The Brown Dwarf Eclipsing Binary 2M0535−05: A Case Study for Activity Effects on Physical Properties of Low-Mass Stars and Brown Dwarfs

Department of Physics & Astronomy, Vanderbilt University, VU Station B 1807, Nashville, TN, USA

Abstract

2M0535−05 is a one-of-a-kind eclipsing binary (EB) comprising two brown dwarfs (BDs), and is an important benchmark for understanding the fundamental properties of BDs and low-mass stars. Because 2M0535−05 presents a peculiar reversal of temperatures with mass (the higher mass, magnetically active BD in the system is cooler than the lower mass companion BD), 2M0535−05 is particularly important as a case study for the effects of magnetic activity on the properties of low-mass objects. Using a large number of low-mass M-dwarfs and EBs in the field, we have developed empirical relations for determining the amount by which the temperatures and radii–and therefore the estimated masses–of low-mass stars and BDs are altered due to chromospheric activity. The relations link the amount by which an active object's temperature is suppressed, and its radius inflated, to the strength of its Hα emission. These relations are found to approximately preserve bolometric luminosity. Applying these relations to 2M0535−05 brings the activity-corrected radii and temperatures of 2M0535−05 into precise agreement with theoretical isochrones for inactive stars. The relations that we present are applicable to BDs and low-mass stars with masses below 0.8 M_⊙ and for which the activity, as measured by Hα, is in the range − 4.6 < log L_Hα/L_bol < −3.3. We discuss implications of this work for determinations of young cluster IMFs, and discuss competing ideas for the physical mechanism by which magnetic fields alter the temperatures and radii of low-mass stars.