polarimetric imaging special masks are available Their specifications are presented in Table 6 Corresponding to the two possible directions along which the prisms can split the image there are two types of Wollaston masks parallel masks in which the strips are parallel to the x axis and perpendicular masks in which the strips are perpendicular to the x axis Note the prisms must be oriented to split the images in a direction perpendicular to the long axis of the masking strips Woll Mask Length Width Inter slit 20 perp Jor 1977 2275 20 par 224 19 6 2277 10 par 225 9 9 1678 Table 6 Wollaston Masks for Polarimetry The values reported in this table are relative to EFOSC2 3 6m The actual values for EFOSC2 NTT will depend on the fabrication process Spectropolarimetry is also possible using the Wollaston Prism together with a grism The requi
130. in V and already after 16 seconds in R For this reason we will neglect the RON contribution in the following Signal to Noise Ratio SNR calculations With this assumption the expected SNR averaged over the entire PSF area is given by Fy SNR x vg xt 23 y Es L sky d Eq 23 can be inverted to compute the time required to achieve a given SNR 108 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 F F For example with a seeing of 1 5 and during the new Moon to reach a SNR 100 with a star of V 20 0 an exposure time of about 90 seconds is required If the objects are very faint the PSN from the sources is also negligible with respect to the noise generated by the sky background In this regime if we assume that the detection limit is given by a SNR 5 we can easily compute the limiting magnitude of an image with an exposure time of t seconds Ssky Mum Mo 2 40 2 5 logFW HM 1 25 log 25 The limiting magnitude with a seeing of 1 5 in a V exposure of 1800 seconds taken during the new Moon is Viim 25 1 If we assume the limiting SNR 3 the correspondent limiting magnitude increases by 0 56 mag Note that the integrated SNR for a point source does not depend on the binning factor b while the SNR in a single pixel scales directly as b In the case of extended sources i e when the angular size of the object is much larger than the seeing it is more convenient to treat each pixel separately in
131. ing are officially supported Note it takes 4 times as long to readout the chip in 1 x 1 mode than in 2 x 2 mode 2 x 1 and 1 x 2 binning also work The user may consider the former if high spectroscopic resolution is required for example when working with slit widths which are less than 170 A binning in X of 1 is almost always unnecessary since the seeing is never good enough to warrant it The observer uses these unsupported readout modes at their own risk and should be aware that the electronics are not optimised for these modes With this template one can obtain 1 or more spectra of 1 or more objects through 1 or more grisms However it is essential that all templates in an OB use the same slit as each slit falls at a different y pixel value and there is no provision for rec entering the object from one exposure to another The acquisition templates EFOSC img acq MoveToSlit EFOSC_img_acq RotateToSlit and EFO0SC img acq MOS may be used in conjunction with this template depending on the nature of the target If the grism used covers the near IR part of the spectrum fringing may become an issue and the user may consider taking internal flats on source see 3 5 7 for details If the user also wants very accurate wavelength calibration remind that the instrument suffers at the moment by significant flexures see fig 26 then one may also consider taking Helium and Argon arc lamps on source These calibration templates can be added to
132. internal lamp is rather red the spectrum of the internal lamp is quite faint in the blue Thus a small amount of reflected light contamination gives a bump in the blue extremes of some of the curves EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 109 10000 8000 Wavelength A Relative Efficiency curves to grism 1 6000 Er E Throughput relative to grism 1 Figure 34 Relative Grism sensitivities These are all relative to Grism 1 which is set to have a value of 1 everywhere The upturn in blue for some grisms is due to reflected light within the instrument rather than a real increase in sensitivity 110 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 A 2 2 Grism throughputs The overall efficiencies of the whole system Telescope EFOSC2 CCD at different wavelengths for different grisms can be measured directly by the instrument throughput of a spectroscopic standard star In Fig 35 the throughputs for several of EFOSC2 s grisms are plotted The throughputs of the missing grisms can be calculated by using Fig 34 and 35 These have been calculated from observations of a number of spectrophotometric standard stars with the throughputs normalised for a 15th magnitude star at all wavelengths Such throughputs are still relative to EFOSC2 3P6 The EFOSC2Q NTT throughputs will be posted to this manual and on the EFOSC2 web page as soon as they will be available Therefore the following sub s
133. ion including coordinates epoch proper motion and differential motion e The Constraint Set to be used in service mode only specifying under which external condi tions airmass seeing transparency lunar illumination the OB should be executed e The time interval information also to be used in Service Mode only specifying the time windows when the OB can be executed e The Calibration Requirements information a free text field where comments can be given to the Service Mode observer or where the Visitor Mode observer can include a reminder on the calibrations needed Obviously none of these last 4 fields is present in a Calibration OB Although the bulk of OBs are prepared in day time it is possible to prepare and or modify them at night while observing A P2PP session is always running on one of the computers in the control room and preparing an OB requires little time once you ve done a few for practice New OBs can be prepared while an exposure is still running New users will be introduced to the use of P2PP by the System Engineer For this reason successful PIs or their delegated observers are warmly invited to arrive at La Silla two days before starting the observations More details on P2PP can be found at the following URL http www eso org observing p2pp P2PP tool html 4 2 What happens at the telescope The Visiting Astronomer VA is assisted at the beginning of his run by the System Engineer in the afte
134. is flexure the y position of the slits can vary by up to 2 pixels depending on EFOSC s rotator angle Especially for narrow slits this has become critical and therefore a step was added where the actual y position of the slit can be measured the template therefore has four parts First it presets the telescope to the coordinates of the Target associated with this Observation Block and rotates the Adaptor to the requested Rotator Offset Angle It then inserts a filter and the slit takes an image of the slit and asks for the actual y position The operator has to manually measure the centre of the slit on the RTD image and enter the value which will then update the database Then the slit is put our of the beam and an image is taken through the Focus Wedge if FocusFlag is set to T to focus the telescope before acquiring the targets into the slit After the iterative focus process is finished the last focus image is used by the operator to perform the first approximate pointing to the desired object When these steps are done the template takes an exposure of Exposure time seconds which is displayed in a MIDAS window for inspection by the operator He she can then perform a combined offset so that the desired object e g as marked on a finding chart is placed on the slit position specified by X pixel coordinate in the 1 x 1 binning system The Y position of the slit is set to the value given in the step before The Perform combined offset flag
135. is is selected during the preparation of the Observation Blocks as described in Chapter 4 The position and size of the window are specified by entering the starting column and row and the number of pixels in each direction Be aware that the dispersion direction is along the columns when defining the windowing for spectroscopy Officially only two clock patterns are implemented for binning 1 x 1 and 2 x 2 Under the median La Silla seeing of 078 a point source will cover 6 7 pixels FWHM and 3 3 pixels with the 2 x 2 binning readout Therefore we tend to over sample the PSF Higher binning ratios are currently under implementation 3x3 and 4x4 for imaging and 3x1 3x2 4x1 4x2 modes for spectroscopy to sample more efficiently the PSF and to cope with bad seeing situations 2 x 1 binning also works but is not officially supported This mode is useful when narrow slits are used for improved spectral resolution Given the pixel size 0 12 px the typical seeing 0 8 1 0 and the dispersions achieved with EFOSC2 most of the time it is worthwhile to bin the CCD 2 x 2 For spectroscopy the rule of thumb is that for slits of widths 1 0 or wider 2 x 2 binning is sufficient For slits narrower than 1 0 2 x 1 or 1 x 1 binning should be used to ensure sufficient sampling in the dispersion direction For imaging only when the seeing is exceptional or when observing very bright objects would 1 x 1 binning be necessary Note that 2 x 2 binning gi
136. ised radiation at fixed angles note in this case there has to be at least 1 value entered against the List of HWP rotator positions The CCD readout binning and windowing can be controlled An identical template is available for circular polarimetry EFOSC img obs QWPolarimetry Parameter Default Description Filter NODEFAULT User specified filter Starplate NODEFAULT User specified Wollaston Mask Grism NODEFAULT User specified Wollaston Prism Move HWP IN T Insert the HWP T F Continuous rotation of HWP F Continuous rotation of HWP T F List of HWP rotator positions 0 22 5 45 0 67 5 Space separated HWP positions deg Exposure time NODEFAULT Exposure time sec CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of Exposures 1 Number of exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 83 4 3 14 EFOSC img obs Coronography The Coronographic mode is very similar to the Simple Imaging Mode already described except that its template lacks the Starplate option Since coronographic imaging always requires the use of a coronographic mask in
