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Operating the Graphical User Interface for UHRF

In April 2005, the new AAO-2 Optical Detector Controllers (ODC), and their associated Graphical User Interface (GUI), were commissioned for use with the MITLL3 and EEV2 CCDs used on the Coudé échelle spectrographs. Since early 2006, the spectrographs themselves are now configured and controlled within the one GUI. This document gives an overview of their operation, and some suggestions should things go wrong.

Contents

Startup, Shutdown, and Problems

The ODC and UHRF Interface



Starting up the GUI

The graphical user interface (GUI) for UHRF and its associated Real Time Display (RTD) can be run up on almost any X11-compliant display. However, they are best run from the one of the twin-headed consoles in the control room. Their login screen enables them to be used as the console for either one of the general purpose PCs in the control room (aatlxa or aatlxb), or one of the rack-mounted instrument control PCs behind the partition ( aatlxx or aatlxy). In general, aatlxx is reserved for UCLES/UHRF, and aatlxy for 2dF/AAOmega, but the two are interchangeable (albeit with separate home directories for the aatinst account). Check the whiteboard in the Control Room to see which machine you should be running on.

  1. If the GUI is still running from the previous night, it should not be necessary to re-start it from scratch. From the AAO CCD Loader, select Commands -> Reconfigure, and check that the UT date, file names, directories, and run number are appropriate. Then click "OK", and away you go.

  2. Otherwise, you will need to restart the GUI from a terminal window, while logged in to the Linux system aatlxx as aatinst. If you're not sure this is the case, then exit from the current Desktop session. Before logging in, you will be asked which host you wish to connect to - select the icon marked aatlxx. The twin-headed monitor will now serve as the console for aatlxx, rather than aatlxb. Login as aatinst (password is on the Control room partition).

  3. Opening a terminal window on aatlxx should give the ">" prompt for the aatinst account. The startup command will depend on which VME system the CCD controller is connected to, and which of its two inputs (0 or 1) the orange fibre-optic link (FOL) cables are plugged into. Each VME system can talk to two CCDs controllers simultaneously, through separate interfaces. The whiteboard in the Control Room should indicate which interface is currently in use. Usually this will be /fol1 on aatvme15, and the startup command will be uhrf2. Occasionally it may be necessary to run from the spare ODC system aatvme6, (in which case you should use uhrf2 swap) or from /fol0 (use uhrf1) instead. For more information and options, see Tony Farrell's software guide.

  4. After logging in as aatinst, type the following commands into this window:

    > cd                           (you must run the GUI from the aatinst home area)
    > uhrf2            (if using the default controller interface on aatvme15), or
    > uhrf1 swap      (if using /fol0 on aatvme6), etc.

    This will establish a number of processes running on various sub-systems, verify the position of each of the spectrograph elements, and bring up the various control GUIs on the workspace. These include the AAO CCD Loader, the Optical Detector User Interface, the Skycat RTD, and lastly the System Configuration window (shown below). This selects the instrument, the data/dummy directories and file root name by default, and allows you to specify the first run number (allowing you to overwrite existing files if you really want to). Check that it all looks right, then select "OK".

    System Configuration
     
     

  5. Although Skycat is the default RTD, the related Gaia tool provides expanded functionality as described below. If you would prefer this as your RTD, then simply exit from Skycat, and in the terminal you started up the GUI in, type

    > gaia &

    to bring up a new RTD, which will automatically connect to the data acquisition system. If you would like the RTD to update less/more often during readout, go to Commands -> Set slice size in the ODC User Interface and choose the number of rows to be read out before refreshing the display.

  6. Just as with IRIS2 and 2dF, the Portable Telescope Control System (PTCS) must also be running. This is started automatically (if not already running) by the ODC system, but will not launch the PTCS GUI. If you would like to have this GUI available (e.g. for commanding offsets, or simply to see what the UT or airmass is), then telnet to aatptcs as aatinst, then type

    > tel

    to launch the PTCS GUI


Problems with start up

If the UHRF + ODC system does not come up properly, there is a hierarchy of fixes:

  1. Are you trying to start it from somewhere other than the aatinst home area?
  2. Is the PTCS display updating? It may need restarting - consult your night assistant or afternoon shift technician.
  3. Reset the GUI tasks - first as a SOFT reset, and then as a HARD reset if that doesn't work.
  4. Reset the VME system.
  5. Kill the UHRF + ODC Interface and start it again.
  6. Kill the UHRF + ODC Interface, manually reset the ODC hardware and start it again.

