Chapter 4. At the Telescope

Sections: The Observer Software | Setting up the RGO | Observing Procedures | Analysing Data
Previous: Description of the Spectrograph | Next: Appendix A: Observer Commands | CONTENTS


4.1 The Observer Software

The CCD is operated by the OBSERVER control system, which runs on the VAX. The CCD is read out by one of two CCD controllers, called either CCD_1 or CCD_2. The particular controller being used for your run will be written on the small whiteboard on the control panel. After readout, the data is stored in the Large eXternal mEMory (or XMEM), which has its own image display which displays the data as it is read. From there, the data is saved onto the disk systems of a MicroVAX 4000. These disks are also accessible via an NFS-mount on the UNIX machines. To start the OBSERVER software, you need to be logged on to the VAX (AAT40A). Note that on the VAX, commands are not case-sensitive. Log in as OBSERVER (password available from your support astronomer). Type RGO which ensures the RGO-specific headers (grating angle, slit width etc.) are written correctly to your data. Then start the OBSERVER software by typing

CCD_n
where n is either 1 or 2 depending on which controller is being used (check the whiteboard). Wait for the Idle: prompt to appear.

Once OBSERVER is started, the screen will be divided into four areas. At the top, the state of the CCD and the current exposure is displayed. Below this is a list of available commands. These two regions are surrounded by a thick bar. Below this is the area where logging commands are written, including error messages, where the data is being written, whether the shutter is open etc. The bottom section is where you type commands. Commands are case-insensitive, and can be abbreviated to minimum-match (so DUMMY can be abbreviated to DUM). The arrow keys may be used to scroll backwards through previous commands, and <ctrl>-p and <ctrl>-n can be used to scroll backwards and forwards through the message window. A summary of commands and information on taking data using OBSERVER is given in Appendix A. Details of special commands for time-series mode are given in Appendix B.
 

4.2 Setting up the RGO

A number of setup procedures are available if you log into the the obsred account on aatssf (password available from your support astronomer, or posted on the wall in the control room). Type AAT to set start up a GUI. The SETUP menu provides the rgoang, focus and rotation routines. Initial setups will be done by the afternoon staff, but you will be expected to check these, and to set up extra settings.

Determination of Wavelength Centre

Use rgoang (also at http://www.aao.gov.au/cgi-bin/rgoang_inputs.pl) to select the appropriate grating angle for your required wavelength range. Because of uncertainties in the calculations in rgoang, and in the grating angle selection, the actual central wavelength can be incorrect by up to 100 pixels, so it is essential to examine calibration arcs to determine the correction factor if the wavelength placement is critical.

A low-resolution arc atlas is given in Appendix F for the Cu Ar, Neon and Cu He arcs. A medium dispersion arc Cu Ar atlas is available online, and a set of offline atlases are kept in a red folder in the control room.

Be warned that the dispersion direction, i.e. whether wavelength increases or decreases along the chip, depends on the camera in use, the orientation of the detector and the sign of the observing order, which depends on the angle of the grating. For example, for the EEV on the 25cm camera with a grating blaze-to-collimator, wavelength decreases with pixel number. On the XMEM display this means that red is at the top, and blue at the bottom. Blaze-to-camera observations are reversed.

Rotation

The rotation of the CCD is checked using an artificial star created using a single hole dekker and the continuum lamp. Select dekker 56, turn the tungsten lamp on, and take a suitable (unbinned, non-saturated) frame using DUMMY to create a non-archived frame. From the AAT utilities select the rotation  program; give it the filename of your artificial star frame in Unix format (which will be something like /vaxdata/ccd_1/020531/a.sdf) and the region of the chip over which you want to check the focus. The program will return the amount of shift between top and bottom of the CCD in elements (pixels), and the amount the CCD dewar has to be rotated to compensate. The dewar can be rotated by the technical staff. Values of the shift less than about 0.5 pixels from top to bottom are acceptable; corrections smaller than this are difficult to achieve reliably.
 

Focus

The spectrograph focus is checked using the arc lamp and the Hartmann shutters. Select dekker 50 again, turn on the arc lamp, narrow the slit to < 60 um, and start the focus program from the AAT utilities. You will need to take four frames, with the Hartmann shutters (A and B) in different positions and at two different collimator focuses. Ensure that frames are unsaturated but with good S/N. The two focus positions should be about 150 units apart, so move the collimator by ~75 units and take two arc frames, one with Hartmann shutter A closed and shutter B open, and one with A open and B closed. Note the names of these frames and the collimator position. Then move the collimator focus by about 150 units (in the opposite direction) and take a second set of frames. Give the focus program the names of these files and the two focus values you used; it will calculate the best focus position for you. You can check this by moving to the best focus position and taking another set of Hartmann exposures; at the best focus there should be no shift between the arc lines on the two frames.

Don't forget to re-open both Hartmann shutters when you have finished!

