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 = 163fdg1 ± 3fdg0. This establishes the actual mass of the object, M_b = 42⁺¹¹ _-18 M_J , in contrast to the minimum mass determined from the radial velocity data only, M_b sin i ~ 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."

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universitt München, and Georg-August-Universität Göttingen.