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ISIS USERS` MANUAL - Isaac Newton Group of Telescopes

1. IPCS field i ina pent ae and the dashed line points at which grating efficiency dr half of its peak wavele igth o of h order is ak gt d 5a TEK 1024 CR The cro he 15 ISIS Users Manual INSTRUMENTS cells which should then be set to the autocollimation angles with the commands REDGRAT or BLUEGRAT The autocollimation angles are 35500 for the red arm and 30800 for the blue arm The grating cell angles are driven by a stepper motor from the ISIS 4ms microprocessor and their positions are encoded by Ferranti 35HA optical absolute encoders The units for these mechanisms are millidegrees and the encoders are accurate to 3 millidegrees and repeatable to 2 millidegrees The grating angle offsets are grating independent The demanded central wavelength can be specified with the ICL procedure CENWAVE see chapter 7 and the grating angle offsets are taken into account by this procedure 2 8 Cameras The ISIS blue and red cameras are of a folded Schmidt design with a focal length of 500 mm giving a scale of 14 9 arcsec mm along the slit The reduction factor along the spectrum is dependent upon the grating angle and is presented graphically for the ISIS grating set in Appendix D The air glass surfaces of
2. OUTER CELL eet ert o ae at as GRATING CELL ai m ME ag J a RED GRATING ASSFMBL Y Figure 6 The ISIS Grating Cells 14 ISIS Users Manual 33 Al mm 3037 es y SR ORDER Fk hice 3471 352 ie ee 3209 10 S2 A mm 4859 L_ Figure 7 Format of the output of the blue cross disperser with IPCS solid lines and EE P88300 CCD dashed lines outlines superimposed The solid lines represent the outline of IPCS field in a typical format and the dashed lines a TEK 1024 chip The crosses ma points at which the grating efficiency drops to half of its peak value in that order The wavelength of each order is marked central INSTRUMENTS ISIS Users Manual First pixel readout Wavelengths are in nm Figure 8 The format of the first and second order spectra on the FOS II Chip
3. 138 13 3 14SET TIME 138 13 3 15SET DATE 138 13 3 165EX 138 13 3 17STANDARD SPEED 139 13 3 1I8IT STAT 139 13 3 19T SHOW 139 13 3 20TELE 139 13 3 21UNJAM 139 13 3 22VHT CONFIG 139 13 4 The Engineering MIMIC 140 14 The DMS User Interface 140 14 1 Use of the Mouse 140 14 2 The Menu Structure 140 14 2 1 The Main Menu 140 14 2 2 The Display Menu 141 14 2 3 The Statistics Menu 141 14 2 4 The Screens Menu 143 VII APPENDICES 144 A Properties of the ISIS Gratings 144 B Grating and Detector Efficiencies 146 C Efficiency of Dichroics and Polarisation optics 147 D Details of Neutral Density Filters 152 E Details of the La Palma Sky 153 E 1 Sky Brightness and Specttum 153 E 2 Extinction at La Palma 153 F The LAPLATE program 155 1X CONTENTS ISIS Users Manual List of Figures l The WHT Cassegrain A amp
4. 125 11 7 3 DMSCLEARBUFF 126 11 7 4 DMS_CLOSE_BUFF 126 11 7 5 DMSMONITOR 126 11 7 6 DMSRESET 126 11 7 7 DMS_START 126 11 8 MIMIC Commands 126 11 8 1 MIMICPAGES 126 11 8 2 MIMIC UPDATE 126 11 8 3 MIMICSTART 126 11 8 4 MIMIC_STOP 127 11 8 5 SCREEN 127 12 DCL Level Commands for the Vax 4000 127 12 1 Tape Writing Commands 127 12 1 1 FITSINIT 127 12 1 2 WRITE FITS 127 13 Local Subsystem Commands 128 13 1 Autoguider Commands 128 13 1 1 NET 128 13 1 2 ACQINT 128 13 1 3 ACQWIND 128 13 1 4 CASS 128 13 1 5 FIELD 128 13 1 6 GUIDE 129 13 1 7 GUIINT 2 0 en 129 13 1 8 GUILOOPS 129 13 1 9 GUISIZE 129 Vil CONTENTS ISIS Users
5. 115 11 4 10FMRESET 115 114 11 FMVTILT 115 11 4 12FSGLOBAL 115 11 5 Data Taking Commands CCD Detectors 115 11 5 1 ABORT 115 11 5 2 ARC 116 11 5 3 BIAS 116 11 5 4 BIN 116 11 5 5 CCDINIT 116 11 5 6 CONTINUE 117 11 5 7 DARK aaa ee ee 117 11 5 8 DIR 117 11 5 9 DISABLE WINDOWS 117 11 5 10DISKSPACE 117 11 56 11 ENABLE_WINDOWS 118 1L 5 12FINISH 118 11 55 I3FLAT 118 11 5 14GLANCE 118 11 5 15KEEP 119 11 5 I6KILLMULT 119 11 5 I7MULTRUN 119 11 55 IS8NEWTIME 119 11 5 19PAUSE 119 11 5 20PROMOTE 120 11 5 21RAT_WAIT 120 11 5 22RUN 120 11 5 23SCRA
6. 86 9 6 5 Data reduction 86 V QUICK REFERENCE GUIDE 87 ill CONTENTS ISIS Users Manual 10 Ouick Reference Guide 87 10 1 Starting Up 87 10 2 Taking Data the Data Acquisition System 87 10 3 Setting Up The CCDs 88 10 3 1 Rotation and Focus 89 10 4 Setting Up The IPCS 89 10 4 1 Starting Up and Scan Correction 89 10 4 2 Setting up the IPCS Format and Focussing ISIS 90 10 4 8 Observing with IPCS 91 10 5 The DMS Display 92 10 6 ISISCommands 92 10 6 1 Slitarea 92 10 6 2 Folds and Filters 92 10 6 3 Gratings and Wavelength Settings 93 10 6 4 Polarisation Module 93 10 6 5 Initialising mechanisms 93 10 7 A amp G Box Commands 94 10 7 1 Comparison lamps 95 10 7 2 Autoguider 95 10 8 Typical Observing Sequence 2 96 10 9 Observing With FOS 97 10 10Offsetting the Telescope 97 10
7. 50 8 3 Setting up the CCD Detectors 51 8 3 1 Rotation 51 8 3 2 Tilt and coarse Focus 52 8 3 3 Collimator Focus 54 8 3 4 Hartmann test using the DMS 55 8 3 5 Hartmann test using the Vax 56 8 3 6 Minimum FWHM using the VAK 56 8 4 Setting up the IPCS 57 ISIS Users Manual CONTENTS 8 4 1 Camera Head Rotation 57 8 4 2 Distortion Correction 58 8 4 3 Collimator Focus 60 8 4 4 Hartmann test using the DMS 60 8 4 5 Hartmann test using the Vax 4000 62 8 4 6 Minimum FWHM using the VA 62 8 5 Installation and Setup for Fibre observing 62 8 5 1 Fibre slit mounting 62 8 5 2 Fibre slit alignment 63 8 5 3 Guide fibre bundle focussing 64 8 54 Spectrograph set up 2 64 8 6 Setting up FOS 65 9 Observing Procedures 66 9 1 Observing with one or two CCDs 66 9 1 1 TVFocus 66 9 1 2 Instrument Calibration Data
8. 67 9 1 3 Acquiring dataonthesky 70 9 1 4 Acquiring faimtobjects 70 9 1 5 Acquiring guide stars 71 9 1 6 Wavelength Calibration 72 9 2 Observing with IPCS only or with CCD and IPCS 73 9 2 1 TVFocus 13 9 2 2 Switching on the IPCS EHT voltage 73 9 2 3 Instrument Calibration Data 74 9 24 Acquiring dataonthesky 76 9 3 Time resolved observations with ISIS 76 9 3 1 Sourcesofdead time 76 9 3 2 Reducing dead time v7 9 3 3 Future developments 79 9 3 4 A note on accurate time and ISIS 79 94 Observing with FOS 80 9 4 1 Data reduction 80 9 5 Spectropolarimetry sosoo a 81 9 5 1 How to derive the Stokesparameters 82 9 5 2 Imaging Polarimetry 83 9 6 Observing with Fibres 84 9 6 1 Telescope focusing on the aperture plate 84 9 6 2 Adjustment of the rotator axis and orientation 84 9 6 3 Field acquisition 85 9 6 4 Calibration
9. 19 29 39 49 Gives the value of the input file commands Gives the coordinates of the field centre for telescope pointing Gives information about fiducial objects equatorial coordinates R A DEC fiducial object label and calculated plate position X Y in millimetres from the plate centre Gives information about the targets equatorial coordinates R A DEC object label and calculated plate position X Y in millimetres from the plate centre The number shown at the end of the output file will be used to assign each fibre to the corresponding hole by means of the object labels
10. and so minimize obscuration losses The optical system has a resolution of 33um FWHM zero slit width at the camera focus corresponding to 13A in first order in the spectral direction and 1 2 arcsec along the slit The electronic iris shutter is located just below the interface between FOS II and ISIS and a pair of Hartmann shutters which can be inserted into and removed from the beam either by operation of a manual lever or by motors controlled by the FOS 4ms controller The focus position and tilt of the detector can be remotely set by the 4ms controller The focus and CCD tilt are defined by the position of three push rods on which the ring bearing the CCD is supported The push rods are moved along axis by three motor micrometers The 4ms microprocessor is located in one of the Cassegrain cubicles and is interfaced to the WHT Utility Network and can accept commands over the Utility Network or from a local terminal The current detector for FOS II is a GEC P8603 CCD with a dye coating to enhance the blue response and the format provided by the spectrograph is shown superimposed upon an outline of this CCD in Figure 8 Because the inter order separation at the blue end of the CCD is small FOS II is used either with a 20 arcsec dekker to limit the spatial coverage or with a GG495 filter in the below slit filter slide to eliminate second order for longslit work The readout noise of the current FOS II CCD chip is 8e r m s 2 11 Miulti Sli
11. Moves the comparison lamp filter wheel B so that the named filter is in the beam Format COMPFILTB lt filtername gt Example COMPFILTB ND3 0 Comments Possible values for filtername are ND2 0 ND1 2 NDO 9 NDO 5 NDO 3 BG24 OPAQUE and CLEAR 11 1 14 COMPLAMPS Switches on or off comparison lamps Format COMPLAMPS lt lampname s gt Examples COMPLAMPS CUAR CUNE COMPLAMPS OFF Comments More than one comparison lamp may be switched on the names being joined together with plus signs Possible comparison lamps are CUAR CUNE W FEAR FENE NAK and ALMGCA Another allowed parameter is OFF which may not be joined with a plus sign to any other allowed parameter 102 ISIS Users Manual COMMAND LISTS 11 1 15 COMPND Sets the comparison lamp neutral density to a specified value Format COMPND lt ndvalue gt Example COMPND 1 5 Comments Selects the combination of neutral density values in the COMPFILTA and COMP FILTB wheels whose sum is closest to the ndvalue moves the filter wheels to those positions 11 1 16 CUARON Moves the mirrors to the ACQCOMP position and switches on the copper argon lamp Format CUARON Comments This command currently will only work if the IPCS is in use 11 1 17 CUNEON Moves the mirrors to the ACQCOMP position and switches on the copper neon lamp Format CUNEON Comments This command currently will only work if the IPCS is in use 11 1 18 MAINFILTC Moves the main colour
12. 10 12 Shutdown e STANDBY shuts down IPCS Then set the switch on the electronics cubicle to OFF e SHUT DOWN the Autoguider type this on the autoguider keyboard e COMPLAMPS OFF e EXIT and then logoff from LPVF and the Vaxstation e Fill CCDs with liquid No e Enter requests for next day in the Telescope Log book and enter faults in the FAULT database on LPVS3 99 COMMAND LISTS ISIS Users Manual Part VI COMMAND LISTS 11 Commands entered at the ICL interface This section describes commands which can be entered at the ICL interface to control one or more subsystems Notation e Examples of commands entered at the terminal are in typewriter font REDGRAT 35000 e Angle brackets denote parameter values or character strings lt angle gt e Square brackets denote optional input Lx y all other parameters are obligatory 11 1 A amp G Box Commands 11 1 1 AGACCESS Unlocks the access door for the main filter slides Format AGACCESS Comments The door must be opened and the closed manually The command does not give control back to the user until this has been done The door will be locked when it is closed there is no separate command for this 11 1 2 AGBARCODES Reads the barcodes on the filters in the main A amp G box filter slides Format AGBARCODES lt function gt Example AGBARCODES UPDATE Comments function can have one of three values READ which reads the barcodes and stores the information in th
13. 9 4 1 Data reduction Data reduction typically involves the following steps Debiassing and flat fielding the data frames Flat fielding is particularly important for removing the many poorly resolved sky lines redward of 7200 A for this reason the resolution of ISIS is preferred if wavelength coverage and throughput are adequate The tungsten lamp is so red that flats are saturated in the red before enough signal is obtained in the blue twilight flats are better Correction of curvature extraction and sky subtraction of first and second order spectra for each object on slit Sky subtraction can be top hat using a few equally weighted columns preferably on either side of the object spectrum for sky and a few equally weighted columns for object ot it can be optimal with the software weighting each object column according to the strength of the signal In practice optimal extraction typically yields only a few 10s of extra signal to noise for an unresolved object Wavelength calibration via arc exposures CuAr or CuNe former probably better has lower density of lines FOS is very stable and wavelength calibration can anyway be checked against the numerous sky lines but it s a good idea to take a few arcs per night Correction for absorption bands due to the atmosphere especially the Fraunhofer A and B bands at 7594 and 6867 A via observation of a star with a featureless spectrum usually a B 80 ISIS U
14. Diffuse scattered light has be shown to be below 2 by observations during commissioning of Quasar absorption lines known to be completely black Ghost images are caused by stray reflections within the spectrograph and can either be in focus images or images of the pupil Pupil images take the form of the telescope pupil with the central obstruction even if the illumination is from the comparison lamp system because the illumination from the integrating sphere is designed to mimic exactly that of the telescope This is not true of the comparison lamps for the fibre optic system There are a number of known ghosts in the ISIS system these are listed below e A ghost spectrum parallel to the primary spectrum which is seen in blue arm observations when a dichroic filter is used It is caused by light reflected off the back surface instead of the front surface of the dichroic It is strongest at wavelengths in the crossover region The offset on the detector from the primary spectrum is 0 2 mm for the older thin dichroics and 0 6 mm for the new thick dichroics e A Narcissus ghost pupil image which is caused by reflection between the surface of the CCD or its surrounds and the cryostat window This appears strongest when caused by strong spectral features just off of the CCD for example when looking at a Copper Argon source at blue wavelengths at low dispersion when the ghost is caused by reflection of the strong red lines from the surrounds
15. ESD Example 1 ESD Comments Enables or disables the distortion correction 1 to enable and 0 to disable 13 2 13 FOCUS Select spectral lines for Hartmann focus test Format FOCUS Comments Allows the user to select three spectral lines from a two dimensional image either IPCS or CCD for use when focussing with the Hartmann shutters and the DMS analysis routines Plots a cut through each line after selection allows the user to accept or reject that line 132 ISIS Users Manual COMMAND LISTS 13 2 14 FOCUS LEFT Analyses an exposure taken with the left Hartmann shutter open and the right closed Format FOCUS LEFT Comments For each line selected by FOCUS or FOCUS SET it calculates the centroid and FWHM of the line at three points along it 13 2 15 FOCUS RIGHT Analyses an exposure taken with the right Hartmann shutter open and the left closed Format FOCUS RIGHT Comments For each line selected by FOCUS or FOCUS SET it calculates the centroid and FWHM of the line at three points along it and the shift relative to the last time FOCUS LEFT was run 13 2 16 FOCUS SET Allows the user to type in the position of lines for use by FOCUS LEFT and FOCUS RIGHT Format FOCUS SET Comments Prompts the user for the positions of three lines for use by FOCUS LEFT and FOCUS RIGHT as an alternative to interactive selection with FOCUS 13 2 17 FRECALL Transfers data from a named file on the DMS disc and displays it in
16. MNRAS 226 341 1987 analysed granularity using Fourier techniques and showed that most of the power is on scales of many pixels gt 5 little power was seen on small scales lt 5 pixels Flat fielding is therefore highly desirable when the noise in the data due to photon noise is less than the power density of the granularity at the spatial frequencies of interest To adequately 34 ISIS Users Manual DETECTORS Table 8 Measured magnitude for one photon second A for the red and blue arms of ISIS Wavelength B 4000 4500 4700 5000 5500 6000 7000 8000 9000 10000 Red arm EEV CCD 17 5 17 1 16 0 14 2 Blue arm EEV CCD Blue arm Tek CCD Blue arm IPCS FOS II 1 order 18 0 17 4 16 3 1 The red arm data are for an uncoated EEV CCD 2 Some of the FOS II data are interpolated from measurements at intermediate wavelengths describe the granularity on a scale of P pixels typically a flat field of at least N counts per pixel should be taken where logo N 3 2 27 P Because there is little power at small scales using a flat field with a small differential shift lt 2 pixels between the image and the flat field will still improve rather than degrade signal to noise of the resulting image However in practice obtaining IPCS II flat fields is very difficult because the required ex posure time would be many hours because of the low count rate limit of the CCD IPCS 6 Overa
17. Synonym Comments RFOLD lt position gt RFOLD MIRROR RED_FOLD Moves stops or initialises the slide containing the folding flat for the red camera Valid parameters are a number in the range 0 to 1 MIRROR 0 CLEAR 1 STOP INIT and REPROGRAM The last option should only be used in exceptional circumstances 11 3 27 RHART Controls the position of the Red beam Hartmann shutters Format Examples Range Comments RHART lt position gt RHART 1 RHART BOTH_IN 0 to 3 with named equivalents Valid parameters are a number in the range 0 to 3 BOTH_IN 3 LEFT_IN 2 RIGHT_IN 1 and BOTH_OUT 0 11 3 28 SLIT Sets the Slit jaws to a specified width Format Example 112 SLIT lt slitwidth gt SLIT 200 ISIS Users Manual COMMAND LISTS Synonym SLITARC also allows STOP as a parameter Units Microns Range 25 to 5000 11 3 29 SLIT DOOR Locks or unlocks the slit area access door Format SLIT DOOR lt position gt Example SLIT_DOOR OPEN Comments This is an interactive procedure to unlock and lock the slit access door Valid parameters are OPEN and CLOSE LOCK and UNLOCK SLIT_DOOR OPEN or SLIT_DOOR UNLOCK will unlock the door and invite you to open it manually SLIT_DOOR CLOSE or SLIT_DOOR LOCK will invite you to check that it is closed and lock it when you have verified this 11 3 30 SLIT_UNIT selects whether the long slit unit or the multi slit and fibre slit unit
18. There is a high speed data interface DICI Dual IPCS CCD Interface between the detectors and the VME memory The system also has an image display facility based on an Opal Graphics Controller Immediately after each exposure the data from all detectors appears in memory in the Detector Memory System DMS Images obtained with CCD detectors are read out into the DMS at the end of an exposure Photon counts from the IPCS 2 are continually transferred to the DMS during an exposure where they are built up into an image The DMS is capable of handling multiple detectors simultaneously reading the data from different detectors into different areas of memory normally referred to as buffers This feature is particularly important for the operation of ISIS 7 3 The SPARCstation Data collected by the Detector Memory System DMS may be saved to the SPARCstation 2 currently LPSS3 for examination using SAOIMAGE or IRAF applications The Sparcstation is intended to meet the need for very rapid on line evaluation of data using standard reduction software The system consists of a Sparcstation 2 with 64 Mbyte of memory and 3 Gbyte of local disk storage connected to the DMS via a commercial S bus to VME adapter This allows very rapid transfer of data from the DMS to the SPARCstation The run number of the saved data is the same as that used on the VAX At present the data are transferred without headers Data may be written from the SPARC to an exa
19. information pertaining to that exposure and transfers both data and headers into an HDS file on the system computer During the observation the system will report the run number allocated and will announce the start and end of the exposure The user will be informed once the data has been written to disk until this notification has been received no further exposure can be carried out on this detector channel Exposures cannot be carried out until the detector has been set up using the SETUP command 120 ISIS Users Manual COMMAND LISTS 11 5 23 SCRATCH Takes an exposure and transfers the data plus headers to a numbered HDS file in the scratch area on the system computer Format SCRATCH lt channel gt lt filenum gt lt obstype gt lt time gt lt string gt Channel The name of the CCD data acquisition channel to be used Filenum The number of the scratch file Obstype The observation type Valid observation types are ARC BIAS DARK FLAT and TARGET Time The exposure time in seconds Title A title for the observation optional Examples SCRATCH RED 5 ARC 60 Comments As for the RUN command except that the data is finally transferred not to the main data area on the system computer but to a scratch area This command is intended primarily for use with setup procedures 11 5 24 SETUP sets up the default detector format and prepares a channel for taking data Format SETUP lt channel gt Channel The
20. the case of a dark exposure The command will be aborted if no exposure is in progress 11 5 7 DARK Takes an exposure without opening the CCD shutter and transfers the data plus headers to an HDS file on the system computer Format DARK lt channel gt lt time gt lt string gt Channel The name of the CCD data acquisition channel to be used Time The exposure time in seconds Title A title for the observation optional Examples DARK RED 9999 Measuring dark counts Comments As for the RUN command except that the CCD shutter is not opened and the observation type is set in the headers as being a DARK exposure 11 5 8 DIR Lists the run and scratch files taken during the night Format DIR Comments Lists the files in the directories to which run and scratch files are currently being written Normal DCL qualifiers e g SIZE are accepted 11 5 9 DISABLE_WINDOWS Disables windows and binning factors previously set up on a CCD detector Format DISABLE WINDOWS lt channel gt Channel The name of the CCD data acquisition channel Examples DISABLE WINDOWS FOS Comments This command disables windowing and binning of the CCD The command does not delete the systems memory of window parameters and binning factors it only stops the system applying it The windows and binning can be reenabled with the command ENABLE_WINDOWS 11 5 10 DISKSPACE Reports the available diskspace on the data disk and on the
21. there is a list of these in the WHT Users Manual e Calibration lamp exposures These should be interspersed with observations of astronom ical targets throughout the night The normal comparison lamps are Copper Argon and Copper Neon to maintain a safe level of illumination it may be necessary to use these in conjunction with neutral density filters especially when working at low dispersion To obtain sufficient counts for a good wavelength fit a comparison lamp exposure time of at least 100 seconds is required 75 OBSERVING PROCEDURES ISIS Users Manual 9 2 4 Acquiring data on the sky The procedures for acquiring data with the IPCS are basically the same as those for acquiring data with CCDs set out in Section 9 1 3 However the data acquisition commands EXPOSE IPCS or EI and KEEP IPCS or KI must be used instead of the CCD commands RUN ARC GLANCE etc If the IPCS and a CCD are being used simultaneously then the old version of the software 50 3 will be running and the old CCD commands e g EXPOSE RED and KEEP RED will need to be used to control the CCD This situation is expected to change by early 1993 When acquiring data with the IPCS some additional precautions should be observed e Always close the IPCS shutter with IPC immediately after a run has completed and never allow the telescope to be moved while the IPCS shutter is open e If you are not sure about the brightness of a new target then set the IPCS to fu
22. with a frame time of 5 ms line ratios showed no sign of nonlinearity at count rates up to 6ct s CCD pixel This corresponds to a rate of 0 75ct s channel at a spectral resolution x8 and spatial resolution x1 There are two real time display screens showing the detection of photon events On the telescope the display is located next to the high tension EHT controls so that the detector can be monitored as the EHT is brought up The second display is in the control room and here the screen must be monitored carefully each time the IPCS shutter is opened The IPCS is easily damaged by bright light and great care must always be taken using it For any new setup new on sky source or new calibration lamp it is safest to include a large amount of neutral density eg ND4 2 in the beam and reduce it gradually For comparison lamps this can be achieved by putting ND3 0in COMPFILTA and ND1 2 in COMPFILTB For sky objects you can do it by putting ND in the main beam filter with the command MAINFILTND ND3 0 There is a red Panic Button and you should keep your finger over this as you open the IPCS shutter each time on a new source of light Operation of this button will close the IPCS shutter immediately but will not affect the EHT voltage Two typical symptoms of a dangerously high tate are a the dots of light on the real time CRT display merge to form a solid splodge of light which is not flickering or b if the IPCS shutte
23. 0 both out 1 L in R out 2 L out R in 3 both in moves blue Hartmann to position n same convention as for RHART moves red collimator to setting n moves blue collimator to setting n moves red filter A to position n N B Check whiteboard amp mimic for current filter slides loaded moves red filter B see whiteboard moves blue filter A to position n moves blue filter B to position n to change grating amp to update MIMIC database on gratings amp ISIS filters ISIS Users Manual QUICK REFERENCE GUIDE 10 6 3 Gratings and Wavelength Settings REDGRAT 0 moves red grating to angle units of 0 001 degs BLUEGRAT 9 moves blue grating to angle CENWAVE RED A moves red grating to wavelength A CENWAVE BLUE A moves blue grating to wavelength A CHANGE use this to change a grating and then to enter the new item in the MIMIC s database MANDATORY for a grating change GRATING_DOOR OPEN unlocks both grating doors N B Do not issue this command until gratings have reached 35000 GRATING_DOOR CLOSE locks both grating doors NB Use CHANGE to change gratings these commands to reset the doors only 10 6 4 Polarisation Module The main commands used for operating the polarisation elements are FCP_OUT Remove calcite block or polaroid from the beam FCP pos Move FCP tray to pos Options are CLEAR remove from beam FIELD_LENS the old position of the FOS field lens POLAROID select the Polaroid analyser position CALCITE mov
24. 1 Comments Starts or stops the Autoguider following a guide star n specifies the rank of the guide star in order of brightness and defaults to 1 13 1 7 GUIINT Changes the integration time when in guiding mode Format GUIINT lt integrationtime gt Example GUIINT 4000 Units Milliseconds 13 1 8 GUILOOPS Changes the number of integrations over which the autoguider averages before sending an error signal to the Vax Format GUILOOPS lt nloop gt Example GUILOOPS 5 Default nloops 1 13 1 9 GUISIZE Changes the size of the guiding box Format GUISIZE lt npixels gt Example GUISIZE 30 Default npixels 15 Comments This can be used to increase the size of the guiding box in bad seeing conditions 13 1 10 GUIWIND Sets the position of the guiding box in CCD pixels Format GUIWIND lt x gt lt y gt Example GUIWIND 150 224 Defaults X and Y default to the position of the currently selected star Comments This can be used to reacquire the guide star when the telescope is moved by an accurately known amount or to start guiding at a predetermined position 13 1 11 SHUT DOWN Shuts down the Autoguider and warms the chip up Format SHUT DOWN Comments Starts a shut down sequence for the Autoguider by warming the CCD chip up above 0 C This process takes about 5 minutes and the observer should check that it works 129 COMMAND LISTS ISIS Users Manual 13 1 12 START UP Starts up the Au
25. AUTOTHETA at values below about 35000 the guide probe vignettes the slit viewing optics Once a suitable star has been found by the autoguider you can start the autoguider guiding and sending error signals to the TCS by typing FON at the ICL interface or GUIDE ON at the autoguider interface The TCS needs the guide probe co ordinates in order to convert these errors into corrections in Altitude and Azimuth so to start guiding you need to type PROBE lt autoradial gt lt autotheta gt AUTOGUIDE ON at the TCS console or the ICL interface There is a programmed function key on the TCS terminal for AUTOGUIDE ON To stop guiding at the end of an exposure type AUTOGUIDE OFF at the TCS or ICL terminal FOFF at the ICL interface or GUIDE OFF at the autoguider interface 9 1 6 Wavelength Calibration It is necessary to intersperse sky observations with comparison lamp observations for wavelength calibration Because of the flexure of ISIS it is necessary to do this rather more often than with for instance the IDS on the INT For observers who need high wavelength accuracy for instance for absolute radial velocity measurements of stars it is advisable to take comparison lamp exposures about every 15 minutes For observers who wish to measure less precise radial velocities for instance in most extragalactic systems or line ratios then comparison lamp exposures every hour should suffice Separate comparison lamp exposures are defini
26. F fo a s aR pes eaten 1 k gt hs bat ye p A Jr KORINE ei ie NA acts k a oe 2 zi Paes yA iogh riia om 4 s wets sai s om x s 4 gE A EREN or q a ae YA oe Wa FIT E Jo A Etx s E h i he oe if d p Pa S heeri x Da it es Ear ot gt CE aii AE o Fa gh tgs Wa j A J t BF EE Erepta KA N r E A E A g a gt aE a Me r a bee e Ji aa be y 500f l RED CAMERA RED PEE ND amp COLOUR F 0 S SHUTTER COLLIMATORS 1650f 1 f11 FAINT OBJECT SPECTROGRAPH ISIS SPECTROGRAPH 4 2M W H T CASSEGRAIN INSTRUMENT Figure 3 Exploded view of the optical components of ISIS and FOS 0 showing the light paths through the components INSTRUMENTS ISIS Users Manual Table 2 The General and Polarimetry Dekker Slides General dekker Polarimetry dekker position 1 2 arcsec hole Right half of shit clear 20 arcsec slot Left half of slit clear Two 20 arcsec slots 100 arcsec apart Comb 9 arcsec holes 13 5 arcsec gaps 1 2 arcsec occulting bar in 20 arcsec slot Comb 4 5 arcsec holes 13 5 arcsec gaps Clear Comb as position 4 but offset by 9 arcsec Clear 3 hole comb Clear 5 hole wide comb on right half of slit Clear Clear must be increased Full details of the Savart plate are given in The ISIS spectropolarimetry users manual e A polaroid filter located in the FCP tray This is used when full spatial coverage is required and it is therefore impossible to use the dekkers
27. Manual 13 1 10GUIWIND 129 13 1 11SHUT DOWN 129 13 1 I2S5TARI2UP 130 13 1 13STATS 130 13 1 14STEMP 130 13 1 I5TEMP 130 13 2 DMS commands 130 13 2 1 IMAGES 130 13 2 2 NET 130 13 2 3 7REGS 131 13 2 4 JIS 131 13 2 5 CALC SDC 131 13 2 6 CLO 131 13 2 7 CRECALL 131 13 2 8 DEV 132 13 2 9 DEV gt STK 132 13 2 10 E STK 132 13 2 JIERUN 132 13 2 12E5D 132 13 2 I3FOCUS 132 13 2 14FOCUS LEFT 133 13 2 15FOCUS RIGHT 133 13 2 16FOCUS SET 133 13 2 I7FRECALL 133 13 2 18 GET FILE 133 13 2 19GET SDC ARRAY 133 13 2 20GR
28. Manual 5 distortion corrections can be stored on the DMS disk with PUT SDC ARRAY and recalled with GET SDC ARRAY After recalling an s distortion correction it is necessary to load and enable it as described above Unlike the first generation IPCS on the INT the s distortion correction is a digital process and no tweaking is necessary or possible 8 4 3 Collimator Focus As with the CCD detectors the final focus is achieved by moving the ISIS collimator and deter mined by using the remotely operated Hartmann shutters Again two methods of determining the Hartmann shifts are provided The collimator position can be set from the ICL interface by typing BCOLL lt position gt where the position is in the range 0 52000 If a dichroic or the flat mirror are in use the spectrograph works best with the collimator near 8000 if the folding prism is in use the collimator should be near 30000 If focus is obtained far from these values it will be necessary to move the image tube in the solenoid to bring the focus near to its nominal value This adjustment should only be attempted by RGO technical staff 8 4 4 Hartmann test using the DMS The focus should be determined with a grating setting and data format appropriate for the observations of the coming night Set the slit width and dekker with SLIT 100 DEKKER 6 A comparison lamp usually the Copper Argon lamp is used for the focus The neutral den sity filters should be s
29. Part VI In this section some abbreviations set up as Defstrings under ICL are used If in doubt about a particular function please refer to Part VI 10 1 Starting Up Create a DECTERM window on the observing VaxStation usually LPV52 and login as OBSERVER Now type LPVF and login to LPVF the VAX 4000 with the same username and password Read the news and the see the diskspace available on the datadisk displayed Type ICL to start the observing system Answer the prompts the MIMIC displays are usually put on LPVS2 As the MIMIC screens fill with mechanism positions and settings check for any bad status colours The colour coding is as follows Green set ok Blue mechanism moving Red error status White not in use During 3pm handover tests SA or observer should check for bad status and move some mechanisms in ISIS A amp G Box Autoguider and AuxPort if being used Also SETUP and WINDOW all the CCDs to be used and take quick arc or test exposures on ISIS FOS AuxPort to check optical paths are clear and data flow to the DMS is ok The Duty Tech will test the Telescope and jointly you should fill in the handover log 10 2 Taking Data the Data Acquisition System A typical command specifies a channel RED BLUE FOS or AUX an exposure time t sec a title an observation type obstype e g ARC BIAS TARGET etc and sometimes the number num of the output file in a scratch area T
30. always point towards the centre of the spectrograph The writing on the grating should be the right way up if it is in the red cell and upside down if it is in the blue cell The grating should be placed in the cell ensuring that it is properly seated The toggle switch should then be moved to the up position the clamps will come on If the clamps release immediately after coming on then the erating is not properly seated After the change is completed the user should press the return key at the ICL interface The erating doors will then be locked provided that they are closed correctly The user should then type in the name of the grating loaded in response to the question The ISIS database will then be updated and the name of the grating loaded should appear on the mimic It is important that the correct grating identification is loaded in the database otherwise the procedure CENWAVE will not work correctly Users should never rely on the information contained in the database nor that on the whiteboard in the control room being correct when they first take over the system The database could be incorrect if a different version of the software has been in use as different versions of the software have separate databases The only way to check that the correct grating is loaded is to run the change procedure open the grating door and look 8 2 2 Changing Filters in the Main A amp G box slides The main neutral density and colour filters
31. are held in two 5 position slides in the lower section of the A amp G box To change a filter within these slides the filter should already be mounted in a holder which can be obtained from RGO technical staff 47 SETUP PROCEDURES ISIS Users Manual To access one of the filter slides the slide to be accessed should be moved to position zero out of the beam and the other slide should be moved into the beam For instance to access a filter in the COLOUR slide type MAINFILTC OUT MAINFILTND 4 The access door on the A amp G Box can then be unlocked with AGACCESS This command will unlock the access door and will not return control to ICL until the door is locked again The door is on the lower half of the A amp G box and has a shiny metal latch which can be opened manually To remove the filter slide from the drive shaft a 3mm Allen key will be required With the access door open an Allen screw can be seen in the centre of a rectangular latch which holds the filter slide in place This screw should be removed and the rectangular latch can be swung aside to allow the filter slide to be withdrawn from the A amp G unit The filter holders can then be interchanged using the same Allen key The slide can then be inserted the latch and Allen screw replaced The access door can then be closed and latched The AGACCESS procedure should then return an ICL prompt and the interlocks should then be released However the microswitch w
32. arms of ISIS by 45 folding mirrors or prisms on the optical axis of the telescope and at the levels of the respective collimators The folding mirror for the blue arm can be replaced by one of a range of dichroic filters which reflects blue light and transmits red light allowing simultaneous use of the blue arm of ISIS with either the red arm or FOS IL 2 2 Polarisation optics There are four optical components immediately above the dekker slide and immediately below the slit assembly which are used exclusively for polarimetric observations The principles behind spectropolarimetric observing and the ISIS FOS II system are described in detail in The ISIS Spectropolarimetry Users manual by J Tinbergen and R G M Rutten Briefly the polarisation optics consist of e A quarterwave plate at present borrowed from the People s Photometer effective over the wavelength range 3000 11000 A which can be inserted into the beam set to any position angle or rotated continuously at a speed of several Hz The quarterwave plate converts circular into linear polarisation so that the Savart plate linear beamsplitting polariser can detect its presence Rotating the quarterwave plate rotates the linear polarisation striking the Savart plate e A halfwave plate 40mm diameter which can similarly be set to any angle or rotated continuously Rotating the halfwave plate through n degrees results is a rotation of 2n degrees of the pola
33. being thinned has a higher Quantum Efficiency QE than the EEV and GEC CCDs particularly at blue wavelengths At far red wavelengths gt 8000A it does suffer from a degree of fringing which causes a modulation of sensitivity with amplitude lt 5 which is very dependent on grating position When using a thinned CCD at red wavelengths it is vital 32 ISIS Users Manual DETECTORS Figure 17 Quantum Efficiency of the CCD types available on the ISIS and FOS II spectrographs to obtain and use flatfields taken at precisely the same grating angle at the target observations 5 The CCD IPCS Detector 5 1 Scientific Description The photon counting detector available on the blue arm of the ISIS spectrograph is the CCD IPCS It is fully described in The PCS I Users Manual by J S B Dick The CCD IPCS provides true photon counting with no readout noise but has an important limit on the maximum photon count rate for a linear response The present version was rebuilt in June 1990 It has an 520 photocathode a 4 stage EMI intensifier image tube with phosphors at the last stage and as back end detector the rebuilt version has a thinned GEC CCD This latter is slightly smaller than the original an RCA CCD so that slightly less spectrum is accommodated The back end CCD has 22um square pixels which can be subdivided into 2 4 or 8 sub pixels in spectral or spatial directions However there is an internal demagnification so that e
34. by 200 pixels 13 2 23 LOAD SDC Transfers an S distortion correction from the DMS to the IPCS Image Processing Chassis Format LOAD SDC 13 2 24 PUT FILE Transfers data from the top item of the DMS stack to a named file on the DMS disc Format PUT FILE lt filename gt Example PUT FILE GECO1 Comments Transfers data to a named file which already exists Files and their dimensions can be listed on the terminal with 7IMAGES The stack area must have the same dimensions as the named file the stack area dimensions can be listed with IS 13 2 25 PUT SDC ARRAY Stores an S distortion correction on the DMS disc Format PUT SDC ARRAY Comments Stores an distortion correction on disc and also outputs details of the correction to the terminal 13 2 26 RECOVER Initialises the DMS display Format RECOVER Synonym START DISPLAY 134 ISIS Users Manual COMMAND LISTS Comments This can be used if the display hangs up or if the lookup table or cursor position appear to be corrupted It can sometimes but not usually recover from the Opal board crash when the display screen goes blue It does not affect the data 13 2 27 RECOVER DATA To ensure that data stored in the DMS is ok after a hardware reset Format RECOVER DATA Comments After a hardware reset of the DMS this procedure will ask the user if valid data is present in the three DMS image buffers FOS EEV and IPCS and if it is will display that data on the D
