A Surprising Dynamical Mass for V773~Tau~B

TL;DR

This study uses high-resolution imaging and spectroscopy to determine the dynamical mass of V773 Tau B, revealing it is likely a multiple star system with significant implications for understanding T Tauri star systems.

Contribution

The paper provides the first dynamical mass estimate for V773 Tau B, suggesting it is a multiple star system, and offers new spectroscopic insights into its nature and variability.

Findings

B's dynamical mass is 1.7-3.0 solar masses, higher than previous estimates.

B is likely a close binary of two ~1.2 solar mass PMS stars.

B exhibits high near-IR variability likely due to circumstellar material.

Abstract

We report on new high-resolution imaging and spectroscopy on the multiple T Tauri star system V773 Tau over the 2003 -- 2009 period. With these data we derive relative astrometry, photometry between the A and B components, and radial velocity (RV) of the A-subsystem components. Combining these new data with previously published astrometry and RVs, we update the relative A-B orbit model. This updated orbit model, the known system distance, and A subsystem parameters yields a dynamical mass for the B component for the first time. Remarkably the derived B dynamical mass is in the range of 1.7 -- 3.0 M$_\sun$. This is much higher than previous estimates, and suggests that like A, B is also a multiple stellar system. Among these data, spatially-resolved spectroscopy provide new insight into the nature of the B component. Similar to A, these near-IR spectra indicate that the dominant source in B is of mid-K spectral type. If B is in fact a multiple star system as suggested by the dynamical mass estimate, the simplest assumption is that B is composed of similar $\sim$ 1.2 M$_\sun$ PMS stars in a close ($<$ 1 AU) binary system. This inference is supported by line-shape changes in near-IR spectroscopy of B, tentatively interpreted as changing RV among components in V773 Tau B. Relative photometry indicate that B is highly variable in the near-IR. The most likely explanation for this variability is circum-B material resulting in variable line-of-sight extinction. The distribution of this material must be significantly affected by both the putative B multiplicity, and the A-B orbit.