Precise orbits and dynamical masses for nine RV exoplanet systems

Gaia-era absolute astrometry has enabled many spectacular science results, including precise dynamical mass estimations for planets, brown dwarfs and low-mass stars. Until Gaia, many exoplanetary systems discovered through the RV method still lack precise dynamical mass characterizations due to a fundamental degeneracy between mass (M) and inclination (i) inherit in RV-only orbital fits. Absolute astrometry from the Hipparcos and Gaia satellites has provided a unique opportunity for us to break this sini degeneracy by measuring orthogonal components of the 3d acceleration of a star together with radial velocity. We perform orbital fits to nine RV systems demonstrating significant accelerations in the Hipparocs-Gaia Catalog of Accelerations (HGCA) using an in-house orbit fitting tool orvara. Out of the nine RV systems, we confirm the planetary nature of six companions: HD 29021b, HD 81040b, HD 87883b, HD 98649b, HD 106252b, and HD 171238b. In addition, we find that HD 196067b is on the planet-brown dwarf boundary and HD 106515Ab and HD 221420b are in the low-mass brown dwarf regime. Although precise dynamical masses are obtained, two-fold degeneracy still exist in the inclinations for each of the orbits due to difficulty in separating prograde from retrograde motion.