The Mass of the Candidate Exoplanet Companion to HD136118 from Hubble Space Telescope Astrometry and High-Precision Radial Velocities

TL;DR

This study combines Hubble astrometry and radial velocity data to precisely determine the orbit and true mass of the exoplanet candidate HD136118b, revealing it as a likely brown dwarf in the brown dwarf desert.

Contribution

It provides the first complete orbital solution and true mass measurement of HD136118b, confirming its classification as a brown dwarf rather than a planet.

Findings

Orbital inclination determined as 163.1 ± 3.0 degrees.

True mass of the companion is 42^{+11}_{-18} MJup.

The object is a likely brown dwarf in the brown dwarf desert.

Abstract

We use Hubble Space Telescope Fine Guidance Sensor astrometry and high-cadence radial velocities for HD136118 from the HET with archival data from Lick to determine the complete set of orbital parameters for HD136118b. We find an orbital inclination for the candidate exoplanet of i_{b} = 163.1 +- 3.0 deg. This establishes the actual mass of the object, M_{b} = 42^{+11}_{-18} MJup, in contrast to the minimum mass determined from the radial velocity data only, M_{b}sin{i} ~ 12 MJup. Therefore, the low-mass companion to HD 136118 is now identified as a likely brown dwarf residing in the "brown dwarf desert".