35. chips contained in Oxford Instruments cryostats the cryostats are painted bright red New chips and types of chips are frequently brought into use but at the time of writing the main chips in use at the WHT are GEC P8603 EEV P88300 and Tek 1024 The properties of these and the next generation of CCD chips the EEV P88500 are tabulated below New types of chips will be announced in Gemini as they become available The Oxford Instruments cryostats contain liquid nitrogen and the CCDs are mounted on a heated copper block By controlling the current into the heating elements and by sensing the chip temperature with a platinum resistor it is possible to maintain the CCD temperature at a preset value to an accuracy of about 0 1 C The value of this preset temperature depends upon the CCD and typical values for the CCD types are listed in the table below The FOS II CCD is mounted differently in that the liquid nitrogen reservoir is much further from the CCD and is connected to by a copper cold finger e A preamplifier box usually painted blue which is mounted on the side of the cryostat e The compact CCD controller designed by NFRA Dwingeloo and described in detail by J D Bregman and A Doorduin in Proc S P LE volume 627 page 616 1986 and by J D Bregman and N R Waltham in Proceedings of the ESO OHP workshop on The Opti misation of the use of CCD Detectors in Astronomy p127 1986 and which is mounted in one of the electro
36. command until the edges of the slit jaws are sharpest 8 Note the new value on the whiteboard 9 TURN THE TV OFF AND RETURN THE OVERRIDE SWITCH TO NOR MAL STATUS Failure to do this could result in the destruction of a TV camera Note that the correct value of TV focus for direct viewing i e with the ACQCOMP mirror in is very different from that for slit viewing The telescope should not normally be focussed on the direct image when using ISIS or FOS However TV focus will be approximately the same for the two different scales when the slit viewing optics are in The normal slit viewing mode is at a scale of 4 5 arcsec mm 66 ISIS Users Manual OBSERVING PROCEDURES 9 1 2 Instrument Calibration Data The standard observing mode with ISIS is to observe with one or more CCDs Decisions which have to be made before the beginning of an observing run include e The grating or gratings to be used and the central wavelengths they will be used at e The dichroic to be used if both arms are required Plots of the reflection and transmission curves of the mounted dichroics should be available in a folder in the control room e The size of the data window The ISIS slit illuminates about 700 pixels on the spatial direction on an EEV CCD slightly less on the Tektronix CCD Windowing the chip saves readout time and observers should not normally use more pixels than the slit illuminates Many observers particularly those interested
37. fibres is orthogonal to the optical axis of the spectrograph A prism is used to make both optical axes coincide This prism is mounted on a holder The incoming light from the fibres crosses 62 ISIS Users Manual SETUP PROCEDURES the holder through two 2mm wide slots Several clips fix the prism to the holder The slit is mounted onto a plate three kinematic seats allow the fibre slit to be aligned with the prism The prism slit system is mounted onto a rotating plate which permits alignment between the slit image and the detector s spatial direction Another plate placed onto kinematic seats holds the prism slit mounting and allows it to be aligned with the optical axis of the spectrograph Finally all these mechanisms are supported by the standard mounting to the ISIS slits but with two peculiarities On the one hand a stop piece is employed to centre the slit image in the detector On the other two pieces to clamp the protective cover of the slit are supported by the plate The bundle exits the mechanical structure of the spectrograph through a window opened in the ISIS box Figure 9 Two portable plates were manufactured to adjust the bundle to the window THe plates are joint to the bundle through a cable gland of type GEWISS GW52006 8 5 2 Fibre slit alignment Two steps are required in order to align the fibre optic system First the slit and the prism are aligned together and next the slit prism subset is aligned
38. focal plane end of one of the fibres at one slit edge the output light is reflected by the collimator mirror This beam will be reflected by the flat mirror and returned onto the collimator mirror which will focus it if the alignment is good onto the opposite edge on the slit from where the light started 8 5 3 Guide fibre bundle focussing In order to focus the guiding system the ends of the bundles must be focused onto the CCD camera This can be done during daylight and it requires two people speaking to each other one of them must be in the control room viewing the bundles image on the screen while the other remains in the dome to perform the focusing The bundles are mounted on an interface which connects them to the CCD camera After illuminating the aperture plate bundles ends the image of the camera bundles ends can be see on the TV monitor in the control room In the dome the micrometric positioning screw can be adjusted until the TV image appears focused The amount of incoming light onto the bundles must be controlled in order to avoid saturation or fine detail loss This focusing method is simple and fairly accurate However if better precision is required a transparency with a fringe pattern can be illuminated behind the coherent bundle the image of this can be focussed accurately on the TV screen 8 5 4 Spectrograph set up The spectrograph setup procedures for long slit observing are described above The plane and ti
39. frequently indeed for many observers one calibration exposure at the beginning of each night will suffice Apart from this the calibration exposures required are the same as are required for ISIS CCD observing Data acquisition procedures are again the same as for ISIS observing except that it is much more likely that the observer will seek to observe objects which cannot be seen on the slit viewing TV with FOS Such objects should be acquired by the BLIND_OFFSET procedure os the Telescope Control Computer outlined in The WHT Users Manual The approximate positions of the first and second order spectra on the CCD are shown in Figure 8 There are two main observing modes with 20 arcsec dekker both orders and long slit with the FCP tray field lens inserted The anamorphotic field lens improves illumination of the grating without it light spills over the edge of the grating and illumination on the detector is reduced at each end of the slit It also incorporates a GG495 yellow filter which blots out the second order The field lens is inserted with ICL command FIELD_LENS During routine FOS observing this and the dekker are the only components that need moving Exposures longer than say half an hour should be split to allow identification of spurious features due to cosmic rays The efficiency of the system atmosphere at zenith telescope instrument detector is shown in Fig 16 In first order it peaks at 17 at 7000
40. instrumentation are of far greater importance when studying short timescale variability than when studying long timescale variability Therefore this section is primarily aimed at observers studying objects which vary on a timescale of seconds or minutes However many of the principles discussed are simply means of maximising observing efficiency and should therefore be of interest to all observers 9 3 1 Sources of dead time Dead time can be defined as the interval between exposures during which the detector is not actually detecting photons from an object There are numerous sources of dead time both 76 ISIS Users Manual OBSERVING PROCEDURES instrumental and human In the following discussion we shall restrict ourselves to the instru mental but it should be emphasized that a great deal can be gained by simply having a carefully prepared observing programme The following list details the most common sources of dead time and the amount of time they each contribute to the total figure The list is in chronological order from typing the exposure command to receiving the data on disk Typing commands This is the most obvious form of dead time and occurs due to the inevitable delay involved in typing a RUN command and its associated parameters Depending on typing speed this can take up to 10 seconds This may sound pedantic but the use of the MULTRUN command see section 9 3 2 actually represents one of the largest and mo
41. is finished 8 2 1 Changing Gratings Although it is possible to change gratings without the ICL interface running this procedure is rather involved and should only be performed with the advice of technical staff With the ICL interface running the procedure is fairly straightforward The grating angle or angles must first be moved to the change position in this position the erating cell is parallel to the back of the spectrograph and to the access doors and the gratings can be removed from their cells and lifted straight through the access doors An interlock prevents the grating cells being unclamped with the gratings at any other angle The procedure for changing gratings is invoked by typing CHANGE at the ICL interface A list of items which can be changed with this procedure is given the relevant grating should be selected The user will then be offered access to the spectrograph if 46 ISIS Users Manual SETUP PROCEDURES the response to this question is YES then the selected grating will be moved to the change position grating angle 35000 and both grating doors will be unlocked It is now possible to open the grating doors which are located on the face of the spectrograph opposite the long arm The door for the blue grating is in the upper left hand corner of this face and the door for the red grating is in the lower right hand corner When the door is opened the grating should lie approximately parallel to t
42. is in the beam Format SLITUNIT lt position gt Example SLIT_UNIT LONG SLIT Synonyms LSLIT SLIT_UNIT LONG_SLIT MSLIT SLIT_UNIT MSLIT_FIBRES Comments Moves stops or initialises the slit unit or reprograms the SMDM which controls it Valid parameters are a position in the range 0 to 1 LONG_SLIT 1 MSLIT_FIBRES 0 STOP INIT and REPROGRAM The last option should only be used in exceptional circumstances 11 4 FOS Commands 11 4 1 FIFOCUS Returns the status of the FOS Focus and updates the MIMIC Format FIFOCUS Synonym FIF Comments AT PRESENT THE FOS MIMIC DOES NOT WORK 11 4 2 FIGLOBAL Returns status of all FOS mechanisms Format FIGLOBAL Synonym FIG Comments AT PRESENT THE FOS MIMIC DOES NOT WORK 11 4 3 FIHARTMANN Returns status of the FOS Hartmann shutters Format FIHARTMANN Synonym FIHA COMMAND LISTS ISIS Users Manual Comments AT PRESENT THE FOS MIMIC DOES NOT WORK 11 4 4 FIHTILT Returns status of the FOS Platform Horizontal Tilt Format FIHTILT Synonym FIHT Comments AT PRESENT THE FOS MIMIC DOES NOT WORK 11 4 5 FIVTILT Returns status of the FOS Platform Vertical Tilt Format FIVTILT Synonym FIVT Comments AT PRESENT THE FOS MIMIC DOES NOT WORK 11 4 6 FMFOCUS Controls the FOS Focus Format FMFOCUS lt focusvalue gt Example FMFOCUS 227 Synonym FMF Units The units are units of 4 microns Range 0 to 511 11 4 7 FMHARTMANN Controls the
43. of the CCD If it is due to a continuum source the pupil image will be smeared in wavelength and may be difficult to recognise as such The intensity of this ghost is at the level of 1074 of the primary source e A grating ghost caused by reflection between the grating and the aspheric plate of the camera when using grating R158R in the red camera The ghosts images of all wavelengths add so this ghost can appear quite strong e An in focus ghost caused by a reflection from the folding prism in either the red arm of ISIS or in FOS e Rowland ghosts which are caused by periodic errors in the ruling of the gratings These appear around strong emission or comparison lines as satellite lines at the level of gt 107 of the primary 3 4 Wood s Anomalies in the ISIS gratings Wood s anomalies are discussed in detail by P G Murdin in ING La Palma Technical Note No 76 in the context of INT IDS gratings and a summary of the physical explanation for Wood s anomaly is repeated here Consider a reflection grating which produces a range of diffracted light in successive orders diffracted away from the normal In some order at some critical wavelength the diffracted light lies in the plane of the grating It is not possible for light beyond this point to be diffracted behind the glass of the grating The power which would be sent into the forbidden region is redistributed back into the allowed orders The power appears as an addition to the
44. of the o and e exit beams of the calcite plate All instrumental conditions grating parameters filters dichroics Dekker slit etc must be the same in both exposures image centering on the slit is the most difficult to control in this respect The derivation of Stokes parameters from the recorded spectra is presented below We factorise the conversion constant for input flux to detector signal into a polarization dependent time independent part G and a time dependent polarization independent part F Gi and G refer to the o and e spectra on a single frame they include grating efficiencies and reflection coefficients of mirrors and the sensitivity of the pixel considered to the polarized light striking it Fo and F45 refer to the two separate frames halfwave at 0 and 45 degrees and include atmo spheric transmission seeing image wander and variations in shutter timing I and Q refer to total and polarized flux input and thei refer to signals recorded by the detector Po Q l is the Q component of the degree of polarization 82 ISIS Users Manual OBSERVING PROCEDURES In this notation we obtain ion 30 Q gt Gy Fo inn HI Q Gi gt Fo us 3079 gt Gy gt Fas i45 1 5 1 Q Gy Fas To derive Stokes parameters from these spectra first divide the o and e ray spectra in each frame to take out the scaling factors F Dividing these ratios again cancels the G factors The Q Stokes parameter in degr
45. provide a colli mated beam of 150mm diameter The coating material on the collimators is optimised for the wavelength range of the particular camera and is silver with a reflective stack overcoat for the red collimator and aluminium for the blue camera As with most astronomical grating spectrographs an image of the pupil is formed on the erating in order to minimise the grating size required The collimators are remotely driven by stepper motors and their position is encoded by the ASL bridge which is also used to encode the slit width The spectrograph arms are normally focussed by driving the collimators and the collimator position is repeatable to better than 10 10 ISIS Users Manual INSTRUMENTS Table 4 Properties of the ISIS gratings used blaze to collimator with the common detectors Grating Blaze ani Wavelength Pixel A Spectral range A Slit Width arcsec Clg EEV Tek IPCS EEV Tek IPCS for 504m detector R158B 3350 2949 3225 R300B 1788 1576 1720 R600B 919 809 887 R1200B 472 420 457 R2400B 224 195 215 Rissk 3318 2970 R316R 1733 1525 R600R 919 809 R1200R 472 420 um With no extra refractive components dichroics prisms Savart plate filters between the slit and the collimators the nominal focus positions for the ISIS collimators are 6000um for the blue arm and 90004m for the red arm The spectrograph should be focussed with the collimators within 3000um
46. the FOS GEC5 image buffer Format FRECALL lt filename gt Example FRECALL GECO1 Comments The file must have dimensions 400 by 590 pixels Once a file has been placed in the buffer it can be transferred to the Vax 4000 disc with KEEP FOS If the icon for this buffer is not displayed when this is done it will be necessary to run RECOVER DATA 13 2 18 GET FILE Transfers data from a named file on the DMS disc to the top of the DMS stack Format GET FILE lt filename gt Example GET FILE GECO1 Comments Files and their dimensions can be listed on the terminal with 7 IMAGES 13 2 19 GET SDC ARRAY Recalls an S distortion correction from the DMS disc Format GET SDC ARRAY Comments Recalls an distortion correction from disc and also outputs details of the cor rection to the terminal 133 COMMAND LISTS ISIS Users Manual 13 2 20 GRUN Opens an image buffer for GEC5 FOS CCD data Format GRUN Comments The buffer is 400 by 590 pixels and can be used to store data from a full frame readout 13 2 21 IRECALL Transfers data from a named file on the DMS disc and displays it in the IPCS image buffer Format IRECALL lt filename gt Example IRECALL IPCSO1 Comments The file must have dimensions 2560 by 200 pixels Once a file has been placed in the buffer it can be transferred to the Vax 4000 disc with KEEP IPCS 13 2 22 IRUN Opens an image buffer for IPCS data Format IRUN Comments The buffer is 2560
47. the refracting elements of the two cameras are coated with anti reflection coatings optimised for the respective wavelength ranges and the reflecting elements are coated with silver plus a reflective stack for the red arm and aluminium for the blue arm 2 9 Cross Dispersers Each arm has a slide for an optional cross dispersing grism although at present only the blue cross disperser has been purchased The cross disperser is a special ruling 100 lines mm fused silica grism blazed at 4400 A This will be used in conjunction prime disperser which is a Bausch and Lomb 75 lines mm grating blazed at 3um to provide complete spectral coverage from 3000 5600 A on an EEV P88300 or Tek 1024 CCD or the IPCS on the blue camera The cross dispersed mode will use orders 5 to 10 and the maximum slit length to avoid order overlap will be 30 arcsec The spectral resolving power of the cross dispersed mode is about 2200 Figure 7 shows the format of the cross dispersed spectrum superimposed on the outlines of the IPCS and a TEK 1024 CCD 2 10 The Faint Object Spectrograph FOS IT The original FOS concept for a high throughput cross dispersed spectrograph FOS I on the INT was described by Breare et al MNRAS 227 909 1987 FOS II for the WHT follows the same basic design but with a higher dispersion and is described by Allington Smith et al MNRAS 238 603 1989 In brief it covers a wavelength range from 4600 9700A in 1st order and 3
48. the slit with the APERTURE command 4 Move to the programme object by typing BLIND_OFFSET lt objectname gt Once the object is centred on the slit it is possible to begin the CCD integrations The WHT tracks well enough that it is standard procedure to begin the integrations before acquiring a guide star Integrations are started with RUN and can be the same length or different lengths If they are the same length and the frames are large then the two CCDs may be reading out into the DMS buffers simultaneously the DMS is capable of handling this although the message Reading CCD on the DMS screen may disappear after the first CCD has finished reading out although the second has not yet finished The DMS command REGS allows one to check whether the CCDs have all finished reading out 9 1 5 Acquiring guide stars Guide star acquisition is facilitated by the Guide Star Server GSS with which it is possible to predict the probe co ordinates for a star from the Hubble Space Telescope Guide Star Catalogue using software running on a Vaxstation in the La Palma cluster The catalogue itself is on two CD roms attached to this Vaxstation To run the GSS star a session on any VAX computer and type DISK USER3 LGSS GSS_INIT GSS This will invoke the GSS programme which is characterised by the prompt GSS gt The fol lowing string of commands input to the GSS programme will generate a file QUTPUT GS with a list of suitable guide st
49. which are used with the Savart plate 2 3 The slit area The slit is common to the two arms of ISIS as well as FOS The slit length is 53mm 4 arcmin and the width is continuously variable between 30 um 0 14 arcsec and 5 mm 22 6 arcsec The slit is polished and aluminised and inclined to the optical axis of the telescope at an angle of 7 5 degrees to allow viewing of the reflected image in the A amp G box TV camera The width is driven by a linear motor controlled by the ISIS 4ms microprocessor and encoded via the ASL transducer bridge which also encodes the collimators The slit unit is a two position carriage one position contains the conventional long slit and the other position is a two position cross slide containing a wide aperture which is used for mounting multi slit masks and the slit end of the ISIS fibre system This cross slide is itself remotely driven from the ISIS 4ms microprocessor Dekkers are mounted in 8 position slides which are inserted in a driven mechanism imme diately above the slit The slides are interchangeable and the procedure for changing them is described is section 8 2 3 At present there are two dekker masks one for general use and one for spectropolarimetry and they contain The long slit unit has gaps at each end and it is important to use a long slit dekker position 6 or 7 when observing and not to observe with the dekker out position 0 Ghosting is reduced considerably by use of t
50. 09 11 3 15ISIS_CONFIG 109 11 3 16ISIS_INIT 109 11 3 I7TISISMOVE 110 11 3 18ISIS_UPDATE 110 11 3 19LID 110 11 3 2 0QW_POLAR 110 11 3 21RCOLL 111 11 3 22REDGRAT 111 11 3 23REDXDISP 111 11 3 24RFILTA 112 11 33 25RFILTB 112 11 3 26RFOLD 112 11 3 27RHART 112 11 33 285LIT 112 CONTENTS ISIS Users Manual 11 3 29SLIT_DOOR 113 11 3 30SLIT_UNIT 113 11 4 FOS Commands 113 11 4 1 FIFOCUS 113 11 4 2 FIGLOBAL 113 11 4 8 FIHARTMANN 113 11 4 4 FIHTILT 114 11 4 5 FIVTILT 114 11 4 6 FMFOCUS 114 11 4 7 FMHARIMANN 114 11 4 8 FMHTILT 114 11 4 9 FMMONITOR
51. 1 23 TV SLIT 5 Selects the slit viewing position at a scale of 5 arcsec mm Format TV_SCALE_5 Comments Procedure which moves the mirrors to the SLIT VIEW position selects a scale of 5 arcsec mm and the correct value of TVFOCUS 11 1 24 TVFILT Moves the filter wheel in front of the TV camera to a named filter Format TVFILT lt filtername gt Example TVFILT R Comments Possible values are B V R CLEAR and EMPTY The TV focus must be adjusted when changing from EMPTY to one of the other positions Note that there may be an opaque mask in position EMPTY if so posi tion CLEAR should be used instead 11 1 25 TVFOCUS Sets the TV focus Format TVFOCUS lt focusvalue gt Example TVFOCUS 15000 Units Microns Range 0 to 17500 Comments To adjust the TV focus so that the TV is focussed on the slit or so that a star is in focus on the TV in direct mode 11 1 26 TVSCALE Sets the TV scale Format TVSCALE lt tvscalevalue gt Example TVSCALE 5 104 ISIS Users Manual COMMAND LISTS Comments Puts the correct focal reduction optics or no optics at all in front of the TV camera for a specified scale in arcsec mm either in slit viewing or direct mode Allowed values of the TV scale are 5 and 12 11 2 Autoguider Commands 11 2 1 ACQINT Changes the Autoguider integration time when acquiring Format ACQINT lt integrationtime gt Example ACQINT 4000 Units Milliseconds Comments Equivalent to lt inte
52. 11 7 O N 0 000 0 000 55 13 40 02 89 28 37 51 7 400 N 0 182 88 770 10 Programme Objects Fibre Hole R A DEC X Y 56 13 40 09 74 28 27 15 57 13 40 16 89 28 26 38 58 13 40 00 04 28 30 00 59 13 39 52 17 28 28 39 60 13 39 46 73 28 27 06 61 13 39 46 80 28 26 29 62 13 39 51 01 28 31 00 63 13 40 23 21 28 34 13 64 13 40 19 41 28 32 50 8 43 48 276 22 110 65 13 40 19 23 28 31 42 9 46 47 785 7 049 x HOLE FIBRE CROSS CHECK x Plate Label M3 WHT AUX APLATE Date 16 11 1992 GS2 20 173 52 414 X2 41 120 60 457 X3 8 314 15 864 X5 31 311 33 904 X6 47 175 54 508 X7 46 949 62 803 X9 34 730 2 561 3 8 3 2 4 O 4 3 26 59 350 40 438 8 9 157 APPENDICES ISIS Users Manual 158 Comments WAA AA WAA AA Fibre Bundle 10 20 30 40 50 O1 Ti 21 31i 41 O0O2 12 22 32 42 O03 13 23 33 43 04 14 24 34 44 05 I15 25 35 45 06 16 26 36 46 O7 17 27 37 47 O8 18 28 38 48 O9
53. 11Blind Offsets 97 10 11 15mall Offsets 97 10 11 2DataTFiles 98 10 12S5hutdown 99 VI COMMAND LISTS 100 11 Commands entered at the ICL interface 100 11 1 A amp G Box Commands 100 11 1 1 AGACCESS 100 11 1 2 AGBARCODES 100 11 1 3 AGINIT 100 11 1 4 AGMIRROR 101 11 1 5 AGUPDATE 101 11 1 6 ARCOFF 101 11 1 7 AUTOFILT 101 11 1 8 AUTOFOCUS 101 11 1 9 AUTORADIAL 101 11 1 10 AUTOTHETA 102 11 1 11 AUXFILTER 102 11 1 12COMPFILTA 102 11 I I3COMPFILTTB 102 11 1 14COMPLAMPS 102 IV ISIS Users Manual CONTENTS IU JI JI5SCOMPND 103 11 1 16CUARON 103 11 1 17CUNEON 103 11 1 18 MAINFILTC 103 11 1 19MAINFILTND 103 11 1
54. 2 beams 330 1100nm actually a Savart plate which equalizes focus for both polarisations The calcite is located immediately below the slit and gives two beams which are both 100 polarised but orthogonally the o and e ray The relative intensity of these beams depends on the polarisation vector size and orientation of the incoming 50 ISIS Users Manual SETUP PROCEDURES beam ii Polaroid HNP B 300 800 nm approx for when full spatial detail is mandatory For linear spectropolarimetry after setting up the spectrograph and acquiring the object one only needs to move the halfwave plate into the beam at a specific angle move the calcite slab into the beam and select the appropriate dekker mask The calcite slab affects the spectrograph focus which is corrected by adding 9200 units to the standard collimator positions The slit view TV camera looks through the halfwave plate which causes the TV image to be highly vignetted and also affects the TV focus The optimal TV focus at scale 5 is about 1500 units less than the standard setting without the halfwave plate If your object is faint it will be necessary to remove the halfwave plates and the dekker in order to put the object on the slit The instrumental setup for circular spectropolarimetry is similar but the quarterwave plate must be used in stead of the halfwave plate For further details see Section 9 5 of this manual and the ISIS Spectropolarimetry Users Manual 8 3
55. 20TV_DIRECT_12 103 11 1 21 TV DIRECT 5 104 11 1 22 TV SLIT 12 104 11 1 23TVSLIT5 104 11 1 24TVFILT 104 11 1 25TVFOCUS 104 11 1 26TVSCALE 104 11 2 AutoguiderCommands 105 11 2 1 ACQINT 105 11 2 2 FIELD 105 11 2 3 FOLLOW 105 11 2 4 GUNNT 105 11 3 ISISCommands 105 11 3 1 ANAMORPHOTIC 105 11 3 2 BCOLL 106 11 3 3 BLUEGRAT 106 11 3 4 BLUEXDISP 106 11 3 5 BFILTA 106 11 3 6 BFHILTB 107 11 3 7 BFOLD 107 11 3 8 BHART 107 11 3 9 CENWAVE 107 11L 3 10CHANGE 2 108 11 3 11DEKKER 108 11 3 12FCP 108 11 3 13GRATING_DOOR 108 11 3 44HW_POLAR 1
56. 500 4900A in 2nd order with dispersions of 8 7 and 4 3A per CCD pixel respectively The optical design of FOS II is due to S P Worswick and is based upon the design by C G Wynne for FOS I The optical design is based upon an F 1 4 Schmidt camera working without a collimator in the diverging f 11 Cassegrain beam The dispersion is provided by a 150 1 mm transmission grating blazed at 7300 A together with a cross dispersing prism The camera has an aspheric corrector plate cemented to the underside of the grism prism assembly and a silver coated spherical mirror This optical arrangement gives a dispersion of 400A mm in lst order and 200A mm in 2nd order A field flattening lens produces a flat focal plane at the detector surface The detector package is small enough to fit within the shadow of the telescope s secondary mirror 13 INSTRUMENTS BLUE GRATING ASSEMBLY BEARING PRE LOAD OPTICAL ENCODER 16 BIT e wee oat ae washa PNEUMATIC CLAMP ASSEMBLY NS BALL AND CONE eg BSS BEARING POSITIONS AND 4 CENTRE OF ROTATION STEPPING MOTOR DRIVE HROUGH WORM amp WHEEL ONE STEP FOR 01 ANGULAR MOVEMENT
57. 95 The filters available in filter wheel B are a clear position ND filters of 0 3 0 5 0 9 1 2 2 0 a BG24 colour filter and a clear position 1 6 Filters Two filter slides situated below the autoguider assembly in the on axis light path provide colour and ND filtering Each slide carries five filters in cells and the cells all carry discrete bar coding for filter identification The filter cell carrier may be removed and alternative cells fitted The filters have a maximum diameter of 85 mm The name of the filter mounted in each position may be determined using a barcode reader The neutral density filters mounted are NDO 3 NDO 9 ND1 2 ND1 8 ND3 0 and the colour filters mounted are UG1 BG38 GG495 RG630 WG320 1 7 Polarisation calibration For polarisation module calibration a special double cell containing two dichroic polymer filters i e Polaroid with their polarising axes orthogonal to each other may be fitted to the carrier Further cells containing either a calcite or quartz crystal may be used for broader wavelength coverage There may be some spatial problems if the required crystal thickness is too great This also applies to the use of two parallel silica plates for partial polarisation 1 8 Auxiliary focus It is possible to change rapidly from long slit spectroscopy to imaging at the Cassegrain focus by inserting a diagonal flat into the light path in the A amp G unit sending the light to a CCD camera mounted at t
58. A and Dec or X and Y until the semi coherent bundles illumination patterns are well centred When the seeing is good 1 5 this centering is easy to obtain as the 7 central fibres of each bundle must appear uniformly illuminated If the seeing is between 1 5 and 4 the centering can be performed by means of the uniform illumination of the external ring in each bundle If the seeing is worse the centering becomes more difficult although basically it still relies on an uniform illumination of the fibres in the semi coherent bundles e If an optimal adjustment has not been obtained for both semi coherent bundles the tele scope rotator must be moved until a better centering of the three guide stars is achieved e Finally when the field has been properly acquired guiding can begin on the TV image of the star on the coherent bundle with the GUIDE or IGUIDE functions of the TV system and Autoguiding can be started with the TCS command TVGUIDE ON The first time this is done it is necessary to verify that the X and Y handset functions of the TCS drive the star along the correct X and Y axes of the TV image If they do not then some adjustment will have to be made Field reversals can be corrected with the Scan Reverse switches on the Westinghouse control panel on the control desk and the angle of the coherent fibre bundle can be rotated at the TV end It is only necessary to set this angle to an accuracy of about 5 9 6 4 Calibrati
59. BORT for a complete stop 11 5 17 MULTRUN Takes a sequence of exposures all of the same exposure time Format MULTRUN lt channel gt lt nruns gt lt time gt L lt title gt Channel The name of the CCD data acquisition channel to be used Time The exposure time in seconds Example MULTRUN RED 25 60 AX DRACO 25 exposures Comments There also commands MULTARC MULTFLAT MULTBIAS MULTDARK which have sim ilar formats except that MULTBIAS does not require a time 11 5 18 NEWTIME Change the exposure time of an exposure in progress Format NEWTIME lt channel gt lt time gt Example NEWTIME RED 1200 Channel The name of the CCD data acquisition channel to be used Time The exposure time in seconds Comments The system will not accept an exposure time less than the current exposed time 11 5 19 PAUSE Pauses a CCD exposure Format PAUSE lt channel gt Channel The name of the CCD data acquisition channel to be used Examples PAUSE RED Comments This command suspends the current CCD exposure closing the CCD shutter The command will be aborted if no exposure is in progress 119 COMMAND LISTS ISIS Users Manual 11 5 20 PROMOTE Promotes a scratch datafile to the main data area on the system computer assigning it a run number in the process Format PROMOTE lt filenum gt Filenum The number of the scratch file Examples PROMOTE 5 Comments The system will report the allocated run number H
60. CS are given in The IPCS Users Manual by J S B Dick and these instructions should be obeyed exactly to ensure safety for the IPCS image intensifier Ensure also that the raw video display in the control room is working and that the Panic Button closes the shutter immediately it has been pressed The ICL commands to open and close the blue arm shutter when the IPCS is on the spec trograph are IPCSOPEN or IPO to open the shutter and IPCSCLOSE or IPC to close the shutter If the Panic Button is pressed to close the shutter then IPCSCLOSE must be issued before attempting to open the shutter again The IPCS is easily damaged by bright light so care must be taken when setting up and observing Particular care is necessary when using the tungsten lamp for the rotation and scan correction setup as this lamp is very bright A substantial amount of neutral density is required to reduce the intensity of the lamp to a safe level and it is recommended that users begin with at least ND4 2 COMPFILTA ND3 0 and COMPFILTB ND1 2 in the beam and reduce it slowly if necessary 8 4 1 Camera Head Rotation The camera head of the IPCS should be rotated until the spectral direction is aligned with the camera pixel direction of the IPCS At present the camera head mechanism is unreliable and this adjustment should only be done by RGO technical staff who should then disconnect the power to the motor which drives the camera head to
61. D shutter appears to stick Issuing the UNJAM command may free the shutter this can be checked with the OPEN and CLOSE commands 13 3 22 VHT CONFIG Displays the virtual head table configuration of a CCD controller Format Comments VHT CONFIG This is actually two commands VHT selects the Virtual Head Table and CON FIG displays the configuration This command is useful because along with the windowing and binning information it also displays the readout speed Quick or Standard selected This information is not available on the Vax Mimic The correct Virtual head must be selected with OV or 1V before this command is issued 139 COMMAND LISTS ISIS Users Manual 13 4 The Engineering MIMIC The Engineering MIMIC can be used to display the status of ISIS and the A amp G box in rather more detail than is provided by the Vax MIMIC Command can also be issued to move mech anisms in and device which is on the network most commonly ISIS and the A amp G box These commands consist of a Mnemonic which identifies the device to be operated on a number which identifies what operation is to be carried out on the mechanism move initialise status request or reprogram and if appropriate i e in the case of moving a mechanism a demanded position in parentheses Details of these commands and how to issue them from the Engineering MIMIC terminal are given in The Engineering Mimic a loosely bound document with a pale green cover
62. DM which con trols the dekker slide Valid parameters are a dekker position in the range 0 to 8 a named dekker as listed on the MIMIC display OUT STOP INIT and RE PROGRAM The last option should only be used in exceptional circumstances 11 3 12 FCP Moves the slide which contains the Field Lens Calcite block and Polaroid Filter Format FCP lt position gt Example FCP CALCITE Synonyms FIELD LENS FCP FIELD_LENS FIELDLENS FCP FIELD_LENS POLAROID FCP POLAROID CALCITE FCP POLAROID FCP_CLEAR FCP CLEAR FCPCLEAR FCP CLEAR Range 0 to 3 or named positions Comments Moves stops or initialises the Field Lens Calcite and Polaroid slide or reprograms the SMDM which controls it Valid parameters are a position in the range 0 to 3 FIELD_LENS 2 CALCITE 3 POLAROID 1 OUT 0 STOP INIT and REPROGRAM The last option should only be used in exceptional circumstances 11 3 13 GRATING_DOOR Locks or unlocks the grating access doors 108 ISIS Users Manual COMMAND LISTS Format GRATING DOOR lt position gt Example GRATING_DOOR OPEN Comments This is an interactive procedure to unlock and lock both grating doors Valid parameters are OPEN and CLOSE LOCK and UNLOCK GRATING_DOOR OPEN or GRATING_DOOR UNLOCK will unlock the doors and invite you to open them manually GRATING_DOOR CLOSE or GRATING_DOOR LOCK will invite you to check that they are closed and lock them when you have v
63. EFT_IN 2 RIGHT_IN 1 and BOTH_OUT 0 11 3 9 CENWAVE Sets a grating to give a specified central wavelength on the detector Format CENWAVE lt gratingname gt lt wavelength gt Example CENWAVE RED 6563 Synonym ISIS_CENWAVE Units wavelength is specified in Angstroms Comments A procedure to work out the grating angle required to give a given central wave length on the detector and then to set the grating angle to that wavelength The grating name which must be RED or BLUE and the required central wave length in Angstroms are specified on the command line The grove spacing on 107 COMMAND LISTS ISIS Users Manual the grating must be correct in the database this can be checked on the mimic screen 11 3 10 CHANGE An interactive procedure to allow the user to change gratings or filters and to update the database Format CHANGE Comments The change procedure allows the user to change gratings or filters It prompts the user for the item that requires changing then moves that mechanism to its change position moves the dekker to the change position if a filter is to be changed and unlocks the relevant door After the change has been made it locks the door and updates the database 11 3 11 DEKKER Moves the Dekker slide Format DEKKER lt position gt Examples DEKKER 2 DEKKER BARRED Range 0 to 8 or named dekkers Comments Moves stops or initialises the dekker slide or reprograms the SM
64. FOS Hartmann shutters Format FMHARTMANN lt position gt Example FMHARTMANN LEFT Synonym FMHA Comments Valid parameters are LEFT left shutter in beam RIGHT right shutter in beam and CLEAR both shutters out of beam 11 4 8 FMHTILT Controls the FOS Platform Horizontal Tilt Format FMHTILT lt value gt Example FMHTILT 199 Synonym FMHT Units Each unit subtends a displacement of 4 microns across the diameter of the plat form Range 0 to 511 114 ISIS Users Manual COMMAND LISTS 11 4 9 FMMONITOR Turns FOS monitor mode on or off Format FMMONITOR lt onoroff gt Example FMMONITOR ON Synonym FMM Comments Valid parameters are ON and OFF 11 4 10 FMRESET Software reset of the FOS 4ms Format FMRESET Synonym FMR 11 4 11 FMVTILT Controls the FOS Platform vertical Tilt Format FMVTILT lt value gt Example FMVTILT 199 Synonym FMVT Units Each unit subtends a displacement of 4 microns across the diameter of the plat form Range 0 to 511 11 4 12 FSGLOBAL Stops all FOS mechanisms Format FSGLOBAL Synonym FSG 11 5 Data Taking Commands CCD Detectors CCD data are taken and stored with the Data Acquisition System which provides a large range of commands for taking data of various types and storing the data with or without the header information in various forms on the Vax discs A description of the system together with a complete list of the commands is given in Will
65. G 4 a a Figure 21 Transmission as a function of w 150 kaa e ps amp APPENDICES ISIS Users Manual D Details of Neutral Density Filters This appendix gives the actual values of the densities of ND filters in both the star beam MAINFILTND and in the calibration lamp beam COMPFILTA B Table 11 ND values of ISIS FOS Main Beam Filters 85mm diameter Nominal ND 0 3 0 6 A A OO D gt J Qa Qna n Qn Oa Or a e Ww OO Table 12 Neutral Densities of ISIS FOS Calibration Beam Filters 75mm diam Nominal ND A A Ct ON r 2 WNW WwW Ww WH 0 0 0 0 0 0 0 0 0 IND 152 ISIS Users Manual APPENDICES E Details of the La Palma Sky E 1 Sky Brightness and Spectrum Typical sky brightness at La Palma in mags per square arcsec are giv
66. G unit 2 2 Geometry of the Autoguider field 4 3 ISIS and FOS II Spectrographs 7 4 Polarimetry and slit area components 9 5 Collimator Assembly 12 6 Grating Cells 14 7 Cross Disperser orders 6 15 8 FOS spectral format 16 9 ISIS and A amp G box fibre layout 19 10 Spectral Attenuationcurves 20 11 Focal Plane Connector for the multi object bundle 20 12 Focal Ratio Degradation efficiency 21 13 Camera connector of the coherent bundle 22 14 Semi coherent bundleends 22 15 Efficiencies of the ISIS gratings 26 16 Total throughput of the FOS IIsystem 27 17 OuantumeficieneyofINGCCDSs 33 18 Schematic diagram of the WHT instrument control system 38 19 Transmission as a function of wavelength for the 6100A dichroic 148 20 Reflectivity as a function of wavelength for the 6100A dichroic 149 21 Transmission as a function of wavelength for the 7500A dichroic 150 22 Reflectivity as a function of wavelength for the 7500A dichroic 151 List of Tables 1 CCD pi
67. However for the telescope focus to be correct it is crucial that the TV camera itself is focussed correctly onto the slit TV focus does not normally change very much unless a change is made to the TV camera itself and the current value of the TV focus is normally written on the white board in the control room However if there is any doubt about the value of the TV focus it is necessary to measure this which can be done during the day 1 Obtain the key to the TV override switch from the technical staff This is normally kept out of the control room and will have to be signed for 2 Override the interlock on the slit viewing TV camera and only this camera This will allow the TV and the lights to be on at the same time 3 Put on a low level of lighting in the dome the drum lights are quite sufficient Ensure by means of a notice than nobody will switch any other lights on in the dome 4 Switch on the TV controller for the slit viewing TV and the TV system VME computer These are in the furthest of the four blue cubicles from the left hand end of the control desk 5 Ensure that the slit viewing mirror is in type AGSLIT at the ICL interface if it is not 6 Switch on the slit viewing TV camera only wait for the delay lights to go out and turn up the gain on the TV SLOWLY until the slit jaws are visible on the small TV direct monitor Watch this monitor all the time while turning up the gain 7 Adjust the TV focus with the TVFOCUS