If none of the above work, please contact your Afternoon Shift Technician or Support Astronomer for assistance.

The procedure for each of these steps (in turn) is:

Reset the GUI tasks

  1. Find the AAO CCD Loader GUI on the display from which the UHRF + ODC Interface is being run.
  2. Select Commands->Reset
  3. A pop-up will appear and ask what type of reset to perform ('soft' or 'hard'). Try a soft reset first.
    • The AAO CCD Loader will reset all its tasks, and re-establish connections with all the other computers it needs to talk to. Eventually the System Configuration GUI (shown above) will appear. Update it if necessary and click "OK". If you are presented with a succession of error dialog boxes instead, then you will need to go to the following section.
    • Try a test exposure.
  4. If the soft reset doesn't work, repeat from step 2 above, but this time do a hard reset.

Reset the VME system

If the above does not work, the VME machine (usually aatvme15, but possibly aatvme6 if running the spare system) which interfaces between the CCD controller, and aatlxx may need to be reset. This can be done by selecting Commands -> Reset VME System from the AAO CCD Loader (or if this GUI is unresponsive, by pressing the marked Reset button on aatvme15 / aatvme6 behind the Control Room partition).

Kill the UHRF + ODC Interface and start it again

  1. Find the aatlxx window from which you started the ODC interface.
  2. In this window type "cleanup". You'll get a long string of messages about things being killed, removed, or otherwise expunged.
  3. Restart the GUI as though starting it from scratch, using the instructions above (i.e., "cd" then "uhrf2", etc. on aatlxx).
  4. If everything comes back up, take a test exposure to check everything is working.

Kill the UHRF + ODC Interface, manually reset the ODC hardware, and start it again

If all the above doesn't work, you may need to manually reset some hardware. It's time to ask for help from your Support Astronomer or Afternoon Technician.

At the end of the night

You can leave all the GUI running at the end of the night. You will get a warning pop-up at 10am AEST that the UT date has changed, to remind you to do a Reconfigure before observing each afternoon.


The ODC and UHRF Interface

Once the GUI is up and running, you should have four displays visible on the desktop:

AAO CCD Loader

This shows the status of various GUI sub-systems (e.g. the UMIT task which gets the instrument configuration from UHRF, the DRT task which records the observations, etc.). These are all green when the GUI is running correctly. Below this is a Messages sub-window which will alert you to any problems by highlighting them in red. There is an "Exit" option in the "File" menu, which is the recommended way to shutdown the system if necessary; when prompted, select "Local Systems" and "aatvme14" to run the cleanup procedure on.

CCD Loader

The Reset option under Commands will do a full reset of all tasks, and bring up the System Configuration window again.

The Reconfigure option will just bring up the System Configuration window again. You should do this at the start of each night to ensure the filename dates and directories have the correct UT date, or if you really wish to overwrite existing data files by setting the First Run Number accordingly (note that the Night Assistant will need to delete runs to be overwritten from their archive log, so be sure to warn them of what you are doing).

Optical Detector User Interface

This is the main configuration and control system for the ODC and for UHRF. It is divided up into two halves: the left half contains 2 tabbed displays, one for configuring exposures and the other for configuring UHRF itself. Click on the "Detector" or "Uhrf" tabs at the top left to switch between these two displays. The right half shows the CCD status and sequence control, and is visible regardless of whether the Detector or Uhrf tab is currently selected. The UHRF control tab is discussed further down, but let's start with a closer look at each of the ODC-related sections:

Detector Setup

Defines the observation parameters, and detector readout windows.

Detector Setup

Next Run: After each exposure completes, the "Next Run" field updates with the next observation number to be written. During an exposure, this field changes to Current Run (e.g. "Glance", "Dummy m", "Run 5"). If you wish to overwrite existing data, you will need to reset the Next Run number using Commands -> Reconfigure in the AAO CCD Loader.

Total Number of Runs: If several identical consecutive exposures are required, the total number of images required can be entered into this field, before starting the first exposure. The number of frames remaining to be taken will be decremented in the Repeats field of the CCD_2 Status (or CCD_1 status if using the second controller interface) section, and in the Repeats Left field of the CCD Run Control section as each one is taken. The field itself will be greyed out until all repeats are completed, after which it will reset itself back to 1. If you wish to change the number of repeats, or the exposure time of each during the sequence, you can do this from the CCD Run Control section. Checking the "nonstop" box will cause exposures to continue indefinitely, until terminated either by unchecking the box, or by clicking "Stop Repeats" in the CCD Run Control section.

