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Proceedings Paper

The opto-mechanical design of the GMT-Consortium Large Earth Finder (G-CLEF)
Author(s): Mark Mueller; Andrew Szentgyorgyi; Daniel Baldwin; Jacob Bean; Sagi Ben-Ami; Patricia Brennan; J. Budynkiewicz; Moo-Yung Chun; Jeffrey D. Crane; Harland Epps; Ian Evans; Janet Evans; Jeff Foster; Anna Frebel; Thomas Gauron; Alex Glenday; Tyson Hare; Bi-Ho Jang; Jeong-Gyun Jang; Andreas Jordan; Jihun Kim; Kang-Min Kim; Claudia Mendes de Oliveira; Mercedes Lopez-Morales; Kenneth McCracken; Stuart McMuldroch; Joseph Miller; Jae Sok Oh; Cem Onyuksel; Mark Ordway; Chan Park; Sung-Joon Park; Charles Paxson; David Phillips; David Plummer; William Podgorski; Andreas Seifahrt; Joao Steiner; Alan Uomoto; Ronald Walsworth; Young-Sam Yu
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Paper Abstract

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber-fed, optical echelle spectrograph selected as the first light instrument for the Giant Magellan Telescope (GMT) now under construction at the Las Campanas Observatory in Chile. G-CLEF has been designed to be a general-purpose echelle spectrograph with precision radial velocity (PRV) capability for exoplanet detection. The radial velocity (RV) precision goal of G-CLEF is 10 cm/sec, necessary for detection of Earth-sized exoplanets. This goal imposes challenging stability requirements on the optical mounts and the overall spectrograph support structures especially when considering the instrument’s operational environment. The accuracy of G-CLEF’s PRV measurements will be influenced by minute changes in temperature and ambient air pressure as well as vibrations and micro gravity-vector variations caused by normal telescope slewing. For these reasons we have chosen to enclose G-CLEF’s spectrograph in a well-insulated, vibration isolated vacuum chamber in a gravity invariant location on GMT’s azimuth platform. Additional design constraints posed by the GMT telescope include: a limited space envelope, a thermal emission ceiling, and a maximum weight allowance. Other factors, such as manufacturability, serviceability, available technology and budget are also significant design drivers. All of the above considerations must be managed while ensuring performance requirements are achieved. In this paper, we discuss the design of G-CLEF’s optical mounts and support structures including the choice of a low coefficient of thermal expansion (CTE) carbon-fiber optical bench to minimize the system’s sensitivity to thermal soaks and gradients. We discuss design choices made to the vacuum chamber geared towards minimize the influence of daily ambient pressure variations on image motion during observation. We discuss the design of G-CLEF’s insulated enclosure and thermal control systems which will maintain the spectrograph at milli-Kelvin level stability while simultaneously limiting thermal emissions into the telescope dome. Also discussed are micro gravity-vector variations caused by normal telescope slewing, their uncorrected influence on image motion, and how they are dealt with in the design. Finally, we discuss G-CLEF’s front-end assembly and fiber-feed system as well as other interface challenges presented by the telescope, enclosure and neighboring instrumentation.

Paper Details

Date Published: 9 August 2016
PDF: 18 pages
Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 9908A2 (9 August 2016); doi: 10.1117/12.2233246
Show Author Affiliations
Mark Mueller, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Andrew Szentgyorgyi, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Daniel Baldwin, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Jacob Bean, The Univ. of Chicago (United States)
Sagi Ben-Ami, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Patricia Brennan, Harvard-Smithsonian Ctr. for Astrophysics (United States)
J. Budynkiewicz, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Moo-Yung Chun, Korea Astronomy and Space Science Institute (Korea, Republic of)
Jeffrey D. Crane, The Observatories of the Carnegie Institution for Science (United States)
Harland Epps, Lick Observatory, Univ. of California, Santa Cruz (United States)
Ian Evans, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Janet Evans, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Jeff Foster, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Anna Frebel, Massachusetts Institute of Technology (United States)
Thomas Gauron, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Alex Glenday, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Tyson Hare, The Observatories of the Carnegie Institution for Science (United States)
Bi-Ho Jang, Korea Astronomy and Space Science Institute (Korea, Republic of)
Jeong-Gyun Jang, Korea Astronomy and Space Science Institute (Korea, Republic of)
Andreas Jordan, Pontificia Univ. Católica de Chile (Chile)
Jihun Kim, Korea Astronomy and Space Science Institute (Korea, Republic of)
Kang-Min Kim, Korea Astronomy and Space Science Institute (Korea, Republic of)
Claudia Mendes de Oliveira, Univ. de São Paulo (Brazil)
Mercedes Lopez-Morales, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Kenneth McCracken, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Stuart McMuldroch, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Joseph Miller, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Jae Sok Oh, Korea Astronomy and Space Science Institute (Korea, Republic of)
Cem Onyuksel, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Mark Ordway, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Chan Park, Korea Astronomy and Space Science Institute (Korea, Republic of)
Sung-Joon Park, Korea Astronomy and Space Science Institute (Korea, Republic of)
Charles Paxson, Harvard-Smithsonian Ctr. for Astrophysics (United States)
David Phillips, Harvard-Smithsonian Ctr. for Astrophysics (United States)
David Plummer, Harvard-Smithsonian Ctr. for Astrophysics (United States)
William Podgorski, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Andreas Seifahrt, The Univ. of Chicago (United States)
Joao Steiner, Univ. de São Paulo (Brazil)
Alan Uomoto, The Observatories of the Carnegie Institution for Science (United States)
Ronald Walsworth, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Young-Sam Yu, Korea Astronomy and Space Science Institute (Korea, Republic of)


Published in SPIE Proceedings Vol. 9908:
Ground-based and Airborne Instrumentation for Astronomy VI
Christopher J. Evans; Luc Simard; Hideki Takami, Editor(s)

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