• Harvard-Smithsonian Ctr. for Astrophysics (United States)
• Dan Baldwin, Andrew Szentgyorgyi, Stuart Barnes, Sagi Ben-Ami, Patricia Brennan, Jamie Budynkiewicz, Charlie Conroy, Ian Evans, Janet Evans, Jeff Foster, Thomas Gauron, Mercedes Lopez-Morales, Kenneth McCracken, Stuart McMuldroch, Joseph Miller, Mark Mueller, Mark Ordway, Charles Paxson, David Phillips, David Plummer, William Podgorski, Ronald Walsworth
• The Univ. of Chicago (United States)
• Jacob Bean, Andreas Seifahrt
• Korea Astronomy and Space Science Institute (Korea, Republic of)
• Moo-Young Chun, Bi-Ho Jang, Jeong-Gyun Jang, Jihun Kim, Kang-Min Kim, Jae Sok Oh, Byeong-Gon Park, Chan Park, Sung-Joon Park, Young-Sam Yu
• The Observatories of the Carnegie Institution for Science (United States)
• Jeffrey D. Crane
• Univ. of California, Santa Cruz (United States)
• Harland Epps
• Kavli Institute for Astrophysics and Space Research (United States)
• Anna Frebel, Dani Guzman
• The Observatories of the Carnegie Institution of Science (United States)
• Tyson Hare
• Pontificia Univ. Católica de Chile (Chile)
• Andres Jordan
• Univ. de São Paulo (Brazil)
• Claudia Mendes de Oliveira, Joao Steiner
• The Univ. of Arizona (United States)
• Daniel Stark
• The Observatories of the Carnegie Institution for Science (United States)
• Alan Uomoto

abstract

The GMT-Consortium Large Earth Finder (G-CLEF) is an echelle spectrograph with precision radial velocity (PRV) capability that will be a first light instrument for the Giant Magellan Telescope (GMT). G-CLEF has a PRV precision goal of 40 cm/sec (10 cm/s for multiple measurements) to enable detection of Earth-like exoplanets in the habitable zones of sun-like stars1. This precision is a primary driver of G-CLEF’s structural design. Extreme stability is necessary to minimize image motions at the CCD detectors. Minute changes in temperature, pressure, and acceleration environments cause structural deformations, inducing image motions which degrade PRV precision. The instrument’s structural design will ensure that the PRV goal is achieved under the environments G-CLEF will be subjected to as installed on the GMT azimuth platform, including:

• Millikelvin (0.001 °K) thermal soaks and gradients
• 10 millibar changes in ambient pressure
• Tip/tilt due to GMT azimuth axis misalignment with gravity, azimuth track height variations, azimuth platform deformation, and centripetal and azimuthal accelerations due to during telescope slewing

Carbon fiber/cyanate composite was selected for the optical bench structure in order to meet performance goals. Low coefficient of thermal expansion (CTE) and high stiffness-to-weight are key features of the composite optical bench design. Manufacturability and serviceability of the instrument are also drivers of the design.

In this paper, we discuss analyses leading to technical choices made to minimize G-CLEF’s sensitivity to changing environments. Finite element analysis (FEA) and image motion sensitivity studies were conducted to determine PRV performance under operational environments. We discuss the design of the optical bench structure to optimize stiffness-to-weight and minimize deformations due to inertial and pressure effects. We also discuss quasi-kinematic mounting of optical elements and assemblies, and optimization of these to ensure minimal image motion under thermal, pressure, and inertial loads expected during PRV observations. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

references

1 Szentgyorgyi, A., et al., "The GMT-Consortium Large Earth Finder (G-CLEF): An Optical Echelle Spectrograph for the Giant Magellan Telescope (GMT)," Proc. SPIE, 9908-76, (2016).

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2 Mueller, M., et al., "The Opto-Mechanical Design of the GMT-Consortium Large Earth Finder (G-CLEF)," Proc. SPIE, 9908-374, (2016)

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3 Jacoby, G., Bernstein, R., Bouchez, A., Colless, M., DePoy, D., Espeland, B., Jaffe, D., Lawrence, J., Marshall, J., McGregor, P. Sharp, R., Szentgyorgyi, A. and Walls, B., "Instrumentation Progress at the Giant Magellan Telescope project," Proc. SPIE, 9908-68 (2016).

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4 Johns, M., McCarthy, et al., "Overview and status of the Giant Magellan Telescope Project," Proc. SPIE, 9906-37, (2016)

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5 Fűrész, G. et al., "The G-CLEF Spectrograph Optical Design: An Update to the White Pupil Echelle Configuration," Proc. SPIE, 9147, (2014).

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6 Podgorski, W. A., et al., "A Novel Systems Engineering Approach to the Design of a Precision Radial Velocity Spectrograph - the GMT-Consortium Large Earth Finder (G-CLEF)," Proc. SPIE, 9147-333, (2014).

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7 Ben-Ami, S., et al., "The Optical Design of the G-CLEF Spectrograph: The First Light Instrument for the GMT," Proc. SPIE, 9908-372, (2016)

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8 Cohen, L. M., "Effects of Temporal Dimensional Instability on the Advanced X-ray Astrophysics Facility (AXAF-I) High Resolution Mirror Assembly (HRMA)"