Preliminary orbits and system masses for five binary T Tauri stars

First visual orbits for the binary T Tauri stars V773 Tau, FO Tau, and FS Tau and revised orbits for DF Tau and GG Tau are presented. The orbits are determined from a compilation of previous high spatial resolution imaging measurements and new astrometric measurements from the Calar Alto 3.5 m telescope. The orbital solutions, which must be considered preliminary because of the short orbital arcs observed, are used in combination with distance estimates to determine the dynamical masses for all five systems. The total mass of the triple system V773 Tau ( whose primary is a K2+ K5 spectroscopic binary) is 3.20 +/- 0.71 M-., and the masses of the four binary pairs range from 0.77 to 1.22 M-.. The orbital solutions for these systems predict projected relative orbital velocities that range from 0.1 to 13.4 km s(-1) ( 2002 epoch); the majority are spectroscopically measurable if spatially resolved. Of particular interest is the GG Tau binary, which has a mass that is consistent with the value determined from circumbinary disk kinematics and an orbit that is coplanar with this disk. The stellar properties of the components of these five systems are determined from spatially resolved optical measurements, assuming dwarflike colors and a dwarflike temperature scale. With luminosity and temperature estimates, theoretical masses are determined from the predictions of four pre-main-sequence evolutionary models and compared with the dynamically determined values as a test of these models. Of the models tested, those of Palla & Stahler and Siess, Dufour, & Forestini predict masses that are the most consistent ( within 1sigma) with the dynamical values over the component mass range of similar to0.3-1.5 M-.. All models support coeval formation of these binaries.