137. ition template since this information is fundamental for retrieving the relevant value from the database It must be noted that the position of the slit is measured by Day Operations from an image taken with the R filter For this reason the acquisition should be done in principle with the same filter In practice the displacements in slit position introduced by the other broad band filters with respect to the R filter are less than one pixel Since the accuracy of guiding and target centring is of the same order all broad band filters can be used for centring the object The user can optionally check the slit position using the same procedure as described in Sec 3 4 2 Both acquisition templates allow the user to focus the telescope before starting the acquisition The focus image is then used for a first approximate centring At this stage it is not important to give a very precise position and thus it is not necessary to see the object to be centred It is sufficient to give the template a tentative position using the cursor instead of the Gaussian centring algorithm if the object is too faint When this is done the real acquisition image will be taken and the iterative centring process will commence Note that by default the acquisition images are taken in fast mode and binning 2 x 2 to reduce the overheads If one wants to use the acquisition frames for scientific purposes one may consider using the same CCD parameters as used for the science
138. ity of the solution is estimated from the rms residual deviations with respect to this polynomial If the rms is poor the corrections are normally not applied to the mirror The bad rms is usually caused by very bad seeing in this case it s not really worth to perform the image analysis The image analysis system can be used in parallel mode during the science exposures In this mode a dichroic is inserted in front of the guide probe which deflects most of the light of the guide star to the Shack Hartmann grid The corrections are calculated and applied between one exposure and the next one The parallel mode requires a guide star brighter than 13th magnitude which is not always available and no jitter between one science exposure and the next More information about the AOS can be found in LSO MAN ESO 40100 1001 1 0 The NTT Active Optics System Users Manual Philippe Gitton 3 2 8 Practical Considerations The AOS is initialised every afternoon by the night assistant A full image analysis will be done at the beginning of the night when it has become sufficiently dark This will generally be immediately after the taking of twilight sky flat fields and takes around 10 minutes This analysis is done not only to improve your images but also to monitor the telescope and detect possible problems The observers may decide to shift these measurements to later in the night if they conflict with urgent observations but the night assistants are in
139. k frames are acquired if the Exposure time is non zero The CCD configuration can be changed such as the binning readout speed and windowing The operator must make sure that all the lights in the dome are OFF To prevent possible light leaks the Calibration Unit is automatically moved IN at the beginning of the execution It is then removed at the end of the exposure sequence Biases frames are needed for every combination of Binning and Readout Speed used during obser vations The best time to take dark current frames is at the end of the night after the telescope has been parked the dome closed and all lights have been switched off One can leave the OB running but make sure that the exposure sequence will terminate before 8 00 AM local time as the staff start working on the telescope after that Parameter Default Description Exposure time 0 Exposure time sec CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of exposures 5 Number of exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 89 4 3 20 EFOSC img cal Flats This calibratio
140. ke under stress or due to tiredness Moreover this forces the observer to think about the observing strategy well in advance This reduces the time lost during the night and maximises the efficiency of the observations Another advantage is that the VA does not need to know how to physically operate the telescope and the instrument since all these operations are executed by the software and supervised by the TIO Of course there are a series of status panels that can be accessed by the VA to check what is going on For example there is a status panel that displays the information which is usually of interest to the astronomer see Fig 31 64 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 EFOSC Status Qwefosc File Std Options EFOSC STATUS DISPLAY RA2000 162134 93 Deczooo 292213 08 Hour Angle Altitude Airmass Remaining time Shutter Status Clo sed Calibration Screen IN Exposure State TRANSFERING Slit slit 1 0 Last Image File EFOSC_Dark 15 fits Filter Expo Id 448 Grism Gr 11 Exposure Type HWP Continuos Movement HWP Angle deg Readout Mode Time sec HWP Position Readout Det Electr SL CU D o 22 39 EfiTemp Sensora C 12 75 Efifemp Sensors C 11 95 T Transfer SLCU WS We Fiera Sensor6 C 11 25 CCD Vacuum mb 4 5e 07 CCD Temp K Figure 31 The EFOSC2 Status Panel EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004
141. l characteristics of the basic set are also included in these references Since the filters are mounted in a parallel beam the focus of the instrument in principle does not change when filters change Some filters however have optical power curvature which introduces focus offsets While this offset is less then 10 encoder units for the broad band filters and thus is practically negligible this is not true for Str mgren and interference filters Please note that since the filters are shared between telescopes plenty of advance notice is required if a filter outside the standard EFOSC2 set is required Observers who wish to bring their own filters are reminded of the image quality requirements EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 11 2 4 4 Grisms and Prisms Grisms are mounted in the grism wheel in the parallel beam of EFOSC2 There are at present 16 grisms available for EFOSC2 Table 5 summarises their properties The values given in the table correspond to CCD 40 with 15y pixels Efficiency curves are given in Appendix A for EFOSC2 3P6 Efficiency curves relative to EFOSC2Q NTT will be added to this manual as soon as they will be available Grism Grating Wavelength range Dispersion Resolution gr mm ABlaze A A pixel FWHM A 1 1 100 4500 3185 10940 6 66 52 2 100 6700 5100 11000 6 60 53 69 3 400 3900 3050 6100 1 50 12 61 4 360 4700 4085 7520 1 68 13 65 5 300 6700 5200
142. lable through the Calibration Unit associated with the adaptor rotator The main component of the calibration system is an integrating sphere mounted on the side of the adaptor Light from the output aperture of the integrating sphere passes through a lens and it is reflected onto the centre of the focal plane by a 45 mirror which is moved into the optical axis On the integrating sphere He Ar and Quartz halogen FIRED Flat internal RED lamps are mounted Additional flatfield or other spectral lamps are mounted in a rack on the floor which is fed to the sphere through an optical fibre The fiber induces some broad absorption features around 724m and 880um The angular size location and shape including central obscuration of the NTT exit pupil are approximately simulated The illumination is homogeneous and unvignetted in a 3 x 6 field and is still usable in a field of 5 x 8 which covers the full EFOSC2 FOV Wavelength calibrations are normally achieved using Helium and Argon lamps only The Quartz halogen lamp is meant to be used for internal spectroscopic flats without the need of moving the telescope to the dome flat field screen This is particularly useful if the observer wants to take flats soon after or before the target observations This lamp can be used also to obtain images of the slits and the MOS plates In this case the typical exposure times are of the order of 0 1s using the R filter For wavelength calibration typical e
143. latest bad pixel map can be found on the web EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 27 2 6 4 Bias Darks and Cosmic Ray Events Several 0 seconds dark exposures can be taken and averaged to produce a frame which will be subtracted from the science images to take out the electronic bias about 220 ADUs CCD 40 has negligible bias structure however it is not safe to assume the bias is always scalar and therefore it is recommended to take several bias exposures every day during the observation run Even though the dark current of CCD 40 is low 3 3 e hour px at least one long dark exposure is useful to monitor the CCD behaviour and any exposure dependent features Taking three dark exposures will allow cosmic rays which are unavoidable in long exposures to be removed The cosmic ray event rate for CCD 40 measured with EFOSC2 mounted at the telescope is about 940 30 events hour for the whole array This corresponds to 0 03 events cm s Typical cosmic ray hits affect several pixels with average peak values of about 900 ADUs A pattern of probable electronic nature is found sporadically in Bias frames taken with binning 2x2 The pattern is different from frame to frame and it may be quite visible or almost absent In the worst case the pattern can reach a level of 30 ADU peak to peak However the mean bias level and standard deviation are apparently not affected and stable A non linear gradient along
144. lose to zenith or horizon Because the pointing model corrects for atmospheric refraction which is wavelength dependent the central wavelength used in the scientific exposures can be set in the TCS telescope control software to achieve a very high precision However for most observations using the default value of 650 nm is sufficient Guiding the telescope during an exposure is usually done by setting one of the two guide probes located in the rotator adaptor on a star and using the autoguider After each telescope preset a list of suitable guide stars is displayed on the autoguider panel The night assistant selects one of them and starts the guiding Note that there is a region within the autoguider position range where the guide probe will cause vignetting in the images This region is marked by a yellow box on the stella display of the autoguider system and the system will stop you selecting a guide star in this region It is important to note that if you are performing a series of jittered exposures with the guiding on you must take care that the offsets do not move the guide star into this region If they do the OB will give an error and guiding will have to be restarted often causing the whole OB to be restarted For this reason users should warn the telescope operator if they have any large offsets in their OBs so For more details on the templates and P2PP see Sec 4 2This is possible because it is defined as a calibration templ
