2MASS Brown Dwarfs and the Substellar Mass Function

Session 55 - New Digital Sky Surveys.
Display session, Wednesday, June 10
Atlas Ballroom,

[55.17] 2MASS Brown Dwarfs and the Substellar Mass Function

I. N. Reid (Palomar Obs., Caltech), D. Kirkpatrick, C. A. Beichman (IPAC, Caltech), J. Liebert, A. Burrows (U. Arizona), M. Skrutskie (U. Massachusetts)

Analysis of a complete sample of brown dwarf candidates with (J-K) > 1.30 and K < 14.5, drawn from 2MASS observations of 420 square degrees, or 1 percent of the sky, confirms 17 sources as extremely cool, meta-M dwarfs. Five of the 17 have detectable (> 2 Åequivalent width) lithium absorption in Keck LRIS spectra, implying masses of less than 0.07 solar masses. While none of these objects has a measured parallax, we have compared the observed effective temperature and lithium-depletion distributions against predictions based on Monte Carlo simulations. The latter use the recent Burrows et al theoretical calculations to model brown dwarf characteristics (L(M, t), Temp(M, t)), and, based on a variety of assumed mass functions and star-formation histories, predict the (K, (J-K)) colour-magnitude diagram described by local brown dwarfs. These simulations can be "observed" with 2MASS-equivalent filter. This paper presents the initial results from comparisons between the models and reality.

Program listing for Wednesday