Determining the true mass of radial-velocity exoplanets with Gaia: 9 planet candidates in the brown-dwarf/stellar regime and 27 confirmed planets

TL;DR

This study uses Gaia astrometry to determine the true masses of hundreds of exoplanet candidates, revealing several in the brown dwarf and stellar regimes and confirming the planetary nature of others, thereby refining our understanding of their characteristics.

Contribution

It applies the GASTON tool to Gaia data to constrain inclinations and true masses, identifying new stellar and brown dwarf candidates among previously uncertain exoplanets.

Findings

9 candidates in stellar or brown dwarf regime, 6 never characterized before

27 confirmed exoplanets with refined mass estimates

Distribution patterns of orbital periods, eccentricities, and metallicities consistent with prior studies

Abstract

Mass is one of the most important parameters for determining the true nature of an astronomical object. Yet, many published exoplanets lack a measurement of their true mass, in particular those detected thanks to radial velocity (RV) variations of their host star. For those, only the minimum mass, or $m\sin i$, is known, owing to the insensitivity of RVs to the inclination of the detected orbit compared to the plane-of-the-sky. The mass that is given in database is generally that of an assumed edge-on system ($\sim$90$^\circ$), but many other inclinations are possible, even extreme values closer to 0$^\circ$ (face-on). In such case, the mass of the published object could be strongly underestimated by up to two orders of magnitude. In the present study, we use GASTON, a tool recently developed in Kiefer et al. (2019) & Kiefer (2019) to take advantage of the voluminous Gaia astrometric database, in order to constrain the inclination and true mass of several hundreds of published exoplanet candidates. We find 9 exoplanet candidates in the stellar or brown dwarf (BD) domain, among which 6 were never characterized. We show that 30 Ari B b, HD 141937 b, HD 148427 b, HD 6718 b, HIP 65891 b, and HD 16760 b have masses larger than 13.5 M$_\text{J}$ at 3-$\sigma$. We also confirm the planetary nature of 27 exoplanets among which HD 10180 c, d and g. Studying the orbital periods, eccentricities and host-star metallicities in the BD domain, we found distributions with respect to true masses consistent with other publications. The distribution of orbital periods shows of a void of BD detections below $\sim$100 days, while eccentricity and metallicity distributions agree with a transition between BDs similar to planets and BDs similar to stars about 40-50 M$_\text{J}$.