145. me is automatically computed as follows e The average bias level is retrieved from a database e A windowed flat with exposure time 1 sec is acquired e The bias level is subtracted from the windowed flat and the mean intensity of the spectrum is computed e From this intensity the exposure time needed to reach the Requested intensity level is calculated Note that the quartz lamp is rather bright and for certain slit and grism combinations especially a wide slit with a low resolution grism the calculated exposure time is less than 1 second for a CCD binning of 2 x 2 resulting in a non uniform illumination of the slit If this happens the program exits with a warning and no spectrum is taken A possible solution is specify a binning of 1 x 1 and rebin the data at data reduction stage Note also that the quartz lamp is rather red and the internal flats have low counts in the blue Furthermore there seems to be some internal reflection in the blue part of the spectrum The user may also want to take normal dome flats for reducing separately the blue part of the spectrum Parameter Default Description Slit NODEFAULT User specified slit Grism NODEFAULT User specified grism Internal lamp name Quartz User specified internal lamp Requested intensity level 40000 Requested intensity level in ADUs CCD readout speed normal CCD read out speed CCD X binning CCD binning factor in X direction 2 CCD Y binning 2 CCD binning factor in Y direction
146. motely from the TIO s console The suitable template EFOSC_img_cal_Flats has been implemented in such a way that the observer needs only to specify the average exposure level in ADUs s he wants to reach in her his frames The correct exposure time will be estimated by the template itself via a test exposure EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 35 To increase the signal to noise ratio it is a good idea to specify exposure levels around 40000 ADUs 3 2 4 Sky Flats A catalogue of empty fields is present in the TCS so that the V A can request the Operator to preset the telescope to the one s he likes The sky gradient can be reduced by pointing the telescope away from the Sun i e east at dusk and west at dawn When in position the suitable template EFOSC_img_cal_SkyFlats can be executed Since we implemented the algorithm developed by Tyson amp Gal there is no need to specify any exposure time but only the average exposure level After an initial test if the computed exposure time is longer than 3 seconds a series of frames the number of which is specified by the user is started The procedure automatically extrapolates the exposure time for subsequent images and applies a user specified offset to the telescope This offset allows the removal of stars present in the field during data reduction Depending on the weather conditions the algorithm gives equally exposed frames with maximum differences of 3000 A
147. n are given in Appendix A 3 2 43 Fringing As discussed in Sec 2 6 5 long R and especially J exposure images are affected by fringing which can significantly undermine accurate photometry An example of fringing in the I band is shown in the left panel of Fig 23 while a cross cut of an I superflat obtained combining 14 exposures of 480s each is shown in the right panel of the same Figure In this case the maximum amplitude of the fringes is of the order of 3 Caution It must be noted that this effect is additive and cannot be removed by a simple flat fielding Therefore the user must be aware that if one really wants to remove the fringe pattern one has to create a so called super flat which is usually built using all the frames taken in the specific passband This works only if the fields are not strongly crowded and if there are no extended objects Otherwise it is necessary to obtain dithered images of some blank fields during the night Once the super flat has been obtained fringe removal can be performed by the adaptive modal filtering see for instance McLean 1997 Basically this method allows the fringe frame to be built and then subtracted from the image to be corrected Since generally one has only one fringe pattern per night and the sky background is changing with time it is necessary to apply a trial and error iterative technique The measured fringing patterns are available at http www eso org sci facilities lasill
148. n be found online at http ww eso org instruments fors tools FORS_Std FORS1_Std html 3 8 1 Flats The template to be used is EFOSC_spec_cal_PolarFlats which allows sky dome flat fields to be taken with the HWP QWP continuously rotating to act as a de polarise The exposure times must be longer than 10 seconds 3 8 2 Target Acquisition Refer to Sec 3 3 6 60 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 3 8 3 Science Exposures The template EF0SC spec obs Polarimetry allows one or more sequences of spectra to be obtained The default sequence takes four images at 0 0 22 5 45 0 and 67 5 respectively for linear polari sation and two images at 45 and 135 respectively for circular polarisation For more details refer to Chap 4 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 61 4 The EFOSC2 Observing Templates 4 1 Observing with P2PP All the instructions for a given observation are specified in a so called Observation Block OB which is produced by the astronomer using the Phase 2 Proposal Preparation facility P2PP This can be done at the astronomer s institute or at La Silla If the OBs are created at the home institute of the astronomer they must be exported from P2PP and the resulting ASCII files brought to La Silla with the astronomer A comprehensive description of P2PP including the latest user manual can be found online at http www eso org observing p2pp There are 2 categories of OBs
149. n by the OS An example of name produced by the template EFOSC img obs Image is EFOSC_Image 12 fits The names are given in such a way to allow an easy search in the stor age directory according to the different image types as shown in the following table The templates automatically update an observation log file each time an exposure is terminated See Appendix C for an example Image type Image names Acquisition EFOSC_Acq fits Imaging EFOSC_Ima fits Spectroscopy EFOSC Spec fits Darks EFOSC_Dark fits Flats EFOSC Flat fits Arcs EFOSC_spec_HeAr fits Focus EFOSC_Foc fits The names of fits files produced by each template are given in Table 9 4 3 2 EFOSC2 Acquisition Templates Acquisition Templates acq determine how a target field is acquired by the telescope They are inserted to the Observation Blocks during the OB building process Telescope presets can only be performed using acquisition templates since observation templates can only offset the telescope Also adaptor rotations are achieved within the acquisition templates only Note that in almost all Acquisition templates the grism and slit are automatically set to Free and the CCD parameters are set to hard coded values The observer has no control over them This is to avoid possible mistakes while preparing OBs with P2PP and consequent time losses during the observations Note that all acquisition templates with the only exception of EFOSC_img_acq_Preset ha
150. n template acquires Number of exposures imaging dome flat fields with levels ap proximately the Requested intensity level through a desired Filter The slit and grism wheels are automatically set to Free The HWP and Calibration Unit positions are checked and if they are in the light path these components are automatically removed The Guide probe is sent to park position to avoid possible vignetting The operator is requested to preset the Telescope and the Dome to the proper positions and to switch ON the Flat Field lamps in the dome The exposure time is computed automatically as follows e The average bias level is retrieved from a database A windowed flat with exposure time 1 sec is acquired The bias level is subtracted from the windowed flat and the mean intensity is computed e The exposure time needed to reach the Requested intensity level is calculated and adopted for subsequent exposures Note that if the computed exposure time is less than 3 sec or greater than 5 min the template will be aborted automatically Currently the lamp intensity is manually controlled using the Flat Field Lamp Control Panel This means that some tuning may be required when observing with very different pass bands The most up to date settings of the lamp intensities for each filter can be found in the EFOSC2 web page Parameter Default Description Filter NODEFAULT User specified filter Requested intensity level 40000 Requested intensity lev
151. n template and go directly to the very short exposure template If the star looks properly positioned in this short exposure continue with the programme templates If not terminate the OB ask the telescope operator to apply the desired telescope offset using the telescope control panel and repeat the OB after skipping the acquisition Parameter Default Description Filter NODEFAULT User specified filter Exposure time NODEFAULT Exposure time sec CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window CCD windowing flag F F no CCD window T CCD windowed Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of Exposures 1 Number of exposures 84 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 15 EFOSC_spec_obs_Spectrum This template is designed for long slit spectroscopy and MOS spectroscopy and acquires Number of Exposures spectroscopic images of duration Exposure time with a user specified Starplate and Grism It is possible to insert a filter even if it is usually and by default set to Free This option may be used for slitless grism prism spectroscopy for example The CCD readout binning and windowing can be controlled Although 2 x 2 and 1 x 1 binn
