We use a cross-calibration of Hipparcos and Gaia DR2 astrometry for β Pic to measure the mass of the giant planet β Pic b (13±3MJup) 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±0.05M⊙). This first model-independent mass for a directly imaged planet is inconsistent with cold-start models given the age of the β 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 β 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 β Pic's disk. It could also potentially signal that β Pic b has migrated inward to its current location, acquiring its eccentricity from interaction with the 3:1 outer Lindblad resonance in the disk.
Cite
@article{arxiv.1812.11530,
title = {A Model-Independent Mass and Moderate Eccentricity for $\beta$ Pic b},
author = {Trent J. Dupuy and Timothy D. Brandt and Kaitlin M. Kratter and Brendan P. Bowler},
journal= {arXiv preprint arXiv:1812.11530},
year = {2019}
}