The Coude Echelle Spectrographs

3.2 Observing with UHRF

Sections: Controlling the spectrograph | Starting the VAX program | Configuring UHRF | Displaying the spectrograph status | Mechanisms to configure interactively | Focusing UHRF | Wavelength placement | FlatfieldingOther useful commands

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Controlling the Spectrograph

Observers control UHRF through the VAX via a user interface based on the ADAM Interactive Command Language (ICL). This software in turn controls a SYNTEL micro-computer that handles all the low-level processing involved in configuring the instrument.

Starting the VAX Program

Usually the afternoon technician has already started up a VAX session on one of the xterms in the control room, but if not, login to the vax observer account (see whiteboard). After login completes... Note that you need to use a  separate OBSERVER window to the one running the detector.

You will be prompted for information on the detector:

DETECTOR - Detector type (CCD or IPCS) /'ccd'/
DPIXEL_SIZE - Dispersion pixel size (microns) /24/
CPIXEL_SIZE - Cross-dispersion pixel size (microns) /196/
Do you want to run setup procedures [No] ?
Answers are for the UHRF_X4 window. These values are used by the software to convert between pixels and mm - enter your
binned pixel sizes. These can be changed anytime by running PIXELS. The setup program should not be used for UHRF. If you get other questions about scales, as sometimes happens, take the default.

Configuring UHRF

Before the observer starts to use UHRF, the support staff will have powered up the hardware and set up the detector. The detector will have been rotated to align the spectral lines with the detector pixels. For more information on these procedures, see Appendices C1 & C4.

You cannot centre UHRF on any arbitrary wavelength. A control file must exist for your required wavelength centre.

The list of control files (complete to April 2000) is given in Section 2.4 and Appendix A4, and are held in the UCLES VAX account at DISK$USER:[UCLES.UHRF] (or /vaxuser/ucles/uhrf from unix machines). To check the current list, type:

If the file you need is missing, but you know the settings (e.g. in /epping/ras/uhrf/uhrf.settings) you can create a new control file:

creates a new UHRF control file. Specify the EMPIRICAL option when prompted, and enter the values requested, in encoder units. STILL WORKS? WHERE DOES IT GO?
NOTE: If you need a new setting you should have contacted your support astronomer well in advance (> 1 week) so he/she can calculate a new file. The procedure for determining a new wavelength file is very time-consuming (see Appendix C11). However, small wavelength shifts (within the CCD frame) are not a problem.
To configure UHRF:
Adopt the named control file.
Configure the hardware using the control file specified by USE.

Displaying the Spectrograph Status

displays spectrograph configuration. Check that the filters selection is correct (usually out of the beam). Items in motion are marked by asterixes (*'s). Reverse video emphasizes anything in an unusual state.
DISP OUTPUT= filename
writes the display to an ASCII file.
R item
reads a specific item, in default units e.g. R UG

RU item units
reads an item in specified units e.g. RU SW PIX

lists current configuration parameters

Mechanisms to Configure Interactively

Not all spectrograph mechanisms are affected by the control file. Slit dimensions, use of the slit or clicer,  filter settings, calibration lamps, and TV mirror controls must all be set interactively.

Many mechanisms have a limited range of travel. MIN and MAX are valid values to set them to their limits, e.g.SL MIN to obtain the shortest possible slit length. See Appendix C6 for a complete list of commands, and their limits.

Focusing UHRF

First focus on the red laser line at 6328.160 Å and inspect the instrumental profile. It should have a Gaussian FWHM of approximately 48 um, plus a low asymmetric tail to higher wavelengths. Tests with a green laser yielded the same value. Note that UHRF resolves the ThAr lines, so these cannot be used to assess the instrumental profile, but they are used to refocus UHRF for each wavelength setting, which is essential. Note that you need to check the focus every time you run CONFIG for optimum focus!

Configure spectrograph to wavelength of interest and use a narrow binned window ( e.g. UHRF_X4).

Alternatively you can use HP OTHER to toggle HP masks.
The presence of significant backlash in the collimator drives means that the focus routine used for UCLES which predicts the optimal collimator setting using linear interpolation, does not work for UHRF.
Instead, for each set of exposures, find the cross-correlation shift in pixels and then calculate the shift based on the scale for the instrumental setup.

There are two routines available:

Start the AAT utilities menu on aatssf by logging into obsred and typing AAT. The focus routine can be found under "setups" ? Run FOCUS and note the shift given in pixels (but IGNORE the prediction for the new collimator setting!).

Or run the FIGARO routine Copy /epping/ras/uhrf/ to your working account. Edit the file. It will contain a procedure something like:


Change the extract and ystract dimensions to match the location of the laser line. To run, type:

chmod u+x          Make it executable
assign D /vaxdata/ccd_1/YYMMDD/    or correct path for exposures a b                                      to run on dummy frames a.sdf and b.sdf

Calculate the focus shift from either routine by:

For every +1 pixel shift resulting from the cross correlation SCROSS hp_down hp_up, move UFC/UFF by -50 ADU at R = 1.0M, -80 ADU at R = 0.6M, and -170 ADU at R = 0.3M.

UFC and UFF read the same encoder, but differ in their positioning accuracy, so UFF must be used for setting within 50 ADUs. Moreover, UFF will position poorly for motions less than about 20 ADUs, so should be driven away by 50 ADUs and back again if necessary. MORE DETAILS

(Note that the HP UP configuration produces brighter spectra than the HP DOWN configuration.)

You should be able to achieve shifts of ~0.02 pixels. TRUE?

If at the laser wavelength, take exposure, YSTRACT a spectrum, and run EMLT to see the FWHM. For UHRF this should be about 50 um, = 2 Tek pixels UPDATE!

Repeat the procedure with the ThAr lamp at each required wavelength centre.

Wavelength Placement

Even after doing a CONFIG, the spectrum positioning may need further adjustment. Force the VAX to use encoder units (ADU) rather than transformed units (e.g. mm) by typing RAW. To return, type REAL.

The most likely parameters to change are:

For UHRF observations with the Tek, bluer wavelengths are at the top of the XMEM display. FIGARO displays the image inverted vertically.

Increasing UG moves the spectrum to the right. The Tek width in UG is about 1200 at R=0.3M; 600 at R=0.6M; 400 at R=1.0M.

Increasing UT moves the spectrum down. The Tek height in UT is about 2500 at R=0.3M; 1300 at R=0.6M; 800 at R=1.0M.


Once satisfactory grating and focus settings are obtained, they can be locked into the control files with


The geometric structure of the image slicer modulates the signal in the spatial direction. Also, all CCDs show some level of fringing in the far red wavelengths. This is clearly visible in the UHRF laser, ThAr, and quartz lamp exposures. Observers may find it useful to take flat field exposures not only through the image slicer but also through the slit, using the maximum slit length. These will provide more uniform illumination in the spatial direction which makes it easier to identify pixel-to-pixel variations.

switches to the slit

sets maximum slit length for continuous coverage.

turns on the lamp

Take flat field exposures.

turn off lamp

returns to slicer for observations.

Other Useful Commands

Ray Stathakis (
Last Update: 27 March 2000