2013AJ....145...20M

We present an eccentric, short-period brown dwarf candidate orbiting the active, slightly evolved subgiant star TYC 2087-00255-1, which has effective temperature T_eff= 5903±42 K, surface gravity log (g) = 4.07±0.16 (cgs), and metallicity [Fe/H] = -0.23±0.07. This candidate was discovered using data from the first two years of the Multi-object APO Radial Velocity Exoplanets Large-area Survey, which is part of the third phase of Sloan Digital Sky Survey. From our 38 radial velocity measurements spread over a two-year time baseline, we derive a Keplerian orbital fit with semi-amplitude K = 3.571 ±0.041 km/s, period P = 9.0090±0.0004 days, and eccentricity e = 0.226 ±0.011. Adopting a mass of 1.16±0.11 M_☉ for the subgiant host star, we infer that the companion has a minimum mass of 40.0±2.5 M_Jup. Assuming an edge-on orbit, the semimajor axis is 0.090±0.003 AU. The host star is photometrically variable at the ∼1% level with a period of ∼13.16 ±0.01 days, indicating that the host star spin and companion orbit are not synchronized. Through adaptive optics imaging we also found a point source 643±10 mas away from TYC 2087-00255-1, which would have a mass of 0.13 M_☉ if it is physically associated with TYC 2087-00255-1 and has the same age. Future proper motion observation should be able to resolve if this tertiary object is physically associated with TYC 2087-00255-1 and make TYC 2087-00255-1 a triple body system. Core Ca II H and K line emission indicate that the host is chromospherically active, at a level that is consistent with the inferred spin period and measured v_rot sin i, but unusual for a subgiant of this T_eff. This activity could be explained by ongoing tidal spin-up of the host star by the companion.