A Coplanar Circumbinary Protoplanetary Disk in the TWA 3 Triple M Dwarf System

We present sensitive ALMA observations of TWA 3, a nearby, young (similar to 10 Myr) hierarchical system composed of three pre-main-sequence M3-M4.5 stars. For the first time, we detected (CO)-C-12 and (CO)-C-13 J = 2-1 emissions from the circumbinary protoplanetary disk around TWA 3A. We jointly fit the protoplanetary disk velocity field, stellar astrometric positions, and stellar radial velocities to infer the architecture of the system. The Aa and Ab stars (0.29 +/- 0.01 M (circle dot) and 0.24 +/- 0.01 M (circle dot), respectively) comprising the tight (P = 35 days) eccentric (e = 0.63 +/- 0.01) spectroscopic binary are coplanar with their circumbinary disk (misalignment <6 degrees with 68% confidence), similar to other short-period binary systems. From models of the spectral energy distribution, we found the inner radius of the circumbinary disk (r (inner) = 0.50-0.75 au) to be consistent with theoretical predictions of dynamical truncation r (cav)/a (inner) approximate to 3. The outer orbit of the tertiary star B (0.40 +/- 0.28 M (circle dot), a similar to 65 +/- 18 au, e = 0.3 +/- 0.2) is not as well constrained as the inner orbit; however, orbits coplanar with the A system are still preferred (misalignment < 20 degrees). To better understand the influence of the B orbit on the TWA 3A circumbinary disk, we performed SPH simulations of the system and found that the outer edge of the gas disk (r (outer) = 8.5 +/- 0.2 au) is most consistent with truncation from a coplanar, circular, or moderately eccentric orbit, supporting the preference from the joint orbital fit.

Automated summary

The sensitive ALMA observations of TWA 3 revealed the structure of a young hierarchical system with three pre-main-sequence stars. The inner and outer orbits of the system's protoplanetary disk are consistent with theoretical predictions, while the influence of the outer orbit of star B on TWA 3A's circumbinary disk is primarily related to coplanarity.