A Disk-based Dynamical Constraint on the Mass of the Young Binary DQ Tau

TL;DR

This study uses ALMA observations and orbital data to precisely measure the mass of the young binary DQ Tau, confirming the effectiveness of disk-based dynamical constraints for stellar mass estimation.

Contribution

It introduces a disk-based dynamical method for measuring binary star masses and validates it against orbital solutions, demonstrating its robustness and applicability to young stars.

Findings

Binary mass is $1.21 ext{--}0.26 M_\\odot$ from combined methods.

Disk and orbital planes are aligned within 3 degrees.

The method is validated for use in large samples of young stars.

Abstract

We present new 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 $M_\ast = 1.27_{-0.27}^{+0.46} \,M_\odot$. 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 $1.21\pm0.26\,M_\odot$ and that the disk and binary orbital planes are aligned within $3^\circ$ (at 3$\sigma$ confidence). The predictions of various theoretical models for pre-main sequence stellar evolution are also consistent with these masses, although more detailed comparisons are difficult due to lingering uncertainties in 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.