Authors

Trent Dupuy (1), Michael Liu (2)

Affiliations

(1) CfA/SAO; (2) IfA/Hawaii

Abstract

Converting direct observations of light into temperatures, surface gravities, and masses is essential for determining the physical properties and origins of extrasolar planets. We critically examine the accuracy of current evolutionary and atmospheric models used to derive physical properties for substellar objects, based on our Keck and CFHT astrometric monitoring of ultracool brown dwarf binaries. In just the last 2 years, we have more than tripled the number of late-M, L, and T dwarf binaries with precise dynamical masses (as good as 2%). By combining high quality data for their fluxes, temperatures, dynamical masses, and ages, these binaries open the door to rigorous tests of models at temperatures and luminosities comparable to that of giant planets found by directly imaging. Our sample includes systems as young as 100-500 Myr, overlapping the ages probed by current and upcoming planet-imaging instruments. For most of the field population, we find systematic errors in the temperatures derived by evolutionary and atmospheric models, at the level of 200 K (or 30-40% in radius). For the binaries with well-determined ages, we find that evolutionary models systematically underpredict the luminosities by a factor of 2 at a given mass. One implication of this finding is that model-derived results for directly imaged substellar objects may systematically overestimate their masses.