152. nce Exposures The template to be used in this mode is EFOSC img obs Coronography which is essentially identical to EFOSC img obs Image The only difference is that the Lyot stop and the Coronographic mask are automatically selected for the grism and Aperture wheels respectively without any intervention from the user 3 5 Spectroscopy 3 5 1 Dome and Sky Spectroscopic Flats Spectroscopic flats should be taken with the same slit and grism as the scientific exposures Spec troscopic flat fields can be obtained using the dome flat field screen or the twilight sky using the template EFOSC_spec_cal_Flats for both cases In this template the user specifies a desired peak exposure level in ADUs A 1 second test exposure is taken to calculate the optimum exposure time with which subsequent exposures are taken To reach a good signal to noise ratio an exposure level of about 40000 ADUs is recommended When taking sky flats using this template the user should specify a high level during evening twilight since the sky is dimming whereas a low level should be specified during morning twilight since the sky is brightening There are different uses for the dome and sky spectroscopic flats Dome flats are obtained with a quartz lamp which produces a black body spectrum free of emission lines A continuum can be fitted and divided from the flat to produce a normalised flat field image which can be used to flat field the scientific data Note that with some
153. nd are therefore more useful than grisms for slit less spectroscopy in particular in combination with narrow band interference filters The resolution depends on the seeing 2 4 5 Grisms nr 7 and 14 Grisms 7 and 14 have quite similar characteristics To clarify the difference between them on 2006 11 28 two standard stars were observed with both grisms and in photometric conditions The response functions are shown in Fig 5 The figure shows that Grism 14 is slightly more efficient near the maximum 2 6 while Grism 7 extends a bit more to the red 100 A A similar conclusion can be reached by looking at Fig 6 where the instrumental spectra of the two standard are shown The more extended spectral range of Grism 7 may allow to include some more arc lines for wavelength calibration However distortions are quite high at the extreme of the spectral range As such the few more lines added might not result in a more accurate wavelength calibration 2 4 6 New VPH Grisms offered as of P82 Starting with P81 two new volume phase holographic grisms VPHG are offered The blue grism 419 covers the wavelength range from 440 nm to 510 nm at a resolution of up to 3200 with a 0 57slit while the red grism 20 covers the range 605 nm to 715 nm at a resolution of up to 3400 with the 0 5 slit The grisms introduce a lateral shift of the beam so the effective field of view is 3 l and 2 8 for the blue and red VPHGs respectively see Table 5
154. ng address http www eso org sci facilities lasilla telescopes ntt index html or in the EMMI user manual http www ls eso org sci facilities lasilla instruments emmi emmiManual html 3 1 1 Telescope Focusing As already introduced in 82 4 7 at the NTT the telescope focus is done through an image analysis and applying a focus offset which is tabulated and proper to the different instruments However the telescopes focus can be checked quickly using using the Focus Wedge For this a hard coded procedure is implemented in all target acquisition templates cf Chap 4 to allow focusing each time the telescope is preset to a new position Following the needs of the observer this step can be skipped A special template EFOSC_img_cal_FocusWithWedge has been implemented in order to allow a Focus Wedge focusing outside of the target acquisition phase This template can be inserted in different points of an observation description to re focus the telescope when staying for a long time on the same target When using the focus wedge stars should be selected in the central region of the CCD since the image quality is better there If the observer is not convinced yet a of the telescope focus obtained through the focus wedge a focus sequence may be also performed 3 1 2 Pointing Tracking and Guiding Tracking of the NTT is quite accurate without guiding no degradation is seen with a seeing of 078 in 15 to 20 minute exposures not too c
155. ns to obtain a rotation curve using Grism 8 2 x 2 binning and the 170 slit Your requirement is that you need to achieve a SNR of 20 per Angstrom per arcsec out to a surface brightness of 20 mag arcsec and so you want to know how much time is needed For a small galaxy one may want to convolve a typical seeing with the galaxy light profile to estimate the surface brightness at which the SNR is calculated For really small galaxies the point source example should be followed From Fig 35 a 15th magnitude star at 5000 observed with Grism 8 gives 26 0 e s hence a surface brightness of 20 mag arcsec 7 will give 0 260 e A s arcsec at the slit Since the slit is 1 0 wide the flux arriving at the detector for every 170 along the slit is 0 260 e s larcsec O for equation 27 We want to estimate the readout noise which corresponds to a 1 0 x 1A bin at 5000A For a CCD binning of 2 x 2 and Grism 8 the area covered by a pixel is 0 314 x 1 98A Hence our area of consideration is 1 61 times that of an image pixel The Read Out Noise for one image pixel is about 10 e7 thus the Read Out Noise for the area under consideration is 10 x v1 61 12 7 e R for equation 27 Note that if the exposures are to be split into n sub exposures R should be multiplied by Jn To estimate the flux from the sky we assume that the sky brightness at 5000 Angstroms is 22 1 mag per arcsec for a 3 day moon Using the throughput value f
156. o CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Telescope RA offset 6 Telescope offset in R A arcsec Telescope DEC offset 4 Telescope offset in DEC arcsec Number of exposures 5 Number of exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 91 4 3 22 EFOSC img cal PolarFlats This calibration template acquires Number of Exposures dome flat fields with HWP inserted and in continuous rotation These flat fields suitable for reducing polarimetric imaging data are taken at an intensity level of approximately the requested intensity level through a desired Filter and Wollaston Mask During the execution the position of the calibration Unit is checked If necessary this component is automatically removed from the light path The Guide probe is parked to avoid possible vignetting The operator is requested to preset the Telescope and the Dome to the proper positions and to switch ON the Flat Field lamps in the dome The exposure time is computed automatically as follows e The average bias level is retrieved from a database A windowed flat with exposure time 1 sec is acquired e The bias level is subtracted from the windowed flat and the mean intensity is computed From this intensity the exposure time needed to rea
157. o half beams which would otherwise coincide in the case of a perfect focus For this reason the focus wedge produces two images for each of the sources in the field Fig 8 shows an example focus image The prism is aligned in such a way that the displacement of the two images occurs along the columns and it gives a null vertical displacement within the errors when EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 17 parc de ED E 4 1 1 Figure 8 An image taken with the focus wedge Each object is split into two In this case the telescope is almost focused since the split images are at nearly the same level with each other Note that the fast readout using two amplifier gives the split appearance of the background 18 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 the telescope is in focus Of course this requires an independent calibration which is performed by the EFOSC support astronomers during technical nights 2 4 8 Wollaston Prisms and Masks The Wollaston prisms can be mounted both in the filter wheel or the grism wheel for Spectropo larimetry and Polarimetric imaging respectively When introduced in the beam the Wollaston prisms produce two images of each object with orthogonal polarisations separated by fixed amounts Two different Wollaston prisms for polarimetric imaging and spectro polarimetry are currently available In the imaging mode they are mounted in the grism wheel while for spectropolar
158. observations are possible although there remain some reflections At 5 arcmin distance the slit is clear of the light and there should be no problems to observe To conclude if targets are close to bright objects it is advisable to rotate the instrument in a way that the object is placed away perpendicular to the slit orientation 3 6 Multi Object Spectroscopy Multi object spectroscopy is actually very similar to normal Spectroscopy described in the previous section The only relevant difference is that special MOS plates are used instead of the long slits cfr Sec 2 4 2 For the preparation of the MOS plates please read the detailed online guide at http www eso org sci facilities lasilla instruments efosc inst ObsMOS htm1 Here some of the issues are briefly discussed The images to be used for preparing the MOS plates must be taken with EFOSC2 see Sec 2 4 2 for the possibility of observing some fields in advance The instrument orientation must be specified in advance and cannot be changed by software in the design stage like in FIMS for FORS on the VLT To speed up the centring procedure and to make it more reliable the users are strongly recommended to include at least three relatively bright stellar objects even near the border of the plate in each field When defining the MOS mask it is very important that these objects are placed exactly in the X centre of the slit lets Failure to do this will lead to misalignment durin
159. on In order to determine the Stokes parameters and therefore the degree of linear polarisation P and the angle of polarisation 0 at least four images rotated by 22 5 with respect to each other must be obtained This is usually done at 0 0 22 5 45 0 and 6725 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 AT If 8 is the HWP rotator angle 8 22 5 x i 1 with 1 2 3 4 and f 8 and f 8 are the fluxes measured for the ordinary and the extraordinary channels the normalised flux differences F B are PEU een F3 poa FCB Then the Stokes parameters are simply given by S 2 d 2 With these definitions the polarisation degree is given by P y Q U 4 while the polarisation angle is given by the following set of equations zatan 5 U gt 0 Q gt 0 ge 90 zatan U lt 0 Q gt 0 5 90 iatam g U lt 0 Q lt 0 180 patan S U gt 0 Q lt 0 For more details see Szeifert 1998 or Lamy amp Hutsemekers 1999 Note also that the asymmetric reflection at M3 seems to introduce a significant amount of instru mental linear polarisation up to 5 see 2 4 9 3 3 4 Circular Polarisation The amount of circular polarisation V can be determined observing with the quarter wave retarder plate at two retarder plate angles of 45 i e a phase difference of 90 by the equation E 2 PE PEF f f being the ordinary and extraordinary beam of the object measured
