Testing Substellar Models with Keck LGS AO Dynamical Masses

Trent Dupuy (IfA/Hawaii)

Substellar theoretical models are now widely used in many areas of
active research, from the determination of the IMF to the
characterization of directly imaged planets.  However, despite their
extensive use, these models have not been tested over much of the
relevant parameter space.  We are using Keck laser guide star adaptive
optics (LGS AO) to monitor the orbits of brown dwarf binaries, thereby
measuring dynamical masses and providing the strongest tests of
substellar models to date.  Our program has already doubled the number
of brown dwarfs with dynamical masses, extending such measurements to
much lower temperatures than previous work.  We find that theoretical
models harbor significant systematic errors as they do not accurately
reproduce observed colors or temperatures.  Also, model luminosities
may be under predicted by a factor of ~2-3, and thus model-derived
masses for directly imaged planets and the IMF may be too high.
Infrared parallaxes from our CFHT/WIRCam astrometric program will be
essential for extending mass measurements to a larger sample of
binaries.  This growing sample of brown dwarf binaries is beginning to
provide novel tests of star/brown dwarf formation models as, for
example, the observed eccentricity distribution can already
discriminate between different brown dwarf formation models.