AN EXPANDED SET OF BROWN DWARF AND VERY LOW MASS STAR MODELS

We present in this paper updated and improved theoretical models of brown dwarfs and late M dwarfs (VLMs). The evolution and characteristics of objects between 0.01 and 0.2 M. are exhaustively investigated and special emphasis is placed on their properties at early ages (10(6)-10(8) yr). The dependence on the helium fraction, deuterium fraction, and metallicity of the masses, effective temperature and luminosities at the edge of the hydrogen main sequence are calculated. We derive luminosity functions for representative mass functions and compare our predictions to recent cluster data. We show that there are distinctive features in the theoretical luminosity functions that can serve as diagnostics of brown dwarf physics. A zero-metallicity model is presented as a bound to or approximation of a putative extreme halo population. This study is a continuation of that of Burrows, Hubbard, & Lunine (1989) and is meant to provide an expanded set of standard stellar models both just above and below the lower main-sequence edge for comparison with the new data in clusters, binaries, and in the field.