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Precise Radial Velocities of Cool Low-mass Stars with iSHELL

Cale, Bryson and Plavchan, Peter and LeBrun, Danny and Gagné, Jonathan and Gao, Peter and Tanner, Angelle and Beichman, Charles and Wang, Sharon Xuesong and Gaidos, Eric and Teske, Johanna and Ciardi, David and Vasisht, Gautam and Kane, Stephen R. and von Braun, Kaspar (2019) Precise Radial Velocities of Cool Low-mass Stars with iSHELL. Astronomical Journal, 158 (5). Art. No. 170. ISSN 1538-3881. doi:10.3847/1538-3881/ab3b0f.

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The coolest dwarf stars are intrinsically faint at visible wavelengths and exhibit rotationally modulated stellar activity from spots and plages. It is advantageous to observe these stars at near-infrared (NIR) wavelengths (1–2.5 μm) where they emit the bulk of their bolometric luminosity and are most quiescent. In this work, we describe our methodology and results in obtaining precise radial velocity (RV) measurements of low-mass stars using K-band spectra taken with the R ~ 80,000 iSHELL spectrograph and the NASA Infrared Telescope Facility using a methane isotopologue gas cell in the calibration unit. Our novel analysis pipeline extracts RVs by minimizing the rms of the residuals between the observed spectrum and a forward model. The model accounts for the gas cell, tellurics, blaze function, multiple sources of quasi-sinusoidal fringing, and line spread function of the spectrograph. The stellar template is derived iteratively using the target observations themselves through averaging barycenter-shifted residuals. We have demonstrated 5 m s^(−1) precision over one-year timescales for the M4 dwarf Barnard's Star and K dwarf 61 Cygni A, and 3 m s^(−1) over a month for the M2 dwarf GJ 15 A. This work demonstrates the potential for iSHELL to determine dynamical masses for candidate exoplanets discovered with the NASA Transiting Exoplanet Survey Satellite mission, and to search for exoplanets orbiting moderately active and/or young K & M dwarfs.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Plavchan, Peter0000-0002-8864-1667
Gagné, Jonathan0000-0002-2592-9612
Gao, Peter0000-0002-8518-9601
Tanner, Angelle0000-0002-2903-2140
Beichman, Charles0000-0002-5627-5471
Wang, Sharon Xuesong0000-0002-6937-9034
Gaidos, Eric0000-0002-5258-6846
Ciardi, David0000-0002-5741-3047
Vasisht, Gautam0000-0002-1871-6264
Kane, Stephen R.0000-0002-7084-0529
von Braun, Kaspar0000-0002-5823-4630
Additional Information:© 2019 The American Astronomical Society. Received 2019 June 6; revised 2019 August 12; accepted 2019 August 12; published 2019 October 10. We acknowledge support from the the National Science Foundation (Astronomy and Astrophysics grant 1716202) and George Mason University start-up funds. All RVs extracted through PySHELL were run on ARGO, a research computing cluster provided by the Office of Research Computing, and the exo-computer cluster, both at George Mason University, VA. We thank John Rayner and the IRTF and iSHELL support astronomers, telescope operators, and engineers for their dedicated efforts in helping enable the collection of the data presented in this paper. We acknowledge Guillem Anglada-Escudé Russel White, Todd Henry, and Bernie Walp for their feedback. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Software: ishell_reduction (, PySHELL (Available upon request), Scipy (Jones et al. 2001), Matplotlib, (Hunter 2007), barycentric (Wright & Eastman 2014).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
George Mason UniversityUNSPECIFIED
Subject Keywords:atmospheric effects – infrared: stars – methods: data analysis – stars: individual (61 Cygni A, Barnard’s Star, GJ 15 A) – techniques: radial velocities
Issue or Number:5
Record Number:CaltechAUTHORS:20191010-094707796
Persistent URL:
Official Citation:Bryson Cale et al 2019 AJ 158 170
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99211
Deposited By: Tony Diaz
Deposited On:10 Oct 2019 18:29
Last Modified:16 Nov 2021 17:44

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