The Coude Echelle Spectrographs

3.1 Observing with UCLES

Sections: Image Display Orientations | Controlling the spectrograph | Starting the VAX program | Configuring UCLES | The UCLES Setup Routine | Displaying the spectrograph status | Mechanisms to configure interactively | Focussing UCLES | Wavelength placement | Other useful commands

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Image Display Orientations

EEV2 display on XMEM                      EEV2 display in IRAF/Figaro
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| red : o | | blue : o |
| : : v | | : : v |
| : : e | | : : e |
| : : r | | : : r |
| : : s | | : : s |
| : : c | | : : c |
| : : a | | : : a |
| : : n | | : : n |
| blue : . | | red : . |
--------------------- ----------------------------

MITLL3 display on XMEM                    MITLL3 display in IRAF/Figaro
-------------------- ---------------------------
| blue : o | | red : o |
| : : v | | : : v |
| : : e | | : : e |
| : : r | | : : r |
| : : s | | : : s |
| : : c | | : : c |
| : : a | | : : a |
| : : n | | : : n |
| red : . | | blue : . |
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Controlling the Spectrograph

Observers control UCLES 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.  We hope to reduce the number of prompts soon, as most take the default. Prompts that require an explicit answer are:

Configuring UCLES

Before the observer starts to use UCLES, the support staff will have powered up the hardware and set up the detector. The detector will have been rotated to align an order near your chosen wavelength with the detector pixels, and the spectrograph focused to ensure that their is adequate travel to reach optimum
focus. For more information on these procedures, see Appendices C1, & C2 .

It is possible to demand any optical wavelength at the centre of the detector.

centres on the blaze peak of the order in which lambda falls, rather than on lambda itself.

The UCLES setup routine

The command CENTRE causes the software to calculate the echelle grating angles to place the specified wavelength in the centre of the field. However, since the centre of the detector may not coincide precisely with the optical axis of the camera, it is usually necessary to determine small offsets to be applied to the calculated angles. Similarly, since the detector is rotated to align the orders with the detector, it is necessary to offset the calculated slit angle so that the slit image is perpendicular to the echelle orders. These offsets are determined by running the SETUP routine. While afternoon staff or the support astronomer may have already carried out this procedure for you, this part of the configuring process is the observer's responsibility.

When UCLES is run, it uses offsets determined the last time it was used. If you suspect that the offsets applied are wrong, i.e. if you can't recognize the ThAr spectrum, you may zero the offsets by using the command OFFSETS. Note also that the ThAr lamp polarity must be correct, or an unrecognizable spectrum will result.

Displaying the Spectrograph Status

Mechanisms to Configure Interactively

Not all spectrograph mechanisms are affected by the control file. Slit dimensions, use of the beam rotator or focal modifiers, 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.

Focussing UCLES

The depth of focus for UCLES is substantial and it will be rare that focus changes are required, but it should nevertheless be checked.

Configure spectrograph to the wavelength of interest. Select a narrow unbinned window ( e.g. TEK1K_SETUP or MITLL?)

Start the AAT utilities menu on aatssf by logging into obsred and typing AAT. The focus routine can be found under "setups" ? Run FOCUS to compute a new collimator focus value. Check the width of the lines. In FIGARO this can be done by: YSTRACT a spectrum, and run EMLT to see the FWHM. For UCLES the FWHM should be about 1.7 Tek pixels.

Wavelength Placement

Even after doing a CONFIG, the spectrum positioning may need further adjustment if, for instance, partial orders are being recorded at one or both sides of the detector or the detector has bad columns, in which case it might be desirable to shift the spectrum in the cross-dispersion direction.

The most likely parameters to change are:

For UCLES observations with the Tek, bluer wavelengths in the order are at the bottom of the display, and bluer orders are at the right of the display. The overscan (if any) is on the right. FIGARO displays the image inverted vertically.

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

Other Useful Commands

Ray Stathakis (
Last Update: 26 November 2003 by Stuart Ryder