A Model-independent Mass and Moderate Eccentricity for β Pic b
Abstract
We use a cross-calibration of Hipparcos and Gaia second data release astrometry for β Pic to measure the mass of the giant planet β 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 ⊙). 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2019
- DOI:
- 10.3847/2041-8213/aafb31
- arXiv:
- arXiv:1812.11530
- Bibcode:
- 2019ApJ...871L...4D
- Keywords:
-
- astrometry;
- planetary systems;
- stars: individual: bet Pic;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- ApJ Letters, accepted