A SURVEY FOR NEW MEMBERS OF TAURUS FROM STELLAR TO PLANETARY MASSES.

Abstract

We present a large sample of new members of the Taurus star-forming region that extend from stellar to planetary masses. To identify candidate members at substellar masses, we have used color-magnitude diagrams and proper motions measured with several wide-field optical and infrared (IR) surveys. At stellar masses, we have considered the candidate members that were found in a recent analysis of high-precision astrometry from the Gaia mission. Using new and archival spectra, we have measured spectral types and assessed membership for these 161 candidates, 79 of which are classified as new members. Our updated census of Taurus now contains 519 known members. According to Gaia data, this census should be nearly complete for spectral types earlier than M6-M7 at A _J < 1. For a large field encompassing ~ 72% of the known members, the census should be complete for K < 15.7 at A _J < 1.5, which corresponds to ~ 5-13 M _Jup for ages of 1-10 Myr based on theoretical evolutionary models. Our survey has doubled the number of known members at ≥M9 and has uncovered the faintest known member in M _K , which should have a mass of ~3-10 ~ M _Jup for ages of 1-10 Myr. We have used mid-IR photometry from the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer to determine whether the new members exhibit excess emission that would indicate the presence of circumstellar disks. The updated disk fraction for Taurus is ~0.7 at ≤M3.5 and ~0.4 at >M3.5.