THE MASS OF THE CANDIDATE EXOPLANET COMPANION TO HD 136118 FROM HUBBLE SPACE TELESCOPE ASTROMETRY AND HIGH-PRECISION RADIAL VELOCITIES*

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{sub b} = 163.{sup 0}1 +- 3.{sup 0}0. This establishes the actual mass of the object, M{sub b} = 42{sup +11}{sub -18} M{sub J} , in contrast to the minimum mass determined from the radial velocity data only, M{sub b} sin i approx 12 M{sub J} . Therefore, the low-mass companion to HD 136118 is now identified as a likely brown dwarf residing in the 'brown dwarf desert'.