Determining the true mass of radial-velocity exoplanets with Gaia

F. Kiefer,A. Lecavelier des Etangs,E. Martioli,G. Hébrard,A. Vidal-Madjar,S. Dalal

doi:10.1051/0004-6361/202039168

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 as a result of radial-velocity (RV) variations of their host star. For those examples, 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 databases is generally that of an assumed edge-on system (~90°), but many other inclinations are possible, even extreme values closer to 0° (face-on). In such a 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 recently developed tool taking advantage of the voluminous Gaia astrometric database to constrain the inclination and true mass of several hundreds of published exoplanet candidates. We find nine exoplanet candidates in the stellar or brown dwarf (BD) domain, among which six 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 MJ at 3σ. We also confirm the planetary nature of 27 exoplanets, including 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 ~100 d, while eccentricity and metallicity distributions agree with a transition between BDs similar to planets and BDs similar to stars in the range 40–50 MJ.

Highlights

A large fraction of exoplanets published in all up-to-date catalogs, such as www.exoplanet.eu (Schneider et al 2011) or the NASA exoplanet archive (Akeson et al 2013), have been detected as a consequence of radial-velocity (RV) variations of their host star
If any observed system is inclined according to an isotropic distribution, there is a nonzero probability 1 − cos Ic, where Ic is the inclination of the candidate orbit, that the m sin i underestimates the true mass of the companion by a factor larger than 1/ sin Ic
We used the GASTON method developed in Kiefer et al (2019) and Kiefer (2019) with Gaia DR1 data to determine the true mass of the 911 RV-detected exoplanet candidates published in the exoplanets.org database

Summary

Introduction

A large fraction of exoplanets published in all up-to-date catalogs, such as www.exoplanet.eu (Schneider et al 2011) or the NASA exoplanet archive (Akeson et al 2013), have been detected as a consequence of radial-velocity (RV) variations of their host star. If the minimum mass m sin i, where i is a common symbolic notation for “orbital inclination”, is located below the planet/brown dwarf (BD) critical mass of 13.5 MJ such detection has to be considered as a new “candidate” planet. If any observed system is inclined according to an isotropic distribution, there is a nonzero probability 1 − cos Ic, where Ic is the inclination of the candidate orbit, that the m sin i underestimates the true mass of the companion by a factor larger than 1/ sin Ic. Assuming Ic = 10◦, this already leads to a factor ∼6, with a probability of 1.5%. Assuming Ic = 10◦, this already leads to a factor ∼6, with a probability of 1.5% Such a small rate, considering the ∼500–1000 planets detected through RVs, implies that the mass is highly underestimated in only a few tens of planets. The RV-detected samples of exoplanets in catalogs are partly biased toward small

Objectives

Discussion

Conclusion