Recording: There are three types of observation:

Exposure Time: Enter the desired exposure time here before starting an exposure. It will be greyed out while the run is in progress, but if you decide to extend the exposure time (and readout has not yet begun), or shorten it, this can be done from the CCD Run Control section.

Readout Speed: Select the desired readout speed, bearing in mind the trade-offs between readout time, read noise, gain, linearity, etc. given by the table of AAO-2 controller perfomance.

Object: Enter the object name here before starting an exposure. It will be greyed out while the run is in progress, but if you decide you need to correct it before readout has completed, this can be done from the CCD Run Control section.

Comment: Enter a comment here before starting an exposure, to be added to the FITS header. It will be greyed out while the run is in progress, but if you decide you need to insert a comment before readout has completed, this can be done from the CCD Run Control section.

CCD Windows: This section allows the observer to load existing CCD readout window definition files, or create and store new ones. Y defines the number of CCD rows to read out, with binning if appropriate. X1 usually defines the CCD columns which make up the data section. X2 usually defines the (virtual) CCD columns which correspond to the Overscan section. Previously-defined CCD windows used with the old VAX-based controllers can be recalled with the "vax" button. More recent user-defined windows can be recalled in text format, or sds format, with the "txt" and "sds" buttons respectively (the ".txt" or ".sds" extension will be added automatically). Any newly-defined windows can be saved as a text file with the "Save Definition to File" button. Note however that this action will save not just the CCD window information, but also much of the "observation definition" information (object name, readout speed, etc.). These will overwrite the existing fields whenever the window definition is re-loaded, unless the "window only" box is ticked.

Validate: Pressing this button will cause all the observation parameters, including CCD window definitions, to be checked for consistency and completeness (e.g., no binning specified), and a warning given if anything is amiss. Starting an exposure will also cause a validation check to be done.

Last FITS Data File Written: The full pathname of the last Normal or Dummy exposure is recorded here, allowing the observer to cut and paste the file name into another application.


CCD Status and Control

This section shows the status of various detector functions. It is comprised of 4 sub-sections.

CCD Status

CCD_2 STATUS: This indicates which detector is connected to the controller, the array temperature and the heater voltage needed to maintain the array at the working temperature. If either the temperature, or heater voltage are out of range (usually as a result of running out of liquid nitrogen), the Status field will change from green to red, and a warning will be given. The current Run type (OBJECT, FLAT, ARC, etc.), Exposure/Readout progress, and Shutter status are also displayed in this section.

Once an exposure is commenced, the time elapsed as a fraction of the total time requested will continuously update in the large grey box at left. The status will change to "Exposing", and a red status bar beneath will also show the progress of the exposure. When the exposure completes, the shutter will close, and 2 beeps will be heard. The status will change to "Reading Out", while a cyan status bar will show the progress of readout. The large grey field at right will show the elapsed time, as a fraction of the expected total readout time. Note that readout times for binned exposures are not currently estimated correctly, so that readout may continue even after the timer has reached the expected time and stopped updating.

CCD RUN SINGLE EXPOSURE: These are the buttons which actually inititate an exposure (or if repeats have been requested, a sequence of repeat exposures). The only difference is that they each define a different observation type, as recorded in the Observing Log and Archive, and in the OBSTYPE keyword in the FITS header. All these buttons are greyed-out while an exposure is in progress.

CCD RUN CONTROL: Once an exposure, or series of repeat exposures is underway, the only to modify the exposure parameters or terminate exposures is with these buttons, as most of the functions in other sections will be greyed-out.

Each of these will bring up a small dialog box into which you type the new value. To pause an exposure in progress (e.g. cloud drifting through the field, so you want to close the shutter briefly) click "Hold". To resume the exposure, click "Continue". To abort an exposure in progress (i.e. not even read it out), click "Abort". You will be asked to confirm if you really do wish to abort, and if you indicate "Yes", the system will reset then issue a confirmation when ready to continue.

CCD RUN SEQUENCE: Just like for IRIS2, observing sequences involving combinations of telescope offsets, instrument reconfigurations, Semel polarimeter sequences, etc. can be implemented via Standard or User sequences using TCL. See the existing sequences for examples, or the Sequencer documentation, for examples of how to go about this. For UHRF, sequences are provided to assist in setting rotation and focus as part of the UHRF setup procedures.


