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Proceedings Paper

Active compensation of flexure on the High-Resolution Optical Spectrograph for Gemini
Author(s): Paolo D'Arrigo; Francisco Diego; David D. Walker
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Paper Abstract

Gravity-induced flexure has been a long-standing challenge in Cassegrain spectrographs at 4-meter class telescopes; it is the more so at the scale of 8-meter telescopes. This is of particular concern for the Gemini high resolution optical spectrograph, which will be Cassegrain-mounted for its routine mode of operation. In this paper we address the general flexure problem, and how to solve it with the use of active optics. We also present the results of an experimental active flexure compensation system for the ISIS (intermediate- dispersion spectroscopic and imaging system) spectrograph on the 4.2 m William Herschel Telescope (WHT). This instrument, called ISAAC (ISIS spectrograph automatic active collimator), is based on the concept of active correction, where spectrum drifts, due to the spectrograph flexing under the effect of gravity, are compensated by the movement of an active optical element (in this case a fine steering tip-tilt collimator mirror). The experiment showed that active compensation can reduce flexure down to less than 3 micrometer over four hours of telescope motions, dramatically improving the spectrograph performance. The results of the experiment are used to discuss a flexure compensation system for the high resolution optical spectrograph (HROS) for the 8 m Gemini telescope.

Paper Details

Date Published: 21 March 1997
PDF: 12 pages
Proc. SPIE 2871, Optical Telescopes of Today and Tomorrow, (21 March 1997); doi: 10.1117/12.269021
Show Author Affiliations
Paolo D'Arrigo, Univ. College London (United Kingdom)
Francisco Diego, Univ. College London (United Kingdom)
David D. Walker, Univ. College London (United Kingdom)

Published in SPIE Proceedings Vol. 2871:
Optical Telescopes of Today and Tomorrow
Arne L. Ardeberg, Editor(s)

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