A Model-independent Mass and Moderate Eccentricity for beta Pic b

Abstract

We use a cross-calibration of Hipparcos and Gaia. second data release astrometry for beta Pic to measure the mass of the giant planet beta Pic. b (13 +/- 3 M-Jup) in a comprehensive joint orbit analysis that includes published relative astrometry and radial velocities. Our mass uncertainty is somewhat higher than previous work because our astrometry from the Hipparcos-Gaia Catalog of Accelerations accounts for the error inflation and systematic terms that are required to bring the two data. sets onto a common astrometric reference frame, and because we fit freely for the host-star mass (1.84 +/- 0.05 M-circle dot). This first model-independent mass for a directly imaged planet is inconsistent with cold-start models given the age of the beta Pic moving group (22 +/- 6 Myr) but consistent with hot and warm-start models, concordant with past work. We find a higher eccentricity (0.24 +/- 0.06) for beta Pic b compared to previous orbital fits. If confirmed by future observations, this eccentricity may help explain inner edge, scale height, and brightness asymmetry of beta Pic's disk. It could also potentially signal that beta Pic b has migrated inward to its current location, acquiring its eccentricity from interaction with the 3:1 outer Lindblad resonance in the disk.