68. Isaac Newton Group of Telescopes William Herschel Telescope ISIS USERS MANUAL Version 1 0 1993 October D Carter C R Benn R G M Rutten J M Breare P J Rudd D L King R E S Clegg V S Dhillon 5 Arribas J L Rasilla A Garcia C R Jenkins P A Charles The Isaac Newton Group of telescopes on La Palma is owned by the UK Science and Engineering Research Council and oper ated by the Royal Greenwich Observatory for the SERC in part nership with the Organisatie voor Zuiver Wetenschappelijk Onder zoek ZWO of the Netherlands the Irish National Board for Sci ence and Technology and the Dublin Institute for Advanced Studies ISIS Users Manual CONTENTS Contents I Description of the Instruments 1 1 The Cassegrain A amp G Box 1 1 1 Design of the A amp G unit l 1 2 Object acquisition 1 1 3 Slit viewing 1 1 4 Autoguider 1 1 4 1 Autoguider Geometry 3 1 5 Comparison lamps 3 16 Filters 5 1 7 Polarisation calibration 5 1 8 Auxiliary focus 5 2 ISIS and FOS II Spectrographs 6 2 1 Overall layout 2 6 2 2 Polarisation optics 2 oa 6 2 3 The slt area 8 24 Fol
69. LLIMATOR BLUE GRATING RED_GRATING The slit jaws cannot be initialised get technical help if they stick Updating the MIMIC for ISIS use ISIS_UPDATE ALL 10 7 A amp G Box Commands AGMIRROR OUT removes all mirrors e g for Hitch Hiker to operate AGCOMP moves mirror to acquisition comparison lamp position AGSLIT moves mirror to slit viewing position AGAUX equivalent to AGMIRROR SMALLFEED for Auxiliary Port imaging AUXFILTER n chooses auxiliary focus filter n 0 5 usually UBVRIZ but check whiteboard for details of last filter set used N B offsets to telescope focus wrt ISIS FOS slit are U Filter 0 24mm R Filter 0 17m Ha 8 2mm Filter 0 28mm and change AUTOFOCUS by approx 500 MAINFILTND number main filter slide to OUT 2 3 4 5 6 see whiteboard MAINFILTC number main filter colour to OUT 2 3 4 5 6 see whiteboard TVFOCUS n moves TV focus to n range 0 18 000 Typically 14000 for 5 mm 12750 for 12 mm for slit viewing TVFILT name TV filter to CLEAR B V R or EMPTY Beware of position empty it may not be TVSCALE s selects TV scales of s 5 or 12 mm 1 5 or 4 arcmin field N B The two TV scales need slightly different TV focus settings 94 ISIS Users Manual QUICK REFERENCE GUIDE Initialising AGINIT mechanism where mechanism can be ACQCOMP AUTOFILT AUTOFOCUS AUTORADIAL AUTOTHETA AUXFILTER COMPFILTA COMPFILTB LARGEFEED MAINFILTC MAINFILTND SLITVIEW SMALLFEED T
70. MAINFILTC FLENS_CALC_POL HW_POLAR QW_POLAR ANAMORPHOTIC and any of the four ISIS filters to the appro priate position 49 SETUP PROCEDURES ISIS Users Manual 8 2 5 Setting Grating Angles The procedure CENWAVE allows the user to set the grating angles to appropriate values for a specified central wavelength however the zero point of the grating angle is not known precisely and has been known to change Observers are recommended to check their central wavelength with an appropriate comparison spectrum and report any discrepancy to the WHT Telescope manager If the exact grating angles are known they can be set with the commands REDGRAT and BLUEGRAT 8 2 6 The Slit Area Unless the spectrograph is being used with multi slits or fibres the slit carriage should be in the long slit position If it is not in the correct position it can be driven there with the ICL command LSLIT The commands SLIT lt width ym gt and DEKKER lt position gt allow the user to determine the width and length of the slit in general for setting up one requires DEKKER 6 long slit or DEKKER 2 20 arcsec for focus and tilt adjustment and dekker 1 narrow for rotation adjustment and determining the s distortion correction for the IPCS It is a mistake to make the slit too narrow for determining focus if it is less that 120m then it will project to less than 2 CCD pixels and the line profiles will be undersampled for the Hartmann test A value in the rang
71. MI image tube there is no way of doing this Beware of possible bright light sources off the edge of the chip After using this command it will be necessary to set up the observing window again with IPCSFORMAT 11 6 15 STANDBY Runs the IPCS EHT down slowly Format STANDBY Comments This is equivalent to setting the rotary switch on the IPCS cubicle on the telescope to STANDBY and pressing the LOAD button In either case it is important to verify that the IPCS EHT has in fact run down by checking the EHT supply on the telescope or the raw video display before switching any lights on in the dome 11 7 Other DMS Commands 11 7 1 DMS_ABORT_READ Aborts a readout from a detector to the DMS Format DMS_ABORT_READ lt buffername gt Example DMS_ABORT_READ ISISCCD1 Comments The buffername must be specified not the detector name valid values are ISIS CCD1 and FOS Only to be used in exceptional circumstances 11 7 2 DMS_ABORT_TRANS Aborts a data transfer from the DMS to the system computer Format DMS_ABORT_TRANS SYS 125 COMMAND LISTS ISIS Users Manual 11 7 3 DMS CLEAR BUFF Clears the DMS buffer for a particular detector Format DMS_CLEAR_BUFF lt buffername gt Example DMS_CLEAR_BUFF IPCS Comments Valid parameters are ISISCCD1 FOS and IPCS 11 7 4 DMS_CLOSE_BUFF Closes all DMS buffers Format DMS_CLOSE_BUFF 11 7 5 DMS MONITOR Switches DMS monitor mode on or off Format DMS MONITO
72. MPS OFF ICL gt AGSLIT To reacquire guide star return to 1 FIELD command Otherwise next object 10 9 Observing With FOS Fill with liquid N in the early evening before observing If all mechanisms are initialised you can set the system for FOS by entering ISISCONFIG FOS or set RFOLD and BFOLD mirrors clear SETUP FOS answer x 400 y 590 As standard FOS dekker is only 20 long Dekker 2 take a test exposure with this dekker to determine where the slit centre is or use bright sky or tungsten lamp to illuminate the dekker 10 10 Offsetting the Telescope 10 11 Blind Offsets BLIND is best for blind offsets to invisible targets whereas OFFSET is okay for small offsets only Use of BLIND ensures that the WHT keeps the correct rotator centre etc during long exposures Proceed as follows Enter coords of standard PPM recommended and faint blind target into the observing catalogue on TCS keyboard Make sure that CALIBRATE and a check for rotator centre position are done at start of night GOCAT offset star Set desired position angle on sky and centre star on slit BLIND blind target Try to find a guide star and start guiding as quickly as possible now 10 11 1 Small Offsets This is used e g to move a few tens of arcsecs from the nucleus of a galaxy The offsets may either be in the form Az Ay arcsecs or A a A co ord differences Proceed as follows e Acquire main target e Set d
73. MS then there is most likely a fault in 44 ISIS Users Manual SETUP PROCEDURES the connection between that NIU and the Utility network Ethernet cable If any of the 4ms or VME microprocessors fail to respond then it is most likely that they are either not running or are not correctly cabelled to the NIUs If a group of devices on the same NIU fails to respond then there may be a fault with that NIU or the cables between that NIU and the utility network NIUs have a recessed reset button at the rear which can be pressed with the sharp end of a pencil If the System Computer fails to respond then it is possible to restart the Utility Network software running on the Microvax At the Operator s console log in to the captive account UNET the password should be available near the console This will stop and restart the Utility Network software on the Vax 4000 If these simple remedies do not work then technical assistance should be sought To run the observing and data taking system the minimum configuration is DMS AGCA ISIS SYS FOS if it is to be used and whichever detectors are to be used It is also convenient to have AUT1 and ENGM communicating via the network Once it has been established that the relevant devices are communicating over the network the user interface to the System computer can be started The user interface is usually run on the Vaxstation located on the control desk though it can be run on a spar
74. MS screen 13 2 28 SEX Sets the IPCS integration time Format lt exposuretime gt SEX Example 1000000 SEX Units Milliseconds Comments This sets the IPCS exposure time but does not begin the integration which must be done with 0 TIM 13 2 29 TIM To begin an IPCS integration Format O TIM Comments Begins an IPCS exposure for the time set by SEX 13 2 30 TIMES Displays IPCS integration timing information Format TIMES 13 2 31 X FIND Calculates position and FWHM in the X direction Format X FIND Comments Allows the user to select a pixel with the cursor then takes a cross section in X centred on that pixel and calculates the location and FWHM of a peak assumed to be situated there 13 2 32 Y FIND Calculates position and FWHM in the Y direction Format Y FIND Comments Allows the user to select a pixel with the cursor then takes a cross section in Y centred on that pixel and calculates the location and FWHM of a peak assumed to be situated there 135 COMMAND LISTS ISIS Users Manual 13 2 33 ZM Allows the zoomed area on the buffer 3 EEV3 image display to be moved Format ZM Comments Allows the user to move the zoomed area around in the buffer 3 image The rectangle can be moved with the mouse pressing on the mouse changes the zoomed area to the current area of the rectangle Pressing the return key exits from ZM 13 3 CCD controller commands 13 3 1 OPEN Interrogates
75. ORPHOTIC IN Valid parameters are IN or OUT NOTE THAT THE ANAMORPHOTIC LENS HAS NOT YET BEEN ACQUIRED AND THIS MECHA NISM HAS BEEN DISABLED UNTIL IT HAS 11 3 2 BCOLL Controls the Blue collimator Format Example Units Range Comments BCOLL lt position gt BCOLL 14800 Microns 0 to 52000 Moves stops or initialises the Blue collimator Valid parameters are a position in microns STOP and INIT 11 3 3 BLUEGRAT Controls the Blue grating Format Example Synonym Units Range Comments BLUEGRAT lt angle gt BLUEGRAT 48912 BGRAT Millidegrees 0 to 110000 Moves stops or initialises the Blue Grating or reprograms the SMDM which controls it Valid parameters are an angle in millidegrees STOP INIT and REPROGRAM The last option should only be used in exceptional circumstances 11 3 4 BLUEXDISP Controls the blue cross disperser Format Example Comments BLUEXDISP lt position gt BLUEXDISP IN Moves stops or initialises the Blue cross disperser or reprograms the SMDM which controls it Valid parameters are IN OUT STOP INIT and REPRO GRAM The last option should only be used in exceptional circumstances THIS ITEM HAS NOT YET BEEN DELIVERED AND THIS COMMAND WILL NOT BE IMPLEMENTED UNTIL IT HAS 11 3 5 BFILTA To move filter slide A in the Blue beam to a given position Format Example Range Comments 106 BFILTA lt position gt BFILTA 2 0 to 2 or a named pos
76. R lt onoroff gt Example DMS_MONITOR ON Comments Can be used to start the IPCS exposure time updating if it is not doing so 11 7 6 DMS_RESET Software reset of the DMS Format DMS_RESET 11 7 7 DMS_START Reads the status of the DMS into the system computer Format DMS_START 11 8 MIMIC Commands 11 8 1 MIMIC PAGES Lists the names of the available MIMIC pages Format MIMIC PAGES Comments Pages can then be selected using SCREEN 11 8 2 MIMIC UPDATE Refreshes the screen if it appears to have become out of date Format MIMIC UPDATE 11 8 3 MIMIC START Starts up the MIMIC Format MIMIC_START Comments An interactive procedure to start up the MIMIC Will prompt for the node name of the Vaxstation to run it on 126 ISIS Users Manual COMMAND LISTS 11 8 4 MIMIC STOP Closed down the MIMIC Format MIMIC_STOP 11 8 5 SCREEN Selects a MIMIC screen Format SCREEN lt screenname gt Example SCREEN ISIS Comments Selects a screen from the list given by MIMIC PAGES This is usually only used if there is a fault with the mouse on the Vaxstation 12 DCL Level Commands for the Vax 4000 These commands can be issued on the Vax 4000 when logged in as OBSERVER and with de fault directory U1 OBSERVER They can either be issued in a separate session from the prompt or from the ICL interface by typing DCL lt COMMAND gt lt parameters gt 12 1 Tape Writing Commands Tapes can be written in two form
77. RATCH as files FOCUSi DST type FIGARO then FOCUS_FWHM and respond to the prompts The parameters which may be changed by the user are the number of images the wavelength direction X or Y the first and last pixels in the orthogonal direction to be used the start collimator position the increment in collimator position whether the maximum pixel value is to be determined for each of the images so that the user can check for saturation whether the region of the spectrum to be used is cursor selected or defaults to the whole spectrum and the number of brightest lines to be used to determine the mean FWHM A version of FIGARO s EMLT program is used to determine the mean FWHM for the bright est lines on each extracted spectrum In focus position is estimated by determining the mini mum in a parabola fitted to the 3 points flanking the lowest measured FWHM in the relation FWHM vs focus position The program plots this relation on a device of the user s choosing e g PERICOM MG IKON_1 CANON_P VAXstation TEK_4010 window 8 5 Installation and Setup for Fibre observing 8 5 1 Fibre slit mounting In order to use ISIS with fibres it is necessary to mount the fibre bundle slit end in a special structure This structure is required to take into account the mechanical performance of the spectrograph and to allow the slit alignment with its optical axis As can be see in Figure 9 the fibres slit is placed such that the optical axis of the
78. S 4ms microprocessor position labelled CASS INST e The A amp G box 4ms microprocessor e The IPCS 4ms microprocessor The last three should only be used by technical staff who have read the appropriate technical documentation but until the FOS D task has been fully commissioned it may be necessary to move some FOS mechanisms and interrogate the status of the mechanisms from this terminal These commands are listed in Part VI 7 8 3 The Detector engineering control terminal The Detector engineering control terminal can be used to communicate with one of the CCD controllers including the autoguider CCD controllers A limited number of CCD commands used for assessing the performance of the CCDs and for taking test exposures when the Vax 4000 system computer is not available are available to users and are documented in Section 13 3 of this manual 42 ISIS Users Manual SETUP PROCEDURES Part IV SETUP AND OBSERVING PROCEDURES 8 Setup Procedures 8 1 Starting the computer systems The mechanisms of ISIS and the A amp G box and the detectors are under the control of a number of microprocessors which communicate with each other and with the Vax 4000 system computer via the Utility network The primary interface from the user is a command language called ICL which runs on the Vax 4000 and the primary source of information for the user is the Mimic display which is a graphical process running on the Microvax 4000 but displaying
79. Setting up the CCD Detectors The CCD setup is carried out with the comparison lamps and these give a reasonably high signal A large number of exposures may be necessary and it is possible to save time by running the CCD in quick mode in which the readout is speeded up At the ICL interface type SPEEDY lt channelname gt This will put the appropriate CCD into quick mode At the end of the setup procedures the CCD should be returned to the standard readout speed At the ICL interface type SLOUCH lt channelname gt 8 3 1 Rotation The long axis of the CCD should be aligned fairly precisely with the dispersion direction of the spectrograph with care it should be possible to do this to an accuracy of 1 minute of arc which corresponds to 0 3 pixels slope of the spectrum from one end to the other The value of doing this alignment well is in the signal to noise ratio of the final spectrum when extracting spectra of faint point sources and in the effective spatial resolution of long slit spectroscopy of extended objects in good seeing This alignment will probably only have to be done when the cryostat has just been put on the spectrograph but it should be checked more frequently As the dispersion direction depends upon the angle of the grooves on the grating this alignment could in principle be grating dependent although with the current set of gratings it is thought not to be To check the alignment take an exposure with GLANCE of t
80. TCH 121 11 5 24SETUP 121 11 5 25SKY 121 11 5 26SLOUCH 121 11 5 27S5PEEDY 122 11 5 28 WINDOW 122 11 5 29WINK 122 11 6 Data Taking Commands IPCS detector 122 vi ISIS Users Manual CONTENTS 11 6 1 EXPOSE 122 11 6 2 EXPOSENP 123 11 6 3 IPCONT 123 11 6 4 IPCSCLOSE 123 11 6 5 IPCSFORMAT 123 11 6 6 IPCSOPEN 124 11 6 7 IPCSSDC 124 11 6 8 IPNEWT 124 11 6 9 IPPAUSE 124 11 6 10IPSTOP 124 11 6 IIIPUPDATE 124 11 6 12KEEP 124 11 6 13C0LEAROVERILLUM 125 11 6 144OVERSCAN 125 11 6 15STANDBY 125 11 7 Other DMS Commands 125 11 7 1 DMS_ABORT_READ 125 11 7 2 DMSABORT TRANS
81. UN 134 13 2 21IRECALL 134 13 2 22IRUN 134 13 2 23LOAD SDC 134 13 2 24PUT FILE 134 13 2 25PUT SDC ARRAY 134 13 2 26RECOVER 134 13 2 27RECOVER DATA 135 13 2 28SEX 135 13 2 29TIM 135 13 2 30TIMES 135 13 2 3IK FIND 135 13 2 32Y FIND 135 13 2 337ZM 136 13 3 CCD controllercommands 136 13 3 1 7 OPEN 136 13 3 2 IP en 136 13 3 3 2P 136 13 3 4 IV 136 13 3 5 2V 137 ISIS Users Manual CONTENTS 13 3 6 CLOSE 137 13 3 7 CLR a 137 13 3 8 NETWORK 137 13 3 9 OPEN 137 13 3 10PIC 137 13 3 11QUICK SPEED 137 13 3 12REBOOT 138 13 33 I3RED
82. VFILT TVFOCUS TVREDUCER to init TVSCALE Updating the MIMIC for A amp G Units AGUPDATE mechanism 10 7 1 Comparison lamps Only the lamps in the horns usually CuAr and CuNe and Tungsten currently give enough light to be useable COMPLAMPS name turns on lamp CUAR CUNE CUAR CUNE W or OFF COMPFILTA name puts in CLEAR NDO 2 NDO 6 NDO 8 ND1 8 ND3 0 GG375 GG495 COMPFILTB name puts in CLEAR ND0O 3 NDO 5 NDO 9 ND1 2 ND2 0 BG24 OPAQUE 10 7 2 Autoguider To start or stop type START UP and SHUT DOWN on the autoguider keyboard Check N3 flow on start up On ball meter immediately above red ccd cryostat reading should be at least 60 AUTORADIAL n n 0 40000 microns AUTOTHETA n n 0 180000 millidegrees N B for values below 35000 the probe may vignette the slit AUTOFOCUS n n 0 6000 microns typically 1500 2500 AUTOFILT selects EMPTY CLEAR OPAQUE B V or I ACQINT n Sets acquisition time n 1000 50000 msec GUIINT n Sets guiding time n 1000 50000 msec typical 1 2s FIELD takes exposures and finds guide star FON initiates following by autoguider PROBE r 9 inform T S of probe position get from CAGB mimic N B MANDATORY otherwise the object may move off the slit AUTOGUIDER ON tell T S to initiate closed loop autoguiding AUTOGUIDER OFF tell T S to stop autoguiding FOFF terminates the autoguider following 95 OUICK REFERENCE GUIDE ISIS Users Manual Other commands available on the autoguider
83. X 71lum and Y 559um 0 32 arcsec W and 2 52 arcsec North on the sky for a plate drilled with North at the top from the centre of the coherent bundle e The telescope is moved South 400 so that the star drifts 400 North away from the field centre In general the pseudo image of the star does not appear at once in the semi coherent bundle placed there This is due to the fact that the telescope s North and the plate s North do not coincide The rotator angle must be adjusted until the star appears in the semi coherent bundle This way a preliminary adjustment of the rotator angle is performed e If the field centre is not perfectly determined the star will not appear perfectly centred in the semi coherent bundle In order to centre the star the telescope must be moved in RA and Dec or X and Y e After centering of the star in the semi coherent bundle the telescope is moved 400 North The star appears in the coherent bundle A new aperture APE1 is created to define that point as the new field centre e The telescope is moved 400 North and the same process as described above is repeated for the other semi coherent bundle All these steps can be repeated as many times as desired in order to obtain a very precise adjustment of the rotator As a reference if the plate is manufactured at sky position angle zero then the cassegrain rotator angle fibres are employed at the auxiliary focus is 314 57 36 and typ
84. a CCD shutter to see whether it is open Format OPEN Comments If the response is 1 then the shutter is open if it is 0 then the shutter is closed Other responses indicate a problem with the shutter 13 3 2 1P Commands after this refer to Physical Head 1 Format 1P Comments After issuing this command further CCD commands will affect Physical Head 1 until this is changed by issuing 2P Commands that require the correct Physical Head to be set include OPEN CLOSE UNJAM RED PIC and CLR Consult RGO technical staff to find out which Physical head number refers to the CCD you are using 13 3 3 2P Commands after this refer to Physical Head 2 Format 2P Comments After issuing this command further CCD commands will affect Physical Head 2 until this is changed by issuing 1P Commands that require the correct Physical Head to be set include OPEN CLOSE UNJAM RED PIC and CLR 13 3 4 1V Commands after this refer to Virtual Head 1 Format 1V Comments After issuing this command further CCD commands will affect Virtual Head 1 until this is changed by issuing 2V Commands that require the correct Virtual Head to be set include QUICK SPEED STANDARD SPEED CONFIG RED PIC CLR and local binning and windowing commands Consult RGO technical staff to find out which Virtual head number refers to the CCD you are using 136 ISIS Users Manual COMMAND LISTS 13 3 5 2V Commands after this refer to Virtual Head 2 Forma
85. age will start and the procedures and command definitions will be loaded The user will then be invited to start the control tasks to do this type STARTUP The user is then given the option of running up the tasks or not the answer to this question is always YES The user will also be asked which Vaxstation to run the MIMIC on this is normally the same Vaxstation as is being used for alphanumeric input although it can be the other one The user is then prompted for the configuration required normally this will be one of the following options e ISIS A amp G CCDs e ISIS A amp G CCDs IPCS e ISIS A amp G FOS CCDs The D tasks will the be started and the various subsystems initialised If the initialisation of one subsystem fails it is possible that other subsystems will not be initialised if this appears to be the case the subsystems can be initialised explicitly with the commands ISIS_BEGIN DMS_BEGIN CAGB_BEGIN DCT_BEGIN FOS_BEGIN AUT_BEGIN and CCDINIT lt ccdname gt starting up ICL will also start up the telescope control system on the Microvax II telescope control computer 8 2 Configuration of the A amp G Box and Spectrograph Gratings and other optical components must only be changed when the telescope is parked at the zenith and whilst the change is being made an entry must be made in the telescope log to the effect that the telescope is not to be moved until the work on the spectrograph or A amp G box
86. an intensity difference between the two spectra Since both spectra are taken under exactly the same conditions the intensity ratio is independent of sky transparency In order to account for differences in the response of the spectrograph and the detector to the highly polarised o and e rays a second exposure with the halfwave plate rotated by 45 degrees is required This offset of 45 degrees in the halfwave plate position angle results in a rotation of the incoming polarisation vector by 90 degrees Due to this rotation on passing the calcite plate the intensity difference will be inverted relative to the first exposure while leaving the instrumental response identical the instrumental response can then be taken out by comparing the two exposures To measure the full linear polarisation vector i e both Stokes Q and U a second set of two exposures is required with the halfwave plate set at 22 5 and 67 5 degrees A standard sequence of exposures is exposure with halfwave plate at 0 0 degrees exposure 2 with halfwave plate at 45 0 degrees exposure 3 with halfwave plate at 22 5 degrees exposure 4 with halfwave plate at 67 5 degrees Exposures 1 and 2 yield the Stokes Q spectrum and exposures 3 and 4 the Stokes U spectrum The angle of the linear polarisation vector as defined by its Q and U components is given relative to some instrumental coordinate system The halfwave plate positions angle may be given any constant offset which
87. and 2560 by 200 for IPCS data Only images of these formats can be stored in these files 13 2 2 NET Checks what devices are accessible across the network from the DMS Format NET 130 ISIS Users Manual COMMAND LISTS Example Comments NET Sends a message to each device in turn across the network and waits for an acknowledgement Logs which devices acknowledge and which do not Useful for diagnosing network problems 13 2 3 REGS Displays the contents of several DMS registers Format Comments 13 2 4 IS REGS Displays the contents of several DMS registers Of particular interest are reg isters 2 and 5 which contain the number of pixels the DMS is expecting from FOS GEC5 and EEV2 respectively Useful for diagnostic purposes if it is sus pected that a CCD readout might have hung or some pixels might have been lost Lists the items on the image stack and their dimensions Format IS 13 2 5 CALC SDC Calculates an IPCS S distortion correction Format CALC SDC Comments Calculates the IPCS 5S distortion correction from a suitable frame in the IPCS buffer of the DMS The frame should be a well exposed image of a continuum source such as a tungsten lamp through a narrow dekker and obtained with X and Y resolution factors of 8 13 2 6 CLO Closes all image buffers Format CLO 13 2 7 CRECALL Transfers data from a named file on the DMS disc and displays it in the EE V2 image buffer Fo
88. and Detector Efficiencies This appendix presents laboratory measurements of the efficiencies of the ISIS gratings and of the CCD and IPCS detectors in use on ISIS 146 ISIS Users Manual APPENDICES C Efficiency of Dichroics and Polarisation optics This appendix presents laboratory measurements of the transmission properties of the five main ISIS dichroics and measurements made using the comparison lamps on the spectrograph of the efficiency of two reddest dichroics in both transmission and reflection The final panel of this appendix shows the throughput of the polarization optics half and quarter wave plates and the Savart plate measured with the comparison lamps 147 APPENDICES EXPORT ULI lpvs3 Sun 20 23 19 31 Oct 93 00r TARGET INDEF apit beanii EA NOAO IRAF E 3 a E A 5 o T T Lea Wa val eng th la l ne avelength for the 6100A dichroic Figure 19 Transmission as a function of w 148 r s mi 20 7 7 1 ER Figure 20 R APPENDICES
89. and GEC5 which is a GEC P8603 In the very near future EE V8 an EEV P88500 will become available The CCD in FOS II is currently a GEC P8603 There is a choice of two readout speeds for the CCDs known as normal and quick It is possible to switch between these modes from the ICL interface with the commands SPEEDY 31 DETECTORS ISIS Users Manual Table 6 CCD types available at the WHT as of May 1993 CCD Type Pixel CCD Format Image Format Read noise e7 Dark Current Operating jm pixels pixels normal quick e hour Temp K EEV P838300 12421152 1280x1180 3 4 5 3 10 140 150 EEV P88500 2172x1152 2200x1180 140 150 GEC P8603 516x380 590 x400 150 Tek 1024 1024x1024 1124x1124 183 Table 7 Recommended bias regions for WHT CCDs CCD Type Recommended bias region in X Recommended bias region in Y pixels pixels EEV P88300 101 1000 EEV P88500 101 1000 GEC P8603 101 500 Tek 1024 101 1000 lt channelname gt and SLOUCH lt channelname gt which select quick and normal speed respec tively The advantages of quick speed are a faster readout less overhead and a higher dynamic range The disadvantage is a higher readout noise column 6 of the table above For each CCD there is a distinct value of the gain the conversion factor between the output of the analogue to digital converter and the number of detected photoelectrons per pixel for each readout speed The values of gain us
90. ane positions X and Y for the fibre masks for the WHT LAPLATE runs starting from a user input file This includes several parameters used by the programme and the equatorial coordinates of the observed objects The programme takes into account effects of precession and nutation of the rota tional orientation of the field for this the equinox and observing date must be included in the input file The effects of thermal contraction and expansion of the brass aperture plate are also considered then the input file must include information about the drilling temperature and the observing temperature Though differential refraction effects cannot be calculated in advance LAPLATE makes a first order correction using the zenith distance at which the field crosses the meridian Regarding this last point APLATE differs from LAPLATE because the latter uses the latitude of the La Palma Observatory LAPLATE Input file The following is an example for an input file DAT for the LAPLATE pro gramme M3 WHT Aux 40ARCMIN 1992 27 1950 0 4 507320565 90 0 0 0 400 0 10 0 25 0 13 40 06 089 28 32 12 41 13 40 38 120 28 33 12 93 G51 13 40 09 742 28 27 15 30 G52 13 39 55 393 28 27 36 92 G53 13 39 33 147 28 32 51 73 G54 13 40 25 376 28 31 01 53 X1 13 40 23 213 28 34 13 26 26 13 40 18 393 28 34 45 30 50 13 40 18 568 28 33 49 75 49 13 40 19 410 28 32 50 81 43 13 40 19 231 28 31 42 95 46 As can be seen in this file each line starts wit
91. ars and their predicted AUTORADIAL and AUTOTHETA values CONFIG WHT CASS ROTATOR lt rotatorposition gt SEARCH lt objectposition gt EXIT Where the rotator position is the sky position angle in degrees and the object position is specified as RA Dec and Equinox in the same format as is used by the Telescope Computer The file QUTPUT GS can then be typed or printed and the guide star acquired To find a guide star search the autoguider field by typing FIELD at the ICL interface or 1 FIELD at the autoguider interface The autoguider will scan the field three times then look for a star on the final readout Ifa suitable star is found then a white cursor appears on the star image It is then possible to guide on that star If the star appears too faint it is possible to increase the guiding integration time 71 OBSERVING PROCEDURES ISIS Users Manual by typing GUIINT lt time gt at the ICL interface or lt time gt GUIINT at the autoguider interface where the time is in milliseconds Guiding integration times can be as short as half a second and a sensible maximum is 10 seconds If no sufficiently bright star is found in the field the procedure is to move guide probe with the ICL AUTOTHETA or AUTORADIAL commands by about the field size The field size is approximately 8000 millidegrees in AUTOTHETA it depends somewhat upon the radial position and about 10000 microns in AUTORADIAL Beware of low values of
92. ation must be adjusted 9 6 1 Telescope focusing on the aperture plate This focusing is performed using the coherent guiding bundle in the following way a bright star is observed with this bundle in order to follow the image variations on the TV screen This process is best done if the coherent bundle can be put in the centre of the aperture plate ie focal plane centre If this is not possible the bundle coordinates must be known accurately so that the telescope can be offset to put the star onto the coherent bundle It is advisable to use the high quality zone of the fibre bundle for focussing 9 6 2 Adjustment of the rotator axis and orientation The rotator axis aperture plate alignment and the orientation of the rotator are crucial when fibre optics are employed An error in the rotator orientation translates to a difference between the North direction of the focal plane and that of the aperture plate For multi object spec troscopy this in turn means a bad field acquisition together with a drastic efficiency decrease In extreme cases the fleld can even not be seen For this reason it is very useful to perform these adjustments as accurately as possible before using the instrument on the first night It is also advisable to check them at the beginning of every subsequent observing night The aperture plates have several holes to allow connection of the semi coherent bundles at 400 North and 400 South from the plate centr
93. ations e g imexamine e IRAF Tek used for displaying line graphics e Console window where UNIX error messages appear e DMS control The interface for transferring data from DMS memory to the Sparcstation local disks is controlled graphically on the Sparcstation itself To transfer a specific buffer to the Sparcstation the user simply moves the pointer to the name or number of that buffer selects it with the mouse then selects with the mouse the SAVE option in the interface window An IRAF format file is then created in a scratch area on one of the Sparcstation discs and the name of the file created is displayed in the interface window At present no header information at all is stored with the data files The images can then be displayed in the SAOIMAGE window with the IRAF command display IRAF contains many facilities for rapid analysis of data of all types users who require specialised facilities are advised to refer to the KPNO user manuals and cook books which are kept in dark blue loose leaved binders in the control room For quick look analysis of images and simple spectroscopic data the IRAF command imexamine has many of the required facilities Typing help lt commandname gt at the IRAF interface produces a detailed description of the command and typing help lt commandname gt lpr will produce a hard copy of the help file on the Sparc laser printer By the end of 1993 the DMS display functions should have been transferre
94. ats FITS format or as a VMS backup of the data files Two tapes are normally written the D tape or archive tape which must be in FITS format and the C tape or copy tape which can either be a direct copy of the D tape or a tape written by the observer in the format of his choice The VMS Backup utility is described in detail in the DEC manual set this section will describe the commands required to produce FITS tapes 12 1 1 FITSINIT To initialise a new FITS tape Format FITSINIT Comments The program requires the tape to be mounted on a tape drive on the one of the Vaxes normally tape drive MUC1 It prompts for the name of the tape user and owner It should only be used for new tapes 12 1 2 WRITE_FITS To write data files to a fits tape Format WRITE_FITS Comments The program requires the tape to be mounted on a tape drive on one of the Vaxes normally tape drive MUC1 If it is a new tape then FITSINIT must be run first The program prompts for the numbers of the first and last files to be written to tape The program will search for files with these numbers on the WHT data disc DISKSWHTDATA and write them as FITS files to the specified tape There is no problem if a file in the sequence is missing If WRITE_FITS is run to a tape 127 COMMAND LISTS ISIS Users Manual which already has Fits files on it the program will search for the end of the tape before starting to write i e it will not overwrite existing fil
95. be transferred to the SPARCstation currently LP553 The integrating TV system is currently stand alone and cannot be controlled across the Utility Network If the ICL d task control route fails for some reason mechanisms can often be controlled more directly from the engineering terminals in the control room by keying in messages to be sent over the utility network At a still lower level duty tecnicians can plug a terminal directly into a microprocessor on the telescope and send commands from there LPVF is linked via DECNET running over a separate Ethernet to the telescope control computer a microVAX II currently LPVB to the VAXstation running the user interface to other VAX 4000 computers on a DEC cluster to the DECservers serving terminals and printers and to SPARCstations on a SPARC cluster Separate Ethernets at the INT and JKT are connected to the WHT ethernet via fibre optic links The DMS and several of the VAXes and SPARCstations can be used for data reduction The DMS provides a few simple analysis functions e g cuts statistics FIGARO and other reduction packages are available on the VAX clusters on both the mountaintop and at sea level IRAF and SAOIMAGE can be run on the SPARCstation on the control desk Section 7 3 Telescope control is effected via commands issued to the control system running on the telescope control computer which is interfaced to the telescope mechanisms via CAMAC Most telescope control commands can b
96. by placing the cursor on the menu name and pressing Srnecr The options are e PREFERENCES this menu has not been implemented and trying to select it will have no effect e DISPLAY Selecting this menu gives various options for changing the contrast and lookup table of the image displayed in the image display area e ZOOM This does not select a menu but is an option After selecting the ZOOM option with SELECT 1 pressing SELECT1 again zooms in while SELECT2 zooms out Moving 140 ISIS Users Manual COMMAND LISTS the mouse on the keypad while the display is zoomed moves the cursor in the image in the same sense as the mouse is being moved on the pad while attempting to keep the cursor in the centre of the screen This results in the image moving on the screen in the opposite sense to that in which the mouse is being moved with some timelag returns the display to normal i e not zoomed and returns the user to the Main menu e STATISTICS Selecting this menu gives various options for defining windows in the data area and for statistical operations on the data within these windows e WINDOWS This menu gives options for defining windows on the DMS screen but is not currently used e 3D MODES This menu gives options for examining three dimensional data arrays These are not useful for any of the ISIS data acquisition modes implemented to date e SCREENS This menu allows the user to selec
97. byte in TAR format or FITS format from IRAF Instructions on starting up the SPARC and on using the various applications are kept in the control room Image examination routines run much faster on the SPARC than on the VAXes IPCS data can be saved to the SPARC while the exposure is building up The windows typically open on the SPARC are e DMS SPARC interface used to save data from any of 7 DMS buffers to the SPARC and also to obtain statistics on any of the images in the buffers size min max and SD 37 38 DATA REDUCTION Image COMPUTER Di sploy MA 7 for dota i reduction assessment Images for SYSTEM ___srehivol n DETECTOR COMPUTER K uemory SYSTEM F commons ond BI si otus informotion 1 TELESCOPE AUTOGUIDER ISIS Users Manual COMPUTERS e SAOIMAGE used for display and mouse controlled examination of the image e IRAF command language used for running other applic
98. ceptional circumstances 11 3 23 REDXDISP Controls the Red cross disperser Format Example Comments REDXDISP lt position gt REDXDISP IN Moves stops or initialises the Red cross disperser or reprograms the SMDM which controls it Valid parameters are IN OUT STOP INIT and REPRO GRAM The last option should only be used in exceptional circumstances THIS ITEM HAS NOT YET BEEN DELIVERED AND THIS COMMAND WILL NOT BE IMPLEMENTED UNTIL IT HAS 111 COMMAND LISTS ISIS Users Manual 11 3 24 RFILTA To move filter slide A in the Red beam to a given position Format Example Range Comments RFILTA lt position gt RFILTA 2 0 to 2 or a named position Moves stops or initialises Red Filter A Valid parameters are a position in the range 0 to 2 a named filter listed on the ISIS MIMIC page OUT STOP INIT and REPROGRAM The last option should only be used in exceptional circumstances 11 3 25 RFILTB To move filter slide B in the Red beam to a given position Format Example Range Comments RFILTB lt position gt RFILTB 2 0 to 2 or a named position Moves stops or initialises Red Filter B Valid parameters are a position in the range 0 to 2 a named filter listed on the ISIS MIMIC page OUT STOP INIT and REPROGRAM The last option should only be used in exceptional circumstances 11 3 26 RFOLD Controls the slide containing the folding flat for the red camera Format Example
