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

We present sensitive, arcsecond-resolution Submillimeter Array observations of the super(12)CO 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 novelMonteCarlo Markov Chain technique to extract theKeplerian velocity field of the disk from these data and estimate the totalmass of the central binary. Assuming the distance inferred from kinematic parallaxmeasurements in the literature (d approximately 73 pc), we determine a total stellarmass M sub(*) = 1.75 super(+0.09) sub(-0.06)M sub([middot in circle]) and a disk inclination i sub(d) = 33.[degrees] 5 super(+0.7) sub(-1.4) from face-on. Thesemeasurements 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 (~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 |i sub(d) - i sub(*)| approximately 0. [degrees] 1 + or - 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 ~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.