AN AGE CONSTRAINT FOR THE VERY LOW MASS STELLAR/BROWN DWARF BINARY 2MASS J03202839-0446358AB

Abstract

2MASS J03202839–0446358AB is a recently identified, late-type M dwarf/T dwarf spectroscopic binary system for which both the radial velocity orbit for the primary and spectral types for both components have been determined. By combining these measurements with predictions from four different sets of evolutionary models, we determine a minimum age of 2.0 ± 0.3 Gyr for this system, corresponding to minimum primary and secondary masses of 0.080 M sun and 0.053 M sun, respectively. We find broad agreement in the inferred age and mass constraints between the evolutionary models, including those that incorporate atmospheric condensate grain opacity; however, we are not able to independently assess their accuracy. The inferred minimum age agrees with the kinematics and absence of magnetic activity in this system, but not the rapid rotation of its primary, further evidence of a breakdown in angular momentum evolution trends amongst the lowest luminosity stars. Assuming a maximum age of 10 Gyr, we constrain the orbital inclination of this system to i gsim 53°. More precise constraints on the orbital inclination and/or component masses of 2MASS 0320–0446AB, through either measurement of the secondary radial velocity orbit (optimally in the 1.2-1.3 μm band) or detection of an eclipse (only 0.3% probability based on geometric constraints), would yield a bounded age estimate for this system, and the opportunity to use it as an empirical test for brown dwarf evolutionary models at late ages.