Testing Theory with Dynamical Masses and Orbits of Ultracool Binaries
Harvard-Smithsonian Center for Astrophysics
Direct mass measurements are essential to test the evolutionary and atmospheric models that underpin studies of very low-mass objects. I will present results from our program to test models using precise dynamical masses (as good as 2%) for ultracool binaries, based on IR parallaxes from CFHT, near-IR spectroscopy, and Keck laser guide star AO astrometric monitoring since 2005. Over the past 3 years we have more than tripled the number of late-M, L, and T dwarf binaries with dynamical masses. I will discuss the discrepancies we have found between models and observations, ranging from problems with colors, temperatures, and even luminosity evolution. The potential luminosity problem implies that model-based mass determinations (e.g., for directly imaged planets) may be systematically overestimating masses. Finally, I will show how our sample of binary orbits provides a novel test of the earliest evolutionary stages, by using the distribution of orbital eccentricities to distinguish between competing models of brown dwarf formation.
Date: Thursday, 3 November 2011 Time: 11:30 Where: Université de Montréal Pavillon Roger-Gaudry, local D-460 Contact: David Lafrenière