A Disk-based Dynamical Mass Estimate for the Young Binary V4046 Sgr

TL;DR

This paper introduces a novel disk-based method using submillimeter observations and Monte Carlo Markov Chain analysis to accurately determine the mass of the young binary system V4046 Sgr, confirming its age and disk properties.

Contribution

The study presents a new, precise disk-based technique for measuring stellar masses in young binaries, validated against radial velocity data and applicable to evolved pre-main sequence systems.

Findings

Measured stellar mass M_star = 1.75 solar masses with few percent uncertainty

Confirmed disk and binary orbital plane alignment within 1 degree

Demonstrated consistency with pre-main sequence evolution models and age estimates of 5-30 Myr

Abstract

We present sensitive, arcsecond-resolution Submillimeter Array observations of the 12CO 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 is approximately 73 pc), we determine a total stellar mass M_star = 1.75^{+0.09}_{-0.06} solar masses and a disk inclination i_d = 33.5^{+0.7}_{-1.4} degrees 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 (~ 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_d - i_star| \approx 0.1\pm1 degree). 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.