Evolutionary Models for Ultracool Dwarfs

Abstract

Ultracool dwarfs have emerged as key targets for searches of transiting exoplanets. Precise estimates of the host parameters (including mass, age, and radius) are fundamental to constrain the physical properties of orbiting exoplanets. We have extended our evolutionary code CLES (Code Liegeois d Evolution Stellaire) to the ultracool dwarf regime. We include relevant equations of state for H, He, as well as C and O elements to cover the temperature-density regime of ultracool dwarf interiors. For various metallicities, we couple the interior models to two sets of model atmospheres as surface boundary conditions. We show that including C and O in the EOS has a significant effect close the H-burning limit mass. The typical systematic error associated with uncertainties in input physics in evolutionary models is $\\sim 0.0005 M_\\odot$. We test model results against observations for objects whose parameters have been determined from independent techniques. We are able to reproduce dynamical mass measurements of LSPM J1314+1320AB within $1\\sigma$ with the condition of varying the metallicity (determined from calibrations) up to $2.5\\sigma$. For GJ 65AB, a $2\\sigma$ agreement is obtained between individual masses from differential astrometry and those from evolutionary models. We provide tables of ultracool dwarf models for various masses and metallicities that can be used as reference when estimating parameters for ultracool objects.