High precision dynamical masses for brown dwarf binaries

We present new dynamical mass estimates for a sample of brown dwarf binaries with sufficient precision (< 10%) to distinguish between current theoretical evolutionary models. This survey, which has targeted 20 sources between spectral types M8 and T5, is enabled by the advent of laser guide star adaptive optics (LGS AO) on the Keck II 10 m telescope. The LGS AO system allows for both high precision (δpos < 1 mas) astrometry and spatially resolved, high-resolution spectroscopy (δrv < 1 km/s). A striking result from this work thus far is that for two systems with precisely determined dynamical masses and similar spectral types, both evolutionary models considered correctly predict the mass in one case but underpredict the mass by several sigma in the other case. We postulate that this discrepancy may either stem from a disjoint between evolutionary and atmospheric models at the M/L transition due to atmospheric dust treatment or potentially from magnetic activity inhibiting convection.