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We report the discovery of a highly eccentric, double-lined spectroscopicbinary star system (TYC 3010-1494-1), comprising two solar-type stars that wehad initially identified as a single star with a brown dwarf companion. At themoderate resolving power of the MARVELS spectrograph and the spectrographs usedfor subsequent radial-velocity (RV) measurements (R ~ <30,000), this particularstellar binary mimics a single-lined binary with an RV signal that would beinduced 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 singlestar with a very low-mass companion: its large eccentricity (e~0.8), itsrelatively long period (P~238 days), and the approximately perpendicularorientation of the semi-major axis with respect to the line of sight (omega~189degrees). As a result of these properties, for ~95% of the orbit the two setsof stellar spectral lines are completely blended, and the RV measurements basedon centroiding on the apparently single-lined spectrum is very well fit by anorbit 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 thetrue, double-lined nature and large RV amplitude of ~15 km/s reveal itself. Thediscovery of this binary system is an important lesson for RV surveys searchingfor substellar companions; at a given resolution and observing cadence, asurvey will be susceptible to these kinds of astrophysical false positives fora range of orbital parameters. Finally, for surveys like MARVELS that lack theresolution for a useful line bisector analysis, it is imperative to monitor thepeak of the cross-correlation function for suspicious changes in width orshape, so that such false positives can be flagged during the candidate vettingprocess.

A Cautionary Tale: MARVELS Brown Dwarf Candidate Reveals Itself To Be A Very Long Period, Highly Eccentric Spectroscopic Stellar Binary