A cautionary tale: Marvels brown dwarf candidate reveals itself to be a very long period, highly eccentric spectroscopic stellar binary

Claude E. Mack, Jian Ge, Rohit Deshpande, John P. Wisniewski, Keivan G. Stassun, B. Scott Gaudi, Scott W. Fleming, Suvrath Mahadevan, Nathan De Lee, Jason Eastman, Luan Ghezzi, Jonay I. González Hernández, Bruno Femenía, Letícia Ferreira, Gustavo Porto De Mello, Justin R. Crepp, Daniel Mata Sánchez, Eric Agol, Thomas G. Beatty, Dmitry BizyaevHoward Brewington, Phillip A. Cargile, Luiz N. Da Costa, Massimiliano Esposito, Garret Ebelke, Leslie Hebb, Peng Jiang, Stephen R. Kane, Brian Lee, Marcio A.G. Maia, Elena Malanushenko, Victor Malanushenko, Daniel Oravetz, Martin Paegert, Kaike Pan, Carlos Allende Prieto, Joshua Pepper, Rafael Rebolo, Arpita Roy, Basílio X. Santiago, Donald P. Schneider, Audrey Simmons, Robert J. Siverd, Stephanie Snedden, Benjamin M. Tofflemire

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9 Scopus citations

Abstract

We report the discovery of a highly eccentric, double-lined spectroscopic binary star system (TYC 3010-1494-1), comprising two solar-type stars that we had initially identified as a single star with a brown dwarf companion. At the moderate resolving power of the MARVELS spectrograph and the spectrographs used for subsequent radial-velocity (RV) measurements (R ≲ 30, 000), this particular stellar binary mimics a single-lined binary with an RV signal that would be induced by a brown dwarf companion (Msin i 50 M Jup) to a solar-type primary. At least three properties of this system allow it to masquerade as a single star with a very-low-mass companion: its large eccentricity (e 0.8), its relatively long period (P 238 days), and the approximately perpendicular orientation of the semi-major axis with respect to the line of sight (ω 189°). As a result of these properties, for 95% of the orbit the two sets of stellar spectral lines are completely blended, and the RV measurements based on centroiding on the apparently single-lined spectrum is very well fit by an orbit solution indicative of a brown dwarf companion on a more circular orbit (e 0.3). Only during the 5% of the orbit near periastron passage does the true, double-lined nature and large RV amplitude of 15 km s-1 reveal itself. The discovery of this binary system is an important lesson for RV surveys searching for substellar companions; at a given resolution and observing cadence, a survey will be susceptible to these kinds of astrophysical false positives for a range of orbital parameters. Finally, for surveys like MARVELS that lack the resolution for a useful line bisector analysis, it is imperative to monitor the peak of the cross-correlation function for suspicious changes in width or shape, so that such false positives can be flagged during the candidate vetting process.

Original languageEnglish (US)
Article number139
JournalAstronomical Journal
Volume145
Issue number5
DOIs
StatePublished - May 2013

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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