Determining the mass of the planetary candidate HD 114762 b using Gaia

TL;DR

Using Gaia astrometry, the paper refines the mass of HD 114762 b, confirming it as an M-dwarf or brown dwarf rather than a planet, based on inclination and mass constraints.

Contribution

This study applies Gaia DR1 astrometric data and the GASTON method to accurately determine the mass and nature of HD 114762 b, clarifying its classification.

Findings

HD 114762 b has a mass of approximately 108 Mjup.

The inclination of the system is about 6.2 degrees.

HD 114762 b is confirmed as an M-dwarf or brown dwarf, not a planet.

Abstract

The first planetary candidate discovered by Latham et al. (1989) with radial velocities around a solar-like star other than the Sun, HD 114762 b, was detected with a minimum mass of 11 Mjup. The small v sin(i)~0 km/s that is otherwise measured by spectral analysis indicated that this companion of a late-F subgiant star better corresponds to a massive brown dwarf (BD) or even a low-mass M-dwarf seen nearly face-on. To our knowledge, the nature of HD 114762 b is still undetermined. The astrometric noise measured for this system in the first data release, DR1, of the Gaia mission allows us to derive new constraints on the astrometric motion of HD 114762 and on the mass of its companion. We use the method GASTON, introduced in a preceding paper, which can simulate Gaia data and determine the distribution of inclinations that are compatible with the astrometric excess noise. With an inclination of 6.2(+1.9)(-1.3) degrees, the mass of the companion is constrained to M_b=108(+31)(-26) Mjup. HD 114762 b thus indeed belongs to the M-dwarf domain, down to brown dwarfs, with M_b>13.5 Mjup at the 3-sigma level, and is not a planet.