The Fundamental Properties of Young Stars

Accurate knowledge of the fundamental properties of stars--mass, temperature, and luminosity--are key to our understanding of stellar evolution. In particular, empirical measurements of stellar mass are difficult to make and are generally limited to stars that dynamically interact with a companion (e.g., eclipsing or astrometric binaries), a precious but ultimately small sample. First, I will discuss my development of a recent technique that uses the rotation of the protoplanetary disk--a consequence of the star formation process and still present around many pre-main sequence stars--to measure the stellar mass. To vet the absolute accuracy of this technique, I led the analysis of an ALMA Cycle 1/2 program to observe the few circumbinary disks around double-lined spectroscopic binary stars, enabling an independent confirmation of the total stellar mass. Our comparison with radial-velocity results demonstrates that the disk-based dynamical mass technique can reliably achieve precise measurements of stellar mass on the order of 2-5%, clearing the way for widespread application of this technique to measure the masses of *single* stars. Second, I will discuss our development of novel statistical techniques for spectroscopic inference. Young stars exhibit rich and variable spectra; although interesting phenomena in their own right, accretion veiling and star spots complicate the retrieval of accurate photospheric properties. Moreover, the uncertain spectral type--effective temperature scale for low mass pre-main sequence stars introduces a systematic error when placing a star on the Hertzsprung Russell diagram. The Gaussian process techniques we have developed to address these problems are also generally applicable to a wide range of spectroscopic problems. Lastly, I will discuss recent progress in measuring the masses of a large sample of single pre-main sequence stars observed with the Submillimeter Array, which will double the number of disk-based dynamical mass estimates of pre-main sequence stars. With ALMA, the disk-based technique holds enormous promise to become the primary means of stellar mass for statistically large samples of pre-main sequence stars, ushering in a new era of high precision in star and planet formation studies.