A DISK-BASED DYNAMICAL MASS ESTIMATE FOR THE YOUNG BINARY V4046 Sgr

We present sensitive, arcsecond-resolution Submillimeter Array observations of the (CO)-C-12 J = 2-1 line emission from the circumstellar disk orbiting the double-lined spectroscopic binary star V4046 Sgr. Based on a simple model of the disk structure, we use a novel Monte Carlo Markov Chain technique to extract the Keplerian velocity field of the disk from these data and estimate the total mass of the central binary. Assuming the distance inferred from kinematic parallax measurements in the literature (d approximate to 73 pc), we determine a total stellar mass M-* = 1.75(-0.06)(+0.06)M(circle dot) and a disk inclination i(d) = 33.degrees 5(+0.7)(-1.4) from face-on. These measurements are in excellent agreement with independent dynamical constraints made from multi- epoch monitoring of the stellar radial velocities, confirming the absolute accuracy of this precise (similar to few percent uncertainties) disk- based method for estimating stellar masses and reaffirming previous assertions that the disk and binary orbital planes are well aligned (with vertical bar i(d) - i(*)vertical bar approximate to 0.degrees 1 +/- 1 degrees). Using these results as a reference, we demonstrate that various pre-main-sequence evolution models make consistent and accurate predictions for the masses of the individual components of the binary, and uniformly imply an advanced age of similar to 5-30 Myr. Taken together, these results verify that V4046 Sgr is one of the precious few nearby and relatively evolved pre-main-sequence systems that still hosts a gas- rich accretion disk.