* Astronomy

Title: Dynamical Mass of GJ 802B: a brown dwarf in a triple system
Authors: M.J. Ireland, A. Kraus, F. Martinache, J.P. Lloyd, P.G. Tuthill

We report a dynamical measurement of the mass of the brown dwarf GJ 802B using aperture-masking interferometry and astrometry. In addition, we report the discovery that GJ 802A is itself a close spectroscopic non-eclipsing binary with a 19 hour period. We find the mass of GJ 802B to be 0.063 ±0.005 solar masses. GJ 802 has kinematics inconsistent with a young star and more consistent with the thick disk population, implying a system age of ~10 GYr. However, model evolutionary tracks for GJ 802B predict system ages of  ~ 2 GYr, suggesting that brown dwarf evolutionary models may be underestimating luminosity for old brown dwarfs.

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