99. ch type of connector is as follows e for individual fibres one hole for each target one for each sky area to be sampled e for the semi coherent bundle one hole 400 North of the field centre relative to observing epoch one 400 South of the field centre relative to observing epoch one for each guide star for manual guiding two at least e for the coherent bundle one hole for the field centre one for the guide stars chosen for telescope tracking one at least The aperture plates can be made by the CAMM3 engraving machine in the same way as the multi slit masks Observers wishing to use the fibre system should provide accurate co ordinates for aperture plate manufacture to La Palma staff at least one month in advance of the observing run 2 12 5 Observing coordinate determination The X Y coordinates of the targets to be observed with multi object spectroscopy can be obtained in two ways 23 INSTRUMENTS ISIS Users Manual e From the astrometry of the field Transformation of the equatorial coordinates of the targets onto the corresponding aperture plate coordinates X Y is performed with the LAPLATE programme which is described in Appendix F and which is a modification of the APLATE programme of the STARLINK package for the geographical coordinates of the ORM LAPLATE takes into account the following parameters telescope focal plane scale thermal dilation coefficient of the apert
100. ctropolarimetry can be employed The analyser is a Savart plate which is placed in the multi slit slide with a field of 80 arcsec diameter As in the case of spectropolarimetry a dekker mask is necessary whose duty fraction is fixed by the angular throw of the below slit analyser and by cross talk scattered light between the separated images in each plane of polarisation The instrument has been successfully used with a dekker consisting of a series of slots 1 2 mm wide with an occulting bar 3 5 mm wide in between This accommodates wavelengths as far as R the throw of the analyser decreases with increasing wavelength This dekker arrangement gives slots on the sky 5 arcsec wide limited in the other direction by the 80 arcsec diameter field of the Savart plate separated by 15 arcsec This pattern is repeated in the narrow direction six times before the field is vignetted by the modulator the half wave plate This dekker is rather conservative and a larger duty fraction could probably be used 83 OBSERVING PROCEDURES ISIS Users Manual The principal limitation in practice is that filters have to be changed manually as the small below slit filter slides in ISIS have to be used Likewise swapping from red to blue channels involves manual operations 9 6 Observing with Fibres In order to set up the telescope when optical fibres are employed the telescope must be focussed on the aperture plate and the rotator axis and orient
101. d the autoguider field is illustrated in figure 2 The autoguider has an azimuthal travel of 180 but use of the first 35 of this will result in the autoguider probe vignetting the slit viewing optics The azimuthal co ordinate of the autoguider is specified in millidegrees and the radial co ordinate in microns and they are related to the distance from the guide star from the slit centre and the position angle of the guide star relative to the slit centre by r 221 7 x Rgs 505 microns 0 1000 x PA PAstit 90 millidegrees Where r and are the co ordinates of the autoguider probe in the frame of the A amp G box Rs and PA are the distance and sky position angle of the guide star relative to the slit and P Asut is the sky position angle of the slit 1 5 Comparison lamps A calibration system is provided consisting of an integrating sphere into which light is fed directly from two hollow cathode lamps Cu Ar and Cu Ne and a Tungsten lamp for a red continuum source Light from a further 6 lamps Fe Ar Fe Ne Th Ar Al Ca Mg Ne Na K Ne and Deuterium is imaged via fused silica lenses onto 3 mm diameter fused silica light guides The Al Ca Mg Ne and Na K Ne multi alkali lamps are primarily for use with TAURUS 2 whilst the Deuterium lamp provides a blue continuum source Any combination of lamps may be used simultaneously The exit pupil of the integrating sphere is fitted with an obscuring disk to simulate t
102. d to the SPARC making the DMS monitor superfluous Header examination and FITSOUT from the SPARC should also be available The mountain top SPARC cluster currently includes 7 SPARCs 3 exabyte and a laser printer There is a SPARC plus exabyte in each telescope building 7 4 The Utility Network The Utility Network is a local Ethernet running between the various focal stations of the WHT and the control room over which the microprocessor systems the 4ms systems which control the instruments and the Engineering Mimic the VME computers which control the Autoguider and the DMS and the CCD controllers communicate Each device communicates via a Network Interface Unit NIU and each NIU can connect up to 4 devices to the Ethernet link The system computer is also connected to the Utility Network via an NIU this allows the transmission of messages from the User Interface to the devices The Utility Network Ethernet is physically separate from the Ethernet which connects the Vaxcluster and various other computers around the site Utility Network messages conform to a local protocol set out in Johnson 1986 Electronics report 412 4 2m WHT Utility Network Instrument Control Recommendations 7 5 The System Computer and User Interface The system computer has two principal roles as part of the data acquisition system 39 COMPUTERS ISIS Users Manual e The system computer running the ADAM control system is responsible for coordinatin
103. ds and Dichroics 2 2 a 8 2 5 Below Slitfilters 10 2 6 Collimators 10 2 7 ThelISISgratings 11 2 8 Cameras 13 2 9 Cross Dispersers 13 2 10 The Faint Object Spectrograph FOS TI 13 2 11 Multi Slt Unit 16 2 12 Then ISIS Fibre System 2 2 aa 17 2 12 1 Auxiliary focus mounting 17 2 12 2 Fibre Bundle 18 2 12 3 Guiding system 18 2 12 4 Apertureplates 23 2 12 5 Observing coordinate determination 23 2 12 6 Overall Performance 24 3 Performance 25 3 1 Throughput 25 3 2 Stability and radial velocities 25 3 3 Scattered Light 25 34 Wood s Anomalies in the ISIS gratings 28 II Detectors 30 CONTENTS ISIS Users Manual 4 CCD Detectors 30 4 1 Schematic view of the CCD systems 30 4 2 CCD chips in current use at the WHT 31 5 The CCD IPCS Detector 33 5 1 Scientific Description 33 5 2 CCD IPCS granularity and Dith
104. ds into the DICI card see below There can be up to 16 individual CCD interface cards in the rack although there are not usually more than three Each pixel when read from the CCD interface card FIFO has 24 bits of which 16 are data bits and 7 are address bits which ensure that the data arrive in the correct buffer in the Detector Memory System The CCD interface card has three lights on the front These are Data Available a green light which indicates that data are available in the FIFO and the CCD controller is sending data FIFO Full a yellow light which indicates that at some point the FIFO has been filled and CCD data have probably been lost G O A T a red light which indicates that CCD Interface card cannot detect the carrier for the optical signal If either the yellow or red lights are showing on the relevant CCD interface card then there is a problem e The Dual IPCS CCD Interface DICI card in the DMS rack e The Detector Memory System This is described in brief in the next chapter 4 2 CCD chips in current use at the WHT The table below summarises the characteristics of the types of CCD chips in current use for all instruments at the WHT Availability of CCDs changes frequently and updates to this information will be published regularly in Gemini At the time of writing the CCDs available on the two arms of ISIS are EEV3 and EE V6 which are EEV P88300s TEK1 which is a Tektronix 1024 square
105. e and the coherent bundle at the field centre The North East orientation of plate is fixed at the time the holes are manufactured In order to adjust the rotator then the following steps are required e Place the coherent bundle in the centre of the aperture plate e Because of the orientation of the Auxiliary port with respect to the ISIS slit the nominal sky position angle of the Cassegrain rotator to align plate and sky axes is 315 and this the Sky Position angle should be set to this as an initial estimate e Acquire a bright star with the telescope and place it on the coherent bundle Determine the rotator centre which should be on the coherent bundle It may be easiest to determine the rotator centre on the direct TV with the ACQCOMP mirror in place then to place the star on the rotator centre move the LARGEFEED mirror in and mark that point as the rotator centre It is very important to determine the rotator centre accurately as otherwise target acquisition will be extremely difficult e Calibrate the telescope pointing with the TCS procedure CALIBRATE Again this can be done either on the coherent bundle or with the direct viewing TV 84 ISIS Users Manual OBSERVING PROCEDURES e Move the star to the centre of the aperture plate and define a telescope Aperture there The coherent bundle centre and the plate centre do not coincide The centre of the aperture plate origin of the coordinates for the plate holes should be
106. e 120 to 180um is recommended 8 2 7 Configuring the Spectrograph for Spectropolarimetry The ISIS spectrograph is fitted with polarisation optics which allows the observer to rapidly convert the instrument into a spectropolarimeter capable of measuring both linear and circular polarisation The polarisation assembly basically consists of two units above the slit a halfwave and a quarterwave plate can be inserted and immediately below the slit either a calcite plate or a polaroid are available as a polarisation analyser In some more detail the following components comprise the ISIS polarisation system in the order the light passes them e Halfwave plate 40 mm diameter effective AA 300 1100 nm mounted so that it can be inserted retracted and set to any position angle or rotated continuously at a speed of several revs sec Rotating the halfwave plate through n degrees results in a rotation of 2n degrees of the polarisation vector of the light e Quarterwave plate at present borrowed from the People s Photometer mounted similarly to the halfwave plate The quarterwave plate converts circular into linear polarisation so that the calcite plate linear beamsplitting polariser can detect its presence e Standard ISIS slit unit with polarisation dekkers mounted A comb type dekker mask is employed to avoid overlap between the two spectra produced by the calcite slab analyser see below e Choice of analyser i calcite slab
107. e 4ms TRANSFER which transfers the information from the 4ms to the system computer and UPDATE which performs both of these function and is the usual option 11 1 3 AGINIT Initialises one of the mechanisms in the Cassegrain A amp G box Format AGINIT lt mechanism gt Examples AGINIT COMPFILTA AGINIT ALL Comments Mechanisms which can be initialised include COMPFILTA COMPFILTB AUT OFILT AUTOFOCUS AUTOTHETA AUTORADIAL AUXFILT TVFOCUS TVFILT TVSCALE ACQCOMP SLITVIEW LARGEFEED and SMALLFEED To initialise all of the A amp G box mechanisms type AGINIT ALL 100 ISIS Users Manual COMMAND LISTS 11 1 4 AGMIRROR Moves a specified A amp G box mirror into the beam or all mirrors out of the beam Format AGMIRROR lt mirrorname gt Example AGMIRROR SLITVIEW Synonyms AGCOMP AGMIRROR ACQCOMP AGSLIT AGMIRROR SLITVIEW Comments Valid parameters are ACQCOMP SLITVIEW LARGEFEED SMALLFEED and OUT 11 1 5 AGUPDATE Updates the status of a mechanism as displayed on the MIMIC display Format AGUPDATE lt mechanism gt Examples AGUPDATE COMPLAMPS AGUPDATE ALL 11 1 6 ARCOFF Turns off all comparison lamps and moves the mirrors to the slit viewing position Format ARCOFF 11 1 7 AUTOFILT sets the position of the Autoguider filter wheel Format AUTOFILT Example AUTOFILT CLEAR Comments Possible values are B V I CLEAR EMPTY and OPAQUE Note that AUTO FOCUS will need to be adjusted when m
108. e Cassegrain A amp G box and contains a frame transfer CCD having 385 by 288 active pixels with 22 um pixels with a peak quantum efficiency of 50 at 7500A This is mounted on a copper block connected to a two stage Peltier thermo electric cooler This cools the CCD to around 35 C to reduce the dark current The CCD must be flushed with Nitrogen when the cooler is in operation to prevent the formation of condensation and ice crystals on the CCD surface If this is not done the CCD could be badly damaged There is a flowmeter on the nitrogen outlet line from the CCD Autoguider the user should check that nitrogen is flowing through this as soon as the CCD begins cooling The limiting magnitude of the autoguider for guiding at 1 Hz is about V 17 5 in good conditions i e l arcsec seeing and a dark sky Autoguider errors are sent to the telescope control system When the telescope is servoing on these errors the telescope tracking errors are reduced to the 0 1 arcsec level The autoguider is provided with a filter wheel with six filter positions The available filters are CLEAR UBK7 EMPTY no filter different focus OPAQUE blanking disk B BG 28 V BG 38 and I RG 630 These filters do not give a standard photometric system and the Johnson letters are given for guidance only The autoguider can be focussed independently to compensate for different filter thicknesses 1 4 1 Autoguider Geometry The relative geometry of the slit an
109. e Vaxstation elsewhere in the control room or the alphanumeric interface can be run on a terminal with the MIMIC being displayed on a Vaxstation If using a Vaxstation for alphanumeric input the user should first log on to this Vaxstation as OBSERVER The password will be known to local staff On the Vaxstation type LPVF This is defined as SET HOST LOG LPVF and a logon message from the Vax 4000 system computer will appear The user should also log on to this computer as OBSERVER The password is the same If using a terminal for alphanumeric input the user should log straight onto this machine The system computer will display various information about new software and about the system Two items require particular attention e The system will try to allocate the device XAAO which is used for data transfer from the DMS If it cannot do this it will display a message to this effect this is usually because there is a terminal somewhere with observer logged on In this case this KAAO must be deallocated at that terminal or the process logged out or deleted Then XAAO must be allocated at the observer s terminal e The system will display the amount of free disk space on the system and data disks If the data disk is full some data from previous night should be deleted after first checking that it has been backed up At the Vaxstation or terminal type ICL 45 SETUP PROCEDURES ISIS Users Manual The ICL command langu
110. e dome lights are out and that it is dark in the dome IMD iat BA BO NR OO 9 Cautiously open the shutter with IPO Be prepared to close immediately with the Panic Button if the level of illumination is too high 10 If the level or uniformity of illumination are too high then cautiously adjust the erating angle and the amount of neutral density The count rate should not exceed about 3 Hz CCD pixel which is equivalent to 0 1 Hz data pixel THE SHUTTER MUST BE CLOSED WHILE MOVING EITHER THE GRATING OR THE FILTER WHEELS OR SLIDES 11 Begin a long exposure with EI It is your duty to ensure that the level of illumination in the dome remains low during the flatfield exposure The dome lights are interlocked so that they should not come on with the IPCS EHT on you must check that this interlock is not overridden You must also ensure that nobody will open the dome before dark if a flatfield is in progress e Twilight sky exposures These are used to determine the uniformity of illumination along the slit It is safer to obtain these at the end of the night when the sky brightness gradually increases rather than at the beginning when it is difficult to estimate the level of illumination Twilight sky exposures should be taken with the comparison mirror out AGSLIT and with the slit width set to the value that has been used during the night They should be taken with the telescope tracking and pointing at a blank area of the sky
111. e issued from the ICL interface and it is intended that in 36 ISIS Users Manual COMPUTERS the future the distinction between operator control of the telescope and observer control of the instrument will blur Most of the information needed by the observer about the status of the system is included in the telescope control information display the instrument control MIMIC and the white board The MIMIC is discussed in Section 7 6 below it displays information contained in the notice boards which are continually updated by the d tasks as a result of the commands and status returns they receive Ephemeral information which is not yet held on line e g contents of filter slides gratings loaded CCD locations is usually recorded on the whiteboard in the control room There is some overlap between the information held on line and that written on the whiteboard Some useful instrumental information e g focus offsets is recorded in the telescope logbook 7 2 The Detector Memory System The Detector Memory System allows detector data to be collected displayed and transferred to the system computer A detailed description of the system is given by Johnson 1986 Electronics report 413 the Detector Memory System The DMS is a purpose built computer based upon a Motorola 68020 microprocessor with a large area of memory 128 Mbytes for storage of detector data The system design is based on the industry standard VME architecture
112. e nucleus diameter is 5 5 pixels on the detector and the separation between the centres of two adjacent fibres is 11 8 pixels All the fibres were numbered at the focal plane fibre end Each fibre number is fixed by its position at the slit Both bundle ends were polished using diamond abrasives from 25 to 0 1 microns of particle size The bundle was tested in the laboratory in order to determine the focal ratio degradation of each fibre Figure 12 shows the results of this test The efficiencies correspond to output beams with the same focal ratio of the input beam f 11 Neither the fibre absorption or reflection losses at the fibre end are considered 2 12 3 Guiding system The autoguider system in the Cassegrain A amp G box cannot be employed when the fibre system is used with ISIS due to the size of the LARGEFEED mirror 18 ess AA AA Ee CEPR sn Be nny OB NR AA NAENDA iy nen tu hala ia ya ii mi wai waa kahi PSA inher WAA AAA A T j ISIS SPECTROGRAPH a peat uN pose Y oa a Figure 9 see annan Roce a Saaai I a a r INSTRUMENTS ISIS Users Manual SPECTRAL ATTENUATION dB km VISIBLE TO NEAR INFRARED a ULTRAVIOLET Uy J 1000 1100 1200 un oO Oo wn Alle
113. e overscan and underscan regions associated with each exposure A single long dark exposure which can also be taken with the DARK command The dark count is very small and a dark frame is usually used to measure the cosmic ray rate If the ICL interface is not running dark frames can be taken with the following procedure 1 Set up the correct buffer with the correct size in the DMS with one of the commands CRUN GRUN or OPN if the latter then the correct arguments must be used 2 At the CCD controller invoke the Network vocabulary with the command NETWORK 3 At the CCD controller set the exposure time with the command lt headno gt lt exposuretime gt SEX where the time is in milliseconds 4 Begin the dark exposure with the command lt headno gt 0 DAR Note that although the network command to take a dark frame is DRK the CCD controller command is DAR 5 The exposure will read out into the DMS buffer and can be stored with KEEP from ICL It is very difficult to setup windows or binning without access to the ICL interface A number of flat fields taken with the Tungsten lamp The grating can be moved to give uniform illumination along the spectrum because the tungsten flatfield should not be used to take out large scale sensitivity variations It cannot be used to take out the large scale variations along the slit because the illumination of the slit by the calibration optics is not exactly the same as the illum
114. e to the Calcite analyser position CALC Inserts calcite block into the beam POL Move Polaroid analyser into the beam HW POLAR MOVE IN or OUT Moves the HW plate into or out of the beam HW POLAR ANGLE n Sets angle of HW plate to n in tenths of a degree HW_POLAR ROTATE n Rotates the HW plate at n Hz HW_POLAR STOP ROTATE Stops the rotation of the HW plate sets angle to 0 HW_POLAR INIT Initialize the halfwave plate QW_POLAR MOVE IN or OUT Moves the QW plate into or out of the beam QW_POLAR ANGLE n Sets angle of QW plate to n in tenths of a degree QW_POLAR ROTATE n Rotates the QW plate at n Hz QW_POLAR STOP ROTATE Stops the rotation of the QW plate sets angle to 0 QW_POLAR INIT Initialize the quarterwave plate 10 6 5 Initialising mechanisms 93 OUICK REFERENCE GUIDE ISIS Users Manual INSLIT initialises slit unit not the slit width INRG initialises red grating INBG initialises blue grating INRFOLD initialises red fold slide INBFOLD initialises blue fold slide INRCOLL initialises red collimator INBCOLL initialises blue collimator INHW initialises 1 2 wave plate INQW initialises 1 4 wave plate INFCP initialises FCP tray INDEK initialises dekker ISIS_INIT mechanism for any ISIS mechanism mechanism INIT for some ISIS mechanisms ISIS mechanism names include DEKKER SLIT_JAWS SLIT_UNIT HW_POLAR QW_POLAR FLENS_CALC_POL BLUE_FOLD RED_FOLD BLUE_FILTER_A BLUE_FILTER_B RED_FILTER_A RED_FILTER_B BLUE_COLLIMATOR RED_CO
115. e typically procedures containing lower level commands to d tasks device tasks which are high level PASCAL programs running on the system computer LP VF as sub processes of the main observer s process There are d tasks for each of the major mechanisms e g ISIS A amp G UES telescope DMS each CCD The d tasks in turn exchange messages over the utility network Ethernet with the Motorola microprocessors controlling individual stepper drive motors barcode readers and shutter modules The messages are typically commands to move status requests and status returns Most of the mechanisms are controlled via Motorola 6809 locally known as 4MS micro processors there is one for each of ISIS A amp G FOS LDSS TAURUS UES and IPCS The TV autoguider and Detector Memory System DMS each use a 68020 processor in a VME chassis housed in the blue control cabinets The CCD controllers including that for the autoguider CCD are based on 68008 microprocessors The microprocessors are programmed in FORTH Each of the microprocessors and the system computer is connected to the utility network via a Network Interface Unit NIU Each NIU can connect up to four microprocessors There are currently two NIUs on the telescope and two in the control room Data from the CCDs is trans mitted via fibre optic links to the autoguider and DMS VME systems Data arriving at the DMS are automatically sent to the data disk on the system computer and may also
116. ead fed by a right angled prism and focal reducing optical system with a field diameter of 1 8 arcmin The autoguider utilises the off axis field The centre of the autoguider field rotates about the centre of the main field at a radius of 110 to 150 mm 8 2 to 11 2 arcmin and the entire probe assembly has a radial displacement of 40 mm The extreme edge of the autoguider field is partially vignetted but only by about 5 The autoguider has an azimuthal scan of 180 degrees so the total area scanned at a field scale of 4 51 arcsec mm equals 152 square arcmin or 0 04 square degrees This gives a good chance of finding a star brighter than 11th magnitude at the galactic equator or 13th magnitude at the galactic pole C W Allen Astrophysical Quantities publ Athlone Press 1976 INSTRUMENTS ISIS Users Manual SLIT VIFWING OPTICS PROBI FOCAL REDUCING LENSES iV CAMERA FIBRE OPTIC FEED MIRROR COMPARISON OPTICS SMALL FEED FLAI PROBE COMPARISON gt LAMPS 3 ACQUISITION COMPARISON MIRROR PROBE INTEGRATING SPHERE ND amp COLOUR FILTERS TAUTOGUIDER COMPARSON PROBE AUTOGUIDER MAIN ND amp COLOUR FILTER SLIDES WILLIAM HERSCHEL TELESCOPE CASSEGRAIN ACQUISITION amp GUIDER UNIT Figure 1 Cutaway view of the WHT Cassegrain A amp G Unit showing the positions of the folding mirrors Autoguider Probe and Calibration Sources ISIS Users Manual INSTRUMENTS The autoguider head is mounted inside th
117. ead out starting from r IPCLEAR clears DMS IPCS buffer 91 OUICK REFERENCE GUIDE ISIS Users Manual 10 5 The DMS Display e Both CCD and IPCS images are read out into the DMS and displayed on the screen e The first CCD exposure read out after startup or a DMS reset will just be displayed as a small ikon Click the cursor on this ikon with the LH mouse button for a full size display You can switch between CCDs and between CCD amp IPCS in this way e The mouse is disabled during CCD readout or when the IPCS display is being updated when a BUSY message is displayed 10 6 ISIS Commands 10 6 1 Slit area SLIT w LSLIT MSLIT DEKKER n SLIT_DOOR OPEN SLIT_DOOR CLOSE 10 6 2 Folds and Filters RFOLD n BFOLD n RHART n BHART n RCOLL n BCOLL n RFILTA n RFILTB n BFILTA n BFILTB n CHANGE 92 sets slit width to w microns selects long slit unit selects multi slit unit moves dekker to position n where 0 out 1 narrow 1 2 2 20 for FOS 6 long slit observing releases slit area access door N B the DEKKER should be in position 0 for access to the slit area locks slit area access door moves red fold to position n 0 flat mirror 1 out moves blue fold to position n 0 out 1 flat 2 dichroic N B As of Oct 91 the BFOLD flat only reflects the central 2 5 arcmins of the field or from 100 700 on the CCD Important limit for Multislit users moves Red Hartmann shutter to position n
118. ed blaze to collimator and the slit width in the table below and the grating angles given by the procedure CENWAVE rely upon the assumption that the grating is mounted blaze to collimator The table below gives the parameters of the gratings and the pixel size and spectral range obtained with EEV and Tektronix CCDs 22 5 and 24 micron pixels respectively and for the blue gratings with the CCD IPCS 10 5 micron pixels The final column in the table below gives the slit width in arcseconds which will project to 50 um on the detector There is also a single silver coated plane mirror in a grating cell originally intended for alignment purposes but which can be used in place of the gratings for direct imaging at a plate scale of 14 9 arcsec mm To use the mirrors for imaging they should me mounted in the grating 11 vy Ta ana N Nan 3 Almm 3037 bu Aymm sog h o me S2 mm 4859 Smm
119. ed for setting up The penalty of the fast readout is a slightly higher readout noise The bias and gain of the CCD will also change 11 5 28 WINDOW Windows a CCD detector Format WINDOW lt channel gt Channel The name of the CCD data acquisition channel to be windowed Examples WINDOW BLUE Comments The system will prompt the user for the number of windows to be set up and the origin and size of each window Windowing and binning of the CCD will be enabled At present use of more than one window on a CCD is not recommended 11 5 29 WINK Takes a scratch exposure as for the SCRATCH command except that no headers are collected Format WINK lt channel gt lt filenum gt lt obstype gt lt time gt TITLE string Channel The name of the CCD data acquisition channel to be used Filenum The number of the scratch file Obstype The observation type Valid observation types are ARC BIAS DARK FLAT and TARGET Time The exposure time in seconds Title A title for the observation optional Examples WINK RED 5 ARC 60 Comments As for the SCRATCH command except that no headers are collected 11 6 Data Taking Commands IPCS detector 11 6 1 EXPOSE Starts an exposure on a specified detector Format EXPOSE lt detectorname gt lt exposuretime gt Example EXPOSE IPCS 1000 Synonym EI EXPOSE IPCS Units seconds Comments If the previous exposure has not been kept EXPOSE will prompt the user to do this b
120. ed with FOCUS Also check line rotation with DMS command X FIND Then use IPROT n to rotate IPCS camera head to position n where n is 32768 rot and rot is 50 IPCS pix displacement from top to bottom ve to move line anticlockwise To reduce centroid differences to 0 change collimator by 600 units for 0 5 IPCS pix 4 ve to make shift go ve N B if you use the DMS command 1 12 13 FOCUS SET the line positions are in screen pixels not IPCS pixels Write them down when you first choose them Best IPCS focus is currently 2 2 5pixels check with the Local IPCS Expert The last BCOLL setting will be written on the whiteboard 10 4 3 Observing with IPCS OVERSCAN mode should always be used for a new objects arc etc and then return to normal format with default proc IPCSWIN or IPCSFORMAT Always observe new objects with your finger on the PANIC button If used it is necessary to IPC before IPO will work If the IPCS Overillumination circuit is tripped then it must be cleared with the command SPO OVERILLUM INIT IPO opens IPCS shutter IPC closes IPCS shutter EI t performs a t secs IPCS exposure short for EXPOSE IPCS KI keeps the exposure transfers it from DMS to the 4000 IPPAUSE pauses the exposure IPCONT restarts the exposure IPSTOP stops aborts the exposure IPNEWT changes the exposure time during the integration IPUPDATE causes exposure time to update on MIMIC IPWIN rw changes Y window to w rows r
121. ee of polarization scale is R 1 Ip 1 ga et vith Ra Jou RFI 145 1 145 1 Note that by multiplying the intermediate ratios instead of dividing them the G ratio relative flat field is obtained The other Stokes parameter Pu is obtained similarly from the pair of exposures with the halfwave plate at 22 5 and 67 5 degrees The raw degree of polarization P and polarization angle 0 are then given by P P6 P and 0 0 5 arctan Pu Po Note that this schematic procedure neglects CCD bias sky background and calibration for instrumental parameters Bias may be subtracted from the data frames as a first step or be treated as part of the sky background sky subtraction and calibration are treated in separate subsections below 9 5 2 Imaging Polarimetry ISIS can be used as an orthodox focal reducer with a convenient plate scale of 0 3 arcsec per 22um pixel The optical quality of the instrument is excellent on axis although towards the edges of the field there is some chromatic distortion this does not matter in a spectrometer The mirror which replaces the grating in this mode is silver coated and so the throughput of the red channel is good 5 reflections at 98 each The mirror should be used at the angle appropriate for the channel in use 55500 for the red arm or 53250 for the blue arm The important use of the instrument in this mode is as a specialised imaging polarimeter as the existing modulator as used for spe
122. either switch the IPCS EHT to standby or else contact RGO technical staff for assistance before opening the slit door Before the slit door is opened the dekker slide must be in position 0 At the ICL interface type DEKKER 0 48 ISIS Users Manual SETUP PROCEDURES wait for the dekker action to complete this mechanism is slow SLIT DOOR OPEN The slit access door can then be opened manually The dekker slide is a horizontal slide at the top of the slit area which can be withdrawn from an angled groove When replacing the dekker slide care must be taken to locate the slide correctly in this groove The two blue beam filter slides are to the right of the slit area and can also be withdrawn and replaced However the grooves that the two slides run in are not identical and these slides cannot be interchanged The same is true of the two red beam slides which are in the lower part of the slit area All the filter slides are somewhat stiff and changing these filters should normally be done by RGO technical staff The dichroic slide is in the centre of the slit area and is rather larger than the filter slides It contains the mounting cells for the dichroics and for the flat mirror these have the shape of a right angled triangle The dichroic slide is held in place by a sprung loaded locator pin this can be released by lifting the plastic knob on the slide The knob can be twisted through 90 degrees when the locator pin will be held
123. en below in dark grey amp bright time These data refer to clear conditions no cloud or dust low aerosols extinction at V between 0 10 0 16 mag airmass Table 13 La Palma Sky Brightness Mag Square Arcsec Data Source JKT Peoples Photometer June 1984 JKT CCD June September 1989 In the Table Dark means Moon below the horizon Grey means above the horizon with phase 0 58 0 67 and bright means above the horizon with phase 0 90 0 96 The sky data are guidelines precise values depend critically on angular distance from the Moon the elevation of the Moon and the atmospheric aerosol amp dust content The dark sky variation between 1984 9 may be partly due to a correlation with phase of the 11 year Solar cycle a variation of 0 5 mag has been reported by the UK Schmidt Telescope but because of the lower geomagnetic latitude of La Palma a slightly smaller ampli tude is expected here Flux calibrated low resolution night sky airglow spectra have been presented by C R Benn Gemini 35 p 20 1992 and by C Jenkins amp S Unger ING La Palma Technical Note No 82 Note that in the red emission lines from OH and H20 molecules dominate the spectrum and so the broad band magnitudes given above do not give a good idea of the sky continuum flux at any particular wavelength E 2 Extinction at La Palma The extinction as a function of wavelength has been tabulated by D L King ING Tech No
124. erified this 11 3 14 HW POLAR Controls the Half Wave Plate Format HW_POLAR lt function gt lt parameter gt Examples HW_POLAR MOVE IN HW_POLAR ROTATE 25 HW_POLAR ANGLE 1800 HW_POLAR STOP ROTATE Synonyms HWIN HW_POLAR MOVE IN HWOUT HW_POLAR MOVE OUT HWP HW_POLAR ANGLE HWPROT HW_POLAR ROTATE Units Angles are specified in units of a tenth of a degree Rotation rates are specified in units of a tenth of a Hz Range Angle in range 0 to 3600 Rotation rate in range 7 to 118 Comments function can have the values ROTATE ANGLE MOVE or STOP The parameter for HW_POLAR ROTATE is a rotation rate in units of a tenth of a Hz this sets the plate in continuous rotation The parameter for HW_POLAR ANGLE is an angle in units of a tenth of a degree this sets the plate to a fixed angle The parameter for HW_POLAR MOVE can be IN or OUT this moves the plate in or out The parameter for HW_POLAR STOP can be ROTATE or MOVE this stops the plate rotating or moving Notes The wave plate must be in before continuous rotation is started and the if the wave plate is rotating it must be stopped before sending it to a fixed angle 11 3 15 ISIS_CONFIG Configures the folding mirror slides for observing with a named combination of arms Format ISIS_CONFIG lt configuration gt Example ISIS_CONFIG BLUEANDRED Comments Valid parameters are RED BLUE FOS BLUEANDRED and BLUEANDFOS 11 3 16 ISIS_INIT Initialises a named mec
125. ering 34 6 Overall performance of the system 35 III Computers and Operations 36 7 Control System 36 7 1 Controlsystemoverview 36 7 2 The Detector Memory S5ystem 37 7 3 Thes5PARGCstation 37 74 The Utility Network 39 7 0 The System Computer and User Interface 39 7 6 The MIMIC display 40 7 7 Generating Data Tapes 41 7 8 Engineering terminals 41 7 8 1 The Engineering MIMIC 42 7 8 2 Direct control of the Cassegrain Instruments 42 7 8 3 The Detector engineering control terminal 42 IV SETUP AND OBSERVING PROCEDURES 43 8 Setup Procedures 43 8 1 Starting the computer systems 43 8 2 Configuration of the A amp G Box and Spectrograph A6 8 2 1 Changing Gratings A6 8 2 2 Changing Filters in the Main A amp G box slides 2 2 AT 8 2 3 Changing components in the slit area 48 8 24 Directing light to the right cameras 49 8 2 5 Setting Grating Angles 50 8 2 6 TheslitArea 50 8 2 7 Configuring the Spectrograph for Spectropolarimetry
126. es are specified in units of a tenth of a Hz Range Angle in range 0 to 3600 Rotation rate in range 7 to 118 110 ISIS Users Manual COMMAND LISTS Comments function can have the values ROTATE ANGLE MOVE or STOP The parameter for QW_POLAR ROTATE is a rotation rate in units of a tenth of a Hz this sets the plate in continuous rotation The parameter for QW_POLAR ANGLE is an angle in units of a tenth of a degree this sets the plate to a fixed angle The parameter for QW_POLAR MOVE can be IN or OUT this moves the plate in or out The parameter for QW_POLAR STOP can be ROTATE or MOVE this stops the plate rotating or moving Notes The wave plate must be in before continuous rotation is started and the if the wave plate is rotating it must be stopped before sending it to a fixed angle 11 3 21 RCOLL Controls the Red collimator Format Example Units Range Comments RCOLL lt position gt RCOLL 7500 Microns 0 to 30000 Moves stops or initialises the Red collimator Valid parameters are a position in microns STOP and INIT 11 3 22 REDGRAT Controls the red grating Format Example Synonym Units Range Comments REDGRAT lt angle gt REDGRAT 56478 RGRAT Millidegrees 0 to 110000 Moves stops or initialises the Red Grating or reprograms the SMDM which controls it Valid parameters are an angle in millidegrees STOP INIT and REPROGRAM The last option should only be used in ex
127. es unless a FITSINIT is issued 13 Local Subsystem Commands 13 1 Autoguider Commands 13 1 1 NET Checks what devices are accessible across the network from the autoguider Format NET Comments Sends a message to each device in turn across the network and waits for an acknowledgement Logs which devices acknowledge and which do not Useful for diagnosing network problems 13 1 2 ACQINT Changes the integration time when in acquisition mode Format ACQINT lt integrationtime gt Example ACQINT 8000 Units Milliseconds 13 1 3 ACQWIND Specifies the acquisition window for the Autoguider Format lt xi gt lt yl gt lt x2 gt lt y2 gt ACQWIND Example 50 50 300 200 ACQWIND Defaults xl 30 yl 30 x2 360 y2 250 Comments Sets the acquisition field on the Autoguider CCD in pixels 13 1 4 CASS selects the Cassegrain Autoguider Format CASS Comments There are also commands to select other autoguiders including UES PRIME and AUTOFIB 13 1 5 FIELD Scans the field searching for guide stars Format lt nstar gt FIELD Example 1 FIELD Comments Causes the CCD autoguider to read out and search for guide stars marking the nstar brightest star in the field to use as a guide star nstar defaults to 1 FIELD is equivalent to 1 FIELD 128 ISIS Users Manual COMMAND LISTS 13 1 6 GUIDE Starts the Autoguider tracking a star or stops it Format GUIDE ON lt n gt or GUIDE OFF Example GUIDE ON
128. esired position angle on sky and centre target on slit e OFFSET type da dd where type is either ARC units are arcsecs on sky or SEC secs of time and arcsecs da dd are the offsets in a 6 in the above units 97 OUICK REFERENCE GUIDE ISIS Users Manual e do FIELD and find a good guide star but don t start guiding yet e PROBE r8 on TCS console e OFFSET type 0 0 to return to main target to check it s still centered on the slit e OFFSET type da dd and start exposures e do FIELD again and quickly start closed loop autoguiding 10 11 2 Data Files e To see what files have been saved on the 4000 look in the directory DISK SWHTDATA OBSDATA dd mm yyyy i From ICL use DCL DIR DCT_OBSDIR dd mon year e To write a FITS tape from the 4000 Login to LPVE as OBSERVER in an independent session ALLOCATE MUDO or MUEO Allocate one of the tape drives that are connected to LPVE MOUNT FOR DENS 6250 MUDO or MUEO Mount the tape FITSINIT and answer the questions WRITE_FITS ditto To write an EXABYTE in FITS format Login to LPVE as OBSERVER Allocate the exabyte ALLOC MUCO or MUEO MOUNT FOREIGN MUCO or MUEO FITSINIT answer the questions WRITE_FITS ditto To write DAT in FITS format Login to LPVE as OBSERVER Allocate the DAT ALLOC MUC3 MOUNT FOREIGN MUC3 FITSINIT answer the questions WRITE_FITS ditto 98 ISIS Users Manual QUICK REFERENCE GUIDE
129. et to give a count rate of no more than one photon pixel second at x8 resolution along the spectrum and x2 resolution alongthe slit The ICL procedure IPCSFORMAT should be used so set up an appropriate data window Close the left Hartmann shutter by typing BHART 1 at the ICL interface and take an exposure of at least 200 seconds by typing IPCSOPEN EXPOSENP IPCS 200 60 ISIS Users Manual SETUP PROCEDURES at the ICL interface When it has finished at the DMS control window type FOCUS select three strong lines evenly spaced from the one end of the spectrum to the other by placing the cursor on each in turn and pressing the space bar on the DMS keyboard Each line profile will be shown on the DMS display and the line can be rejected if it appears too weak or blended with or close to another line The best results will come from strong isolated lines When three lines have been selected type FOCUS LEFT at the DMS control window The DMS will then list the centroid and an estimate of the full width half maximum in DMS pixel units at three positions along each line and store these values The arrangement of the listed positions on the alphanumeric screen maps to the DMS display so the first position listed is in the top left hand corner of the image as displayed on the DMS display Now open the left Hartmann shutter and close the right by typing BHART 2 at the ICL interface and take a similar exposure A
