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

January 2013 • 2013AJ....145...20M

Authors • Ma, Bo • Ge, Jian • Barnes, Rory • Crepp, Justin R. • De Lee, Nathan • Dutra-Ferreira, Leticia • Esposito, Massimiliano • Femenia, Bruno • Fleming, Scott W. • Gaudi, B. Scott • Ghezzi, Luan • Hebb, Leslie • Gonzalez Hernandez, Jonay I. • Lee, Brian L. • Porto de Mello, G. F. • Stassun, Keivan G. • Wang, Ji • Wisniewski, John P. • Agol, Eric • Bizyaev, Dmitry • Cargile, Phillip • Chang, Liang • Nicolaci da Costa, Luiz • Eastman, Jason D. • Gary, Bruce • Jiang, Peng • Kane, Stephen R. • Li, Rui • Liu, Jian • Mahadevan, Suvrath • Maia, Marcio A. G. • Muna, Demitri • Nguyen, Duy Cuong • Ogando, Ricardo L. C. • Oravetz, Daniel • Pepper, Joshua • Paegert, Martin • Allende Prieto, Carlos • Rebolo, Rafael • Santiago, Basilio X. • Schneider, Donald P. • Shelden, Alaina • Simmons, Audrey • Sivarani, Thirupathi • van Eyken, J. C. • Wan, Xiaoke • Weaver, Benjamin A. • Zhao, Bo

Abstract • 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^-1, 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 _rotsin 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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Julian van Eyken

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