Dynamical Mass of the Young Brown Dwarf Companion PZ Tel B

Abstract

Dynamical masses of giant planets and brown dwarfs are critical tools for empirically validating substellar evolutionary models and their underlying assumptions. We present a measurement of the dynamical mass and an updated orbit of PZ Tel B, a young brown dwarf companion orbiting a late-G member of the $\beta$ Pic moving group. PZ Tel A exhibits an astrometric acceleration between Hipparcos and Gaia EDR3, which enables the direct determination of the companion's mass. We have also acquired new Keck/NIRC2 adaptive optics imaging of the system, which increases the total baseline of relative astrometry to 15 years. Our joint orbit fit yields a dynamical mass of $27_{-9}^{+25}{M}_{\mathrm{Jup}}$, semi-major axis of $27_{-4}^{+14}\mathrm{au}$, eccentricity of $0.52_{-0.10}^{+0.08}$, and inclination of $91.73_{-0.32}^{+0.36}{}^{\circ }$. The companion's mass is consistent within $1.1\sigma$ of predictions from four grids of hot-start evolutionary models. The joint orbit fit also indicates a more modest eccentricity of PZ Tel B than previous results. PZ Tel joins a small number of young ($<200\mathrm{Myr}$) systems with benchmark substellar companions that have dynamical masses and precise ages from moving group membership.

14 pages, 5 figures, accepted to AJ

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