160. on CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of exposures 1 Number of exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 99 4 3 29 EFOSC spec cal ArcFF This template takes internal arc lamp exposures followed by external dome flat field exposures It is intended to be used as part of the automatic calibrations generated by the CALOB program to be run in the morning following observations It will be executed when necessary by the day time TIOs and is not intended for our users visiting astronomers should use separate arc and flat field templates 100 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 30 EFOSC img cal FocusWithWedge This calibration template acquires an image with a specified Exposure time through the Focus Wedge and a Filter The Focus Wedge splits each star image into 2 horizontally It is set up in such a way that the two images are level with each other when the telescope is focused but are tilted if the focus is off The telescope operator will be prompted to identify the stars in the image and the program will work out the tilt angle and hence the offset in focus The operator will be given the option to offset the focus or not
161. oscopy Helium LAMP1 and Argon LAMP 2 lamps are available It acquires arc line spectra through the desired Filter usually Free Starplate and Grism The user can control the exposure time of the 2 lamps independently The Calibration Unit is automatically moved IN and OUT at the beginning and at the end of the execution respectively Once the Calibration Unit is moved in the lamps are turned on sequentially and the shutter is opened for the desired duration for each of the lamp There is a lamp preheating of a few seconds before each exposure The CCD configuration can be changed such as the binning readout speed and windowing For a discussion of wavelength calibration issues please see 3 5 3 A table of the recommended exposure times are available online at http www eso org sci facilities lasilla instruments efosc inst Perf HeAr html These values may change from time to time due to ageing of the lamps The user may want to experiment with the exposure times during afternoon calibration to optimise the line intensities Parameter Default Description Filter Free User specified filter Starplate NODEFAULT User specified slit Grism NODEFAULT User specified grism He lamp exposure time NODEFAULT Exposure time for He lamp sec Ar lamp exposure time NODEFAULT Exposure time for Ar lamp sec CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y directi
162. pectroscopy Free Free Filt Grism Prism Out Spectropolarimetry Slit Mask Woll Prism Grism In Table 1 EFOSC2 Observing Modes Note that while all other modes are compatible among each other Polarimetric Imaging and Spec tropolarimetry Modes with the same Wollaston Prism are not simultaneously possible In fact they require the Wollaston Prism to be mounted in two different wheels The only possible configuration which allows both modes is to mount the 10 Wollaston Prism in the filter wheel for Spectropo larimetry and the 20 Wollaston Prism in the grism wheel for Polarimetric Imaging 2 4 Instrument Setup Because of the many operation modes of EFOSC2 not all the available slits filters and grisms can be permanently mounted Please discuss your setup requirements with your System Engineer well in advance In particular at least one day before starting observations the Visiting Astronomer must submit a setup request This is done by filling a WEB form http www eso org sci bin sciops efosc cgi If the WEB form is offline please send the request to 1s dnosCeso org Note that while filters can be easily exchanged changing slits and or grisms is time consuming since they require precise alignment Hence last minute changes should be avoided as much as possible The installation of the movable slit is particularly cumbersome since the aperture wheel has to be dismounted and therefore all slit alignments are lost
163. quired calibrations before a slit is dismounted from the wheel Additional to the standard slits two sets of slits were made with the same selection of widths as the standard slits with 15mm offsets in the dispersion direction both to the blue and to the red with respect to a central slit These sets of offcentred slits may be of particular interest when used in combination with Grism 19 or Grism 20 the new blue volume phase holographic grisms see 2 4 6 The increased spectral coverage yielded by these slits in combination with some grisms is given in Table 2 and it is visually illustrated by the figures in Appendix H 8 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 2 4 2 MOS Plates With EFOSC2 it is possible to perform simultaneous spectroscopy of a large number of objects through suitable slits produced on special metallic plates by a punching machine Three punching heads are available which produce slit lets with the values specified in Table 3 PUNCH HEAD WIDTH LENGTH 5 1 02 8 6 7 1 34 8 6 3 1 87 EW Table 3 Available Punching Heads While the width of the slits is fixed by the punching head the length can be increased to the required value by successive punchings For this reason the values reported in Table 3 must be regarded as minimum lengths Typically up to 25 and 15 slits can be produced with the shorter and longer punch heads respectively The field of view is the
164. rall Efficiency The figures derived in the following subsections are still relative to EFOSC2 3P6 In particular the pixel size 0 12 instead of 0 158 the telescope clear collecting area and the zero points were changed by moving EFOSC2 to the NTT However the basic concepts do applies to EFOSC2 NTT too and the aforementioned quantities were only mildly changed Old EFOSC2 zero points are available in EFOSC2 3P6 user manual at http www 1s eso org sci facilities lasilla instruments efosc 3p6 manual EFOSC2manual_ v2 0 ps gz In planning their observing strategy users can refers to the EFOSC2 exposure time calculator available at http www eso org observing etc bin gen form INS NAME EFOSC2 INS MODE imaging Using the zero points from the photometry it is possible to compute the overall efficiency e A of the whole system 3 6m telescope EFOSC2 CCD according to the following formula 18 c AA Ate F 2 5log e mo sel A Atel gl he where c and AA are the central wavelength and the width of the bandpass respectively Az is the clear collecting area of the telescope F4 0 is the flux from a Oth magnitude standard star and h and c have their usual meanings In Table 12 we report the results calculated from Eq 18 and the relevant adopted values Aye 88564 3 cm was used filter X AX F 0 Efficiency um um 107 W em um U 0 35 0 05 4 35 21 5 B 0 44 0 09 7 20 26 0 V 0 55 0 11 3 92
165. red slits are produced by mounting the suitable Wollaston mask on top of a normal slit Since the dispersion axis of EFOSC2 is always along the y axis of the CCD the two spectra must be split along the x axis for spectropolarimetry A possible alternative is represented by the punching of suitable slits on MOS plates cfr Sec 2 4 2 This may be useful for example if 2 targets are located so that only one of them can be imaged at a time with the current set of masks 2 4 9 Half Quarter Wave Plate Two rotating super achromatic Half and Quarter Wave Plate HWP and QWP have been added to EFOSC2 as the first element in the parallel beam after the collimator The two plates share the same physical position and therefore they are mutually exclusive see also Fig 1 With such devices 1t is possible to take either a full linear or circular polarisation measurement without rotating the adaptor The usual practice is to obtain frames at 0 0 22 5 45 and 67 5 with the HWP or at 45 0 and 135 0 with the QWP The HWP QWP can be moved IN and OUT set to a particular angle or to continuous rotation The HWP QWP as seen from the CCD rotates clockwise It makes a complete turn in 2 3 4 0 seconds EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 19 This must be taken into account when selecting the exposure times for a good de polarisation At least 20 seconds is recommended The image quality of the HWP is not exceptional There seems to be a
166. rnoon and always by the Telescope amp Instrument Operator TIO during the night The TIO is in charge of operating both the telescope and the instrument The VA interacts with the system through P2PP where s he can build modify and finally select the Observation Block to be executed Once this is done the TIO fetches the OB from P2PP to the Broker for Observation Blocks BOB where a final check can be performed before the OB is executed An example of BOB is shown in Fig 30 An OD may be composed of several Templates which are executed in the order specified by the astronomer Sometimes the astronomer may want to skip or pause the execution of a template within the OB for instance to check the signal to noise ratio before executing the next template This is possible by simply instructing the TIO who can introduce the suitable flags skip or pause using the BOB panel As long as the template has not started the parameters in it can be changed Once a template is executing however there is no way of changing the parameters except via the EFOSC2 Control Panel the OS Panel Note that not all parameters can be changed in this way however it is possible to change the exposure time of the observation Once an OB is executed it may be reset and re executed with the option of changing some of the parameters beforehand The possibility of preparing the observations in advance has the obvious advantage of reducing the chance of making a mista
167. rom Fig 35 gives a sky surface brightness of 0 038 e s larcsec 7 Since the slit width is 1 0 and the spectrum is extracted over a region of 1 0 along the slit the sky contribution to a 1 Angstrom region in the 1 dimensional spectrum will be 0 038 e s S for equation 27 Plugging in the values for O R and S in equation 27 it follows that to get a S N R of 20 per Angstrom per arcsec along the slit an exposure time of 2200 seconds is required EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 113 B He Ar Exposure Times Tablel4 reports the typical exposure times for the He and Ar comparison lamps The values have been obtained using a CCD binning of 2 x 2 and a slit of 170 and should be changed according to the setup used For example the exposure times should be halved for a 2 0 slit and doubled for a 05 slit The exposure time should be multiplied by 4 for 1 x 1 binning These values might change with time since the arc lamps usually loose their efficiency with time For this reason it is recommended to check the exposure level at the telescope to make sure that they are high enough to allow a good wavelength calibration For this reason the numbers reported in Table 14 should be considered as minimum values An up to date list of the recommended exposure times can also be found online at the EFOSC2 web page http www eso org sci facilities lasilla instruments efosc inst Perf_HeAr html Grism He Ar Grism
