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Proceedings Paper

WISDOM: the WIYN spectrograph for Doppler monitoring: a NASA-NSF concept for an extreme precision radial velocity instrument in support of TESS
Author(s): Gábor Fűrész; Robert Simcoe; Stuart I. Barnes; Lars A. Buchhave; Mark Egan; Rick Foster; Tim Hellickson; Andrew Malonis; David Phillips; Stephen Shectman; Ronald Walsworth; Josh Winn; Deborah Woods
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Paper Abstract

The Kepler mission highlighted that precision radial velocity (PRV) follow-up is a real bottleneck in supporting transiting exoplanet surveys. The limited availability of PRV instruments, and the desire to break the “1 m/s” precision barrier, prompted the formation of a NASA-NSF collaboration ‘NN-EXPLORE’ to call for proposals designing a new Extreme Precision Doppler Spectrograph (EPDS). By securing a significant fraction of telescope time on the 3.5m WIYN at Kitt Peak, and aiming for unprecedented long-term precision, the EPDS instrument will provide a unique tool for U.S. astronomers in characterizing exoplanet candidates identified by TESS. One of the two funded instrument concept studies is led by the Massachusetts Institute of Technology, in consortium with Lincoln Laboratories, Harvard-Smithsonian Center for Astrophysics and the Carnegie Observatories. This paper describes the instrument concept WISDOM (WIYN Spectrograph for DOppler Monitoring) prepared by this team. WISDOM is a fiber fed, environmentally controlled, high resolution (R=110k), asymmetric white-pupil echelle spectrograph, covering a wide 380-1300nm wavelength region. Its R4 and R6 echelle gratings provide the main dispersion, symmetrically mounted on either side of a vertically aligned, vacuum-enclosed carbon fiber optical bench. Each grating feeds two cameras and thus the resulting wavelength range per camera is narrow enough that the VPHG cross-dispersers and employed anti-reflection coatings are highly efficient. The instrument operates near room temperature, and so thermal background for the near-infrared arm is mitigated by thermal blocking filters and a short (1.7μm) cutoff HgCdTe detector. To achieve high resolution while maintaining small overall instrument size (100/125mm beam diameter), imposed by the limited available space within the observatory building, we chose to slice the telescope pupil 6 ways before coupling light into fibers. An atmospheric dispersion corrector and fast tip-tilt system assures maximal light gathering within the 1.2″ entrance aperture. The six octagonal fibers corresponding to each slice of the pupil employ ball-lens double scramblers to stabilize the near- and far-fields. Three apiece are coupled into each of two rectangular fibers, to mitigate modal nose and present a rectilinear illumination pattern at the spectrograph's slit plane. Wavelength solutions are derived from ThAr lamps and an extremely wide coverage dual-channel laser frequency comb. Data is reduced on the fly for evaluation by a custom pipeline, while daily archives and extended scope data reduction products are stored on NExScI servers, also managing archives and access privileges for GTO and GO programs. Note: individual papers, submitted along this main paper, describe the details of subsystems such as the optical design (Barnes et al., 9908-247), the fiber link design (Fűrész et al., 9908-281), and the pupil slicer (Egan et al., 9912-183).

Paper Details

Date Published: 4 August 2016
PDF: 22 pages
Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 990814 (4 August 2016); doi: 10.1117/12.2234376
Show Author Affiliations
Gábor Fűrész, MIT Kavli Institute for Astrophysics and Space Research (United States)
Robert Simcoe, MIT Kavli Institute for Astrophysics and Space Research (United States)
Stuart I. Barnes, Stuart Barnes Optical Design (Germany)
Lars A. Buchhave, Univ. of Copenhagen (Denmark)
Mark Egan, MIT Kavli Institute for Astrophysics and Space Research (United States)
Rick Foster, MIT Kavli Institute for Astrophysics and Space Research (United States)
Tim Hellickson, MIT Kavli Institute for Astrophysics and Space Research (United States)
Andrew Malonis, MIT Kavli Institute for Astrophysics and Space Research (United States)
David Phillips, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Stephen Shectman, Carnegie Observatories (United States)
Ronald Walsworth, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Josh Winn, MIT Kavli Institute for Astrophysics and Space Research (United States)
Deborah Woods, MIT Lincoln Lab. (United States)

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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