Abstract
The first planetary candidate discovered by Latham et al. (1989, Nature, 339, 38) with radial velocities around a solar-like star other than the Sun, HD 114762 b, was detected with a minimum mass of 11 MJ. The small v sin i ∼ 0 km s−1 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 6.26.2+1.9−1.3 degree, the mass of the companion is constrained to Mb = 108+31−26 MJ. HD 114762 b thus indeed belongs to the M-dwarf domain, down to brown dwarfs, with Mb > 13.5 MJ at the 3σ level, and is not a planet.
Highlights
The HD 114762 system was discovered by Latham et al (1989) to host a possible brown dwarf or giant planet with a period of 84 days and a minimum mass of 11 MJ
Not long after its discovery, it was found that the hosting star, a very metal-poor late-F subgiant, had a remarkably small v sin i ∼ 0 − 1.5 km s−1 compared to its expected rotational speed vrot ∼ 8 km s−1 (Cochran et al 1991; Hale 1995)
Based on the Gaia astrometry that was published in the first data release of the mission (DR1; Gaia Collaboration 2016b,a), we addressed the puzzling question of the true nature of HD 114762 b
Summary
The HD 114762 system was discovered by Latham et al (1989) to host a possible brown dwarf or giant planet with a period of 84 days and a minimum mass of 11 MJ. Not long after its discovery, it was found that the hosting star, a very metal-poor late-F subgiant, had a remarkably small v sin i ∼ 0 − 1.5 km s−1 compared to its expected rotational speed vrot ∼ 8 km s−1 (Cochran et al 1991; Hale 1995) This implied a far from edge-on inclination, which led to a reconsideration of the companion mass as lying beyond the planetary mass regime (>20 MJ) and within the brown dwarf mass-domain. Applying the analysis and methods developed in K19, called GASTON, to the case of HD 114762, we here add new constraints on the inclination of the orbit and mass of its companion This is based on DR1 of the Gaia mission (Gaia Collaboration 2016a).
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