Revisiting the Membership, Multiplicity, and Age of the Beta Pictoris Moving Group in the Gaia Era

Abstract

Determining the precise ages of young (tens to a few hundred Myr) kinematic (``moving") groups is important for placing star, protoplanetary disk, and planet observations on an evolutionary timeline. The nearby $\sim$25 Myr-old ${\hat{I}}^2$ Pictoris Moving Group (BPMG) is an important benchmark for studying stars and planetary systems at the end of the primordial disk phase. Gaia DR3 astrometry and photometry, combined with ground-based observations and more sophisticated stellar models, permit a systematic re-evaluation of BPMG membership and age. We combined Gaia astrometry with previously published radial velocities to evaluate moving group membership in a Bayesian framework. To minimize the effect of unresolved stellar multiplicity on age estimates, we identified and excluded multi-star systems using Gaia astrometry, ground-based adaptive optics imaging, and multi-epoch radial velocities, as well as literature identifications. We estimated age using isochrone and lithium-depletion-boundary fitting with models that account for the effect of magnetic activity and spots on young, rapidly rotating stars. We find that age estimates are highly model-dependent; Dartmouth magnetic models with ages of 23$\pm$8 Myr and 33${}_{-11}^{+9}$ Myr provide best fits to the lithium depletion boundary and Gaia $M_G$ vs. $B_P$-$R_P$ color-magnitude diagram, respectively, whereas a Dartmouth standard model with an age of 11${}_{-3}^{+4}$ Myr provides a best fit to the 2MASS-Gaia $M_{K_S}$ vs. $B_P$-$R_P$ color-magnitude diagram.

18 pages, 7 figures, 3 tables, accepted for publication in MNRAS Main Journal Dec 2023