168. same as in the imaging mode see 82 6 Punch heads break from time to time due to wear and tear The process of changing them is extremely delicate and requires a specialist who may not be on the mountain and may take up to a day You are encouraged to use punch head no 7 if possible Up to 5 MOS plates can be loaded simultaneously They are punched off line so additional plates can be punched at any time To create multi slit masks pre imaging must be acquired using EFOSC 2 with the same position angle as for the actual observations The La Silla Science Operations department will on a best effort basis obtain pre imaging frames during technical reserved time for up to 20 min per night of spectroscopic observations allocated to the programme provided that the list of coordinates filters exposure times and position angles are received at least 6 weeks before the observing run The request should be sent to the La Silla Shift Leader lasilla eso org Important note EFOSC2 shares the same program xm for the mask design as EMMI on the NT T This is NOT the same as FIMS on the VLT Especially important is that the image cannot be rotated nor shifted in the program Hence it is vitally important that the correct coordinates and position angle is specified in the pre imaging request Once the images are available the visiting astronomer is responsible for preparing designing the masks Detailed instructions are available on http www eso org
169. scope pointing into the wind or wait for the wind to pick up again Problems may also occur when M1 is significantly warmer than the ambient temperature This last problem is now reduced thanks to the fans that have been installed around M1 and a special M2 baffle to improve the air flow The focus offset between the image analysis camera and EFOSC2 is calibrated and monitored Therefore the focus correction given by the active optics system should leave the instrument at the right focus This is usually checked once at the beginning of night then relied upon for the remaining of the night 3 2 9 The EFOSC2 PSF and Image quality The Focal Reducing optics of EFOSC2 considerably distort the PSF and this distortion varies across the CCD The best most circular PSF occurs close to the centre of the CCD NTT Nasmyth stations work at f 11 while the 3 6m Cassegrain focus works at f 8 Therefore a better image quality is achieved at the NTT with respect to EFOSC2 3P6 The PSF distortion as a function of position on the CCD was measured to reach 10 beyond ap proximately 2 from the centre The elongation of stars in an image taken in good conditions is shown as a function of position on the CCD and of the radial distance from the centre in fig 19 and fig 20 respectively In fig 19 the length of the segments is proportional to the star elongation 1 37A B 9 It must be noted that this represents the minimum distortion that one should expect which is
170. scopic capabilities would be needed at the NTT both for the commissioning phase and for the first visitor programs The obvious choice was to build a copy of EFOSC later called EFOSC1 on the 3 6m telescope in view of its moderate size and above all the possibility of using the instrument later on the 2 2m telescope The original idea was to build an identical copy of the 3 6m telescope instrument but it soon became clear that a different mechanical design would be needed to mount the instrument on the NTT and to accommodate a large format CCD It was also clear from the experience with the 3 6m version that a number of improvements were desirable in particular a better UV response a lower sky background compensation and provisions for easier handling of the optical components In 1997 EFOSCI was de commissioned and EFOSC2 was finally moved to the 3 6m where it was offered until ESO period P80 As of April 2008 EFOSC2 is offered at the NTT together with the multimode infrared instrument SoFI 2 2 General Description Briefly EFOSC2 is a focal reducer using multi layer coated all transmission optics Figure 1 gives a general and schematic view of the optical and mechanical design of the instrument The EFOSC2 camera is opened to F 4 9 and its focal length is 200mm The NTT Nasmyth stations work at f 11 The F 4 9 camera focuses the beam onto the CCD whose pixel size is 154 This turns into a pixel scale of 0 12 px The interchangeable op
171. serving block which is what is used to execute the observations 62 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 El E el Observation Blocks Next observation blocks 73 HE2149m0516 072 D 0174 A UNKNOWN EFOSC img acq MoveToSlit Interactive pointing to slit posit DET WIN 1 UIT 1 20 READ SPEED fast WIN 1 BINX 2 o WIN 1 BINY 2 PIXEL X 1150 INS E FILT1 NAME V 641 SLIT 1 NAME slit 1 0 EL y PRESET NEW T COMBINED OFFSET T popu TARG ALPHA 215143 200 TARG DELTA 050247 000 TARG EQUINOX 2000 ROT OFFANGLE 9999 0 EFOSC_spec_obs_Spectrum Spectroscopy EFOSC_spec_obs_Spectrum Spectroscopy EFOSC_spec_cal_Arcs Arc calibration lamps Template log messages H N d Click amp drag with button 1 on the sash to redistribute the size of the 2 panes gi Start Reset status Figure 30 The Broker for Observation Blocks BOB panel In this example an OB has been fetched from the visitor s P2PP session The OB consists of 4 templates The first template acquisition is expanded and being examined and its parameters can be changed Two flags have been introduced by the TIO a skip flag for the 3rd template and a pause flag at the last template The observations will be started when the TIO clicks on the start button on the lower left EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 63 e Target informat
172. spec obs Spectrum setting the exposure time by hand Parameter Default Description Filter Free User specified filter Slit NODEFAULT User specified slit Grism NODEFAULT User specified grism Requested intensity level 40000 Requested intensity level in ADUs CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of exposures 5 Number of exposures 96 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 26 EFOSC_spec_cal_IntFlats This calibration template is mainly used for taking internal spectroscopic flats usually on source since the telescope does not need to be moved to the flat field screen Currently Ne Ar He and Quartz lamps are available but internal spectroscopic flats should only be taken with the Quartz lamp This template acquires Number of exposures internal flats taken with a lamp specified by the Internal lamp name with a level approximately the Requested intensity level through a de sired Slit and Grism The Calibration Unit is automatically moved IN and OUT at the beginning and at the end of the execution respectively The exposure ti
173. stead of Filter The 10 prism cannot be used since the parallel Wollaston Mask WollMask should be chosen for Starplate Typically the half wave plate should be moved in and set to fixed values continuous rotation F and a list of HWP rotator positions This template acquires Number of Exposures spectropolarimetric images for each of the positions specified in List of HWP rotator positions using Wollaston Mask a Grism and the Wollaston Prism The CCD readout binning and windowing can be controlled The template EF0SC img acq MoveToPixel template should be used with the parallel Wollaston Mask WollMask chosen for Starplate Note the choice of x pixel positions is limited by the locations of the transparent sections of the SpectroPolarimetric Wollaston mask slit Any one of the 2 available SpectroPolarimetric Masks Slits may be mounted in the aperture wheel but the name in P2PP will be the same The Wollaston Prism in the grism wheel must be aligned in manner appropriate for a parallel mask For a detailed description of the SpectroPolarimetry mode plus examples please see http www eso org sci facilities lasilla instruments efosc inst bsSciSpec html An identical template is available for circular polarimetry EFOSC spec obs QWPolarimetry Parameter Default Description Wollaston Prism NODEFAULT Desired Wollaston Prism in filter wheel Starplate NODEFAULT User specified Wollaston Mask Grism NODEFAULT User specified grism
174. stead of computing an integrated SN R If the surface brightness of the source is m mag arcsec the expected SNR is Sx SN Re 0 16 b Vg xt 26 li Jmm ee ES where s 100 4x mo m An imaging exposure time calculator for EFOSC2 developed by J Brewer can be found online at http www eso org observing etc bin gen form INS NAME EFOSC2 INS MODE imaging A 2 Spectroscopy In planning their observing strategy users can refers to the EFOSC2 exposure time calculator available at http www eso org observing etc bin gen form INS NAME EFOSC2 INS MODE spectro A 2 1 Relative Grism sensitivities The relative Grism throughputs sensitivities are displayed in Fig 34 These are all measured relative to Grism 1 which is the EFOSC2 grism with the widest spectral range For their measurements spectra were taken with all the grisms with an internal lamp with fixed intensity With the spectrum for Grism 1 normalised to have a value of 1 everywhere the throughputs of different grisms relative to Grism 1 are calculated Fig 34 is useful for finding the most efficient grism at the spectral range that you want For example at 8000A Grism 2 is the most efficient Beware that in Fig 34 for some Grisms there seems to be an upturn or bump in the blue extreme of the curve This is due to reflected light in the instrument and not due to a real improvement in sensitivity As the sensitivity in UV drops dramatically and the
