Very Low Mass Stellar and Substellar Companions to Solar-like Stars From MARVELS IV: A Candidate Brown Dwarf or Low-Mass Stellar Companion to HIP 67526

Abstract

We report the discovery of a candidate brown dwarf or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 years. Our Keplerian fit using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of $90.2695^{+0.0188}_{-0.0187}$ days, an eccentricity of $0.4375 \pm 0.0040$ and a semi-amplitude of $2948.14^{+16.65}_{-16.55}$ m s$^{-1}$. Using additional high-resolution spectroscopy, we find the host star has an effective temperature $T_{\rm{eff}}=6004 \pm 34$ K, a surface gravity $\log g$ [cgs] $=4.55 \pm 0.17$ and a metallicity [Fe/H] $=+0.04 \pm 0.06$. The stellar mass and radius determined through the empirical relationship of Torres et al. (2010), yields 1.10$\pm$0.09 $M_{\sun}$ and 0.92$\pm$0.19 $R_{\sun}$. The minimum mass of MARVELS-5b is $65.0 \pm 2.9 M_{Jup}$, indicating that it is likely to be either a brown dwarf or a very low mass star, thus occupying a relatively sparsely-populated region of the mass function of companions to solar-type stars. The distance to this system is 101$\pm$10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2$M_{\sun}$ at a separation larger than 40 AU.