Very-Low-Mass Stellar and Substellar Companions to Solar-Like Stars From Marvels. III. A Short-period Brown Dwarf Candidate Around An Active GOIV Subgiant
Ma, Bo; Ge, J; Barnes, R; Crepp, J. R; De Lee, N; Dutra-Ferreira, L; Esposito, M; Femenia, B; Fleming, S. W; Gaudi, B. S; Ghezzi, L; Hebb, L; Gonzalez Hernandez, J. I; Lee, B. L; Porto de Mello, G. F; Stassun, K. G; Wang, J; Wisniewski, J. P; Agol, E; Bizyaev, D; Cargile, P; Chang, L; Nicolaci da Costa, L; Eastman, J. D; Gary, B; Jiang, P; Kane, S. R; Li, R; Liu, J; Mahadevan, S; Maia, M. A. G; Muna, D; Nguyen, D. C; Ogando, R. L. C; Oravetz, D; Pepper, J; Paegert, M; Prieto, C. A; Rebolo, R; Santiago, B. X; Schneider, D. P; Shelden, A; Simmons, A; Sivarani, T; van Eyken, J. C; Wan, X; Weaver, B. A; Zhao, Bo
Date:
2013-01
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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