A Cautionary Tale: MARVELS Brown Dwarf Candidate Reveals Itself To Be A Very Long Period, Highly Eccentric Spectroscopic Stellar Binary
Creators: name: Mack, Claude E.
name: Ge, Jian
name: Deshpande, Rohit
name: Wisniewski, John P.
name: Stassun, Keivan G.
name: Gaudi, B. Scott
name: Fleming, Scott W.
name: Mahadevan, Suvrath
name: De Lee, Nathan
name: Eastman, Jason
name: Ghezzi, Luan
name: Hernandez, Jonay I. Gonzalez
name: Femenia, Bruno
name: Ferreira, Leticia
name: de Mello, Gustavo Porto
name: Crepp, Justin R.
name: Sanchez, Daniel Mata
name: Agol, Eric
name: Beatty, Thomas G.
name: Bizyaev, Dmitry
name: Brewington, Howard
name: Cargile, Phillip A.
name: da Costa, Luiz N.
name: Esposito, Massimiliano
name: Ebelke, Garret
name: Hebb, Leslie
name: Jiang, Peng
name: Kane, Stephen R.
name: Lee, Brian
name: Maia, Marcio A. G.
name: Malanushenko, Elena
name: Malanushenko, Victor
name: Oravetz, Daniel
name: Paegert, Martin
name: Pan, Kaike
name: Prieto, Carlos Allende
name: Peper, Joshua
name: Rebolo, Rafael
name: Roy, Arpita
name: Santiago, Basilio X.
name: Schneider, Donald P.
name: Simmons, Audrey
name: Siverd, Robert J.
name: Snedden, Stephanie
name: Tofflemire, Benjamin M.
Publisher: name: arXiv
Year: 2013
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 ~ &lt;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 (omega~189 degrees). 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 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.
description: 16 pages, 11 figures, 6 tables