Messages

This section displays the system responses to various commands, and the progress of exposures and observing sequences. Also shown here are the names of the data and dummy files as they are written to disk, and the amount of disk space remaining. If you see a warning that there is space for fewer than 100 images, please alert your Support Astronomer or the Night Assistant, who will then free up more disk space.

Messages


The UHRF Interface

Clicking on the "Uhrf" tab will replace the Detector Setup display with one for controlling and viewing the status of UHRF itself. This tab contains two more tabs - the main one labelled "UHRF Control", and a second one labelled "Configure with Control File".

UHRF Control

This section shows the status of various elements within the spectrograph, and allows them to be configured, either via "radio buttons" (where there are only 2 options), pull-down menus (for several fixed options), or numerical entry fields. Selecting a new value or position for an element will not actually cause it to be reconfigured, but the background colour for that element will change from green to red to indicate that the current position does not actually match that selected. Pressing the blue CONFIGURE button at the bottom will cause that element to be moved, and the background colour will change to flashing cyan. Once the requested position has been achieved, the background colour will change to steady green again. The elements which might normally be set to CLEAR or OUT for observing (e.g. Post-Slit Filters, Hartmann Mask, etc.) will have their pull-down menu tab marked in red if set to any other position. This does not necessarily mean that they are out of position, but does allow the observer to tell at a glance if the spectrograph is ready to observe or not.

Several elements can be configured in parallel by selecting new values for each, then pressing CONFIGURE once at the end. A third option is to right-click on any element name, which will bring up a popup dialog box. Entering a new value in this box and clicking "OK" will cause that change to be executed. More information on each of these elements is given below, or refer to the UHRF manual.

UHRF display

Slit Slide: This can be set to either:



Calibration Lamp: This can be set to one of:


Lamp Filter 1/2: These can be set to any of 8 positions, usually CLEAR but Neutral Density (ND) and glass colour filters are available if required. The UHRF Quartz flatfield lamp occupies position 8 of Lamp Filter wheel 2, but is positioned by the Calibration Lamp control.


Slit Width: This allows the observer to specify a slit width, in any one of arcseconds on the sky; millimetres at the focal plane; or pixels (after binning, as specified in the Detector Setup section) on the detector. Simply click in the field you wish to specify, delete the current value, and enter the new value (or select from the pull-down menu any recent previous value wish to recall). Then click on the "set arcsec", "set mm", or "set pixels" button to the right of the value just entered. The equivalent values in mm and pixels (if you entered arcsec) are computed and updated. The slit width will not actually be adjusted until either the "CONFIGURE" button is pressed, or the observer right-clicks on the red Slit Width field and selects "OK" in the pop-up window. Note that either MIN or MAX may be entered in any of the 3 fields to specify the minimum or maximum slit width physically achievable. This section is greyed out when the Slit Slide is set to "Slicer".


Slit Length: As with the Slit Width field, the observer has the choice of specifying a slit length in either arcseconds, millimetres, or pixels (after binning, as specified in the Detector Setup section). Enter a new value in any of the 3 fields, or recall a previous value from the pull-down menu, then press the adjacent "set" button. The slit length will not actually be adjusted until either the "CONFIGURE" button is pressed, or the observer right-clicks on the red Slit Length field and selects "OK" in the pop-up window. Note that either MIN or MAX may be entered in any of the 3 fields to specify the minimum or maximum slit length physically achievable. MIN is useful to produce an "artifical star" spectrum for order-tracing when the primary targets have a weak or broken continuum. This section is greyed out when the Slit Slide is set to "Slicer".


Slit Shutter: This shows the current state of the shutter at the coudé slithead; usually SHUT, but it should indicate OPEN while an exposure is in progress.


Camera Shutter: This is supposed to show the current state of the shutter immediately in front of the CCD. This shutter is usually OPEN, unless it has been tripped by someone opening either the main door to the spectrograph room, or to the coudé slithead. Due to interlock modifications, this element is not currently updated in software. A better indicator is the brown UCLES shutter control box - when the Camera Shutter is indeed OPEN, the "CES" LED should be flashing red, but if SHUT it will be a steady green. The shutter can be opened manually from the rack in the coudé east anteroom.


Focal Modifier 1: This should be set to UHRF.


