* Astronomy

Title: Very Low-mass Stellar and Substellar Companions to Solar-like Stars from Marvels Iii: A Short-Period Brown Dwarf Candidate Around An Active G0Iv Subgiant
Authors: Bo Ma (Univ. Florida), Jian Ge, Rory Barnes, Justin R. Crepp, Nathan De Lee, Leticia Dutra-Ferreira, Massimiliano Esposito, Bruno Femenia, Scott W. Fleming, B. Scott Gaudi, Luan Ghezzi, Leslie Hebb, Jonay I. Gonzalez Hernandez, Brian L. Lee, G. F. Porto de Mello, Keivan G. Stassun, Ji Wang, John P. Wisniewski, Eric Agol, Dmitry Bizyaev, Phillip Cargile, Liang Chang, Luiz Nicolaci da Costa, Jason D. Eastman, Bruce Gary, Peng Jiang, Stephen R. Kane, Rui Li, Jian Liu, Suvrath Mahadevan, Marcio A. G. Maia, Demitri Muna, Duy Cuong Nguyen, Ricardo L. C. Ogando, Daniel Oravetz, Joshua Pepper, Martin Paegert, Carlos Allende Prieto, Rafael Rebolo, Basilio X. Santiago, Donald P. Schneider, Alaina Shelden, Audrey Simmons, Thirupathi Sivarani, J. C. van Eyken, Xiaoke Wan, Benjamin A. Weaver, Bo Zhao

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 (MARVELS), 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 solar masses for the subgiant host star, we infer that the companion has a minimum mass of 40.0±2.5 Jupiter masses. 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 synchronised. 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 solar masses 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.

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