1206.4930 (Keivan G. Stassun et al.)

An Empirical Correction for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-Mass Stars and Brown Dwarfs    [PDF]

Keivan G. Stassun, Kaitlin M. Kratter, Aleks Scholz, Trent J. Dupuy

We present an empirical relations for correcting the estimated masses, effective temperatures, and radii of chromospherically active low-mass stars and brown dwarfs. We base our corrections on a large set of low-mass stars in the field with Halpha activity measurements, and on a set of low-mass eclipsing binaries with X-ray activity measurements from which we indirectly infer the Halpha activity. Both samples yield consistent relations linking the amount by which an active object's temperature is suppressed, and the amount by which its radius is inflated, to the strength of its Halpha emission. Bolometric luminosity is found to be approximately preserved by these temperature and radius corrections. We apply these relations to the peculiar brown-dwarf eclipsing binary 2M0535-05, in which the active, higher-mass brown dwarf has a cooler temperature than its inactive, lower-mass companion. We find that the Halpha-corrected temperatures bring the inferred masses of the brown dwarfs into agreement with theoretical isochrones. These empirical relations are applicable to brown dwarfs and low-mass stars with masses below 0.8 Msun and for which the activity, as measured by the fractional Halpha luminosity, is in the range -4.6 < log LHa/Lbol < -3.3. We expect these corrections to be most useful for improving temperatures and radii of low-mass stars and brown dwarfs over their active lifetimes (few Gyr) and thereby also the inferred masses of objects with unknown ages or distances (and therefore unknown luminosities). We also discuss the implications of this work for improved determinations of young cluster initial mass functions.

View original: http://arxiv.org/abs/1206.4930