Post-Slit Filter 1/2: These can be set to any of 8 positions, usually CLEAR but Neutral Density (ND) and glass colour filters are available if required.


Uhrf Echelle: This should be set to IN, so that the UHRF collimator + échelle unit is moved in front of the UCLES collimator unit.


Uhrf Theta / Uhrf Gamma / Slit Angle: These fields show the current échelle theta and gamma angles required to place the wavelength of interest near the centre of the CCD, and a horizontal slit image in the central order. Usually theta and gamma are loaded from a UHRF configuration file, while a Slit Angle of -0.205 degrees is the nominal default for the UHRF setup procedures. It is possible to tweak these manually by entering new values in each field then pressing "CONFIGURE", but one should be very careful in doing this.



Uhrf Theta Offset / Uhrf Gamma Offset / Slit Angle Offset: These 3 fields contain numerical offsets to be applied to the loaded theta, gamma, and slit angles before being sent to the UHRF control micro. In practice, fixed offsets are not as useful for changing UHRF wavelengths as they are for UCLES, so grating angle offsets are not used at all.


Hartmann Upper / Hartmann Lower: Unlike UCLES which uses a single rotatable flap as a Hartmann mask, UHRF has two separate flaps which each cover one half of the collimator for knife-edge focus checks by the support astronomer and technical staff. They should be OPEN for observing - if they are set to SHUT, it will be marked in red to alert the observer. If one is shut and the other open, they can be reversed using the "Swap Hartmann" button.


XDisperser: There are 4 cross dispersing gratings blazed for different wavebands: U (2400 lines/mm), B (1800 lines/mm), V (1200 lines/mm), and R (1200 lines/mm). The choice of which one to use for a given wavelength is usually included in the configuration file.


Secondary Collimator: The focus value for the secondary collimator is set within the configuration file, and should not need adjustment.


Collimator Coarse Focus / Collimator Fine Focus: Whenever the central wavelength of UHRF is changed, the spectrograph will need to be refocused. Even after returning to a given wavelength, the focus may still need adjusting due to the positioning accuracy of the drives, and reading accuracy of the encoder. There are TCL sequences provided to compute focus adjustments from the laser, or the ThAr lines. To set the focus, first enter the required value in the "Collimator Coarse Focus" field, and press "Configure". This sets the focus position to within about 30 ADU. Press the "Update FF" button a few times to get a more precise average reading of the actual focus position. Then enter the desired value again in the "Collimator Fine Focus" field, and press "Configure". The fine control has a maximum range of around +/- 100 ADU and can be driven out of range. If this happens you will see "ERROR" in the Fine Focus field. In this case, you will need to reset the focus value using the coarse control - drive it up by 100 units or so (if that was the direction you were trying to go), then re-enter the desired value in the Fine Focus field. Press "Update FF" a few times to see if this has reached the required value, to an accuracy of 5 ADU or so.


Wavelength Summary: This section is mainly for information only, and indicates the last-requested central wavelength and order. Depending on how much theta and gamma have been adjusted since then, this may or may not correspond exactly to the wavelength in the centre of the CCD. If you have a better idea of the current central wavelength, then enter its value in the box provided and press the "New Wavelength" button. This will reset the value of the LAMBDAC keyword in subsequent runs.


CONFIGURE: Pressing this button will send a series of requests to the UHRF control micro to move any of the elements whose requested position is different from their current position (within an ADU or so), as indicated by having their fields highlighted in red.



UHRF Wavelength Setup

From the main Uhrf tab, clicking on the "Configure with Control File" tab will replace the main UHRF configuration screen with the following display. This is the primary means of configuring the spectrograph to a new wavelength.

Wavelength Setup


LOAD CONTROL FILE: Click this button to bring up a file browser, which lists all the known wavelength configuration files for UHRF. Select one, click "OK" in the browser and the filename will appear in the "Last Control File Loaded" field.


C Binned Pixel Size microns / D Binned Pixel Size microns: These are for information only, confirming that the system recognises the current equivalent pixel sizes in the spatial (C) and spectral (D) axes.


OK: Pressing this button will send the necessary commands to the UHRF control micro to move the grating, collimator, etc. The display will switch back to the UHRF Control tab, and the elements currently in motion will flash cyan until they have arrived at their requested locations. In the event that any element does not arrive within a reasonable time, the system will send another request automatically, which will usually be enough to ensure all movements are completed.


