Orbit and Stellar Properties of the Young Triple V807 Tau

We present new orbital measurements of the pre-main sequence triple system, V807 Tau, using adaptive optics imaging at the Keck Observatory. We computed an orbit for the close pair, V807 Tau Ba-Bb, with a period of 12.312 +/- 0.058 years and a semi-major axis of 38.59 +/- 0.16 mas. By modeling the center of mass motion of the components in the close pair relative to the wide component, V807 Tau A, we measured a mass ratio of 0.843 +/- 0.050 for Bb/Ba. Combined with the total mass from the relative orbit, we derived individual masses of M_Ba = 0.564 +/- 0.018 (d/140 pc)^3 Msun and M_Bb = 0.476 +/- 0.017 (d/140 pc)^3 Msun at an average distance of 140 pc to the Taurus star forming region. We computed spectral energy distributions to determine the luminosities of the three components. We also measured their spectral types, effective temperatures, and rotational velocities based on spatially resolved spectra obtained at the Keck Observatory. If the rotational axes are aligned, then the projected rotational velocities imply that V807 Tau Ba and Bb are rotating much faster than V807 Tau A. The uncertainty in the stellar effective temperatures and distance to the system currently limit the comparison of our dynamical mass measurements with predictions based on evolutionary tracks for pre-main sequence stars. We also report preliminary results from a program to map the 3.6 cm radio emission from V807 Tau using the Very Long Baseline Array. With continued monitoring, these observations will provide a precise parallax for placing the dynamical masses on an absolute scale.
Comment: 44 pages, 11 figures, 9 tables; Accepted for publication in the Astrophysical Journal