High Precision Dynamical Masses of Pre-Main Sequence Stars with ALMA and Gaia

The Keplerian rotation in protoplanetary disks can be used to robustly measure stellar masses at very high precision if the source distance is known. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of spatially and spectrally resolved $^{12}$CO (2--1) emission towards the disks around 2MASS J16262774--2527247 (the tertiary companion to ROXs 12 at 5100 au), CT Cha, and DH Tau. We employ detailed modeling of the Keplerian rotation profile, coupled with accurate distances from $Gaia$, to directly measure the stellar masses with $\sim$2\% precision. We also compare these direct mass measurements with the masses inferred from evolutionary models, determined in a statistically rigorous way. We find that 2MASS J16262774--2527247 has a mass of $0.535^{+0.006}_{-0.007}~M_{\odot}$ and CT Cha has a mass of $0.796^{+0.015}_{-0.014}~M_{\odot}$, broadly consistent with evolutionary models, although potentially significant differences remain. DH Tau has a mass of $0.101^{+0.004}_{-0.003}~M_{\odot}$, but it suffers from strong foreground absorption that may affect our mass estimate. The combination of ALMA, $Gaia$, and codes like \texttt{pdspy}, presented here, can be used to infer the dynamical masses for large samples of young stars and substellar objects, and place constraints on evolutionary models.