Skycat Image Display

The image display for the ODC is built upon the ESO Skycat RTD tool, with some extra capabilities added to enable interaction between the ODC  system and the telescope. The display is updated in "real time", that is after each readout "slice" of the array. The slice size is 1024 rows by default, but this can be changed with the Commands -> Set slice size option of the Optical Detector User Interface.

When viewing old images while taking new data, you may wish to temporarily suspend the real-time display. You can do this by selecting AAO-Detectors -> Disconnect, then AAO-Detectors -> CCD_2 (or CCD_1) when you are ready to resume the real-time display.

Some information on the main features of Skycat can be found on the ESO Skycat Web pages.

You can call up coordinates for objects from databases like NED or SIMBAD using the Data Servers -> Catalogs menu, and selecting the appropriate catalog. You will get a pop-up window in which you can enter an object name or co-ordinates, after which the catalog will be searched and a list of possible options returned. You can then highlight your object in this list of sources, and send the coordinates of that object to the CCS and slew the telescope by selecting Telescope -> Slew to Selected Object. (If Skycat has just been started, you will need to precede this with a Telescope -> Reset Server Connection... )

You can also call up targets from a catalog of your own, as in this example, in which object ID, RA, and Dec are separated by a <TAB>, you should save it with a ".tab" extension, then call it up from Data-Servers -> Local Catalogs -> Load from file... Note that even a single extraneous character in any line of this file can result in the catalog file not being loaded at all, or cause Skycat to hang after requesting a Slew.

gaia

Using GAIA as the Real Time Display

The Starlink GAIA image display shown above (click on the image to see it at full resolution) is also based around Skycat, and allows the use of "plug-ins" for expanded functionality. Chris Tinney at the AAO has developed one such plugin which enables quick estimation of the seeing and S/N in any order of a UHRF spectrum, which others may find of use. To use this, exit from Skycat, then start up gaia from the same terminal that the ODC was started from:

> gaia &

This will now connect automatically to the data acquisition system. There is a new File -> Open latest... option (or Ctrl + Shift + o) which, if you have already displayed an image from a directory, will find the newest image in that directory and display it. The spectral profile tool can be selected either from View -> Pick Spectrum... ; Image-Analysis -> Mean X & Y profiles... ; or just Ctrl + p.


spectral profile

Once selected, gaia will wait for you to click and drag out a box encompassing part of a single order. After a brief period, the panel at left will appear, showing collapsed profiles in X and Y (note that unlike the View -> Slice... option in Skycat, you will not be prompted before marking the box on the display). By indicating which direction is spectral/spatial, and selecting the pixel scale, gain and read noise appropriate to your binning and readout speed, the FWHM of a cut through the mean spectral profile is determined both in pixels and in arcseconds. The mean profile is shown in black, the fitted background in blue, and the fitted Gaussian in red. You also get the median count level in the spectral direction (shown in green in the second plot), which is used to estimate integrated counts per pixel above background, i.e., how many counts you are collecting from your object, to monitor S/N, seeing, cloud, etc.

You can drag the box around the image, stretch it, etc. and the profiles will update. The marked box stays put when you load a new image, so all you have to do is hit the "Update" button at the bottom to get the same information from the same part of your spectrum for every exposure. You can use the left mouse button in either plot window to select an area to zoom in on, or the right mouse button to zoom out again.


PTCS

The Portable Telescope Control System (PTCS) GUI duplicates much of the functionality of the telescope control console and night assistant's terminal. From the "Commands" menu, select "New Target¨ and enter the RA, Dec, Epoch, proper motion, etc., then hit "Slew" to send the coordinates to the Control Computer System (CCS); this may take a few seconds - watch the CCS terminal, which should load the new coordinates and commence the slew. Although the PTCS cannot access or store a file of coordinates like the CCS can, it is possible to call up catalogued objects by name, or from an input catalogue provided by the observer, using the "Slew to Catalog Object" function within the Skycat display.

To command a specific offset, the observer must first click on the green "Control OFF" button, which will then change to "Control ON" highlighted in yellow. Select Commands -> Offsets... and enter the offsets in arcseconds. Note that for RA, the offsets are in arcseconds on the sky, not arcseconds of polar axis rotation as they are on the night assistant's console. To go back to the Base position, select "Centre". Note also that switching Control ON (which can also be commanded from an Observing Sequence) makes the current telescope position the new Base position.

PTCS


Stuart Ryder, sdr -@- aao.gov.au