Orbital Motion, Variability, and Masses in the T Tauri Triple System
  We present results from adaptive optics imaging of the T Tauri triple system
obtained at the Keck and Gemini Observatories in 2015-2019. We fit the orbital
motion of T Tau Sb relative to Sa and model the astrometric motion of their
center of mass relative to T Tau N. Using the distance measured by Gaia, we
derived dynamical masses of M_Sa = 2.05 +/- 0.14 Msun and M_Sb = 0.43 +/- 0.06
Msun. The precision in the masses is expected to improve with continued
observations that map the motion through a complete orbital period; this is
particularly important as the system approaches periastron passage in 2023.
Based on published properties and recent evolutionary tracks, we estimate a
mass of ~ 2 Msun for T Tau N, suggesting that T Tau N is similar in mass to T
Tau Sa. Narrow-band infrared photometry shows that T Tau N remained relatively
constant between late 2017 and early 2019 with an average value of K = 5.54 +/-
0.07 mag. Using T Tau N to calibrate relative flux measurements since 2015, we
found that T Tau Sa varied dramatically between 7.0 to 8.8 mag in the K-band
over timescales of a few months, while T Tau Sb faded steadily from 8.5 to 11.1
mag in the K-band. Over the 27 year orbital period of the T Tau S binary, both
components have shown 3-4 magnitudes of variability in the K-band, relative to
T Tau N.
