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Proceedings Paper

Optomechanical design concept for GMACS: a wide-field multi-object moderate resolution optical spectrograph for the Giant Magellan Telescope (GMT)
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Paper Abstract

We describe the conceptual optomechanical design for GMACS, a wide-field, multi-object, moderate-resolution optical spectrograph for the Giant Magellan Telescope (GMT). GMACS is a candidate first-light instrument for the GMT and will be one of several instruments housed in the Gregorian Instrument Rotator (GIR) located at the Gregorian focus. The instrument samples a 9 arcminute x 18 arcminute field of view providing two resolution modes (i.e, low resolution, R ~ 2000, and moderate resolution, R ~ 4000) over a 3700 Å to 10200 Å wavelength range. To minimize the size of the optics, four fold mirrors at the GMT focal plane redirect the full field into four individual "arms", that each comprises a double spectrograph with a red and blue channel. Hence, each arm samples a 4.5 arcminute x 9 arcminute field of view. The optical layout naturally leads to three separate optomechanical assemblies: a focal plane assembly, and two identical optics modules. The focal plane assembly contains the last element of the telescope's wide-field corrector, slit-mask, tent-mirror assembly, and slit-mask magazine. Each of the two optics modules supports two of the four instrument arms and houses the aft-optics (i.e. collimators, dichroics, gratings, and cameras). A grating exchange mechanism, and articulated gratings and cameras facilitate multiple resolution modes. In this paper we describe the details of the GMACS optomechanical design, including the requirements and considerations leading to the design, mechanism details, optics mounts, and predicted flexure performance.

Paper Details

Date Published: 24 September 2012
PDF: 12 pages
Proc. SPIE 8446, Ground-based and Airborne Instrumentation for Astronomy IV, 84467N (24 September 2012); doi: 10.1117/12.926437
Show Author Affiliations
Stephen A. Smee, The Johns Hopkins Univ. (United States)
Travis Prochaska, Texas A&M Univ. (United States)
Stephen A. Shectman, Carnegie Observatories (United States)
Randolph P. Hammond, The Johns Hopkins Univ. (United States)
Robert H. Barkhouser, The Johns Hopkins Univ. (United States)
D. L. DePoy, Texas A&M Univ. (United States)
J. L. Marshall, Texas A&M Univ. (United States)


Published in SPIE Proceedings Vol. 8446:
Ground-based and Airborne Instrumentation for Astronomy IV
Ian S. McLean; Suzanne K. Ramsay; Hideki Takami, Editor(s)

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