A DISK-BASED DYNAMICAL CONSTRAINT ON THE MASS OF THE YOUNG BINARY DQ TAU

We present new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of CO J = 2-1 line emission from the DQ. Tau circumbinary disk. These data are used to tomographically reconstruct the Keplerian disk velocity field in a forward-modeling inference framework, and thereby provide a dynamical constraint on the mass of the DQ. Tau binary of M-* = 1.27(-0.27)(+0.46)M(circle dot). Those results are compared with an updated and improved orbital solution for this double-lined system based on long-term monitoring of its stellar radial velocities. Both of these independent dynamical constraints on the binary mass are in excellent agreement: taken together, they demonstrate that the DQ. Tau system mass is 1.21 +/- 0.26 M-circle dot and that the disk and binary orbital planes are aligned within 3 degrees (at 3 sigma confidence). The predictions of various theoretical models for pre-main-sequence stellar evolution are also consistent with these masses, though more detailed comparisons are difficult due to lingering uncertainties regarding the photospheric properties of the individual components. DQ. Tau is the third, nearly equal-mass, double-lined spectroscopic binary with a circumbinary disk that has been dynamically weighed with these two independent techniques: all show consistent results, validating the overall accuracy of the disk-based approach and demonstrating that it can be robustly applied to large samples of young, single stars as ALMA ramps up to operations at full capacity.