130. f the slope on the DMS display will depend upon which CCD on chip amplifier is being used so this will have to be established by trial and error Getting the rotation right is largely a matter of trial and error and can be a time consuming process When the rotation is correct all seven screws holding the two rings together should be tightened 8 3 2 Tilt and coarse Focus The tilt of the cryostat can be adjusted in two dimensions to ensure that the CCD is coplanar with the focal plane of the spectrograph The cryostat is held to the mounting ring by three clamps on the mounting ring which each hold a capstan attached to the cryostat flange against the mounting ring The height of the cryostat can be adjusted by rotating the capstans and can be measured with three micrometers mounted on the cryostat flange alongside each capstan which can be brought against a metal stud in the surface of the mounting ring The capstans 52 ISIS Users Manual SETUP PROCEDURES can be locked by tightening the thread that they run through with an Allen screw in the cryostat flange The tilt of the CCD can be checked with the FOCUS procedure on the DMS With a slit width of around 150um and a long slit dekker position set the exposure time filters and central wavelength to give a uniform distribution of line from one of the comparison lamps make sure that there are reasonably strong lines near each end of the spectrum The exposure time should be se
131. ffective sizes at the photocathode are 3 8x larger The maximum available area is 256 x 320 pixels In the spectral direction with x8 subdivision there are 2560 pixels each with an effective size of 10 5um with no subdivision there are 320 pixels of 844m each In the spatial direction no subdivision x1 yields 1 2 arcsec pixel and x8 gives 0 16 arcsec pixel The CCD IPCS resolution obtained depends very slightly on wavelength worse to the blue a resolution FWHM of 32pm i e 3 0 pixels at x8 is obtained at 4300A Observers familiar with IPCS I detectors used at the AAT and on the INT will find many things in common between the systems The principal difference is that the CCD IPCS has a GEC CCD as back end detector whereas IPCS I has a Plumbicon TV tube Also IPCS II has 33 DETECTORS ISIS Users Manual a linear response up to somewhat higher photon count rates than does IPCS I see below The maximum count rate per CCD pixel for a deviation from linearity less than 10 is dependent upon the frame size higher maximum rate for a smaller frame and upon the dis tribution in intensity of the source higher maximum rate for emission line than continuum sources In tests with a prototype CCD IPCS in 1987 with full format 250 x 320 CCD pixels and frame time of 17 ms about 5 loss was found at a measured rate of 1 ct s CCD pixel In a spectroscopic format 64 x 320 at x 8 spectral resolution
132. filter slide to a given position Format MAINFILTC lt filterposition gt Examples MAINFILTC 3 MAINFILTC GG395 Comments The position can be specified as a filter position number in the range 2 6 as the name of a filter which has been identified by its barcode or as OUT to remove the filters from the beam 11 1 19 MAINFILTND Moves the main neutral density filter slide to a given position Format MAINFILTND lt filterposition gt Examples MAINFILTND 3 MAINFILTND ND2 0 Comments The position can be specified as a filter position number in the range 2 6 as the name of a filter which has been identified by its barcode or as OUT to remove the filters from the beam 11 1 20 TV_DIRECT_12 Selects the direct viewing position at a scale of 12 arcsec mm Format TV DIRECT 12 Comments Procedure which moves the mirrors to the ACOCOMP position selects a scale of 12 arcsec mm and the correct value of TVFOCUS 103 COMMAND LISTS ISIS Users Manual 11 1 21 TV DIRECT 5 Selects the slit viewing position at a scale of 5 arcsec mm Format TV_DIRECT_5 Comments Procedure which moves the mirrors to the ACQCOMP position selects a scale of 5 arcsec mm and the correct value of TVFOCUS 11 1 22 TV SLIT 12 Selects the slit viewing position at a scale of 12 arcsec mm Format TV_SCALE_12 Comments Procedure which moves the mirrors to the SLIT VIEW position selects a scale of 12 arcsec mm and the correct value of TVFOCUS 11
133. g the entire data acquisition process The commands for doing this are listed in Part VI e The data acquisition system writes the data to files on the system computer datadisk ready to be archived On completion of an exposure the data is normally transferred from the DMS to the system computer via a DR 11W interface The header information associated with that data will have been collected by the system computer either during the exposure or on completion of the exposure Data and headers are then merged into a datafile on the system computer disk The datafile is in HDS NDF format the header information being stored in the standard FITS extension to this format Finally two copies of the data are written to tape a FITS format tape for the La Palma archive and either a FITS tape or a VAX backup tape for the observer The system computer is networked to various data reduction computers currently a VAX 4000 plus several VAXstations Data can be copied across to these machines for immediate processing 7 6 The MIMIC display The MIMIC display running on the VAXstation 3100 gives mainly graphical representations of the current status of the telescope instruments and detectors There are a number of pages which can be selected using the mouse Current pages include e TELESCOPE Current position on sky airmass parallactic angle etc e CAGB Light path and status of mechanisms in the A amp G box only e ISIS SUMMARY Ligh
134. gration time of between 5 and 30 seconds When using both arms it is possible to make the best of the disparity in the required exposure times for comparison lamps in the blue and red channels by completing the entire red exposure including clearing exposing and reading out the CCD and keeping the file to the Vax disc while the blue CCD is integrating At the ICL interface 1 Ensure that the acquisition and comparison mirror is in if it is not put it in by typing AGCOMP 2 Switch on the required comparison lamp s with the command COMPLAMPS 3 Start the blue exposure with ARC BLUE lt exposuretime gt where the exposure time is 100 300 seconds 69 OBSERVING PROCEDURES ISIS Users Manual 4 When the packet collection is complete start the red exposure with ARC RED lt exposuretime gt where the exposure time is in the range 10 30 seconds 5 Wait for the red exposure to finish reading out when it has finished the icon for the red CCD frame will appear on the DMS display screen and the message PICTURE action complete will appear at the ICL interface 6 Wait for the blue frame to finish reading out again waiting for the icon to be redrawn and the PICTURE action complete message to appear at the ICL interface If the difference between the two exposure times is less than about 60 seconds then the blue frame will begin reading out before the transfer of the red data to disc has taken place This
135. grationtime gt AIT at the Autoguider terminal 11 2 2 FIELD Causes the CCD autoguider to read out its whole field of view and look for a suitable guide star Format FIELD Comments Does not return control to the user until this process is complete Equivalent to 1 FIELD at the autoguider interface 11 2 3 FOLLOW Causes the CCD Autoguider to follow a star image and to send error signals to the Telescope Control Computer or to stop doing so Format FOLLOW lt onoroff gt lt n gt Examples FOLLOW ON 1 Synonyms FON FOLLOW ON 1 FOFF FOLLOW OFF 1 Comments Valid values of the first parameter are ON and OFF the second is the number of Autoguider integrations per guiding error is normally 1 Equivalent ton 1 GUI and GUI OFF at the Autoguider terminal FOLLOW does not start the telescope autoguiding it is necessary to issue the PROBE and AUTOGUIDER commands to the TCS either through the ICL interface or at the TCS terminal to do this For details of these commands refer to THE WHT USERS MANUAL 11 2 4 GUIINT Changes the Autoguider integration time when guiding Format GUIINT lt integrationtime gt Example GUIINT 4000 Units Milliseconds Comments Equivalent to lt integrationtime gt GIT at the Autoguider terminal 11 3 ISIS Commands 11 3 1 ANAMORPHOTIC Moves the Anamorphotic lens in or out 105 COMMAND LISTS ISIS Users Manual Format Example Comments ANAMORPHOTIC lt direction gt ANAM
136. h a keyword Each keyword defines ao Sao ao iao UU eee e o a eH OOH A oO the data type given to the program A brief description is provided below L is the plate label Normally the plate label will be the observed field This label can contain up to 40 characters It must identify clearly the field to avoid confusion in those cases where other fibre observing programmes use similar sky regions 40ARCMIN defines the telescope field diameter With the aid of this informa tion the programme checks if all the objects are on the telescope field however this command concerns the Anglo Australian telescope and actually is has not been modified to be used for 155 APPENDICES ISIS Users Manual the La Palma telescopes Then the information obtained from this command is useless in this case D is the observing date in decimal years This is reguired in order to correct for the rotational effects of precession and nutation But as this correction is a rotational correction the plates can be used again at a later date if the objects have no large proper mo tions The rotational correction in this case is made adjusting the rotator and plate orientations section 9 6 2 E is the reference equinox for the objects equatorial coordinates Also this will be used to correct rotational effects S is the focal plane scale in units of mm This value depends on the telescope and the telescope focal plane used T are two temperature va
137. hanism Format ISIS_INIT lt mechanism gt 109 COMMAND LISTS ISIS Users Manual Example ISIS_INIT RED_GRATING Comments Mechanisms which can be initialised include RED_GRATING BLUE_GRATING RED_COLLIMATOR BLUE_COLLIMATOR RED_FILTER_A RED_FILTER_B BLUE_FILTER_A BLUE_FILTER_B DEKKER SLIT_UNIT HW_POLAR QW_POLAR RED_FOLD BLUE_FOLD and FLENS_CALC_POLAR 11 3 17 ISIS MOVE Moves a specified mechanism Format ISIS MOVE lt mechanism gt lt position gt Example ISIS MOVE RED GRATING 45789 Comments The list of mechanisms which can be moved includes those which can be initialised with ISIS_INIT plus ANAMORPHOTIC LID COVER and SLIT_JAW5 11 3 18 ISIS UPDATE Updates the status of a mechanism on the MIMIC display Format ISIS UPDATE lt mechanism gt Example ISIS_UPDATE SLIT Comments The list of mechanisms which can be updated is the same as that which can be moved with ISIS_MOVE 11 3 19 LID Opens or closes the Lid Cover Format LID lt direction gt Example LID OPEN Comments Valid parameters are OPEN and CLOSE 11 3 20 QW POLAR Controls the Quarter Wave Plate Format QW_POLAR lt function gt lt parameter gt Examples QWPOLAR MOVE IN QW_POLAR ROTATE 25 QW_POLAR ANGLE 1800 QW_POLAR STOP ROTATE Synonyms QWIN QW_POLAR MOVE IN QWOUT QW_POLAR MOVE OUT QWP QW_POLAR ANGLE QWPROT QW_POLAR ROTATE Units Angles are specified in units of a tenth of a degree Rotation rat
138. he DAS commands are RUN chann t title Take an exposure of an astronomical target TARGET chann t title Same as RUN FLAT chann t title Take a flat field exposure SKY chann t title Take a sky flat exposure ARC chann t title Take an arc doesn t control the lamps 87 OUICK REFERENCE GUIDE ISIS Users Manual MAP chann 1 title Take a dekker map exposure DARK chann t title Take a dark exposure shutter not opened BIAS chann title Take a 0 sec exposure FLASH chann title Ditto with preflash GLANCE chann obstype t A quicklook put data in DMS only no headers KEEP chann title Keep a GLANCE file SCRATCH chann num obstype t title As RUN but data saved as file num in scratch area WINK chann num obstype t title As SCRATCH but no headers are collected PROMOTE num Promote scratch file num to normal RUN file status It is possible to take a set of n identical exposures with the command MULTRUN chann n title and there are similar commands MULTFLAT MULTARC etc DAS commands to modify or end exposures are PAUSE chann Pause an exposure CONTINUE chann Continue a paused exposure FINISH chann End an exposure and save the data ABORT chann End an exposure and discard the data NEWTIME chann t Set a new exposure time The command DIR lists the RUN and SCRATCH files taken during the night 10 3 Setting Up The CCDs The typical configuration is CCD1 RED CCD2 BLUE CCD3 FOS or AUX This may change DET SHOW CONF shows the ac
139. he auxiliary port At this f 11 Cassegrain focus the telescope scale is 4 51 arcsec mm at the detector which gives a scale of 0 10 arcsecs per 22 wm CCD pixel At present GEC P8603 EEV P88300 and Tek 1024 square CCDs are offered at the Auxiliary focus these detectors are described in more detail in Chapter 2 Table 1 summarises the pixel and field sizes given by these CCDs The unvignetted field at the Auxiliary port is currently limited by the shutter to 2 0 arcmin diameter thus the final unvignetted field is the intersection of this circle with the rectangle given in the table INSTRUMENTS ISIS Users Manual 2 ISIS and FOS II Spectrographs 2 1 Overall layout ISIS and FOS II comprise three spectrographs sharing a common slit unit dekker slide optics for spectropolarimetry and some filter slides FOS II lies directly below the optical path and is designed to provide the highest throughput at a dispersion of 400 A mm in first order and 200 A mm in second order Each of the two arms of ISIS is a conventional spectrograph with interchangeable reflection gratings and a horizontal optical layout The optical components of the two arms and the anti reflection coatings on those components are optimised for specific wavelength ranges The upper arm is optimised for the range 3000 6000 A and is called the BLUE arm whilst the lower arm is optimised for the range 5000 10000 A and is called the RED arm Light is fed into the two
140. he data in the DMS buffer may then be transferred to the Vax disc with KEEP otherwise the disc file must be closed with CLOSE Does not close the IPCS shutter 11 6 11 IPUPDATE Updates the IPCS exposed time on the MIMIC display Format IPUPDATE Comments Causes the IPCS exposes time to update on the MIMIC display if for some reason it is not doing so 11 6 12 KEEP Transfers a data frame from the DMS buffer to the Vax 4000 Data disc Format KEEP lt detectorname gt Example KEEP IPCS Synonym KI KEEP IPCS 124 ISIS Users Manual COMMAND LISTS Comments Transfers the data to a disc file in the directory DCT OBSDIR on the Vax 4000 The disc file will be given a name which consists of a file number which is sequential and the name of the DMS buffer that the data came from 11 6 13 CLEAR_OVERILLUM Clears the Overillumination status Format CLEAR_OVERILLUM Comments An overillumination trip closes the shutter and will not allow the user to open it until the overillumination status has been cleared It is important for the user to establish why the overillumination condition occurred and to ensure that it will not happen again before issuing this command 11 6 14 OVERSCAN Sets the area of the CCD read out to be the whole area of the chip Format OVERSCAN Comments This ensures the whole of the CCD is read out but unlike the overscan switch on the INT IPCS it does not scan the whole of the output of the E
141. he drawing board stage and it is by no means clear when if ever they will become available to the community this will depend on demand from users and the availability of engineering effort 9 3 4 A note on accurate time and ISIS A long standing problem with ISIS has been the lack of accurate shutter timings The current system uses clocks on the CCD controllers to write shutter opening and closing times to the file headers The clocks are relatively inaccurate and can drift by a few seconds over the course of a night The present solution is to synchronise the clocks with UTC at the start of each night using the commands DATE TIME HH MM SS SET TIME and DD MM YY SET DATE on the engineering terminal This system is clearly inadequate especially when accurate times are required On the JKT and INT the shutter timings are obtained directly from the time service Work is currently underway to create a similar system on the WHT and we expect it to be fully 79 OBSERVING PROCEDURES ISIS Users Manual operational by the end of 1993 Until then we advise all observers who require accurate timings to contact their support astronomer for further details 9 4 Observing with FOS Procedures for observing with FOS are in general similar to those used when observing with CCDs on ISIS Section 9 1 FOS is a simpler spectrograph and has no moving parts A conse quence of this is that it is not necessary to take wavelength calibration exposures so
142. he first exposure These Hartmann shifts indicate how far from the focal plane the CCD is at each point and the aim of the tilt adjustment is to make all of the shifts the same If the shifts are more than 3 pixels then the spectrograph is probably too far out of focus for this procedure to succeed and it will be necessary to adjust the collimator position with BCOLL or RCOLL or else to move all three capstans so that the spectrograph is closer to focus The relative Hartmann shift from one end of the spectrum to the other or from one end of the slit to the other should be no more than about 0 2 pixels If they are more than this then the capstans will need to be adjusted There are three capstans labelled A B and C The 53 SETUP PROCEDURES ISIS Users Manual dispersion is horizontal when the telescope is parked at the zenith moving capstan B affects the tilt along the slit whereas moving capstan A or C affects both the tilt along the spectrum and that along the slit For this reason it is easier to adjust the tilt along the spectrum first and then the tilt along the slit To move a capstan the micrometer should be read then backed off The small Allen screw should be loosened until the capstan is free to rotate It may be possible to rotate the capstan without releasing the clamp this is probably the best thing to do if the amount of capstan rotation is less than one complete turn If it is larger the clamp should be released the ca
143. he latter can be resolved by allocating multiple windows so that one window contains the spectrum and another the bias strip although the multiple windows option will not be available until next year Binning the chip With the CCD controller it is possible to change the clocking routines to provide on chip binning in which the summed charge from several adjacent pixels is read out as a single charge This reduces the number of pixels which are read out and transferred and therefore also reduces the read out time by a factor which depends on the number of pixels in the binned chip An added advantage of binning is that the summed charge from the adjacent pixels is measured with the read out noise corresponding to a single pixel Hence the effective read out noise is reduced by a factor equal to the square root of the number of pixels in the bin The disadvantage of binning is that it reduces spatial resolution and the dynamic range of the chip since the larger pixels still have the count limit of a single pixel If neither of these is a problem then the use of on chip binning on its own or in combination with windowing should be considered Selecting the read out speed There are currently two read out speeds available when using ISIS READOUT_SPEED FAST and READOUT_SPEED STANDARD the speed must be typed in upper case For an EEV chip the full frame read out time in standard mode is approx imately 110 s with a read out noise of approximate
144. he long slit dekkers 2 4 Folds and Dichroics There is a remotely driven three position slide which mechanism contains options for the blue fold One of these positions is usually clear the others contain any of a folding prism a 45 degree mirror or any of a number of dichroic filters which are listed in Table 3 and described in more detail in Appendix C There are three interchangeable slides for this slide mechanism the procedure for changing these is described in Section 8 2 3 If the folding prism is used then ISIS Users Manual INSTRUMENTS SLIT CARRIAGE amp CROSS SLIDE DEKKER SLIDE ASS Y LONG SLIT ASS Y MUL TISOBJECT SLIDE APERTURE PLATE OR FISRE OFTIC FEED BLUE FILTER SLIDES SLIT ASSEMBLY BSASEPLATE RED FILTER l Blue FOLD SLIDES ASS Y RED FOLD ASS Y 4 2m SIS SLIT AREA EXPLODED VIEW roma St pt a Figure 4 The Polarimetry optics slit area components folds and below slit filters of ISIS and FOS T INSTRUMENTS ISIS Users Manual Table 3 Dichroic Filters for the blue fold slides Dichroic Half Power point of Width of crossover Half power point of Focus Offset for Name crossover A A blue rolloff A Red Arm microns Noon mI mI MM bk Ot Ot St Ot ST ST Ol oc cc Cc Co cD the blue arm of ISIS will require a substantial refocus in the sense that the blue collimator position must be increased by about 26000 microns compared with the value fo
145. he operation of the shutter The shutter can be opened with the command IPO and closed either with the command IPC or by pressing the Panic Button but this does not mean that an exposure has been taken An exposure should be started with the command EXPOSE IPCS after the shutter has been opened and the shutter should be closed with the command IPC immediately an exposure has ended The Panic Button is present to enable the user to close the shutter immediately if the level of illumination is too high If this is used the software does not know that the shutter has been closed and the observer must also close the shutter in software with IPC before the software will allow the shutter to be opened again If the shutter is opened and the level of illumination is much too high an overillumination trip will occur This causes the shutter to close and an overillumination status to be set in the IPCS 4ms the shutter cannot be opened until this status has been cleared This can be done with OVERILLUM_INIT It is important to establish the cause of the overillumination trip before opening the shutter again An overillumination trip does not affect the EHT supply and thus does not provide any protection in case of shutter failure and provides only limited protection if the cause of the overillumination is lights in the dome 9 2 1 TV Focus The TV focus must be set as described in Section 9 1 1 with the added proviso that this
146. he telescope entrance aperture obscuration i e the secondary mirror structure The reverse side of the acquisition mirror is used to feed the calibration light to the instrument Line maps of the Cu Ar Cu Ne and Th Ar lamps are published in ING Technical Note 84 by J E Sinclair Two eight position filter wheels are provided for the comparison system The filters available in filter wheel A are a clear position ND filters of 0 2 0 6 0 8 1 8 3 0 and colour filters GG375 ISIS Users Manual INSTRUMENTS PAS IT SLIT AUTOEUINER SCAN AREA Figure 2 The relative geometry of the Cassegrain Autoguider field Short bar the 4 arcmin slit Long straight line normal to the slit Solid short arc position angle degrees E of N of the slit Black dot in box guide star in CCD autoguider field Dotted line position angle of guide star The autoguider probe moves in an annulus between the dashed lines between 8 4 arcmin ro and 11 4 arcmin from the slit centre but to avoid vignetting the slit viewing optics should be restricted to the shaded area at 6 gt 30 The co ordinates of the guide probe are r and and the equations relating these co ordinates and the slit orientation are given in the text ISIS Users Manual INSTRUMENTS Table 1 CCD pizel and field sizes at the Auziliary port CCD Pixel size arcsec Field size arcmin GEC P8603 0 10 0 950 638 EEV P88300 0 10 2 1x1 9 Tek 1024 0 11 1 8x 1 8 and GG4
147. he tungsten lamp through the narrow dekker dekker 1 Filters exposure time and grating angle should be adjusted to give a fairly uniform count level along the spectrum The count level should not exceed 32767 anywhere along the spectrum If the spectrum displayed on the DMS screen is vertical as it will be for an EEV P88200 chip the X position of the spectrum should be measured as near as possible to each end with the DMS command X FIND If the spectrum on the DMS screen is horizontal as 51 SETUP PROCEDURES ISIS Users Manual it will be for an EEV P88300 chip the Y position of the spectrum should be measured at each end with the DMS command Y FIND At the DMS control window type X FIND or Y FIND Locate the cursor on one end of the spectrum with the DMS mouse then press the space bar on the keyboard not one of the mouse buttons to accept the cursor position A profile across the spectrum will be displayed on the DMS display screen and on the alphanumeric screen the position which is the raw cursor position in the spectral direction and the centroid in the spatial direction will be displayed For the centroiding algorithm to work well the peak of the profile should be near the centre of the display if it is not then press the space bar to return to the main display and repeat the process This should be repeated at the other end of the spectrum and the difference between the two centroids noted If this is more than abou
148. he user s choosing e g PERICOM MG IKON_1 CANON_P VAXstation TEK_4010 window 8 3 6 Minimum FWHM using the VAX The correct position of the collimator may also be determined not as accurately from a plot of line FWHM vs collimator position Take a series of regularly spaced exposures copy them to SCRATCH as files FOCUSi DST type FIGARO then FOCUS_FWHM and respond to the prompts The parameters which may be changed by the user are the number of images the wavelength direction X or Y the first and last pixels in the orthogonal direction to be used the start 56 ISIS Users Manual SETUP PROCEDURES collimator position the increment in collimator position whether the maximum pixel value is to be determined for each of the images so that the user can check for saturation whether the region of the spectrum to be used is cursor selected or defaults to the whole spectrum and the number of brightest lines to be used to determine the mean FWHM A version of FIGARO s EMLT program is used to determine the mean FWHM for the bright est lines on each extracted spectrum In focus position is estimated by determining the mini mum in a parabola fitted to the 3 points flanking the lowest measured FWHM in the relation FWHM vs focus position The program plots this relation on a device of the user s choosing e g PERICOM MG IKON_1 CANON_P VAXstation TEK_4010 window 8 4 Setting up the IPCS Instructions for starting up the IP
149. hen the differential shifts are satisfactory the micrometer readings should be noted in the ISIS log together with the date and details of the cryostat used The micrometers should then be backed off and the firmness of the clamps checked It is not normally necessary to tighten the small Allen screws unless the capstan is particularly loose 8 3 3 Collimator Focus The final focus is achieved by moving the ISIS collimators in practice this is all that most users will have to do The grating setting set by the ICL procedure CENWAVE and the CCD window set by the ICL procedure WINDOW should be appropriate for the observations of the coming night The collimator position can be set from the ICL interface by typing BCOLL lt position gt where the position is in the range 0 52000 RCOLL lt position gt where the position is in the range 0 30000 The spectrograph works best with the collimators near 8000 except if the blue camera is in use with the folding prism in which case the focus position should be near 30000 If focus is obtained far from these values the spectrograph will be astigmatic and although the comparison lines may be in focus the resolution along the slit will be degraded In this case it will be necessary to rotate the three capstans by the same amount to bring the CCD into approximate focus near 54 ISIS Users Manual SETUP PROCEDURES the optimum value of the collimator position Movement of the capstans is described
150. hey will be somewhat broader At the end of the focus procedure both Hartmann shutters should be opened by typing BHART 0 OT RHART 0 The focus is somewhat temperature dependent but unless there is a sudden change of am bient temperature the spectrograph once in focus should remain so for several days 8 3 5 Hartmann test using the Vax Using the command ARC or RUN obtain 3 or 5 pairs of Hartmann left and right arc lamp exposures at different values of the collimator position Copy them onto a scratch area on one of the Vaxcluster scratch disks as files HART_Li DST and HART_Ri DST where i takes values e g 1 3 or 1 5 Type FIGARO then FOCUS_HART and respond to the prompts The parameters which may be changed by the user are the number of left right pairs of images the wavelength direction X or Y the first and last pixels in the orthogonal direction to be used the start collimator position the increment in collimator position and whether the maximum pixel value is to be determined for each of the images so that the user can check for saturation The cross correlation between spectra extracted from left and right images is performed by the FIGARO routine SCROSS In focus position is determined in two ways by linear interpolation between two values flanking zero line shift and by fitting a least squares straight line to the relation between focus position and line shift The program plots this relation on a device of t
151. hich detects that the door is closed does not always operate and it may be necessary to open and close the door again until it does 8 2 3 Changing components in the slit area The slit area contains the dekker slide the dichroic and folding flat slide and the four ISIS filter slides two in the blue beam after the blue fold and two in the red and FOS beams between the blue and red folds Slides not in use are kept in a steel cupboard behind the WHT engineering console or else in the grating cupboard on the observing floor Care must be taken when working in the slit area because it is possible to knock the slit jaws out of alignment To realign the slit jaws it is necessary to remove ISIS from the telescope and this is equivalent to an extra instrument change The slit area access door is interlocked with the dekker slide it is only possible to open the slit door when the dekker is in position 0 when it offers some protection to the slit unit However with the door open it is then possible to move the dekker away from position 0 and it would then be easy to disturb the slit alignment Users must not do this and if they require any mechanism moved when the slit access door is open they must contact RGO technical staff If the IPCS EHT supply is on then only a minimum of light can be used in the slit area with the door open and in the dark it is more likely that mechanisms will be disturbed by accident Under these circumstances users must
152. his spectrograph face with the handles towards the door The grating clamps are operated by nitrogen pressure and are activated by a toggle switch For the red grating the switch is situated above the grating cell and for the blue grating below the grating cell If this toggle switch is moved to the down position the grating clamps will release this should only be done with the telescope at the zenith and the user should keep one hand on one of the handles on the grating itself while releasing the clamps The grating can then be withdrawn from the cell and taken out of the spectrograph All except the tallest of observers should use a set of steps while changing the blue grating its cell is both higher off the ground and deeper inside the spectrograph than that of the red grating Gratings are normally kept in wooden boxes in a metal storage cabinet on the observing floor The boxes are clearly labelled with the identifier of the grating they contain The gratings should be kept in these boxes whenever they are not in use and under no circumstances should they be left out on the observing floor Users should never touch the surface of a grating Any blemishes on the surface should be reported to the telescope manager users should never attempt to clean them off Replacing a grating in the cell is the reverse of removing one ISIS gratings are always used blaze to collimator so the arrow showing the direction of the blaze angle should
153. home disk of the OBSERVER Format DISKSPACE 117 COMMAND LISTS ISIS Users Manual 11 5 11 ENABLE WINDOWS Enables windows and binning factors previously disabled on a CCD detector Format Channel Examples Comments ENABLE WINDOWS lt channel gt The name of the CCD data acquisition channel ENABLE WINDOWS FOS Where windowing and binning of the CCD have been disabled using the DIS ABLE WINDOWS command this command reenables them 11 5 12 FINISH Terminate an exposure early saving data and headers to disk Format Channel Examples Comments FINISH lt channel gt The name of the CCD data acquisition channel to be used FINISH RED This command terminates the current CCD exposure saving the data to disk as if the exposure had completed normally 11 5 13 FLAT This is equivalent to the RUN command but intended for exposures of flat fields rather than astronomical targets Format Channel Time Title Examples Comments FLAT lt channel gt lt time gt lt string gt The name of the CCD data acquisition channel to be used The exposure time in seconds A title for the observation optional FLAT BLUE 1 5 Tungsten flat 5500 Angstrom As for the RUN command except that the observation type is set in the headers as being a flatfield exposure 11 5 14 GLANCE Takes an exposure and transfers the data into the Detector Memory System for inspection but not to the system computer For
154. iam Herschel Telescope Instrument control and data acquisition system user manual by S W Unger amp G T Rixon and only a subset of the commands relevant to observing with CCDs on ISIS are listed here Many commands do almost identical things for instance the commands RUN FLAT ARC and SKY differ only in one header item in the data file The commands SCRATCH and PROMOTE are intended for use by automatic setup procedures yet to be written 11 5 1 ABORT Terminate an exposure early abandoning the data Format ABORT lt channel gt Channel The name of the CCD data acquisition channel to be used Examples ABORT RED 115 COMMAND LISTS ISIS Users Manual Comments This command terminates the current CCD exposure throwing away the data 11 5 2 ARC This is equivalent to the RUN command but intended for exposures of arc lamps rather than observations of astronomical targets Format ARC lt channel gt lt time gt lt string gt Channel The name of the CCD data acquisition channel to be used Time The exposure time in seconds Title A title for the observation optional Examples ARC RED 1 5 CuAr arc 5500 Angstrom Comments As for the RUN command except that the observation type is set in the headers as being an arc exposure 11 5 3 BIAS Takes a single bias frame a zero second exposure and transfers the data plus headers to an HDS file on the system computer Format BIAS lt channel gt L lt
155. ibre slit can be seen on the collimator mirror Its centering and orientation can be checked this way e ISIS long slit can be positioned with the software command LSLIT Looking at the col limator mirror the movement of both the fibre slit and long slit can be followed Then differences in their centering and orientation can be seen e For a correct centering the position of the fibre slit must coincide with that of the long slit This can be achieved by sliding the slit mounting on the slit unit 63 SETUP PROCEDURES ISIS Users Manual e The white light illumination of the bundle is removed and instead the focal plane end of its central fibre number 31 is illuminated with a laser beam e The output light cone illuminates the collimator mirror Since the FRD of this cone is larger than the mirror the mechanical mirror holder becomes illuminated as well e The light cone can be centred on the collimator by moving the screws on the kinematic seats of the slit supporting plate This way the alignment between the optical axis of the fibres and the one of the spectrograph is obtained The alignment process described up to now can be checked by means of a method which is similar to the autocollimation one This method is as follows a flat mirror is placed at the diffraction grating position facing the collimator mirror the grating encoders position for the red arm to reach this situation is 35500 When a laser beam illuminates the
156. ical offset values between APEO and APE1 are X 4 2 and Y 4 2 9 6 3 Field acquisition The first step to do when performing fibre optic multi object spectroscopy is to select a field and to put the observing fibres on the aperture plate To insert the fibres in the corresponding holes is an easy task but it must be performed with caution in order to avoid damaging the fibres ends Also it must be taken note of to which star in the field each fibre corresponds Although it is not strictly needed it can be useful as well to order the stars by magnitudes in such a way that to avoid contamination two adjacent spectra do not produce large luminosity differences onto the detector 10 to 15 minutes are required in order to insert 61 fibres in the plate Briefly the field acquisition consists of pointing of the telescope towards the coordinates of the centre of the field to be observed It is then expected that the 3 guide stars will appear correctly centred on the TV screen Step by step this process is as follows e Point the telescope towards the RA and Dec of the field centre e Perform an aperture offset to aperture APE 1 e If the rotator is well centred and oriented the image of the guide stars for the coherent bundle and two patterns for the two semi coherent ones will be seen on the guiding monitor 85 OBSERVING PROCEDURES ISIS Users Manual e In order to correct the telescope pointing the telescope must be moved in R
157. ical operations on data within these windows These include cross sections in X and Y made by collapsing a window onto the X or Y axis These functions perform differently depending upon whether they are operating on IPCS data or CCD data for IPCS data they sum the data in the perpendicular direction whereas for CCD data they average them This difference must be borne in mind 141 COMMAND LISTS ISIS Users Manual when for instance estimating count rates per pixel for IPCS data and estimating atmospheric transparency from a CCD spectrum of a spectrophotometric standard At present only two windows are available for all data screens and all buffers these remain in place until adjusted with the SET WINDOW options even when the user switches between IPCS and CCD data A future enhancement will provide separately defined windows for each data buffer With the X CUT and Y CUT functions it is possible to perform a preliminary sky subtraction To do this Window 1 is placed on the object spectrum and Window 2 on a suitable sky area It is not necessary to make Window 2 exactly the same width as Window 1 as appropriate scaling is applied It is not necessary to place Window 2 precisely in the spectral direction as the limits in this direction of the sky region are changed to those of Window 1 Options available from the Statistics menu are e SET WINDOW 1 After selecting this option with the user can adjust the size of Window 1 by moving the m
158. ication of the holes to be drilled in the Aperture Plates J tect Position Deng Position Dall rameter Gam Single Fibre xl yl x1l y1 1 983 Semi coherent bundle x2 y2 x2 y2 1 500 Semi coherent bundle pin raars oso Coherent bundle x3 y3 x3 y3 0 590 6 300 Coherent bundle pin x3 v3 3 010 e A lens relay system to produce the image of the guiding bundles on the detector e A Melles Griot mechanical system for the manual focussing of the guiding bundles 2 12 4 Aperture plates For multi object spectroscopy the acquisition of the field is performed by means of an aperture plate of type FOCAP This aperture plate is a 3mm thick brass plate The plate is drilled at precise locations with holes to accept fibre connectors The holes must be made for each of the three types of connectors for the individual fibres for the two semi coherent bundles and for the coherent bundle The characteristics of the holes are specified in the Table 5 it is assumed that the OY direction corresponds to the North direction during the observing epoch The vertical displacement that the coherent bundle has with respect to the object coordinates allows it to be observed by the northern part of the bundle where the packing quality is best see section 2 12 3 A high precision on the order of 204m both for the coordinates and the hole diameters is fundamental for accurate field acquisition The number of holes to be performed for ea