As a further check, or to see if there has been a shift in focus (unusual), take a narrow slit arc with both Hartmann shutters open, at the nominal focus. Run the EMLT routine in FIGARO:

Select x1 and x2 to be ~ 10 rows near the centre of the window. EMLT will give approximate widths in pixels for the 10 strongest lines, and a weighted average. This average should be the equivalent of ~35 - 45 µm depending on the setup. Recent problems have shown the importance of focusing the spectrograph close to the slit to avoid distortions and light loss. Ensure that the final collimator setting lies between 600 and 800 µm (without the calcite or a below-slit filter). If not, contact your support astronomer or a technician.

Note that if you are setting up a polarimetry run, you will need to run the focus through the calcite, for both the e and o rays. These will give different collimator settings. The best you can do is to take the average. This procedure should be done early on in the setup as the calcite sometimes shifts the focus outside the available range, and the CCD will need to be taken off and shimmed (have spacers added by a technician).

4.3 Observing Procedures

In this section, we give some recommendations for observing with the RGO. These are based on past experience with the instrument, and should be taken as guidelines only.

4.4 Analysing Data

Data may be analysed as it comes in on the Sun workstation, using Figaro, IRAF, or any other package of your choice. You should do this under the obsred account on aatssf (password available from your support astronomer, or posted on the wall in the control room). The VAX disks are cross-mounted on the Suns: the archival disk DISK$INST is mounted as /vaxinst/, and the scratch disk DISK$DATA is visible as /vaxdata/. However, accessing the data across the network to the VAX is rather slow. A better way is to use the unix_server facility. Type from within OBSERVER (this is the default) which automatically transfers files to the Sun as they are created. As obsred at the console aatssf, type "xhost aatssf" while will enable a GUI to come up on the console of aatssf after the first readout. The data is copied to aatssf in Figaro format, and you can select conversion to FITS or IRAF at the GUI.

The files will appear in the following locations:

/data/ssf/1/obsred/ndf/ccd_1/date/ for Figaro files

/data/ssf/1/obsred/fits/ccd_1/date/ for FITS files

/data/ssf/1/obsred/iraf/ccd_1/date/ for IRAF files

where date is today's date, YYMMDD.

These files are not the source of the data archive (which is taken from the VAX) so can be freely modified or deleted - in particular if you run out of space. After your run the next observer may do the same, so save or copy any work you wish to save at the end of your run. The disk is read-only accessible from other suns.

The AATRGO pipeline package

A pipeline software package is now available for the RGO spectrograph. AATRGO is a package written by Jim Lewis, and supported at the AAT by Ray Stathakis. At present it is recommended for quick-look applications during observing, but it has the potential to be used as a full-look reduction system.

To start the package, start up IRAF on an xgterm (either yourself or through the utilities menu AAT) and type:

cl> rgo

cl> pipeline

cl> spec1

cl> setup aatrgo

cl> aatrgo.

After a short delay, a control window appears (see Figure 4.1) followed by an empty monitor window. Since the AAT data headers are incomplete, the grating details need to be entered, as well as the file name of the observation and the calibration arc (if any). For a quick-look result, activate the radio buttons ``dispersion correct data'', ``plot resulting spectra'' and ``redo previous reductions''. Other options need more tweaking of parameters. Then just press ``reduce'' and you'll get a wavelength-calibrated, extracted spectrum drawn in splot. Type ``q'' in the splot window to return to the control window and reduce the next spectrum. You cannot reduce a spectrum more than once (with different parameters, say) unless the redo option is selected. Once the spectrum is plotted, the usual, and many, options of splot are now available - type ``?'' in the splot window to get a list of options in the monitor window. Type ``q'' to exit splot help in the monitor window, and then ``q'' in the splot window to exit splot.

Figure 4.1 Control window for the aatrgo pipeline program.

AATRGO pipeline

Progress of the processing is given in the monitor window, so it is useful to keep the window open. More details of parameters used can be found in the log which is available as a button in the control window. Other buttons provide choice of parameters used in the different stages of processing, similarly to the usual IRAF epar command. The buttons toggle the parameter windows open and closed. For full-look reduction, you'll need to fine tune these parameters to suit your data set. Input lists of files can be entered instead of individual files using the ``@'' symbol.

After you leave the telescope

Several software packages exist for the analysis of spectral data: RGO data should pose no problems while using any of these packages.

If you are using Figaro to reduce your data, there is a guide available at http://www.aao.gov.au/figaro/. This gives a description of the various Figaro tasks you can use to correct, extract and calibrate your spectra.

If you are using IRAF, there are some excellent documents available to lead you throught the reduction steps: A User's Guide to CCD Reductions with IRAF is a guide to the basic stages of reducing CCD data, both imaging and spectral; and A User's Guide to Reducing Slit Spectra with IRAF shows you how to extract and calibrate your spectra. These documents are available at the IRAF website, http://iraf.tuc.noao.edu/iraf/web/iraf-homepage.html .



Sections: The Observer Software | Setting up the RGO | Observing Procedures | Analysing Data
Previous: Description of the Spectrograph | Next: Appendix A: Observer Commands | CONTENTS


Ray Stathakis
Last Updated 2/4/2002