STRUCTURAL EFFECTS OF MAGNETIC FIELDS IN BROWN DWARFS

In the brown dwarf (BD) binary 2M0535-05, Stassun et al. have reported that the more massive primary has a lower T-eff than the less massive secondary. Here, we report results obtained by an evolutionary code in which the criterion for the onset of convection in the primary is modified in the presence of a magnetic field. Structural alterations to the primary lead to a lower T-eff and a larger radius than would occur in a non-magnetic BD of the same age mass and age. The observed value of T-eff can be explained if the field in the primary increases in strength from 120-320 G at the surface to 5-13 MG at the center. With zero field in the secondary, our models indicate that both components can be co-eval with an age of 1.0-1.3 Myr. Because the binary is so young, the components have not yet had time to synchronize their rotations: differences in angular velocity may explain why one component has developed a field while the other has not.