175. structed to do this test every night During the night it is usually advisable to repeat the image analysis procedure If the conditions improve noticeably the mirror settings from the initial analysis are likely insufficiently accurate to make full use of this A significant change may also be seen when moving to a different field and it is necessary to redo the image analysis at this new position To judge on the necessity keep a careful eye on the image quality your frames Images elongated by more than about 10 indicate residual astigmatism in the presence of some defocus which is generally the first indicator of imperfect settings For the majority of NTT observations whether imaging or spectroscopy better seeing will give improved signal to noise Under good conditions the time spent on an extra image analysis will generally be a good investment However there are several conditions where little or no improvement can be expected from an image analysis The first is when the seeing is poor significantly above 170 In that case the default setting is normally sufficient Second if windshake of the telescope is important especially when observing into the wind at wind speeds of 10 m s or more Finally if there is little 38 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 wind the solutions will not be good this typically happens when the wind drops below 2 3 m s In the last case either try doing an image analysis with the tele
176. t Ccd40 html The CCD is driven by the new ESO FIERA controller FIERA has two amplifiers L and R and offers 3 different read out speeds Three modes are currently offered slow normal and fast As it is shown in Table 7 there is not a big improvement in terms of R O N using the slow mode For this reason the normal mode should be used for the scientific images The bias level for the three modes is 220 ADUs The CCD system CCD FIERA controller shows a linearity better than 0 4 over the full range of the 16 bit analog to digital converter ADC The system linearity has been explored in a range of 2000 e up to 83000 e The electronics have been tuned so that the ADC will saturate before non linearity is reached Hence the full range 200 65535 is usable for scientific purposes Even in cases of strong saturation the residual effect is very small and it is completely removed by taking a few bias frames When a short read out time is required for instance during the acquisition phase the fast mode can be used Using 2 x 2 binning allows the CCD to be read in about 9 seconds at an equivalent data transfer rate of 113 kpx s7 The user must be aware that this mode makes use of both amplifiers EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 23 2 a c o o o o gt O o o e LO LO o e o eet e eo e Y e e Q N Prescan Figure 11 Location of the data section and the bias sections on the EFOS
177. t name ESO VLT DIC TPL 1 4 Data dictionary for TPL EF0SC spec obs Spectrum Template signature ID Spectroscopy Template name EFO0SC spec obs Spectrum seq Sequencer script 2003 09 29T22 54 50 TPL start time 0 gt LS7_UM133 100155087 gt 71 B 0032 B 1 0 Version of the template 3 Number of exposures within templat 1 Exposure number within template SCIENCE Observation category SPECTRUM Observation technique 116 HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH HIERARCH EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO ESO
178. the beam Failure to do this will lead to dust and imperfections on the plate not being properly flat fielded out We remind the observer that the Lyot stop must be aligned before starting the observations using a bright star see also Sec 2 4 10 This is usually done at the beginning of the first night of a Coronographic run 3 4 2 Target Acquisition To allow for a proper positioning of the target behind one of the spots of the coronographic mask it is necessary to measure accurately their centres This is usually achieved by obtaining an image of the coronographic mask during the afternoon in 1 x 1 binning Proceed in the same way described in the previous section It is worth noting that especially when using the smaller spots it is important to use the same filter which will be used during the target acquisition phase to avoid possible offsets Since the objects to be masked are usually very bright most likely the acquisition will be done with a narrow band filter 50 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 To have a clean image of the spots we suggest that in both cases you divide a frame taken with the coronographic plate by one taken without it Once a good image of the Coronographic mask has been produced the centre of the spots must be measured accurately X and Y pixel coordinates in 1 x 1 binning and noted down since it will serve as input for the acquisition template EFOSC_img_acq MoveToPixel 3 4 3 Scie
179. the end of the science OB or executed independently Parameter Default Description Filter Free user specified filter Starplate NODEFAULT User specified slit or MOS plate Grism NODEFAULT User specified grism Exposure time NODEFAULT Exposure time sec CCD readout speed normal CCD read out speed CCD X binning 2 CCD binning factor in X direction CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of Exposures 1 Number of exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 85 4 3 16 EFOSC_spec_obs_MOS This template is new for P82 For the user it is identical to EFOSC_spec_obs_Spectrum but it should be used for MOS observations Internally it will store the slitlet positions in the FITS headers in the output file which are required for pipeline processing of the data and may also be of use to users in their own reductions 86 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 4 3 17 EFOSC_spec_obs Polarimetry The SpectroPolarimetry mode is very similar to the Long Slit Spectroscopy mode except that the 20 Wollaston prism has to be chosen for the filter wheel the template helpfully labels the field Wollaston Prism in
180. tical elements slits filters grisms etc are mounted in three wheels which are referred to as aperture wheel filter wheel and grism wheel The aperture wheel is located in the focal plane of the telescope in front of the collimator so that the projected scale for slits is the telescope scale 573 mm The filter and grism wheels are located in the parallel beam between the collimator and the camera Thus in principle grisms and filters mounted on these wheels do not introduce focus offsets In practice however some elements may have optical power and it is recommended to check the focus during the instrument set up phase Defocusing introduced by filters and grisms is negligible so is secondary chromatic aberration which has been largely eliminated by using special glass FK 54 for the optics For all practical purposes the EFOSC2 focus is stable and independent of temperature wavelength or mode of operation It was therefore possible to build EFOSC2 without a remote focusing unit the focus is checked during maintenance prior to a run and very accurately set Thus the observer only has to be concerned with focusing the telescope The optical transmission curve is shown in Fig 2 where the transmission of EFOSCI is also plotted for comparison The rapid decrease of efficiency below 4000 is due to intrinsic losses in optical cement and glass and increased glass air interface losses 2 3 EFOSC2 Modes One of the most outstanding fe
181. time sec CCD readout speed fast CCD read out speed CCD X binning CCD binning factor in X direction 2 CCD Y binning 2 CCD binning factor in Y direction CCD windowing flag F F no CCD window T CCD windowed First column of window 1 If ST T first column of window First row of window 1 If ST T first row of window Number of columns 2048 Number of CCD columns in window Number of rows 2048 Number of CCD rows in window Number of exposures 1 Number of exposures EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 95 4 3 25 EFOSC spec cal Flats This template is designed for taking both Dome and Sky Flat Fields in spectroscopic mode and does not use the Tyson amp Gal algorithm The operator is requested to preset the Telescope and the Dome to the proper positions and to switch ON the Flat Field lamps in the dome for dome FF only There are several lamps available and their intensity levels can be adjusted remotely by a graphical control panel by the operator This calibration template acquires Number of exposures dome sky flat fields for spectroscopy with a level approximately the Requested intensity level through the desired Slit and Grism Al though the Filter position is by default set to Free a filter can be inserted when performing grism prism slitless spectroscopy Before the exposure the HWP and Calibration Unit positions are checked and they are automatically removed if they are in the light path The expos
182. ts a filter and takes a short image through the Focus Wedge to focus the telescope before acquiring the target into the slit After the iterative focus process is terminated the last focus image is used by the operator to perform the first approximate pointing to the desired object Note that the exposure time for the focus image in all acquisition templates is hard coded to 20 seconds because no matter what the field is with this exposure time it is always possible to find suitable stars for focusing Note that it is possible to skip the focusing by setting the Focus flag to F When these steps are done the template takes an exposure of Exposure time seconds which is displayed in a MIDAS window for inspection by the operator He she can then perform a combined offset so that the desired object e g as marked on a finding chart is placed on the slit position specified by X pixel coordinate in the 1 x 1 binning system The Y position of the slit is automatically selected from an internal database according to the Slit for reference and is updated by Operations when a new instrument set up is performed Since this parameter depends on the slit used the astronomer must supply its name The Perform combined offset flag should be set to T if the telescope is to be positioned accurately by offsetting the guide probe in this iterative process Note that if the Rotator Offset Angle is set to 9999 the Rotator Angle will be set to the parallactic angl
183. uisition template presets the telescope to the coordinates of the target associated with this Observation Block At the end of the execution the operator is requested to find a guide star and to activate the autoguider There is no further operator intervention No CCD frame is produced by this template which is meant to be used to quickly preset the telescope to targets which do not require an accurate centring Its use restricted to imaging only is limited by the pointing accuracy of the telescope 5 This template also allows the user to preset the Rotator Offset Angle to the desired value Note that if it set to 9999 the Rotator Angle will be set to the parallactic angle corresponding to the start of the exposure Parameter Default Description Rotator Offset Angle 0 Rotator Offset Angle deg see definition in 3 1 3 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 73 4 3 4 EFOSC_img_acq MoveToPixel This template performs an interactive presetting to a specific pixel position for imaging It has three parts First it presets the telescope to the coordinates of the Target associated with the Observation Block and it rotates the Adaptor to the requested Rotator Offset Angle It then inserts the filter and takes a short image through the Focus Wedge to focus the telescope before the fine positioning After the iterative focus process is terminated the last focus image is used by the operator to perform th
