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Telephone: 61-2-3724800 Facsimile: 61-2-3724880

The UCL Coudé Echelle Spectrographs

S. G. Ryan, A. C. Fish

AAO MANUAL: UM 25.2, April 1995


The UCL Coudé Echelle Spectrographs

S.G. Ryan A.C. Fish

April 1995

Anglo-Australian Observatory
2 Dept. of Physics and Astronomy, University College London

This manual is available as a postscript file including figures by anonymous ftp to, or as hardcopy by request to the Librarian, AAO.


The Spectrographs

The UCL Coudé Echelle Spectrographs form the high resolution optical spectroscopic facility at the AAT. The Anglo-Australian Telescope (AAT) was originally designed to include a classical photographic coudé spectrograph. The mechanical support structure for a horizontal layout was installed with the telescope, but the spectrograph didn't materialize due to financial pressures. Around the early 1980s, AAT users became increasingly aware of the need for a high resolving power facility and in 1983 the Advisory Committee for Instrumentation at the AAT (ACIAAT) gave a high priority to the construction of an echelle spectrograph. The f/36 coudé focus was preferred over Cassegrain for several reasons. (a) Mechanical and thermal stability is guaranteed in this environment and simple mechanical structures and mechanisms can be employed. (b) The large space available allows a large collimated beam size which can partially overcome the throughput disadvantage due to light losses in the five mirror coudé train. (c) Optical components can be remotely interchangeable and duplicated with coatings optimised for different wavelength bands. (d) The coudé environment lends itself to an open, optical bench layout which can accommodate future and unexpected enhancements. (e) The coudé system can be permanently operational, permitting fast changeover from other foci during the night due to instrument failure, changing observing conditions, flexible scheduling etc.

The result of ACIAAT's recommendations is the University College London Echelle Spectrograph (UCLES), located in the east coudé room on the 4 floor of the AAT building. UCLES can record spectra of astronomical sources as faint as V = 16--17 with a resolving power () of 55,000--115,000 depending upon the detector used. The spectrograph is operated entirely under computer control from within the ADAM software environment. UCLES was built by David Walker and his team at the Department of Physics and Astronomy, University College London under contract to the AAO.

In the early 1990, the Ultra High Resolution Facility (UHRF) was added to the coudé spectrograph. Built by the Optical Sciences Laboratory of University College London, this cross--dispersed echelle provides resolving powers of 300000, 600000, and 1000000, intended primarily for interstellar line studies. UHRF shares pre--slit optics with UCLES, and is controlled from the same software. Funding for UHRF was provided by a grant from SERC and the AAO.

The User Manual

This version of the manual was produced following unification of UCLES and UHRF under a common control system. It draws heavily on the two earlier manuals ``The UCL Echelle Spectrograph" by R. D. Robinson, F. Diego, A. C. Fish, W. F. Lupton, M. Pettini, & D. D. Walker, and ``Ultra High Resolution Facility Operating Manual" by J. Spyromilio. These works have been extensively plagiarized, and are acknowledged as the foundation documents of this new manual.

Part I of the manual describes the spectrograph and provides information necessary to plan an observing proposal. We describe the components in Section gif and Section gif, and provide a summary of detector options in Section gif. Information required for observing proposals is provided in Section gif. Part II is a user's guide to the practical aspects of observing with the spectrographs. Section gif describes how to configure the spectrograph for the observations, Section gif summarises operation of the detectors, and Section gif sets out options for inspecting the data as it is acquired. Part III contains more detailed information intended for observatory staff more so than for observers, but which can nevertheless prove valuable to the latter.

The appendices contain compilations of useful data, including tables giving the spectral parameters of each echelle order, examples of echellograms, examples of data and status displays produced by the control software, and a complete list of available commands. The final appendix describes one of the software packages for reducing echelle data.

Other reading

For additional information on these spectrographs, readers may wish to consult the following papers:

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Helen Davies