159. if it seems out of date MIMIC_START Start up Normally done in START UP in ICL MIMIC_STOP Close down Normally done in the ICL EXIT command SCREEN Select a screen e g ISIS Normally done with the mouse 7 7 Generating Data Tapes ING telescope data are recorded to disk in NDF format and to tape in FITS format The preferred medium is Digital Audio Tape DAT the second choice is Exabyte tape It is the responsibility of the observer or the support astronomer if present to generate the archive tape D tape and operations staff will normally provide a copy tape C tape in FITS format on 9 track tape Exabyte or DAT at the request of the observer Alternatively the observer can create his or her own copy of the data in FITS format or with the VMS BACKUP utility on any of these media D tapes can be created on any Vax in the cluster which has access to the required storage device but the normal procedure is to do this on the main data reduction Vax LPVE The observer should log onto this machine in the OBSERVER account mount the tape on the required drive then use the utilities FITSINIT and WRITE_FITS which are described in Part VI to create the D tape A Tape Copy request form should then be filled out indicating what kind of C tape is required 7 8 Engineering terminals In addition to the DMS and the Autoguider terminals which are located on the control desk there are three other terminals which allow access to various sub
160. in point sources will require much less of the slit and in many cases a hundred pixels 33 arcsec will suffice e Whether on chip binning is required to reduce the effect of readout noise it is possible using the BIN procedure to set any binning factors in either direction binning factors of up to 4 in each direction are normal Procedures for configuring the spectrograph for the beginning of observing are described in Part IV The centre of the slit on the CCD can be determined by taking a short exposure of a tungsten lamp through the narrow dekker dekker position 1 and measuring the centre in pixels with the DMS command Y FIND Before beginning to take exposures with a CCD it is necessary to set the CCD up with the ICL command SETUP lt ccdname gt This will prompt the user for the size of the CCD data array this includes underscan and overscan regions and is 400 by 590 for the FOS and GEC5 CCDs 1280 by 1180 for EEV P88300s and 1124 by 1124 for the Tektronix CCD If windowing or binning is required this can then be set up with the ICL procedures WINDOW and BIN There are a number of faults that can occur when reading CCD data into the DMS buffers e If the CCD fibre optic interface card at the top of the second blue cabinet from the left hand end of the control desk displays a light labelled G O A T then there is probably a fault with an optical fibre cable A duty tech should be called e If there is an error light on the DICI ca
161. in section 8 3 2 One complete turn of each capstan will move the CCD with respect to the focal plane of the spectrograph by 0 5 mm which will cause a Hartmann shift of 3 5 CCD pixels This is equivalent to approximately 10000 units of collimator movement A clockwise rotation of the capstans will be compensated by a negative collimator movement on either arm 8 3 4 Hartmann test using the DMS Set the slit width and dekker with SLIT 150 DEKKER 6 The comparison lamp filters and the exposure time should be set to give a reasonably strong comparison spectrum but the intensities in the lines to be used as measured with the CAL CULATE option on the DMS STATISTICS menu should not exceed 32767 Close the left Hartmann shutter by typing BHART 1 or RHART 1 at the ICL interface and take an exposure by typing GLANCE RED ARC lt time gt or GLANCE BLUE ARC lt time gt When it has read out at the DMS control window type FOCUS select three strong lines evenly spaced from the one end of the spectrum to the other by placing the cursor on each in turn and pressing the space bar on the DMS keyboard Each line profile will be shown on the DMS display and the line can be rejected if it appears too weak or blended with or close to another line The best results will come from strong isolated lines When three lines have been selected type FOCUS LEFT at the DMS control window The DMS will then list the centroid and an e
162. ination by the sky A flatfield taken with a wide slit can be used for correcting for small scale sensitivity variations along either dimension of the CCD A flatfield taken with a narrow slit will contain additional small scale variations of illumination in the spatial direction which will appear as horizontal stripes on the image These are due to variations in the slit width the slit jaws are not precisely straight and parallel To obtain flatfield exposures the following steps must be followed 1 Put the acquisition and comparison mirror into the beam with the ICL command AGCOMP or AGMIRROR ACQCOMP 2 Turn on the tungsten lamp with the ICL command COMPLAMPS W 3 Adjust the comparison neutral density filters with the ICL commands COMPFILTA and COMPFILTB ISIS Users Manual OBSERVING PROCEDURES 4 Turn out the lights in the dome if possible 5 Take trial exposures with GLANCE and adjust the exposure time and filters to give a maximum level in the region of 20000 40000 ADU 6 Take the final exposures with RUN or FLAT or keep the trials if the level is right e An exposure of the twilight sky with the spectrograph set up precisely as it is intended to use it during the night In particular the slit width should be the same as that intended for the night time observations Twilight sky exposures can be taken about 20 minutes after sunset with the telescope pointing at the zenith They are used for calibrating the sensitivit
163. indicates the end of file for the LAPLATE programme After this ending point other useful information not relevant for the programme can be added LAPLATE Output file What follows is an example for an output file LOG for the LAPLATE pro gramme It contains the corresponding output for each input parameter in the input file as for the example shown before and in the same order Comments on the Output file e The first line is a warning message because the focal plane scale used is not the default one provided by the programme This message is not important as LAPLATE uses the focal plane scale specified by the user e The date refers to the time at which the data are processed k k WARNING Unusual plate scale Date 16 11 1992 14 21 156 ISIS Users Manual APPENDICES kk Label M3 WHT AUX Plate Field 40 arcminute Observers Plate Scale 4 507 arcsec mm Observing date Drilling at 25 C Julian Epoch Observn 1992 9 Rotator Position Angle 90 00 Equinox of Position 1950 0 Plate Centre R A DEC 13 40 02 89 28 31 11 7 5 Fiducial Objects Fibre Hole R A DEC K Y 51 13 40 25 37 28 31 01 5 HC X1 65 789 2 097 52 13 39 39 75 28 30 59 1 HSC 525 67 664 2 890 53 13 39 58 03 28 33 28 4 HSC X8 14 275 30 314 54 13 40 02 89 28 31
164. ion it is important to exclude 25 INSTRUMENTS ISIS Users Manual OO wd O R316R RISBR ee R600R or Wn Ri200R EFFICIENCY S UJI Oo EFFICIENCIES OF ISIS RED GRATINGS RO OD pai 5 So 500 600 700 800 900 1000 WAVELENGTH nm 80 J On R12008 o 5 R3008 R600B R1588 p O H 24008 EFFICIENCY UJ O 20 EFFICIENCIES OF ISIS BLUE GRATINGS 10 400 450 500 550 WAVELENGTH nm Figure 15 The upper panel shows the efficiencies of the ISIS red gratings and the lower panel those of the blue gratings as measure in the laboratory 26 ISIS Users Manual INSTRUMENTS First order TOTAL efficiency 2 oO 0 08 Efficiency 0 06 eater Hewes 0 04 0 02 Q s 7 5000 5000 OGO 83009 2000 Wovelength Secono order TOTAL effic ency 0 935 9 030 oO OQ KI uw Oo O KI oO Efficiency 0 015 0010 9 005 3600 3800 4000 4200 4400 4600 4800 Wove ength A Figure 16 Total efficiency of the FOS II system including atmosphere telescope spectrograph and detector in first order upper panel and second order lower panel as derived from observations of standard stars taken in October 1987 27 INSTRUMENTS ISIS Users Manual light of wavelengths other than those reguired particularly wavelengths outside the range for which the coatings are optimised from the optics by use of appropriate colour filters
165. is field take calibration exposures use colour or neutral density filters and image by deflecting the on axis field to the auxiliary port 1 2 Object acquisition Object acquisition is carried out via an extendable probe carrying a mirror feeding a Westing house ISEC TV camera When used direct not the usual mode of acquisition when ISIS is in use this provides a 1 5 arcmin field at the telescope scale of 4 51 arcsec mm7 It is possible to insert a focal reducing system which provides a larger field of 4 arcmin at a scale of 12 arcsec mm The TV camera is provided with a filter wheel with six filter positions The available filters are CLEAR UBK7 B BG 28 V BG 38 R RG 630 and EMPTY no filter Note that the empty position will give a different focus position for the TV These filters do not give a standard photometric system and the Johnson letters are given for guidance only The TV can be focussed independently to compensate for different filter thicknesses 1 3 Slit viewing The normal method of acquisition when ISIS is being used is to view the slit which is tilted by 7 5 degrees and can be imaged via a one to one transfer lens and flat into the same TV camera used for direct viewing acquisition with field sizes identical to those provided by the acquisition system 1 4 Autoguider The CCD Autoguider is described in detailin The WHT Autoguider System User Guide by P J Rudd The autoguider consists of a CCD detector h
166. is helps in obtaining a more precise field acquisition Finally some positions free of stars must also be chosen in order to perform sky corrections 2 12 6 Overall Performance Geometrical losses mainly caused by focal ratio degradation give a mean efficiency of around 25 of the value when observing directly through the slit Transmission losses in the 2 5 metre fibre length are small except shortward of 4200 A between 7200 and 7500 A and longward of 8700 A However acquisition is critical and much larger losses can be produced if the astrometry is not better than 0 5 arcsec for any reason Some on sky measurements taken in 1 3 arcsec seeing show that the total sensitivity of the system is 1 photon s A at 4500 A for a star of B 15 with the TEK1 CCD on the blue arm and 1 7 photon s A at 7000 A for a star of R 15 with the EEV3 CCD on the red arm There is a fibre to fibre scatter of 30 in each of these values The efficiency is very sensitive to the acquisition procedure a shift of 1 arcsec from the best position loses about 55 of the light and a shift of 11 arcmin in the Cassegrain rotator position angle loses about 50 of the light although this latter figure depends upon the radial distribution of objects 24 ISIS Users Manual INSTRUMENTS 3 Performance 3 1 Throughput Nearly all of the light losses within ISIS are due to reflective and air glass surfaces There is a small loss of light lt 10 in each came
167. is not a problem at all the DMS is capable of having data written to one buffer by a CCD controller whilst data is being read from another 9 1 3 Acquiring data on the sky The commands for controlling the telescope are detailed in the WHT manual and any of these commands except use of the handset can be issued from the ICL interface instead of the Tele scope Control System TCS interface If these commands are typed at the ICL interface the telescope D task relays them to the TCS and they are echoed on the TCS control terminal The position information is input to the TCS by one of the methods described in the WHT manual If a particular sky position angle is required for an extended object or for two or more objects in a line this is specified by the TCS command ROT SKY lt position angle gt When observing point sources for which the sky position angle is not important the command ROT VFLOAT will ensure that the sky position angle is set to the parallactic angle when the object is acquired If spectrophotometric accuracy is of prime importance and the observer does not wish to autoguide the command ROT VERTICAL will put the slit vertical and leave it there i e the rotator will not track The sky position angle and the parallactic angle will then always coincide All position angles are measured in the conventional sense from North through East If the observer has very precise positions and the pointing of the telescope has been cal ibra
168. ition Moves stops or initialises Blue Filter A Valid parameters are a position in the range 0 to 2 a named filter listed on the ISIS MIMIC page OUT STOP ISIS Users Manual COMMAND LISTS INIT and REPROGRAM The last option should only be used in exceptional circumstances 11 3 6 BFILTB To move filter slide B in the Blue beam to a given position Format BFILTB lt position gt Example BFILTB 2 Range 0 to 2 or a named position Comments Moves stops or initialises Blue Filter B Valid parameters are a position in the range 0 to 2 a named filter listed on the ISIS MIMIC page OUT STOP INIT and REPROGRAM The last option should only be used in exceptional circumstances 11 3 7 BFOLD Controls the slide containing the folding flat for the blue camera and the dichroic mirror Format BFOLD lt position gt Example BFOLD DICHROIC Synonym BLUE_FOLD Comments Moves stops or initialises the slide containing the folding flat for the blue camera and the dichroic mirror Valid parameters are a number in the range 0 to 2 MIR ROR 1 DICHROIC 2 CLEAR 0 STOP INIT and REPROGRAM The last option should only be used in exceptional circumstances 11 3 8 BHART Controls the position of the Blue beam Hartmann shutters Format BHART lt position gt Examples BHART 1 BHART BOTH_IN Range 0 to 3 with named equivalents Comments Valid parameters are a number in the range 0 to 3 BOTH_IN 3 L
169. keyboard n ACQINT sets integration time for the field in millisecs n GUIINT sets guiding time for the field in millisecs usually 1000 4000 1 FIELD does 4 pictures and marks brightest star excluding edge region GUIDE ON to start guiding averaging over 2 integrations GUIDE OFF to stop guiding n GUISIZE to change the size of the guiding box gt gt and lt lt to rotate colour look up table TAU and TAU to change horizontal scale of guide error display SCALE and SCALE similarly vertical scale To use the artificial star ICL gt AUTOFILT OPAQUE Autoguider gt 4000 GUIINT ICL gt COMPLAMPS W ICL gt COMPFILTA NDO 3 Autoguider gt 1 FIELD Autoguider gt GUIDE ON this gives a star of magnitude 10 4 10 8 Typical Observing Sequence e Move telescope to target e ICL gt DEKKER 0 for a good image of the field with the TV e ICL gt AGSLIT and centre star on slit e ICL gt FIELD take a field amp find guide star e ICL gt PROBE r 8 e ICL gt FON begin following star e CL gt AUTOGUIDER ON close guiding loop e ICL gt DEKKER n select dekker to be used 6 for long slit spectra e ICL gt RUN GLANCE SKY etc take exposure on sky e If arc exposure is needed ICL gt AUTOGUIDER OFF ICL gt FOFF ICL gt AGCOMP ICL gt COMPLAMPS CUNE Cor CUAR ICL gt ARC RED BLUE FOS etc take arc exposure 96 ISIS Users Manual QUICK REFERENCE GUIDE When arc exposure is completed ICL gt COMPLA
170. ll frame readout mode and insert neutral density removing it gradually whilst keeping a safe level of illumination Use the real time video display to estimate a safe level of illumination e Never move a filter or the blue grating with the IPCS shutter open e If observing in cloud always watch the real time video display whilst integrating in case the target brightens suddenly e If observing comparison lamps simultaneously always set the illumination to a safe level for the IPCS increasing the exposure time for the CCD if necessary As with the CCDs calibration lamp exposures should be taken approximately every 15 30 minutes or on a 5 degree change in elevation or on any change of the rotator position angle If observing simultaneously with the IPCS and a CCD the DMS is capable of handling both detectors simultaneously It is not necessary to ensure that the IPCS integration finishes before CCD readout begins the DMS can be integrating in an IPCS buffer while a CCD reads out into a different buffer and it can also handle data transfer from a CCD buffer to the Vax or the Sparcstation whilst an IPCS integration is in progress 9 3 Time resolved observations with ISIS Time resolved observations can be defined as those in which one is studying an astrophysical phenomenon which varies in time The timescales may vary from milliseconds to years depend ing on the object under study Clearly inefficiencies in observing procedure and
171. ll performance of the system Table 8 gives sensitivity values for ISIS and FOS II measured from wide slit observations of spec trophotometric standards in the case of ISIS with the low dispersion 158 line mm gratings These measurements give the overall performance for the entire system including atmosphere telescope spectrograph and detectors The performance is expressed as a magnitude AB mag nitude in Oke s system see for instance Oke Astrophys J suppl 27 21 1974 which gives a measured count rate of 1 photon second A at the detector When comparing these values with observed count rates measured from CCD data it is important to convert to detected photons using the correct gain electrons ADU factor and to subtract the correct bias value When comparing with data measured of the DMS display using the X CUT and Y CUT functions in the STATISTICS menu it is also important to remember that the DMS averages CCD data it does not sum it On the other hand for IPCS data the DMS does sum 35 COMPUTERS ISIS Users Manual Part III Computers and Operations 7 Control System 7 1 Control system overview The main elements of the control system are shown in Fig 18 ISIS mechanisms are controlled by the observer typing commands at the ICL instrument control interface The ICL interface runs on the system computer currently a Vax 4000 called LPVF and the display is via the Observer s Vaxstation 3100 LPVS2 ICL commands ar
172. lt of the fibre slit can in principle be different from those of the long slit the difference in the plane of the slits causes a difference of the distances from the fibre and long slits to two collimators Because spatial resolution is important the spectrograph should be set up to provide a collimated beam onto the grating The nominal values of the collimator settings for long slit observing to provide such a situation are 7000um for the Blue arm and 9000um for the red arm The procedure to ensure that the spectrograph is correctly set up for fibre observing is as follows e With the slit unit in the long slit position set the two collimators to their nominal values e Ensure that the spectrograph can be focussed with the collimators near these values by making adjustments to the capstans on the CCD cryostats as described in Section 8 3 2 64 ISIS Users Manual SETUP PROCEDURES e Ensure that the tilts of the focal planes are correct again by adjusting the capstans as described in Section 8 3 2 e Ensure that the rotation of the CCDs is such as to align the long axis of the chip with the dispersion direction again as described in Section 8 3 1 e Move the slit carriage to the multislit position with the command MSLIT and remove the Acquisition and Comparison mirror e Switch on the fibre calibration lamp e Using the Hartmann procedures focus the spectral lines from the fibres onto the CCDs by moving the collimators e Cor
173. lue the drilling temperature and an estimation of the observing temperature These are used to correct effects of expansion or contraction of the brass aperture plate Default values for these temperatures will be 20 and 5 degrees C is for the equatorial coordinates of the centre of the observed field The tele scope will be pointed to this position on the sky X is to insert two extra fiducial positions at the specified distances in arcsec from the nominal plate centre In the example these positions are the plate centre and a point 400 arcsec North These holes are employed to connect the semi coherent guiding bundles to be used for the rotator adjusting In general the plates must have two extra fiducial holes one 400 arcsec North from the plate centre and another one 400 arcsec South F corresponds to the fiducial objects positions These are the equatorial coordi nates of the guide stars A fiducial object position must be specified in the following format F right_ascension declination equinox comments Each equinox and comment are optional arguments The equinox must be spec ified if the object position is referred to a different equinox from the one defined in the E command P are the positions for the targets with a similar format to that used for the fiducial objects P right_ascension declination equinox comments A point will be added on the line next to the last line containing positional data This point
174. ly 4 electrons The equivalent figures for fast mode are 70 s and 5 electrons The fast read out speed also gives a slightly larger dynamic range Clearly if the observations are sky limited there is little to gain in terms of signal to noise by using STANDARD although there is evidence that the charge transfer may be poorer please consult your support astronomer for details Accumulating the data in the DMS It is possible to accumulate data in the DMS using datacubes These are three dimensional data structures in which individual frames form the planes This removes the significant dead time due to transferring data from the DMS to the VAX Using datacubes it is possible to obtain dead times of approximately 5 s with a CCD in fast read out mode and windowed 100 x 100 The DMS can hold datacubes of up to 32 MBytes in size and hence approximately 800 frames of 100 x 100 pixels There are two drawbacks to this method Firstly no file headers and hence exposure start times are saved and secondly there is a large overhead when the datacube is transferred to the VAX At the present time the datacube option is not offered on a routine basis and any users who are interested in employing this method should first contact their support astronomer Using the IPCS In terms of signal to noise there are few occasions when it is advisable to use the IPCS on the blue arm of ISIS instead of the TEK CCD However the IPCS does have the advantage of a lo
175. mat Channel Time Obstype Examples Comments 118 GLANCE lt channel gt lt obstype gt lt time gt The name of the CCD data acquisition channel to be used The exposure time in seconds The observation type Valid observation types are ARC BIAS DARK FLAT and TARGET GLANCE RED ARC 5 This command is intended for a quick look at the data to verify for example that the intensity level is as expected before carrying out a proper exposure The data will be lost when the next exposure is carried out on the same data acquisition channel To save the data use the KEEP command ISIS Users Manual COMMAND LISTS 11 5 15 KEEP Copies a previously completed glance exposure to disk on the system computer collecting head ers and assigning a run number in the process Format KEEP lt channel gt lt title gt Channel The name of the CCD data acquisition channel to be used Title A title for the observation optional helpitemExamples KEEP RED Comments The system will report the allocated run number 11 5 16 KILLMULT Stops a sequence of multiple exposures Format KILLMULT lt channel gt Channel The name of the CCD data acquisition channel Example KILLMULT RED Comments The current exposure in the series is left to complete normally and all pending exposures are cancelled The channel becomes ready for another command when the current exposure completes KILLMULT can be followed by FINISH or A
176. me obtained for focus by measuring the line centres with 10 Y FIND at opposite ends of the slit The focus and tilt of the FOS CCD are determined by the positions of 3 push rods on which the ring bearing the CCD is supported These push rods are moved along their axes by 3 motor micrometers which are controlled from the engineering terminal The commands available are HELP lists all available commands STATS lists status of Hartmanns motor micrometers focus and tilt xxx FOCUS adjusts focus to position xxx 0 511 Each motor micrometer moves by the same amount ALLSTOP stops all mechanisms immediately xxx 1MOVE moves motor micrometer to position xxx 0 511 xxx 2MOVE moves motor micrometer 2 to position xxx 0 511 xxx 3MOVE moves motor micrometer 3 to position xxx 0 511 65 OBSERVING PROCEDURES ISIS Users Manual xxx HANGLE sets horizontal tilt to xxx 255 255 xxx VANGLE sets vertical tilt to xxx 255 255 a b HARTS operates Hartmann shutters a b OPEN or CLOSED The most recent setting of the motor micrometers focus and tilt is recorded in the FOS instrument logbook Check whether this is for FOS in the configuration that is required 9 Observing Procedures 9 1 Observing with one or two CCDs 9 1 1 TV Focus Normal practice is for the telescope operator to focus the telescope on the TV image reflected from the slit jaws The slit image is of course focussed onto the detector
177. mperature the spectrograph once in focus should remain so for several days 8 4 5 Hartmann test using the Vax 4000 Using the command EI obtain 3 or 5 pairs of Hartmann left and right arc lamp exposures and copy them onto a scratch area on the Vaxcluster as files HART Li DST and HART_Ri DST where i takes values e g 1 3 or 1 5 Type FIGARO then FOCUS_HART and respond to the prompts The parameters which may be changed by the user are the number of left right pairs of images the wavelength direction X or Y the first and last pixels in the orthogonal direction to be used the start collimator position the increment in collimator position and whether the maximum pixel value is to be determined for each of the images so that the user can check for saturation The cross correlation between spectra extracted from left and right images is performed by the FIGARO routine SCROSS In focus position is determined in two ways by linear interpolation between two values flanking zero line shift and by fitting a least squares straight line to the relation between focus position and line shift The program plots this relation on a device of the user s choosing e g PERICOM MG IKON_1 CANON_P VAXstation TEK_4010 window 8 4 6 Minimum FWHM using the VAX The correct position of the collimator may also be determined not as accurately from a plot of line FWHM vs collimator position Take a series of regularly spaced exposures copy them to SC
178. must be done with the IPCS EHT supply off as no lights are permitted in the dome with the EHT on 9 2 2 Switching on the IPCS EHT voltage The procedure for running up the IPCS EHT voltage is given in The IPCS IT Users Manual and it is important that the instructions for doing this are followed exactly In particular it is vital that the observer monitors the real time video display in the IPCS electronics cubicle on the telescope as the voltage runs up and is prepared to set the IPCS to STANDBY if the level of illumination is too high 73 OBSERVING PROCEDURES ISIS Users Manual The observer should also check on the IPCS II chassis in the blue instrument cabinets that the corrections for dither and 5 distortion are enabled These are enabled if three green lights on a module towards the right hand end of the chassis are lit If the dither correction is not enabled at the ICL interface type SEND IPCS OBEY DITH_SWITCH MOVE 1 1 If the S distortion correction is not enabled at the DMS control window type 1 ESD 9 2 3 Instrument Calibration Data Decisions which have to be made before beginning an observing run with the IPCS include e The grating to be used and the central wavelength that it will be used at e The dichroic flat mirror or folding prism to be used e The format of the IPCS data window in terms of area and resolution If the window is larger the frame time will be longer and thus the li
179. name of the CCD data acquisition channel to be used Examples SETUP RED Comments The system will read the default detector format from the configuration database and set the detector up accordingly The user will be informed when the set up is complete No exposures can be made until the channel has been set up by this command 11 5 25 SKY This is equivalent to the RUN command but intended for sky exposures rather than observations of astronomical targets Format SKY lt channel gt lt time gt lt string gt Channel The name of the CCD data acquisition channel to be used Time The exposure time in seconds Title A title for the observation optional Examples SKY TAURUS 1 5 TITLE Twilight flatfield B filter Comments As for the RUN command except that the observation type is set in the headers as being a sky flat field 11 5 26 SLOUCH Sets the CCD readout speed to STANDARD SPEED Format SLOUCH lt channel gt Channel The name of the CCD data acquisition channel Example SLOUCH RED Synonym READOUT SPEED SLOUCH Comments This sets the CCD to its standard readout mode used for normal observing 121 COMMAND LISTS ISIS Users Manual 11 5 27 SPEEDY Sets the CCD readout speed to QUICK SPEED Format SPEEDY lt channel gt Channel The name of the CCD data acquisition channel Example SPEEDY RED Synonym READOUT SPEED SPEEDY Comments This sets the CCD to its fast readout mode usually only us
180. nearity at high count rates worse Each CCD pixel is subdivided into a number of smaller pixels which is a power of 2 up to a maximum of 8 in each direction these factors are known as X and Y resolution factors The X resolution factor is normally set to 8 which offers the maximum sampling in the spectral direction and gives 2560 pixels along the spectrum In normal use the Y resolution factor will be either 2 or 4 giving a spatial pixel size of 0 7 or 0 35 arcsec respectively At the beginning of the setup and when moving to a new target whose brightness is unknown it is advisable to run the IPCS in full frame readout mode To do this type OVERSCAN but note that unlike IPCS I on the INT there is no way of observing the whole of the output of the image intensifier tube the overscan mode on IPCS II simply offers a readout of the whole of the CCD To resume observing after running in full frame readout mode it will be necessary to repeat the setup of the detector format with IPCSFORMAT Procedures for configuring the spectrograph for the beginning of observing are described in Part IV The centre of the slit on the detector can be defined by observing the tungsten lamp through a narrow Dekker and appropriate neutral density filters The IPCS data window format can be set with the interactive ICL procedure IPCSFORMAT and adjusted until the narrow dekker spectrum falls in the centre of the data window Note that there are some restrictions up
181. nics racks on the Cassegrain cable wrap The compact controller contains the following components A low heat dissipation power supply A CPU card containing an MC68008 microprocessor running a PROM based FORTH system A Temperature shutter and preflash control card for each CCD head controlled by the controller Cards which provide and sequence the clock and bias voltages for each CCD 30 ISIS Users Manual DETECTORS An analogue to digital converter card containing a 16 bit analogue to digital converter A Correlated Double Sampler CDS board A fibre optic transmitter and multiplex control card A floppy disc controller for FORTH software development A real time board with opto isolated RS232 ports for communication with the Utility Network and with terminals e A fibre optic cable run with a number of connectors passing through the cassegrain cable wrap The fibre optic cables usually have a bright yellow sheath e The Fibre Optic Multiplexer FOX unit containing the CCD Interface sequencer and one CCD interface card for each controller in the upper rack of the Detector Memory System cabinet in the control room The CCD interface card includes a fibre optic receiver which decodes the serial data from the optical fibre and a 512 by 24 bit FIFO buffer into which the data is placed in parallel form The Interface Sequencer card is responsible for reading data from the CCD interface car
182. nuation 0 04 180 200 220 240 260 280 300 320 340 360 380 400 Wavelength AA Figure 10 Attenuation curves for Polymicro high OF FH series optical fibre CONNECTOR A SILICA MICROTUBE C Za L STAINLESS STEEL MICROTUBE B FIBRE Figure 11 Focal Plane connector for the fibre multi object bundle 20 ISIS Users Manual INSTRUMENTS 40 EFFICIENCY f 11 in f 11 out yA 0 30 40 FIBRE NUMBER Figure 12 Focal Ratio Degradation Fibre Efficiency The guiding system consists of three fibre bundles two semicoherent and one coherent to carry the image of three stars to a CCD camera The image of the guide star obtained with the coherent bundle can be use by the TV software to generate error signals for the telescope control computer in order to improve the tracking of the telescope This image and the two semi coherent ones can also be used for the set up of the telescope rotator see section 9 6 2 and for the acquisition of the field see section 9 6 3 The guiding system includes A coherent bundle manufactured by ORIEL it covers a rectangular area of 1 89 X 2 38 mm 8 5 X 10 7 arcsec on the sky One half has a better packing quality than the other half and therefore it is used to monitor the object The focal plane bundle end is connected to the aperture plate via a connector This connector has a pin to fix the orientation North of the bundle In order to group together the three guiding bundles
183. of these nominal values otherwise the spectrograph will be astigmatic and the best focus on a spectral line will result in a degradation of the spatial resolution along the slit If the best focus falls outside this tolerance then the detector must be moved until the best focus is within this range The procedure for doing this is described in Chapter 5 2 7 The ISIS gratings Nine gratings are provided for ISIS four for the red arm and five for the blue arm The first letter of the grating name denotes the method of manufacture eight of the nine gratings are copies of ruled masters manufactured by Milton Roy whilst H2400B is a holographic grating manufactured by Jobin Yvon The number denotes the number of lines per millimeter The last letter of the name indicates which arm of ISIS it is intended for those ending in B are intended for the blue arm and those ending in R for the red arm However the grating cells are identical and all gratings will mount in either arm All gratings have a ruled area of 154 x 206 mm Grating R1200B was ruled in two halves this can be seen quite easily if the grating is held up to the light Gratings can be used either blaze to collimator or blaze to camera Use blaze to camera gives somewhat higher dispersion but as the anamorphic reduction factor is reversed this is at the expense of a greatly reduced slit to plate reduction factor especially at high dispersions The ISIS gratings are almost invariably us
184. on The calibration lamp for the fibre system is not yet driven from the A amp G box 4ms microproces sor although it is planned to implement this diring 1993 At present the power to the calibration lamp will need to be switched on by the observer usually from one of the power points on the inside of the telescope fork To take a calibration exposure all of the A amp G box mirrors must be withdrawn with the ICL command AGMIRROR OUT The frequency recommended for calibration exposures depends upon the specific application and is the same as that for normal CCD ob serving The calibration lamps are bright and only short exposures 1 5 seconds are required The gain of the TV systems must be turned down while calibration exposures are in progress 9 6 5 Data reduction Fibre data can be reduced in the FIGARO data reduction system using the spectrum following and extraction procedures FINDSP OVERPF and POLEXT More detail on data reduction pro cedures is given in The ISIS Fibre system Technical Report and User Manual by J L Rasilla et al and in the Starlink FIGARO documentation 86 ISIS Users Manual QUICK REFERENCE GUIDE Part V QUICK REFERENCE GUIDE 10 Quick Reference Guide This section is intended to provide a guide for the experienced user and contains one line summaries of some of the most commonly used commands arranged approximately in the order of an observing session More detail of the individual commands is given in
185. on a Vaxstation usually a Vaxstation 3100 which runs DECWINDOWS MOTIF which is a variant of X Windows In order to display the data in real time and in order to control the Autoguider and DMS it is necessary to run the Sparcstation called Ipss3 which is located to the left of the Vaxstation The Sparcstation also runs MOTIF but this is a slightly different implementation from that on the Vaxstation The other important interface for the user is the Detector Memory System DMS running Imageforth 68K which provides a display of the data and a number of setup routines This section describes how to check that all of the necessary systems are running and are communicating over the utility network and to get the user interfaces running Because the DMS local control does not run through terminals but through a window on the Sparcstation the observer account on the Sparcstation should be started up first On the Sparcstation lpss3 logon as observer the password will be known to local support staff Note that the Sparcstation runs the UNIX operating system which is case sensitive and all commands typed in including usernames and passwords must be in the correct case MOTIF will start automatically but the application to control the DMS must be started individually from the Applications menu From the Applications menu start the following applications e IRAF DMS This application will start the SAOIMAGE display server a terminal window r
186. on the parameters supplied to IPCSFORMAT these are detailed in the description of the procedure given in Part VI of this manual and explained in detail in Chapter 4 of the IPCS User s Manual The IPCS II dark count is negligible in use on ISIS and any attempt to measure it will result instead in a measure of the light leaking into the detector Three types of calibration exposure are useful when observing with the IPCS T4 ISIS Users Manual OBSERVING PROCEDURES e Flat field exposures Because of the low granularity of the current IPCS image intensifiers the introduction of dither and the low count rate limit imposed by the hardware it is very hard to get sufficient counts in a flatfield actually to improve the data An integra tion time of at least three hours would be required to give 1000 photons pixel in normal observing format in which each CCD pixel is divided into 16 or 32 data frame pixels To obtain a flatfield ENSURE THAT THE IPCS SHUTTER IS CLOSED WITH IPC Insert the acquisition and comparison mirror in the A amp G box with AGCOMP switch on the tungsten lamp with COMPLAMPS W Set the grating angle to about 6000A The illumination is more uniform in the red set the Dekker to a long slit position such as 6 but not to position 0 Set the slit width to around 500 um Insert neutral density at least ND3 0 is required initially with COMPFILTA COMPFILTB or MAINFILTND Ensure that th
187. ouse on the reflective pad After then pressing the user can adjust the position of the window by moving the mouse The user can return to adjusting the size with and the position with as many times as necessary returns to the Statistics menu e SET WINDOW This allows the user to adjust the size and position of Window 2 and the function of the keys is exactly the same as for SET WINDOW1 e CALCULATE This calculates and displays near the bottom right hand corner of the display the location and size in X and Y of the window selected with one of the SET WINDOW options or the WINDOW USE option and the mean maximum minimum and standard deviation of all the pixel values within that window It leaves the user in the Statistics menu e PIXEL After selecting this function with the user can move the cursor around in the image display area and read out individual pixel values with SELECT 1 toggles between a zoomed and unzoomed display returns to the unzoomed display and returns the user to the Statistics menu e X CUT This option collapses the selected window onto the X axis and plots the result For IPCS data it sums the pixels in Y and for CCD data it averages them If the WINDOWI WINDOW 2 option is selected with WINDOW USE then the left and right boundaries of WINDOW2 will be changed to match those of WINDOW1 and the data from WINDOW 2 will be scaled by the ratio of the window widths before subtraction The plo
