A Census of the TW Hya Association with Gaia*

Abstract I have used high-precision photometry and astrometry from the third data release of Gaia to perform a survey for members of the TW Hya association (TWA). I have identified candidate members that appear to share similar kinematics and ages with bona fide members compiled by Gagné et al. (2017), and I have assessed their membership using radial velocities and spectroscopic diagnostics of age from various sources. My new catalog of adopted members contains 67 Gaia sources in 55 systems. The histogram of spectral types for TWA peaks near M5 (∼0.15 M ⊙ ), resembling the distributions measured for other nearby young associations. The UVW velocities of its members indicate that the association is expanding. The rate of expansion corresponds to an age of 9.6 − 0.8 + 0.9 Myr. In a Gaia color–magnitude diagram, the members of TWA exhibit well-defined sequences of single stars and unresolved binary stars. The combined sequence of low-mass stars in TWA is indicative of an age of 11.4 − 1.2 + 1.3 Myr when compared to the sequence for Upper Centaurus Lupus/Lower Centaurus Crux, for which an age of 20 Myr is assumed. Based on these expansion and isochronal ages, I have adopted an age of 10 ± 2 Myr for TWA. Finally, I have used mid-infrared photometry from the Wide-field Infrared Survey Explorer to check for excess emission from circumstellar disks among the TWA members. Fourteen members have detected disks, all of which have been reported in previous studies. The fraction of members at ≤ M6 (≳0.1 M ⊙ ) that have full, transitional, or evolved disks is 10/52 = 0.19 − 0.06 + 0.08 . That value is similar to the fraction previously measured for the Upper Sco association, which is roughly coeval with TWA.