The Mass Of The Candidate Exoplanet Companion To HD 136118 From Hubble Space Telescope Astrometry And High-Precision Radial Velocities

Abstract

We use Hubble Space Telescope fine guidance sensor astrometry and high-cadence radial velocities for HD 136118 from the Hobby-Eberly Telescope with archival data from Lick to determine the complete set of orbital parameters for HD 136118 b. We find an orbital inclination for the candidate exoplanet of i(b) = 163 degrees.1 +/- 3 degrees.0. This establishes the actual mass of the object, M(b) = 42(-18)(+11) M(J), in contrast to the minimum mass determined from the radial velocity data only, M(b) sin i similar to 12 M(J). Therefore, the low-mass companion to HD 136118 is now identified as a likely brown dwarf residing in the "brown dwarf desert."