188. out and the slide can then be withdrawn carefully through the slit access door When the slide is replaced the user must ensure that the locator pin is correctly engaged The slit door should be closed and latched and is then locked by the command SLIT_DOOR CLOSE The procedure CHANGE has been written to take the user through the process of changing the below slit filters The procedure will move the dekker to position 0 unlock the slit door and when the change has been completed will lock the door and update the database 8 24 Directing light to the right cameras The light path is shown on the CAGB ISIS and ISIS_SLIT screens of the Mimic display The spectrograph can be configured for any combination of channels with the ISIS_CONFIG com mand or the folding mirrors moved explicitly with BFOLD and RFOLD To get light from the comparison lamps to the cameras the user must ensure that the ACQCOMP mirror is in place in the A amp G box that nothing else is between the mirror and the slit particularly that the Lid Cover is open that a comparison lamp is on and if the IPCS is in use that an appropriate neutral density filter is in the comparison beam A typical sequence of commands is ISIS_CONFIG BLUEANDRED Both blue and red channels AGMIRROR ACQCOMP COMPLAMPS CUAR Copper Argon Lamp COMPFILTA ND3 0O If the IPCS is in use COMPFILTB ND1 8 If the IPCS is in use LID OPEN It may be necessary to move any of MAINFILTND
189. oving from B V or I to EMPTY but not when moving from B V or I to CLEAR 11 1 8 AUTOFOCUS Sets the Autoguider focus Format AUTOFOCUS lt focusvalue gt Example AUTOFOCUS 3500 Units Microns Range 0 to 6000 Comments The autoguider focus must be adjusted after the telescope focus has been set to focus on a guide star 11 1 9 AUTORADIAL sets the radial position of the guide probe Format AUTORADIAL lt radialposition gt Example AUTORADIAL 10000 Units Microns Range 0 to 40000 101 COMMAND LISTS ISIS Users Manual 11 1 10 AUTOTHETA Sets the angular position of the guide probe Format AUTOTHETA lt thetaposition gt Example AUTOTHETA 50000 Units Millidegrees Range 0 to 180000 Comments Note that values less that 35000 may cause the probe to vignette the slit viewing optics 11 1 11 AUXFILTER Moves the auxiliary port filter wheel to a given position Format AUXFILTER lt filterposition gt Example AUXFILTER 3 Range 0 to 5 Comments The filter wheel has positions 0 to 5 and the names of the filters mounted in each position are usually listed on the white board in the control room 11 1 12 COMPFILTA Moves the comparison lamp filter wheel A so that the named filter is in the beam Format COMPFILTA lt filtername gt Example COMPFILTA ND3 0 Comments Possible values for filtername are ND3 0 ND1 8 ND0 8 NDO 6 ND 0 2 GG375 GG495 and CLEAR 11 1 13 COMPFILTB
190. owever since the headers for the observation are collected when the data is originally taken the run number will not appear in the headers 11 5 21 RAT_WAIT RAT_WAITs for an exposure to complete before returning control to ICL Format RAT WAIT lt channel gt lt timeout gt Channel The name of the CCD data acquisition channel to be used Timeout The maximum time to wait seconds Examples RAT_WAIT RED 90 Comments The commands for carrying out CCD exposures normally return control to ICL before they complete Whilst this is desirable in normal operation it makes it impossible to write ICL procedures to carry out a number of exposures sequen tially as in a focus run for example Such ICL procedures can be produced using the WAIT command see section for examples The timeout parameter of the WAIT command forces it to return an error to ICL if the exposure does not complete it is recommended that timeouts be made generous 11 5 22 RUN Takes an exposure of an astronomical target and transfers the data plus headers to an HDS file on the system computer Format RUN lt channel gt lt time gt lt string gt Channel The name of the CCD data acquisition channel to be used Time The exposure time in seconds Title A title for the observation optional Examples RUN RED 1 5 NGC1068 nucleus Synonym TARGET Comments This command takes a single exposure of an astronomical target collects header
191. p G box by means of the interface using kinematic seats in order to be relocated accurately 2 12 2 Fibre Bundle The ISIS Multi object fibre optic bundle consists of 61 Polymicro Technologies FHP400 475 510 fibres of 2 6m length each Figure 10 shows their attenuation curves On the auxiliary focus the 400 um diameter fibre core covers an area of 1 8 arcsec in diameter on the sky The focal plane end of the fibre is inserted into a connector which serves to protect and accurately align the fibre on the aperture plate Figure 11 shows this connector where A is the focal plane terminal B is a stainless steel microtube with diameters 685 1100 inner outer and C is a silica microtube TPS530 660 of Polymicro Technologies B holds the fibre to the terminal while C ensures that the fibre is concentric Epoxy resin Epotek354 was used only between the fibre and C and between C and B In this way stresses caused to the fibre end are reduced For the mounting corresponding to the slit 61 holes have been made in an aluminium alloy piece The hole diameter is 680 um and the separation between hole centres is 860 um Then the separation between the centres of two adjacent fibres is 2 15 times the fibre nucleus diameter This is enough to avoid optical cross talk except for extreme conditions A TSP530 660 silica microtube has been used to ensure the concentricity between the fibres and the holes Keeping in mind the 3 3 ISIS reduction factor the fibr
192. polarimetric observations and certainly for the usually bright polarimetric standard stars a CCD is strongly preferred as a detector over the IPCS Currently the polarisation optics have been used with the red and blue cameras of ISIS In principle the polarisation module also functions with FOS but this option has not been tested extensively Note that experiments with the dichroic beamsplitter in position showed reflected light from the rear of this component Such light is displaced along the slit partly into the spectrum of the other polarisation this spoils the polarimetry so for the time being we must reluctantly advise against use of the dichroic 9 5 1 How to derive the Stokes parameters The staring mode uses the calcite plate which yields 2 spectra of opposite polarization The polarization information one Stokes parameter per exposure is contained in the ratio at each wavelength of the intensities in the 2 spectra but it is mixed up with the system gain ratio for the pixels concerned The effect of the unknown gain is eliminated by inverting the sign of the polarization effects in a second exposure while leaving the gain ratios identical Inversion of linear polarization effects and therefore of the Stokes parameters is accomplished by rotating the halfwave plate by 45 degrees while the polarization effects are inverted the system gains remain the same since these are determined by the built in polarization
193. posures together with a slightly higher dynamic range at the expense of some what higher readout noise If you wish to run the CCD in this mode you must issue this command after every hard or soft reset of the CCD controller This command is only available from the VHT vocabulary if it appears not to work type VHT then try again his instruction can also be issued over the network from the DMS terminal to do this type gt CCDn where n is 1 2 3 or 4 and denotes the network address of the CCD in question then type SPEEDY 13 3 12 REBOOT Software reset of the CCD controller Format REBOOT 13 3 13 RED Reads out a CCD Format RED Comments Reads out a CCD into an existing DMS buffer Useful in diagnosing CCD prob lems This command currently only works from the Network vocabu lary invoked by typing NETWORK 13 3 14 SET TIME Sets the internal clock of the CCD controller Format lt HH MM SS gt SET TIME Example 14 28 00 SET TIME Comments This affects the time stamp which will appear in the headers of CCD exposures If accurate times are required this should be reset every night Currently the seconds must be zero 13 3 15 SET DATE Sets the date for the internal clock of the CCD controller Format lt dd mm yy gt SET DATE Example 01 10 93 SET DATE Comments This affects the date recorded in the headers of CCD exposures 13 3 16 SEX Sets exposure time Format lt headnumber gt lt exposu
194. preserved Options which can be selected with SELECT L are e CCDS Data from one of the CCDs is displayed Individual CCDs can be selected using the icons alongside the main display area e IPCS 8 1 This option has not been implemented e IPCS 1 1 The IPCS data buffer is selected The whole display is not necessarily used in the vertical direction and for the IPCS the pixels do not necessarily have the correct aspect ratio on the screen The remaining screens are not used for displaying ISIS data 143 APPENDICES ISIS Users Manual Part VII APPENDICES A Properties of the ISIS Gratings In this appendix the properties of the ISIS gratings are presented in graphical form the grating setting slit to detector reduction factor vignetting factor and reciprocal dispersion A mm are presented as a function of wavelength for all red and blue gratings For completeness graphs for both blaze to collimator and blaze to camera are presented although only use of the former is recommended and graphs for grating H2400B in the red arm are also presented although this is not a particularly efficient combination The explanation and the program used to generate the plots are due to C R Jenkins The grating equation is sin sinr A d for a first order spectrum The camera collimator angle in ISIS is nominally 40 although the exact value will be slightly different for each channel rtr with app
195. previous one with EAGLE GET 5DC ARRAY and enable it with 1 ESD all on the DMS terminal N B Always check IPCS with OVERSCAN first There can be a bright ghost that appears at the top of the IPCS field and which is believed to be caused by reflection off the ANAMOR PHOTIC slide if it is not fully out 10 4 2 Setting up the IPCS Format and Focussing ISIS LOAD IPCSFORMAT Use default formats from the following table The IPCSY2 settings put the 1 2 arcsec dekker in the centre of the frame as of 28 10 90 Or make your own format with IPCSFORMAT N B Current size limit for DMS IPCS buffer is 2560 x 480 Note that the number of rows read into the DMS buffer must be less than the number of rows read out of the IPCS To change the Y window only use IPCSWIN Max rows 64 spectral direction fixed at 320 X8 Focus Setup for CuAr arc with Acen 4500 slit width 150 microns and COMPFILTA ND1 8 depends on grating A typical focus procedure would be OVERSCAN use full IPCS frame BHART 1 Left Hartmann shutter in Right out 90 ISIS Users Manual QUICK REFERENCE GUIDE EI 120 120 sec exposure short for EXPOSE IPCS DMS gt FOCUS choose 3 strong unblended lines left middle amp right end DMS gt FOCUS LEFT BHART 2 Right shutter in Left out EI 120 DMS gt FOCUS RIGHT which will give centroid differences at 3 points along each line The centre positions at each point indicates rotation and can be analys
196. pstan turned by an appropriate amount with one hand and the clamp applied again all the while the other hand should be used to hold the cryostat firmly in place After the clamp has been tightened the micrometer can be read again The micrometers should never be used to take the weight of the cryostat and should only be brought into contact with the studs when the capstans are firmly clamped One complete turn of a capstan will result in a change in the micrometer reading of 0 5 millimetres A one pixel differential shift along the spectrum will require a movement of capstan A or C of 4 complete turns or 2 turns of each in opposite directions which will keep the focus in the centre of the chip the same A one pixel differential shift along the slit 600 CCD pixels will require 7 complete turns of capstan B to correct it The sign of the differential Hartmann shift measured by this procedure will depend upon the way that the CCD is mounted in the cryostat and which on chip amplifier is being used The telescope manager or technical staff may know the direction but if they are not available it can be established by trial and error The Hartmann test should be repeated after every move of the capstans it should not be necessary to run the FOCUS routine each time because the lines should not shift very far If FOCUS LEFT gives widely different centroids or widths for what should be the same line then it may be necessary to run FOCUS again W
197. r a mirror or dichroic If a dichroic filter is in the beam the optical thickness of the material introduces a focus offset for the red arm or FOS The focus offset for the red arm in microns is tabulated above The value of the red collimator position is always higher if a dichroic is in the beam than if the red fold position is clear The 7500 A dichroic gives only a 2 arcminute unvignetted field along the slit and is generally used for stellar observations The red fold consists of a remotely driven two position slide one position is clear while the other contains a silver mirror with a reflective stack overcoat to send light into the red arm 2 5 Below Slit filters There are four 2 position remotely driven filter slides two in the blue arm beam just after the blue fold and two below the blue fold but above the red fold the latter two are for use with both the red arm of ISIS and FOS II There is a range of neutral density and colour filters for use in these slides The blue arm filter slides are normally used to hold neutral density filters for when the IPCS is in use the red arm filter slides are used to hold long pass filters to cut out second order blue light The red arm filters slides cal also hold a coloured field lens for use with FOS II in multi slit mode Procedures for changing the below slit filters are described in Section 8 2 3 2 6 Collimators Both collimators are off axis parabaloids with a focal length of 1650mm and
198. r is closed the glow on the real time display takes more than 2 5secs to fade 5 2 CCD IPCS granularity and Dithering The CCD IPCS has sensitivity variations over its field of view which are due to physical ir regularities in the photocathodes inside the intensifier The spatial variation in sensitivity is referred to as granularity because of the grainy appearance it gives to images In order to reduce the effect of granularity due to last three stages of intensification a scheme of dithering was introduced for the IPCS I Jorden amp Fordham Q J R A S 27 166 1986 By moving the image around on the last three photocathodes in the intensifier the signal in a given pixel averaged over time is proportional to the mean sensitivity within the scanned area Hence the pixel to pixel granularity is typically reduced by a factor of two A similar technique is used with the IPCS II but this also counteracts the fixed pattern noise due to the centroiding algorithm used in that detector the granularity of the first photocathode is not diminished by these techniques since the image on this photocathode cannot be scanned The effects of granularity may be reduced by dividing an acquired image by a flat field so compensating for the pixel to pixel variations in sensitivity The exposure required for a correct flat field depends on the spatial scale of both the granularity and the information content within an image Jenkins
199. ra due to optical vignetting and for the highest dispersions there is some loss due to overfilling of the grating see Appendix D The throughput of ISIS has been measured by C R Jenkins and P Terry and their results are discussed in detail in ING La Palma Technical Note no 88 Briefly the throughput of the red channel without the grating is measured to be 51 and that of the blue channel without the grating to be 42 These measurements were made with a HeNe laser at 6300 A and thus for the blue arm are slightly beyond the wavelength range over which it is optimised The values for the red arm are also slightly low as the red fold mirror in use at the time was below its specification The efficiencies of the ISIS gratings have been measured in the laboratory and are presented in Figure 15 The holographic grating has a lower efficiency than the ruled gratings and is also used at a grating angle such that the beam overfills the grating resulting in some light loss The calculated peak efficiency for FOS II is 70 in first order at 7300 A and 50 in second order at 4100 A The diagrams below show the calculated efficiency as a function of wavelength and the measured efficiency of the entire system including telescope atmosphere and detector as a function of wavelength The efficiency of the overall system is dependent upon the throughput of atmosphere tele scope and instrument and the efficiency of the detector Measured values of the n
200. ransfer the data to disk on the VAX This process takes approximately 45 s for a full EEV chip and also involves the writing of file headers or packets Clearly by reducing the number of DMS VAX transfers and the size of the transferred frames the dead time can be reduced see section 9 3 2 9 3 2 Reducing dead time There are a number of ways in which dead time can be reduced Below we list the methods currently available and give some indication of how effective they each are Using MULTRUN This is a useful ICL command which should be used when it is necessary to take repeated exposures of a single object The procedure does not do anything partic ularly clever it simply sets up an exposure loop which removes the dead time involved in typing repeated RUN commands The loop can be aborted by typing KILLMULT The saving in dead time is surprising particularly towards the end of a night 77 OBSERVING PROCEDURES ISIS Users Manual 78 Windowing the chip By windowing a CCD only a subset of the chip is read out and transferred to the VAX This significantly reduces read out time by an amount which scales with the number of pixels in the window It makes little difference if this window is chosen at the top middle or bottom of the chip The only disadvantages of this method are that one obtains a reduced field of view and reduces or removes entirely the bias strip The former is not really a problem for spectroscopy and t
201. rd or a FIFO FULL light on the CCD fibre optic interface card then the DICI should be reset and the exposure repeated e If the data are clearly scrambled or show a series of diagonal stripes then the CCD controller thinks the data frame is a different size to the DMS The DMS should be reset and the SETUP and WINDOW commands should be repeated at the ICL interface FOR EVERY CCD IN USE e If the previous procedure does not work then the CCD controller should be rebooted with the REBOOT command rather than switching it off and on and the procedure repeated e If the CCD shutter fails to open this will send a message to the ICL interface This could be due to a fault on a shutter cable to low nitrogen pressure to the telescope or to a mechanical failure of the shutter However before calling for technical assistance it is worth typing UNJAM at the relevant CCD controller to see whether this cures the fault 67 OBSERVING PROCEDURES ISIS Users Manual Once the CCD has been set up to obtain images of the correct format and the spectrograph has been set up correctly then the observer can begin taking calibration exposures Normally the following calibration exposures are required 68 e A number of Bias frames which are dark exposures with zero exposure time These can be taken with the BIAS command These are often not required because the bias is structureless and its absolute level can be determined from th
202. re is not much light leakage or dark current since the last read out In addition since the read out noise is known to be a function of read out speed it should be possible to offer a greater variety of read out speeds and noise levels For even greater reductions in dead time it should be possible to store a series of short expo sures on chip The interval between exposures can be very short especially if the image window is almost one dimensional ze spectroscopic A small box defined by a dekker consisting of N rows at the top of the CCD is illuminated On completion the box is moved quickly down the chip and the clear area can be exposed again This can be repeated until the chip is full The whole frame can then be read out from the bottom of the CCD The exposure time T per box can be in the range 1 65535 ms For an EEV chip it takes about 0 04 ms to shift down one row of data thus the total time per box T N x 0 04 ms For a box of size 10 rows and a 60 s exposure the total time interval between boxes would be 60 0004 s Even if such a system were available now it would still be impaired by the relatively slow DMS VAX link However work is in progress to replace this next year with a system which saves the data directly onto the observing SPARCstation This should provide an order of magnitude improvement in the dead time due to archiving data on disk It should be noted that most of the above enhancements are still at t
203. rect for any residual tilt along the fibre slit by making balanced moved of the CCD capstans i e always keeping the centre of the focal plane in the same case The difference between the collimator position for best focus for the long slit and for the fibres should be the same and of the same sign for both red and blue arms 8 6 Setting up FOS The fixed format of FOS makes it a very stable instrument However it is a good idea occasion ally to check the focus and alignment Moreover the best focus setting will need to be reset if either a below slit filter or more particularly the field lens are used with FOS in any mechanism below the slit To check the focus set the ISIS slit width to 40um turn on an arc lamp put in the comparison lamp mirror and take a short exposure Select a strong but unsaturated line and use the DMS command 10 Y FIND to measure its FWHM If the line is in focus the FWHM should be about 1 6 pixels slightly better in the blue If the FWHM exceeds 1 8 pixels the focus must be adjusted by control of the motor micrometers see below A more accurate check of the focus can be made by comparing exposures taken with either the left or right Hartmann shutter closed these exposures can be analysed with the Hartmann routines described in Section 8 3 3 For data reduction routines to work well the slit must be aligned with the CCD rows to within 0 2 pixel over the full slit length This can be checked using the data fra
204. retime gt SEX Example 1 10000 SEX Units Milliseconds Comments Local command to set exposure time The first parameter is the CCD head number and is 1 or 2 This command currently only works from the Network vocabulary invoked by typing NETWORK 138 ISIS Users Manual COMMAND LISTS 13 3 17 STANDARD SPEED Changes the readout rate to the slower and lower noise of the two allowed values Format Comments STANDARD SPEED This resets the readout speed of the CCD back to the default slower speed with reduced readout noise This command is only available from the VHT vocabulary if it appears not to work type VHT then try again This instruction can also be issued over the network from the DMS terminal to do this type gt CCDn where n is 1 2 3 or 4 and denotes the network address of the CCD in question then type SLOUCH 13 3 18 T STAT Displays the temperature of the CCD chip in the current physical head Format T STAT 13 3 19 T SHOW Displays temperature information for both Physical heads Format T SHOW 13 3 20 TELE Displays telemetry from a CCD controller Format Example Comments lt headnumber gt TELE 2 TELE Displays voltages and currents from the CCD controller with their nominal val ues This is useful for diagnosing faults with CCDs and controllers 13 3 21 UNJAM Unjams a CCD shutter which is stuck Format Comments UNJAM This is the first thing to try if a CC
205. risation vector of the light The halfwave plate is usually mounted below the quarterwave plate which gives the largest field of view and best slit viewing for linear polarisation studies It is possible to interchange these plates although this requires that ISIS be taken off the telescope e A calcite block or Savart plate located in the FCP Field lens Calcite Polaroid tray immediately below the slit This is effective over the wavelength range 3300 11000 A and gives two beams separated by an amount which depends upon wavelength but is in the range 2 1 2 6 mm over the effective wavelength range The two beams are 100 polarised orthogonally and their relative intensity depends upon the polarisation vector of the incoming beam Use of the Savart plate requires the spectrograph to be refocussed by 9600um in the Blue arm and 9300um in the red in the sense that both collimator positions ISIS Users Manual INSTRUMENTS A amp G BOX STARLIGHT X DISPERSION OPTIONAL POLARISATION 500f l BLUE CAMERA GRATING 220 x 165 ERA SHUTT ANAMORPH CAMERA SHUTTER MULTI OBJECT SLITS NK age AA LI NA SLIT ae GRATING 220 x 165 HARTMANN SHUTTERS BLUE FOLDS WA BLUE FILTER ND amp COLOUR Hare apc j 5 ve o en aite J pn INEA j ag Eang r ee 3 h 2 ka pee rn ete g 4 ge NA T i e A koee 2 ote AA ima i i 5 ae 1 pi ji ar YI KA eee aon q
206. rly tilted then the camera head should be rotated First check that the power lead to the motor which drives the camera head rotation is connected The camera head can then be rotated from the ICL interface by typing IPROT lt value gt where value in an integer between 0 and 65535 which represents the amount the camera head is to be rotated Each step represents 4 4 seconds of arc and the value is biased by 32768 so that 32760 rotates 8 steps in a negative direction and 32778 rotates 10 steps in a positive direction A value of 32768 stops the rotation As a rough guide a slope of 1 pixel over the length of the spectrum at x2 resolution implies that a rotation of 25 units is required and to rotate the spectrum clockwise on the DMS display a negative rotation of the camera head is required This process should be rotated until the spectrum is straight to an accuracy of about 0 5 pixel slope at x2 resolution or 1 pixel at x4 resolution When the rotation is correct it is advisable to disconnect the power lead to the rotation drive motor 8 4 2 S Distortion Correction The IPCS II S distortion correction is a rebinning operation performed by the DMS and the parameters for the correction are determined by the DMS Set up the spectrograph and comparison lamp unit to give a narrow tungsten spectrum with reasonably uniform illumination along the spectrum 58 ISIS Users Manual SETUP PROCEDURES DEKKER 1 to give a narro
207. rmat Example Comments CRECALL lt filename gt CRECALL EEVO1 The file must have dimensions 800 by 1180 pixels Once a file has been placed in the buffer it can be transferred to the Vax 4000 disc with KEEP RED If the icon for this buffer is not displayed when this is done it will be necessary to run RECOVER DATA 131 COMMAND LISTS ISIS Users Manual 13 2 8 DEV Lists the image buffers which are open Format DEV Comments Used to check whether the image buffers have the correct format 13 2 9 DEV gt STK Makes the top item of the DMS stack equivalent to a particular data buffer Format lt buffernumber gt DEV gt STK Example 2 DEV gt STK Comments Valid values of buffernumber are 1 for the FOS GEC5 buffer 2 for the EEV2 buffer and 4 for the IPCS buffer This command is useful when data transfer to the Vax 4000 is not possible as data from the top of the stack can be stored on the DMS disc with PUT FILE The command assigns pointers and it is not necessary to repeat each time a new frame is read into the buffer this frame will automatically become the top item on the stack 13 2 10 E STK Erases the image stack if it has become full Format E STK 13 2 11 ERUN Opens an image buffer for EEV2 CCD data Format ERUN Comments The buffer is 800 by 1180 pixels and can be used to store data from a full frame readout 13 2 12 ESD Enables or disables the IPCS S distortion correction Format lt n gt
208. ropriate sign conventions for and r Solving these two equations gives _ A sin 8 A sin 7 i 0059 2 1 cos 0 T where the positive sign corresponds to the normal condition for ISIS namely blaze to collimator The grating setting for each channel is then given by multiplying 2 in degrees by 100 and adding an offset which is the autocollimation angle for each grating mount These offsets are 30800 for the blue channel and 35500 for the red In solving for the grating setting one has to check for the cases where the angle of incidence exceeds 90 or where the discriminant becomes imaginary corresponding to the wavelength where constructive interference cannot be achieved The reduction factor follows simply it is COST feoll COS 2 team where feou is 1650 mm and feam is 500 mm The gratings in ISIS are 200 x 150 mm and the cameras have sufficient aperture to accommodate the fully dilated 200 mm beam Most of the vignetting excluding refinements of matching central obstructions between camera and telescope pupil occurs simply because light misses the grating at high angles of incidence The fractional loss is 214 sin 24 y 7 where w is given by cos b 200 150 cose 144 ISIS Users Manual APPENDICES This internal vignetting only exceeds 1 for the 1200 and 2400 gratings The dispersion is given by AA 7 d cos Tr As feam 145 APPENDICES ISIS Users Manual B Grating
209. ry port to plug the fibres e Fibre optic bundle One bundle with 61 fibres allows up to 61 objects to be observed simultaneously The diameter of the fibre core is 400 microns or 1 8 arcsec e Guiding system One coherent fibre bundle and two semicoherent fibre bundles allow autoguiding or manual guiding These bundles also enable the focussing and set up of the telescope e Calibration system Wavelength calibration is provided by a box which can be mounted on the opposite side of the A amp G box from the Auxiliary port in which any of Argon Neon or Mercury lamps can be located The calibration lamps provide a diffuse illumination over the entire Auxiliary port of the A amp G box no attempt is made to mimic the pupil of the telescope 2 12 1 Auxiliary focus mounting The Cassegrain focal plane is inaccessible when the ISIS spectrograph is mounted on the tele scope An auxiliary focus is needed when fibre systems are used This auxiliary focus is available at a side of the Cassegrain acquisition and guiding box It is accessed via a large flat mirror which is inserted at a 45 angle to the main telescope beam The large flat mirror provides a full 15 arcmin field The optical characteristics of the Cassegrain focus are well established theoretically and they would be expected to be the same on the auxiliary focus In order to corroborate this an experimental scale has be obtained for the auxiliary focal plane within this work For m
210. sers Manual OBSERVING PROCEDURES star such as Feige 34 Correction for atmospheric extinction at the airmass observed using the theoretical curve from La Palma technical note 31 Correction for the spectral response of FOS via observation of a spectrophotometric standard star with a wide slit to give e g uJy through the slit as a function of wavelength FOS wavelength response is surprisingly bumpy with features of strength 5 on a scale of 200A Smoothing of second order spectrum to resolution of first order and merging of first and second order spectra into one Thus as well as spectra of targets observers may want to take bias frames twilight flats tungsten lamp flats arc lamp exposures and spectra of B stars and spectrophotometric stan dards Much of the above can be carried out using FIGARO software The software available for spectrum extraction SCP and SAM is described in Starlink User Notes 148 and 149 9 5 Spectropolarimetry Different modes of using the polarisation optics are conceivable here we will describe what may be considered a common user mode for measuring linear polarisation which is adequate for most purposes This so called staring mode uses the calcite plate analyzer to separate the light into an ordinary and an extra ordinary beam which results in two spectra on the detector One component of the polarisation vector e g the Stokes Q parameter of the incoming beam is converted to
211. spectral response with a sharp cut on at the critical wavelength and a steep decline to the red This additional efficiency is almost entirely polarised perpendicular to the grating rulings 28 ISIS Users Manual INSTRUMENTS Wood s anomalies occur at wavelengths A d sin a 1 n where d is the grating groove separation a is the grating angle the angle between the grating normal and the collimator axis and n is a positive or negative integer There are known to be Wood s anomalies in ISIS at 7200 A 1200 grating n 2 6400 A 600 grating n 4 and 4400 A 600 grating n 2 29 DETECTORS ISIS Users Manual Part Il Detectors 4 CCD Detectors CCDs are widely used in astronomy and are the major detectors for almost all of the instruments of the Isaac Newton Group Descriptions of CCDs and their operation at a non technical level are given in a number of astronomical publications two recent reviews have been given by C D Mackay in Annual Reviews of Astronomy and Astrophysics volume 24 page 255 and by P R Jorden in Modern Technology and its Influence on Astronomy edited by J V Wall and A Boksenberg published by Cambridge University Press page 271 4 1 Schematic view of the CCD systems The CCD systems in use at the WHT are described by P R Jorden et al in Proc SPIE In brief the CCD systems consist of the following components ordered approximately by the data path from detector to user e CCD
212. st straightforward reductions in dead time that can be made The control system Once the command has been typed it is passed over the Utility Network to the specified CCD controller and the chip is then cleared in preparation for the exposure The travel time of the command from ICL to the CCD controller is of order a few seconds and for the time being represents an irreducible minimum in dead time Clearing the chip This is a surprisingly large contributor to dead time a full EEV chip takes approximately 15 seconds to clear At present other than windowing or binning the chip and hence reducing the number of pixels there is little that can be done to reduce this Reading out the chip When an exposure has completed a process known as clocking is used to transfer the charge from the chip Once this process is complete each charge packet is detected as a voltage across a capacitance the voltage is amplified by an on chip amplifier and then digitised The data is then passed from the CCD controller through optical fibres to the FOX card in the control room and onto the DMS via DICI This process which we will refer to as read out is the dominant source of dead time when observing It takes approximately 110 s to read out a full EEV chip although this can be reduced significantly by windowing binning and changing the read out speed see section 9 3 2 Archiving the data to disk Once on the DMS the usual procedure is to t
213. stimate of the full width half maximum in CCD pixel units at three positions along each line and store these values The arrangement of the listed positions on the alphanumeric screen maps to the DMS display so the first position listed is in the top left hand corner of the image as displayed on the DMS display Now open the left Hartmann shutter and close the right by typing BHART 2 or RHART 2 55 SETUP PROCEDURES ISIS Users Manual at the ICL interface and take a similar exposure At the DMS control window type FOCUS RIGHT This routine will list the positions and the full width half maxima of the lines together with the shifts since the first exposure These Hartmann shifts indicate how far from the focal plane the photocathode is at each point The amount of collimator movement required can be calculated from the mean Hartmann shift a Hartmann shift of 0 5 pixels implies that the collimator needs to be moved about 1000 microns The direction of the shift will depend upon which on chip amplifier is being used and will have to be determined by trial and error After each move of the collimator the Hartmann test should be repeated After a move of the Blue collimator it probably will be necessary to run FOCUS again as unclamping and clamping this collimator can cause line shifts of several pixels The final FWHM of the lines with a narrow slit should be in the region 1 5 to 2 pixels although with the 150um slit recommended t
214. stop it from rotating of its own accord Set up the spectrograph and comparison lamp unit to give a narrow tungsten spectrum with reasonably uniform illumination along the spectrum 57 SETUP PROCEDURES ISIS Users Manual DEKKER 1 to give a narrow dekker AGMIRROR ACQCOMP CENWAVE BLUE 6500 illumination is more uniform in the red COMPFILTA ND3 0 COMPFILTB ND1 2 SLIT 200 COMPLAMPS W Open the shutter carefully in OVERSCAN mode to check the count rate and adjust the com parison filters slit width and grating angle if necessary Set up the IPCS using the ICL procedure IPCSFORMAT to have a window about 30 camera pixels wide with the spectrum from the narrow dekker in the centre and with full x8 resolution in the X direction and x2 or x4 resolution in the Y direction Alternatively the ICL procedure IPCSSDC should do the automatically although it may be necessary to adjust the start pixel of the window in the Y direction see the JPC S IT Users Manual for details of how to do this Open the shutter and take an exposure of at least 200 seconds to a reasonable count level When the exposure has finished at the DMS control window type Y FIND Using the DMS mouse put the cursor a little way in from one end of the spectrum and press the space bar The DMS will determine the centroid in the Y direction of the spectrum Press the space bar again and repeat the process at the other end of the spectrum If the spectrum is clea
215. string gt Channel The name of the CCD data acquisition channel to be used Title A title for the observation optional Examples BIAS RED Bias frame 5 Comments As for the RUN command except that exposure time will be zero and the ob servation type is set in the headers as being a BIAS exposure 11 5 4 BIN Bins a CCD detector Format BIN lt channel gt lt xbin gt lt ybin gt Channel The name of the CCD data acquisition channel to be binned X bin The binning factor in X This must be an integer in the range 1 10 Ybin The binning factor in Y This must be an integer in the range 1 10 Examples BIN RED 2 2 Comments This command sets the binning factors on the named channel in both X and Y and enables windowing and binning on the CCD 11 5 5 CCDINIT Initialises a CCD Format CCDINIT lt detectorname gt Example CCDINIT RED Comments Initialises a CCD and updates the MIMIC display with data from the CCD con troller This is performed in the startup sequence and this command is only required if the startup sequence fails 116 ISIS Users Manual COMMAND LISTS 11 5 6 CONTINUE Continue a paused CCD exposure Format CONTINUE lt channel gt Channel The name of the CCD data acquisition channel to be used Examples CONTINUE RED Comments This command resumes a paused CCD exposure opening the CCD shutter The shutter will not be opened if it was closed when the exposure was paused as in
216. systems These are located on a table behind the data reduction vaxstation LPVS3 and close to the door which leads to the dome area One of the three terminals is a network monitor which should only be used by La Palma technical staff Use of the other terminals is normally restricted to technical staff and support astronomers and with the increasing reliability of the Vax control system should occur only rarely 41 COMPUTERS ISIS Users Manual 7 8 1 The Engineering MIMIC The Engineering MIMIC is a 4ms computer which is used to run a schematic display representing the status of ISIS and the A amp G box There are three diagrammatic pages representing the A amp G box the ISIS slit are and the rest of ISIS Commands are available to switch between these display pages to examine a particular mechanism in detail and to move mechanisms in these and other subsystems by issuing network commands These are detailed in a guide called The WHT Engineering MIMIC a pale green loosely bound document of which there should be at least one copy in the control room To use the engineering mimic select MIMIC on the rotary switch labelled A 7 8 2 Direct control of the Cassegrain Instruments It is possible to communicate with any of a number of other 4ms microprocessors using terminal A by selecting the appropriate position on the rotary switch marked A The microprocessors include e The FOS 4ms microprocessor e The ISI
217. t 0 3 pixels then the rotation alignment should be adjusted The CCD mounting ring is fixed to the mounting ring on the spectrograph by seven 6mm Allen screws which pass through slots in the CCD mounting ring into the spectrograph mounting ting There are two further Allen screws which hold the spectrograph mounting ring to the spectrograph these lie on a horizontal line through the centre of the mounting ring and are recessed more deeply than the other screws These two screws should not be loosened If the seven screws are loosened the cryostat and mounting ring can be rotated a small amount the limit is set by the length of the slots in the CCD mounting ring There is a micrometer gauge fixed to the CCD mounting ring to the left of the cryostat this can be brought against a block which is fixed to the spectrograph mounting ring to give a measure of the relative position angle of the two rings The cryostat should be rotated by backing off the micrometer loosening the screws rotating the cryostat manually tightening at least three of the screws and then measuring the position angle with the micrometer The micrometer gauge should not be used to push the cryostat around The mounting ring on the red arm is stiffer than that on the blue arm and needs to be pushed around quite hard A 1 pixel slope from end to end on the CCD will require a movement of the cryostat position angle equivalent to slightly under 0 2mm on the micrometer The direction o
