Theoretical models of low-mass stars and brown dwarfs. I - The lower main sequence

Theoretical models are calculated for stars on the hydrogen-burning lower main sequence having masses less than or equal to 0.55 solar mass. Particular attention has been paid to the treatment of the atmosphere and envelope and to the choice of the radiative opacities and equation of state. The dependence of the model properties on the outer boundary conditions is examined, with a detailed comparison of models constructed using two independent determinations of the equation of state. It is found that the theoretically inferred properties of stars of mass less than about 0.10 solar mass can differ noticeably depending on the assumed input physics.