184. um Efficiency of CCD 40 sls Bad Pixel Map of CCD 40 2o so s o m RR RR ERR REG R Clock induced charge generation in the EFOSC2 CCD Artefacts in Arc images Dome flat lamps control panel BPOSC2 Sit Griemianionm uou sog ue Bu SS Ue e deg ute Pa a Oe es Meme R Plat Wield oc oc tees ode ec Bk HB S3 ea Pee Pee EE ESE ditonton comia ha eee eo A a A GA eo ee Go a eS Left The dark shaded area shows the regions of the detector that will be affected by some degree of vignetting after changing to the slower f 11 ratio of the NTT It corresponds to 8 of the active field of view Right a blue dome flat field after the installation of EFOSC2 at the NTE 26 4 4 uoa oko mk om RR mm Ratio of dome flat fields taken at different rotator angle The px to px differences are less P re ee oe ee ee eh ee WS Ree Ra wd a RES Fringing inthe Band es arcadea aE EEN ee a a ae Reges A window to reduce read out time for polarimetry the source must be centred at pixel 427 157 not that the RTD does not have the full FITS header so this px will correspond to another position in the RTD 0000000048 Comparison of a two beam image without left and with right Moon The shift in dispersion direction of spectra taken at different rotator angles Illustration of the effect of differential atmospheric refraction The three spectra of standard stars have been taken with grism 7 at different airm
185. ure time is automatically computed as follows e The average bias level is retrieved from a database e A windowed flat with exposure time 1 sec is acquired e The bias level is subtracted from the windowed flat and the peak intensity is computed from the spectrum This is done by performing a mesh of the central 50 columns and applying a heavy median filtering e From this intensity the exposure time needed to reach the Requested intensity level is calculated Note that since this template is designed for a stable light source the computed exposure time is fixed and hence when taking sky flats the levels will change in successive exposures due to darkening or brightening of the sky For evening sky flats the Requested intensity level should be set to about 40000 whereas for morning sky flats it should be set to about 10000 Note also that as a lot of light is required for these flats they should be taken when the sky is bright i e before imaging sky flats in the evening and after imaging sky flats in the morning Occasionally when taking flats for MOS the template calculates a wrong exposure time This may be caused by the window of the test spectrum falling onto regions between slit lets by overlapping slits or by a mismatch between the regions of the spectrum sampled by the test spectrum and the rest of the slitlets If this happens the user can either experiment with the Requested intensity level or take the spectrum using EFO0SC
186. ve a special logical Preset Flag If this flag is set to T the telescope and the rotator will preset to the required position if it is set to F the template will be executed with the telescope and rotator presets skipped This is particularly useful for instance when the telescope and rotator adaptor are already at the desired position and the observer wants only to perform a combined offset to re centre the object in the slit With the exception of EF0SC img acq Preset all Acquisition Templates gives the user an option to focus the telescope after the telescope preset and before the combined offset for fine positioning the telescope If the Focus Flag is set to Y the telescope will be focused with the Focus Wedge When working with P2PP the observer must remember that all Science OBs must have an acquisition template attached and it must be the first template in the sequence Only one Acquisition Template is allowed for each OB The only exception are the OBs created EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Template lt imagename gt ACQUISITION TEMPLATES EFOSC_img_acq_MOS EFOSC_AcqMOS EFOSC_img_acq_MoveToPixel EFOSC_AcqPix EFOSC img acq MoveToSlit EFOSC_AcqSlit EFOSC img acq NarrowSlit EFOSC_AcqSlit EFOSC img acq Polarimetry EFOSC_AcqPol EFOSC img acq Preset NONE EFOSC img acq RotateToSlit EFOSC_AcqRotslit OBSERVATION TEMPLATES IMAGING
187. ves shorter readout times and smaller images 2Mb instead of 8Mb Finally it allows a larger number of twilight sky flats to be taken and improves the signal to noise ratio Due to a problem in clock pattern skipping pixels takes more time than reading them The CCD is read from the left side For this reason windowing saves time only if the starting row is close to the left part of the CCD This should be taken into account when the observer wants to have the best time resolution for photometry For example if you want to use only the central part of the CCD just take a window that starts from 1 1 and includes the central rectangle 2 6 3 Bad Pixels and Columns In Fig 13 a bad pixel map of CCD 40 is presented There are a few bad columns among which the one at X 986 is particularly bad and should be avoided When placing a stellar object for spectroscopy a position around 1100 1150 should be used This strip is free from bad pixels The latest bad pixel map can be found on this webpage http www eso org sci facilities lasilla instruments efosc inst BADPIXMASK index html The user can also construct their own bad pixel map by taking dome flat field images with high and low counts the division of these 2 gives an indication on the linearity of the pixel 26 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 CCD 40 Bad Pixel Map 2000 1500 1000 500 0 500 1000 1500 2000 Figure 13 Bad pixel map of CCD 40 The
188. wavelength dependent optical aberrations introduced by the EFOSC2 grisms The spectral resolution therefore only depends on the slit width or the seeing for slit less spectroscopy and the dispersion and is constant along the spectrum 12 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Some of the grisms introduce strong fringing redwards of about 7000A Sometimes afternoon dome flats do not always adequately remove all the fringing and this may be due to a small amount of telescope instrument flexure This is usually corrected by proper flat fielding using internal flats taken at the position of the observed object See 2 6 5 for a discussion on fringing and ways to remove it Some grisms are also affected by second order contamination Grisms for which 2nd order contami nation was found are marked at http www eso org sci facilities lasilla instruments efosc inst Efosc2Grisms html and a report is available at http www eso org sci facilities lasilla instruments efosc inst 2ndorder pdf The possibility of reducing the 2nd order contamination using order sorting filters is under investi gation Figure 4 shows in schematic form the EFOSC2 grisms spectral coverage dispersion and wavelength of the peak efficiency Grisms 19 and 20 are not plotted in the figure and described in some detail below see 2 4 6 In addition to the grisms 2 prisms are available These low dispersion devices do not show zeroth order images a
189. ween 5 and 7 positions are available for user selected elements at any given time Fixed slits of widths 03 0 5 0 7 1 1 0 172 15 20 5 0 10 0 and 1570 are available for use with EFOSC2 The length of these slits is about 4 1 Each time a fixed slit is mounted in the aperture wheel it rests in a slightly different position The typical displacement in the Y position i e along the dispersion direction is of the order of a few pixels This means that comparison spectra taken after two different setups might show small shifts In addition to the fixed slits a 1 5 movable slit has been manufactured at La Silla This slit can be displaced in order to adjust the wavelength range covered by the grisms This is a time consuming operation and cannot be done during the night The slit can be displaced by 10mm with respect to the centre position by means of an adjustment screw A ruler with 0 5mm rulings placed under the slit is used for positioning The relation between the slit displacement in mm AY and the wavelength shift of the spectrum AA in A is TE where D is the dispersion of the grism in pix as given in Table 5 Moving the slit outwards in the wheel turning the screw clockwise corresponds to shifting the spectral lines towards the blue the spectral coverage shifts to the red One should always check the shift by taking a He Ar spectrum and visually determining the wave length range Observers should obtain all the re
190. xposure times are reported in Table 14 Helium Argon arc spectra often show a variety of unwanted features including extra lines which are often highly curved big splotches of light etc These are illustrated in Fig 15 All of these are due to a combination of reflections in the optics the very bright emission lines in the arc lamp spectra and possible higher order spectra At first glance these features look quite terrible as they are displayed on the Real Time Display RTD but in fact they are quite faint and the problem is with the display cuts automatically selected by the RTD These have never been a problem during actual observing where the spectral lines are much fainter and such features are much fainter than the noise For dome flats lamps of different power are available They are controlled remotely via a panel on one of the displays Fig 16 Normally the user does not have to set the lamp intensities but specifies a desired mean level in ADUs in the dome flat field templates The lamp intensities will be set by the telescope operator according to your setup 30 EFOSC2 USER S MANUAL 4 0 LSO MAN ESO 36100 0004 Gh st lines Figure 15 Artefacts in an Arc image This is illustrated by an image of the He Ar arc lines for Grism 9 As well as the arc lines there is reflected light from the Argon Lamp at the top of the frame Very faint ghost lines resulted from reflection can also be seen in the image as lines which

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