218. t 2V Comments After issuing this command further CCD commands will affect Virtual Head 2 until this is changed by issuing 1V Commands that require the correct Virtual Head to be set include QUICK SPEED STANDARD SPEED CONFIG RED PIC CLR and local binning and windowing commands Consult RGO technical staff to find out which Virtual head number refers to the CCD you are using 13 3 6 CLOSE Closes a CCD shutter Format CLOSE 13 3 7 CLR Clears a CCD Format CLR Comments This command currently only works from the Network vocabulary invoked by typing NETWORK 13 3 8 NETWORK Invokes the Network vocabulary Format NETWORK 13 3 9 OPEN Opens a CCD shutter Format OPEN 13 3 10 PIC Takes an exposure and reads it out Format lt headnumber gt 0 PIC Comments Local command to clear the chip take an exposure of an exposure time previously set up with the SEX command and read the chip out A buffer must have been set up in the DMS to receive the data The first parameter is the head number and is 1 or 2 The second parameter can be used to delay the start time This command currently only works from the Network vocabulary invoked by typing NETWORK 13 3 11 QUICK SPEED Changes the readout rate to the faster and higher noise of the two allowed values Format QUICK SPEED 137 COMMAND LISTS ISIS Users Manual Comments This provides a quicker readout of the CCD and hence less dead time between ex
219. t Unit The wide aperture in the slit unit can accommodate multi slit masks containing slits for ob servation of up to 10 separate objects The total field of view is 4 by 2 arcminutes for FOS II 16 ISIS Users Manual INSTRUMENTS and 4 by 0 9 arcminutes for the red and blue arms of ISIS The multi slit masks are made from 0 55mm brass plate on La Palma with a CAMM3 engraving machine which is controlled by a PC Use of multi slits has now been superseded by the Low Dispersion Survey Spectrograph LDSS which is built specifically for multi object work and the multi slit unit is not currently offered to users 2 12 Then ISIS Fibre System The ISIS fibre system enables the ISIS spectrograph on the WHT to be fed with fibre optic bundles The bundles link the auxiliary focus located on the acquisition and guiding box with the ISIS slit area see figure 9 Below this position ISIS can be configured in the same way as for the long slit unit Then both arms and FOS can be used in the usual form However several ISIS facilities including autoguider and comparison lamps cannot be used The ISIS fibres system is composed of the following elements e Auxiliary focus As the Cassegrain focus is inaccessible when ISIS is mounted on the telescope the fibres will be placed at the Auxiliary Port of the A amp G box This focus with a 15 arcmin field is fed through the large mirror of the A amp G box FOCAP aperture plates are used at this auxilia
220. t between types of data i e CCD or IPCS and will in future be used to select between display formats 14 2 2 The Display Menu The display menu allows the user to choose between lookup tables and to change the contrast of the display There are two lookup tables a colour table and a greyscale When driven from the Mouse interface the chosen table always covers a range between 0 and 2 where n is in the range 1 to 16 However the display wraps around so the full range of allowed data values 0 to 65535 is covered by 26 7 wraps of the lookup table The following options can be selected by placing the cursor on the option name on the display menu and pressing e GREY Selects the Greyscale lookup table and leaves the user in the Display menu e COLOUR Selects the Colour lookup table and leaves the user in the Display menu e REVERSE Reverses the lookup table and leaves the user in the Display menu e SHIFT After selecting this option with SeLecti pressing again increases the contrast of the display i e reduces the range that one wrap of the lookup table covers by a factor of two decreases the contrast of the display i e increases the range that one wrap of the lookup table covers by a factor two returns the user to the Display menu leaving the lookup table as it was last set e NORMAL 14 2 3 The Statistics Menu The Statistics menu allows the user to define windows and perform statist
221. t dekker BCR HART 1 Close blue or red arm left Hartmann shutter only GLANCE BLUE RED ARC Take a tsec test exposure DMS gt FOCUS and select 3 strong unblended lines with the cursor DMS gt FOCUS LEFT See the 9 centroid positions amp FWHM values listed BCR HART 2 Close the blue or red arm right shutter only GLANCE BLUE RED ARC t Take a second tsec test exposure DMS gt FOCUS RIGHT List new positions FWHMs and Hartmann shifts If average shift gt 0 lpixel move collimator and loop back to BCR HART 1 line Moving the BLUE or RED collimator position RCOLL BCOLL command by 1000 units will change the Hartmann shift by 0 5 pixels See Whiteboard for the direction to go Current collimator settings are on the white board 10 4 Setting Up The IPCS 10 4 1 Starting Up and Scan Correction Check the N supply is ok the shutter is closed and lights are out Fast start the EHT supply on the IPCS rack mounted on the Cassegrain cage As of February 1993 the old data acquisition system is needed with IPCS i e use EXPOSE and KEEP commands Perform scan correction on the DMS by typing IPCSSCAN and following 89 OUICK REFERENCE GUIDE ISIS Users Manual Table 10 Some default IPCS Formats on aris on axis Full frame On azis is Rows read out Start of window Read into buffer Y res spatial Spectral X res spectral PROC IPCSY4 IPCSY8 OVERSCAN IPCSY2 instructions use CALC SDC or load
222. t paths and status of mechanisms in the acquisition and guidance unit slit area and spectrograph including TV comparison lamps autoguider main filters auxiliary port filters dekker slide slit unit above and below slit polarimetry modules ISIS filters Hartmann shutters collimators gratings and detectors e CCDs Focal station chip name size windows binning temperature and difference from nominal readout speed exposure status shutter status requested exposure time exposed time UT start for each CCD e CCDs SUMMARY Temperature exposure times times to go windows for each CCD e IPCS Status of the IPCS e IPCS WINDOW Size and position of the IPCS window A small version of the CCD summary page is permanently displayed There are in addition individual pages for CAGB AUTOguider ISIS_SLIT and FOS but the information from these has been incorporated into the ISIS SUMMARY page The current state of any mechanism or light path is identified by its represented colour on the MIMIC screen The colour scheme is 40 ISIS Users Manual COMPUTERS WHITE mechanism is ok although not in use RED mechanism is in error BLUE mechanism is moving GREEN mechanism is successfully in use YELLOW the current selected light path The following ICL commands relate to the MIMIC they are only normally needed when problems occur MIMIC PAGES List names of available MIMIC pages screens MIMIC UPDATE Refresh current screen
223. t the DMS control window type FOCUS RIGHT This routine will list the positions and the full width half maxima of the lines together with the shifts since the first exposure These Hartmann shifts indicate how far from the focal plane the photocathode is at each point The amount of collimator movement required can be calculated from the mean Hartmann shift a Hartmann shift of 1 pixel implies that the collimator needs to be moved about 1000 microns A positive Hartmann shift implies that the collimator must be moved to lower values As the IPCS data builds up in the DMS you can type FOCUS RIGHT part way through the exposure to see how it is going then repeat it at the end After each move of the collimator the Hartmann test should be repeated It probably will be necessary to run FOCUS again as unclamping and clamping this collimator can cause line shifts of several pixels The final FWHM of the lines should be around 3 5 pixels it is rather better in the red and rather worse in the blue If with the spectrograph in focus and a narrow slit in place the FWHM is much greater than this then the Image Tube focus is incorrect and should be adjusted This must only be done by RGO technical staff At the end of the focus procedure both Hartmann shutters should be opened by typing BHART 0 61 SETUP PROCEDURES ISIS Users Manual The focus is somewhat temperature dependent but unless there is a sudden change of am bient te
224. t to give a reasonably strong signal but the lines to be used must not exceed 32767 adu at any point along their length Set up a CCD window about 600 pixels wide with the ICL procedure WINDOW close the left Hartmann shutter by typing BHART 1 or RHART 1 at the ICL interface and take an exposure with GLANCE When it has read out at the DMS control window type FOCUS select three strong lines evenly spaced from the one end of the spectrum to the other by placing the cursor on each in turn and pressing the space bar on the DMS keyboard Each line profile will be shown on the DMS display and the line can be rejected if it appears too weak or blended with or close to another line The best results will come from strong isolated lines When three lines have been selected type FOCUS LEFT at the DMS control window The programme will then list the centroid and an estimate of the full width half maximum at three positions along each line The arrangement of the listed positions on the alphanumeric screen maps to the DMS display so the first position listed is in the top left hand corner of the image as displayed on the DMS display Now open the left Hartmann shutter and close the right by typing RHART 2 or BHART 2 at the ICL interface and take another exposure At the DMS control window type FOCUS RIGHT This routine will list the positions and the full width half maxima of the lines together with the shifts since t
225. t will remain displayed until is pressed when the user will be returned to the Statistics menu e Y CUT This option collapses the selected window onto the Y axis and plots the result For IPCS data it sums the pixels in X and for CCD data it averages them If the WINDOW1 WINDOW 2 option is selected with WINDOW USE then the upper and lower boundaries of WINDOW2 will be changed to match those of WINDOW1 and the data from WINDOW 2 will be scaled by the ratio of the window widths before subtraction The plot will remain displayed until is pressed when the user will be returned to the Statistics menu 142 ISIS Users Manual COMMAND LISTS e Z CUT This option is not applicable to any of the current ISIS data taking modes e WINDOW USE This option selects the window to which X CUT Y CUT or CAL CULATE will be applied After selecting this option with further presses of will cycle between WINDOW1 WINDOW2 and WINDOW1 WINDOW2 The current selection is displayed just below the menu returns the user to the Statistics menu 14 2 4 The Screens Menu The Screens menu allows the user to determine which data buffer is displayed in the image area and how the data is displayed In each case the mapping between the data buffer and the image display is such that the whole data buffer is displayed For windowed CCD data the window is displayed in its correct position on the chip For all CCD data the aspect ratio of the detector is
226. te No 31 a data file and interpolation program are stored in the LPINFO directories at Cambridge and La Palma These data are valid only for a very clear night with low aerosol content and correspond to an extinction of 0 10 mag airmass in the V band A value of 0 15 is more typical and values above 0 18 will usually include a contribution from dust The actual extinction for any clear night can be obtained from the Carlsberg Meridian Circle data also stored in LPINFO and for values at V between 0 08 amp 0 16 the extinction curve usually has the same shape as King s curve The King extinction curve is repeated here m is the value in magnitudes per airmass Note the low value at 5500A Sahara dust can extinguish starlight and reflect light from the Moon and street lamps Although it is thought normally to be grey in extinction at optical wavelengths D Jones Tech Note No 10 D Stickland et al Observatory 107 74 1987 very non grey extinction has been reported once Andrews amp Williams ibzd 109 15 1989 153 APPENDICES ISIS Users Manual Table 14 La Palma Standard Extinction Curve 154 ISIS Users Manual APPENDICES F The LAPLATE program The programme LAPLATE is a modification of the programme APLATE Starlink User Note SUN 89 developed at the Anglo Australian Observatory AAO This programme converts a list of equatorial coordinates right_ascension and declination into focal pl
227. ted correctly with the TCS CALIBRATE procedure then the objects should appear close to the Cassegrain rotator centre In this case it is best to define an aperture with the TCS ENTER APERTURE command and move the objects directly into the slit with the TCS APERTURE com mand It is normally best to acquire directly onto the slit at a scale of 4 5 arcsec mm If the TV focus has been set correctly it should be possible to check the focus on the slit if the object is bright enough If there are two objects which are further apart than the TV field of view at this scale it may be necessary to go to 12 arcsec mm to get both onto the slit When acquiring more than one object on the slit it is best to use the TCS TWEAK command which will allow small adjustments of position and position angle whether the telescope is autoguiding or not 9 1 4 Acquiring faint objects If the objects are two faint to see on the slit viewing TV then they should be acquired using the TCS BLIND_OFFSET command For each object the observer should bring accurate positions of the object and of an offset star which will be visible on the slit viewing TV Each position should be entered as a catalogue entry in the TCS The procedure for acquisition is as follows 70 ISIS Users Manual OBSERVING PROCEDURES 1 Acquire the offset star on the rotator centre by typing GOCAT lt offsetstar gt 2 Centre the star up on the rotator centre using the handset 3 Move the star into
228. tely required for objects separated by more than 5 degrees in elevation and for observations at different mount position angles In particular observations of extended objects at different position angles must be calibrated separately The procedure for taking calibration lamp exposures is described in section 9 1 2 It may be possible to autoguide through a wavelength calibration exposure this depends upon the 12 ISIS Users Manual OBSERVING PROCEDURES brightness of the guide star and the probe co ordinates If not it will be necessary to switch the autoguider off during the calibration exposure and re acquire the guide star afterwards 9 2 Observing with IPCS only or with CCD and IPCS Procedures for setting up and using the IPCS are described in full in The PCS H Users Manual by J S B Dick and it is important that observers who intend to use the IPCS read this manual The IPCS is easily damaged by bright light Thus it is important that before opening the shutter the observer should be aware of the degree of illumination which will fall on the detector If the observer is unsure of this then they must insert neutral density into the beam with MAINFILTND or alternatively with COMPFILTA or COMPFILTB if the exposure is of a comparison lamp and gradually reduce the level of neutral density until the level of illumination is the maximum that can be tolerated Unlike the CCD systems starting and ending IPCS exposures is independent of t
229. the other end of the coherent bundle was shaped to accommodate the semi coherent bundles Figure 13 Two semi coherent bundles 2 35 m long each containing 15 fibres the central fibre and 6 ones in the first ring are of type FHP100 110 125 while the 8 fibres in the second ring are of type FHP200 240 270 The 7 central fibres were introduced in a polymide microtube of type PPC406 444 This group covers an area of 1 6 arcsec on the sky The second ring of fibres was glued surrounding this microtube In order to protect it the whole structure was inserted in a stainless steel tube of type 1100 1470 Each of the semi coherent bundles built this way covers an area of 4 arcsec on the sky Figure 14 The orientation North of each bundle is marked by a pin A piece to group the 3 guiding bundle ends when connected at the CCD camera This can be rotated and must be mounted at a certain orientation which is clearly marked e A Westinghouse ISEC TV camera 21 INSTRUMENTS ISIS Users Manual AA S GUIDE BUNDLE MANDREL ADJUSTMENT SLIDE GUIDE BUNDLE MANDREL ENDS BONDED TO CO HERENT BUNDLE 212 FIELD LENS Figure 13 The TV camera end of the coherent and semi coherent bundles SEMI COHERENT BUNDLES FOCAL PLANE END CCD CAMARA END 1mm 4 51 a SCB BLUE SCB RED Figure 14 Schematic of the focal plane and TV camera ends of the two semi coherent bundles 22 ISIS Users Manual INSTRUMENTS Table 5 Specif
230. tial resolution factor along the slit This can be 1 coarsest resolution 2 4 or 8 e Number of CCD pixels read into the buffer in the spectral direction This may not exceed 320 e Resolution factor in the spectral direction This can be 1 2 4 or 8 and is normally 8 The procedure sets the start of the CCD window in the spectral direction to pixel 30 to avoid the unthinned region of the CCD For details of how to adjust this and for details of how to set up more complicated windows refer to Chapter 4 of the IPCS H Users Manual 123 COMMAND LISTS ISIS Users Manual 11 6 6 IPCSOPEN Opens the IPCS shutter Format IPCSOPEN Synonym IPO Comments Please watch the raw video display when the shutter is opened 11 6 7 IPCSSDC To set the IPCS format up in a way suitable for calculating the S distortion correction Format IPCSSDC Comments Sets up an IPCS window at full resolution in both directions centred in Y on the part on the chip on which the image of the narrow dekker will fall 11 6 8 IPNEWT Changes the exposure time for an IPCS exposure Format IPNEWT lt newexposuretime gt Example IPNEWT 2400 Units seconds Comments The new time should be greater than the exposed time so far 11 6 9 IPPAUSE Pauses an IPCS exposure Format IPPAUSE Comments Pauses data collection during an IPCS exposure but does not close the shutter 11 6 10 IPSTOP Stops an IPCS exposure Format IPSTOP Comments T
231. toguider Format START UP Comments Starts up the Autoguider by turning on the nitrogen flushing and cooling the chip to around 30 C If in any doubt the observer should verify by checking the flowmeter attached to the outlet that the nitrogen flow has indeed been turned on 13 1 13 STATS Causes a statistics summary for the current guiding run to be displayed on the autoguider display screen This display includes mean and standard deviation of the seeing and transparency values which are useful for assessment of the weather conditions Format STATS Comments This command appears not to work at present 13 1 14 STEMP Sets the target temperature for the autoguider chip Format STEMP lt temperature gt Example STEMP 25 Units Degrees C 13 1 15 TEMP Causes the temperature on the autoguider display to be updated Format TEMP 13 2 DMS commands The DMS has many functions in addition to those provided by the user interface the mouse Those described here are useful for setting up the detectors for diagnostic information when something goes wrong or for taking and temporary storage of data if the Vax 4000 or the parallel link between the Vax 4000 and the DMS is not available 13 2 1 IMAGES Lists the image files available on the DMS disc Format IMAGES Commets Lists the named images on the DMS disc available for temporary storage of data Images of three formats exist full format for large and small CCDs
232. tual configuration Check when CCDs were last filled with liquid Ny and fill if necessary Check CCD temperatures are correct see MIMIC screen for CCD1 etc SETUP RED BLUE FOS AUX to setup the default formats 1280 in X 1180 in Y for EEV3 amp EEV6 1124 x 1124 for Tek WINDOW RED BLUE FOS AUX to window just answer the questions DISABLE WINDOWS RED BLUE FOS AUX to disable windows and ENABLE WINDOWS to restore SEND CCDn OBEY CANCEL WINDOWS MOVE Ato clear windows completely h head number To change CCD readout speeds 88 ISIS Users Manual QUICK REFERENCE GUIDE SLOUCH RED BLUE FOS AUX set slow readout speed SPEEDY RED BLUE FOS AUX set fast speed NB slightly higher readout noise BIN RED BLUE FOS AUX set on chip binning factors in X and Y To manually open and close the CCD shutters use OPn CLn where n R B F or A 10 3 1 Rotation and Focus Rotation Use the narrow 1 2 dekker and tungsten lamp On the DMS measure the po sition of the left amp right ends of the narrow spectrum with Y FIND command Rotate cryostat manually as described in section 8 3 1 if shift exceeds 0 3 pixels Focus Setup a wide window on chip with WINDOW params RED CCD1 EEV3 chip 1 210 1278 720 BLUE CCD2 Tek chip 1 160 1122 680 Use arc lamps CuNe is usually best around 7000A for the RED arm CuAr around 4500A for the BLUE arm The focus loop is SLIT 200 Set slit width of 200 um DEKKER 6 select the long sli
233. ually expressed in e adu will be known to local staff All CCDs produce an image which is larger in both dimensions than the active area of the CCD this area is given in column 4 above The additional image area consists of underscan and overscan and dark reference regions The difference between these types of reference regions and the location of the regions for CCD types in use on the WHT are discussed by P R Jorden in ING La Palma Technical Note no 79 The bias level in each data frame which is an electronic offset with a low frequency time dependence is estimated most reliably from the serial underscan region in regions of the image frame which are given in the table below On chip binning and windowing are available for any CCD and the parameters can be controlled using the ICL commands BIN and WINDOW On chip binning is useful not only in reducing the amount of data read out from the CCD and thus the dead time between exposures but also in reducing the effective readout noise in the data Because the readout noise occurs only once for each summed pixel the effective readout noise is reduced by the a factor of the square root of the number of pixels summed On the other hand because the output of the analogue to digital converter limits the amount of charge that can be read from the CCD in any one pixel on chip binning reduces the maximum dynamic range that the CCD can provide by this same factor The Tektronix CCD
234. ulti object spectroscopy with fibre optics an accurate focal plane scale determination is necessary because the fibre positions X and Y on the focal plane are calculated from the object R A and DEC coordinates through the scale An error of 0 2 in the scale results in a loss of 50 of the star s light on a fibre at the edge of the field 17 INSTRUMENTS ISIS Users Manual To obtain the focal plane scale several photographic plates of good astrometric fields have been taken With the star positions on the plates and their astrometry apparent celestial coordinates have been found Finally effects of annual aberration diurnal aberration light deflection atmospheric refraction have been taken into account to find the angular separation between each star pair The average of the ratios between the separation of each star pair in plate and celestial coordinates yields the focal plane scale The value of the auxiliary focal plane scale found in this way is 221 863 0 134 microns arcsec ie 4 507 0 003 arcsec mm The mounting for the fibre system at the auxiliary focus consists of two main structures an interface for the auxiliary port and a plate holder The fibres are placed at the auxiliary port using aperture plates FOCAP system see section 2 12 4 These aperture plates are held in position by four flanges on the plate holder Three pilot pins determine the aperture plate position Finally the plate holder is mounted on the A am
235. umber of photons AA s detected for objects of accurately known magnitude are presented in Section 6 3 2 Stability and radial velocities The original specification for ISIS was to have flexure no more that 5um hour along and per pendicular to the slit during telescope tracking However measurements of the flexure caused by movements in elevation and movements of the instrument rotator suggest that flexure during tracking could be up to 15um hour The cause of the extra flexure is not yet known and until it is corrected it is recommended that observers requiring accurate radial velocities should take a calibration lamp exposure every 15 minutes Measurements of radial velocity standard stars taken during commissioning show that if care is taken with the calibration exposures it is possible to measure radial velocities to an r m s accuracy in the range 1 2 km s with the highest dispersion gratings H2400B and R1200R with either arm of ISIS The systematic offset between ISIS radial velocities and the IAU velocity system is measured to be Viau V srs 8 9 4 9km s from blue arm observations of radial velocity standard stars and nebulae The stability of FOS II has been measured to be better than 1um hour when tracking an object through the zenith 3 3 Scattered Light scattered light in ISIS is minimised by the use of optimised anti reflection coatings and if scattered light would be a serious problem for a particular observat
236. unning IRAF and the graphical tool for controlling data transfer from the DMS to the Sparcstation It is advisable to start this application first e DMS WINDOW This application will start a terminal window for local control of the Detector Memory System this is also a FORTH system so should also respond ok if it is running Next it is important to check that the Vax 4000 and the DMS are running The Vax 4000 is at the far end of the control room from the control desk and is clearly labelled The operator console for the Vax 4000 is near the computer and it will be fairly clear from the paper output of this whether the computer is running The DMS is in a VME rack in the second of the four blue cabinets to the left of the control desk Its user interface consists of a terminal mouse and display screen towards the left hand end of the control desk If the DMS appears not to be running or to be running in a non standard configuration or you are unsure of the configuration toggle the switch labelled RESET on the module labelled VMPU of the DMS The display 43 SETUP PROCEDURES ISIS Users Manual Table 9 Microprocessors on the Utility Network DMS The detector memory system itself FOS The 4ms microprocessor controlling the Faint Object Spectrograph AGCA The 4ms microprocessor controlling the Cassegrain A amp G Box ISIS The 4ms microprocessor controlling the ISIS Spectrograph TAUR The 4ms microprocessor controlling the Taur
237. ure plate material astronomical coordinates for the centre of the field and possible proper motions of the targets These are all considered by the programme in order to obtain the appropriate corrections of the X Y coordinates e By taking photographic plates of the field in advance The positions can be measured with a microdensitometer or other coordinate measuring machine Several error sources can contribute to the field acquisition for example poor astrometry the drilled holes for the stars do not coincide with the apparent positions or bad centering of the field and rotator adjustment Taking direct plates eliminates some sources of astrometric error at the expense of requiring extra observing time Besides the coordinates of the targets at least three other field stars must be chosen for telescope guiding These stars must fulfil the following requirements e They must have magnitude 12 to 13 in V Brighter stars are close to the Earth and can have large proper motions so that it is in general difficult to obtain good astrometry of them Less bright stars are difficult to observe e They must have similar brightness If not simultaneous observation on the monitor could be prevented as the brightest ones can saturate the camera while the weakest remain unseen e They must be as separated from each other as possible in the field and preferably along the East West direction which is free of atmospheric refraction Th
238. us Fabry Perot UES The 4ms microprocessor controlling the Utrecht Echelle Spectrograph LDSS The 4ms microprocessor controlling the Low Dispersion Survey Spectrograph CCDO The spare CCD controller CCD1 The controller for the Red Arm CCD CCD2 The controller for the Blue Arm CCD CCD3 The controller for the FOS CCD CCD4 The controller for the UES CCD IPCS The 4ms microprocessor controlling the Image Photon Counting System AUTI The VME microprocessor controlling the CCD Autoguider SYS The Vax 4000 System Computer ENGM The Engineering Mimic which is a 4ms microprocessor screen will refresh and the control window on the Sparcstation will display a system message then leave a standard Forth prompt ok and a carriage return When the DMS is running it is possible to check which other subsystems are communicating over the Utility Network At the DMS control window type NET The DMS will then attempt to communicate with each of the subsystems in turn and after each attempt will report either NO RESPONSE FROM lt DEVICE gt OT Acknowledgement received from lt DEVICE gt The devices are If the DMS does not receive an acknowledgement even from itself there is most likely a fault with the Network Interface Unit NIU connecting the DMS to the Utility network or with the cables between the DMS and the NIU If the DMS receives acknowledgements only from those devices which are connected to the same NIU as the D
239. ut EXPOSE will store the data only in the DMS not in a disc file EXPOSE IPCS does not open the shutter at the start of the exposure nor close it at the end this must be done explicitly 122 ISIS Users Manual COMMAND LISTS 11 6 2 EXPOSENP Starts an exposure on a specified detector without collecting the archive packets Format EXPOSENP lt detectorname gt lt exposuretime gt Example EXPOSENP IPCS 1000 Synonym ENPI EXPOSE IPCS Units seconds Comments This command works as expose but does not collect archive packets This saves time if you do no expect to KEEP the data However if you run KEEP after EXPOSENP then KEEP will collect the archive packets 11 6 3 IPCONT Continues a paused IPCS exposure Format IPCONT Comments To continue an exposure paused by IPPAUSE 11 6 4 IPCSCLOSE Closes the IPCS shutter Format IPCSCLOSE Synonym IPC 11 6 5 IPCSFORMAT sets up the data window and resolution parameters for taking IPCS data Format IPCSFORMAT Comments This is an interactive procedure which prompts for the parameters required to set up the IPCS and the DMS for a given data format Briefly these are e Number of CCD rows the spatial direction read out NROWS This must be in the range 64 to 256 e Start row on CCD This must be chosen so that the entire region read out is on the chip e Number of CCD rows read into buffer This should not exceed NROWS 7 and may not exceed 255 e Spa
240. w dekker AGMIRROR ACQCOMP CENWAVE BLUE 6500 illumination is more uniform in the red COMPFILTA ND3 0 COMPFILTB ND1 2 SLIT 200 COMPLAMPS W Open the shutter carefully in OVERSCAN mode to check the count rate and adjust the com parison filters slit width and grating angle if necessary The s distortion correction must be calculated at full x8 resolution in both X and Y direc tions even if this resolution will not be used for the observations Run the ICL procedure IPCSSDC which will set up a full resolution window 30 camera pixels wide centred on the spectrum If after running this procedure the tungsten spectrum is not in the centre of the window the value of the Y starting pixel of the CCD window must be changed this can be done with SEND IPCS OBEY Y_CCD_WIN MOVE lt ystart gt 30 The existing s distortion correction must be turned off by typing at the DMS control window O ESD At the ICL terminal take a fairly long exposure it is important to have a strong signal in the curve IPCSOPEN EXPOSENP IPCS 1000 After this exposure has finished close the IPCS shutter with IPCSCLOSE then at the DMS control window type CALC SDC This calculates the s distortion correction and takes about 80 seconds during which time the DMS will not respond After the correction has been calculated it must be loaded and enabled on the DMS control window with LOAD SDC 1 ESD 59 SETUP PROCEDURES ISIS Users
241. wer dead time The IPCS is not an integrating detector This means that as the individual photons are recorded their positions are immediately passed to the DMS At the end of an exposure there is no chip read out only the normal ISIS Users Manual OBSERVING PROCEDURES overhead of writing the data to the VAX and even this can be overcome by using datacubes in the DMS It is even possible to time tag each photon so that one can choose the time resolution and signal to noise per frame at the data reduction stage However this mode is still to be fully tested If the IPCS can produce an acceptable signal to noise and the very highest time resolution is required it should be considered as the detector for the blue arm of ISIS 9 3 3 Future developments By reprogramming the CCD controller it should be possible to reduce dead times still further For example at present the CCDs are cleared prior to all exposures The charge is transferred to the output but not digitised This operation takes approximately 10 us per pixel and hence 15 seconds for a full EEV chip There are alternatives It is possible to flush the charge out almost instantaneously by using all of the CCD clocks simultaneously instead of one by one as in the normal horizontal clocking process Alternatively since each full frame read out essentially clears the CCD anyway we could avoid clearing the chip altogether assuming that the previous frame was not over exposed and the
242. which is usually to be found near the engineering MIMIC terminal 14 The DMS User Interface The Detector Memory System has a mouse driven user interface which provides the user with some data assessment facilities The mouse has three buttons and is moved around on a reflecting pad The mouse drives a cursor on the screen which is in the form of a cross The cursor can be moved anywhere on the screen The screen consists of an image display area and a menu area the menu area appears in the top right hand corner of the screen When CCD data is displayed there are also one or more icons small CCD images these enable the user to switch between CCD buffers displayed in the main display area 14 1 Use of the Mouse Moving the mouse on the reflective pad moves the cursor anywhere on the screen including the menu area the icons and the image area The mouse has three buttons which are designated the left hand key the centre key and the right hand key is used to select a function or to perform an operation is only used in those instances where two functions can be performed from a single menu option such as increasing or decreasing the contrast and ESCAPE is used to return to the menu from an option or to return to the main menu from another menu 14 2 The Menu Structure 14 2 1 The Main Menu The Main Menu enables the user to select any of the other available menus and the ZOOM function Any item can be selected
243. will only affect the instrumental reference system The ori entation of the instrumental reference system relative to the N S meridian has to be calibrated by observing a polarisation standard star It is important to keep the orientation of the instru ment fixed relative to the sky e t set Cassegrain rotator tracking Be sure to write down the 81 OBSERVING PROCEDURES ISIS Users Manual position angle of the halfwave plate and of the Cassegrain rotator and to understand the exact definitions Since the calcite plate produces two slit images slightly offset in the spatial direction the o and e rays a dekker mask has to be used to prevent confusion between different parts of the slit This implies that continuous long slit observations are not feasible in this observing mode To facilitate semi long slit observations a comb Dekker may be used to observe a series of regularly spaced apertures along the slit simultaneously For a more detailed description of observational considerations see the ISIS Spectropolarimetry Users Manual The ISIS polarisation module has been proven to be capable of measuring polarisation reli ably to an accuracy better than 0 1 High accuracy polarimetry requires many photons as a rule of thumb for planning observations the uncertainty in one Stokes parameter 1 VN where N is the total number of photons per resolution element obtained in two exposures The generally high count rates necessary for spectro
244. with the optical axis of the spectrograph The slit prism alignment is conveniently performed in the laboratory The focal plane bundle end is illuminated with a laser beam the output light at the other end of the bundle enters the prism The screws at the kinematic seats are adjusted in such a way that the output light from the slit does not become vignetted by the two slots of the prism holder In order to align the slit prism set with the axis of the spectrograph ISIS must not be mounted on the telescope In this process basically the bundle slit must be aligned and centred on the detector and also the optical axis of the central fibre of the bundle must be centred with the collimator s axis The following steps are required e The Dekker must be placed in position zero with the command DEKKER 0 e The bundle slit is placed in position on the spectrograph In order to do so the software command SLIT_DOOR OPEN is used to open the door giving access to slit units The com mand MSLIT gives access to the unit supporting the slit mounting This mounting is put on the unit by introducing the bundle through the ISIS window above mentioned e The diffraction grating is removed using the CHANGE procedure from ICL From this posi tion one of the collimator mirrors can be see Either the blue or red arm can be used for the alignment e The focal plane bundle end is illuminated with white light From the grating position the image of the f
245. xel and field sizes at the Auxiliary port 5 2 ISIS FOS Dekker Slides 8 3 Dichroic Filters 10 4 ISIS grating properties 11 5 Aperture Plate Drilling Specification 23 6 CCD types 32 7 Recommended Bias regions 32 8 Measured sensitivity of the ISIS system 35 9 Microprocessors on the Utility Network 44 10 Default IPCS Formats 90 11 ND values of ISIS FOS Main Beam Filters 85mm diameter 152 12 Neutral Densities of ISIS FOS Calibration Beam Filters 75mm diam 152 13 La Palma Sky Brightness Mag Square Arcsec 153 14 La Palma Standard Extinction Curve 154 ISIS Users Manual INSTRUMENTS Part I Description of the Instruments 1 The Cassegrain A amp G Box 1 1 Design of the A amp G unit The layout of the A amp G Unit is shown in Figure 1 It is described in some detail by P A Ellis in ING La Palma Technical Note no 56 Briefly the unit has a full field of 15 arcmin diameter at the nominal telescope focus 150 mm below the A amp G to instrument interface Facilities are provided to view the on axis field either directly or reflected from the ISIS slit jaws autoguide using the off ax
246. y variations in the spatial direction To take twilight sky exposures 1 Take the acquisition and comparison mirror out of the beam if it is in with the ICL command AGSLIT or AGMIRROR SLITVIEW or AGMIRROR OUT If a comparison lamp is on you will need to turn it off with COMPLAMPS OFF first 2 Verify that the dome and primary mirror covers are open 3 Take trial exposures with GLANCE and adjust the exposure time and main filter slide filters with the ICL command MAINFILTND to give a maximum level of no more than 40000 ADU The twilight sky exposures do not require a very high signal level because they will be collapsed in the spectral direction before being used anyway 4 Take the final exposures or keep the trials if the level is right e Exposures of comparison sources usually copper argon or copper neon interspersed with observations on the sky The comparison lamps are really rather faint in the blue and exposure times of between one and five minutes depending upon the dispersion and slit width will be required to give adequate signal in the blue The copper argon lamp usually gives the most usable lines here At wavelengths longer than 5850 A the copper neon lamp has a number of strong clean lines and at wavelengths longer than 6965 A the copper argon lamp does too Thus it is usually possible to obtain a high signal to noise comparison spectrum containing a number of good lines using one or both of these lamps in an inte

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