Very low mass stellar and substellar companions to solar-like stars from MARVELS. II. A short-period companion orbiting an F star with evidence of a stellar tertiary and significant mutual inclination

Abstract

We report the discovery via radial velocity (RV) measurements of a short-period (P = 2.430420±0.000006 days) companion to the F-type main-sequence star TYC 2930-00872-1. A long-term trend in the RV data also suggests the presence of a tertiary stellar companion with P > 2000 days. High-resolution spectroscopy of the host star yields T/sub eff/ = 6427 ± 33 K, log /sub g/ = 4.52 ± 0.14, and [Fe/H] = −0.04 ± 0.05. These parameters, combined with the broadband spectral energy distribution (SED) and a parallax, allow us to infer a mass and radius of the host star of M /sub 1/ = 1.21 ± 0.08 M⨀ and R1 = 1.09+0.15 −0.13 R⨀. The minimum mass of the inner companion is below the hydrogen-burning limit; however, the true mass is likely to be substantially higher. We are able to exclude transits of the inner companion with high confidence. Further, the host star spectrum exhibits a clear signature of Ca H and K core emission, indicating stellar activity, but a lack of photometric variability and small v sin I suggest that the primary’s spin axis is oriented in a pole-on configuration. The rotational period of the primary estimated through an activity–rotation relation matches the orbital period of the inner companion to within 1.5 σ, suggesting that the primary and inner companion are tidally locked. If the inner companion’s orbital angular momentum vector is aligned with the stellar spin axis as expected through tidal evolution, then it has a stellar mass of ∼0.3–0.4 M⨀. Direct imaging limits the existence of stellar companions to projected separations <30 AU. No set of spectral lines and no significant flux contribution to the SED from either companion are detected, which places individual upper mass limits of M/sub {2, 3}/ ≳1.0 M⨀, provided they are not stellar remnants. If the tertiary is not a stellar remnant, then it likely has a mass of ∼0.5–0.6M⨀, and its orbit is likely significantly inclined from that of the secondary, suggesting that the Kozai–Lidov mechanism may have driven the dynamical evolution of this system.