The Masses of a Sample of Radial-velocity Exoplanets with Astrometric Measurements

Being one of the most fundamental physical parameter of astronomical objects, mass plays a vital role in the study of exoplanets, including their temperature structure, chemical composition, formation, and evolution. However, nearly a quarter of the known confirmed exoplanets lack measurements of their masses. This is particularly severe for those discovered via the radial velocity (RV) technique, which alone could only yield the minimum mass of planets. In this study, we use published RV data combined with astrometric data from a cross-calibrated Hipparcos-Gaia Catalog of Accelerations to jointly constrain the masses of 115 RV-detected substellar companions, by conducting full orbital fits using the public tool orvara. Among them, 9 exoplanets with ${M}_{{\rm{p}}}\,\sin \,i\lt 13.5\ {M}_{\mathrm{Jup}}$ are reclassified to the brown dwarf (BD) regime, and 16 BD candidates ( $13.5\leqslant {M}_{{\rm{p}}}\,\sin \,i\lt 80\,{M}_{\mathrm{Jup}}$ ) turn out to be low-mass M dwarfs. We point out the presence of a transition in the BD regime as seen in the distributions of host star metallicity and orbital eccentricity with respect to planet masses. We confirm the previous findings that companions with masses below 42.5 M _Jup might primarily form in the protoplanetary disk through core accretion or disk gravitational instability, while those with masses above 42.5 M _Jup formed through the gravitational instability of a molecular cloud like stars. Selection effects and detection biases, which may affect our analysis to some extent, are discussed.