The Prospects for Finding Brown Dwarfs in Eclipsing Binary Systems and Measuring Brown Dwarf Properties

Abstract

We present the results of a simulation to investigate the prospects of measuring mass, age, radius, metallicity and luminosity data for brown dwarfs in fully eclipsing binary systems around late K and early M dwarfs identified by ultra-wide-field transit surveys. These surveys will monitor approximately a million K and M dwarfs at a level sufficient to detect transits of low luminosity companions. We look at the current observational evidence for such systems, and suggest that about 1% of late K and early-mid M dwarfs could have a very close BD companion. With this assumption, and using the SuperWASP transit survey as an example, our simulation predicts that 400 brown dwarfs in fully eclipsing binary systems could be discovered. All of these eclipsing binaries could yield accurate brown dwarf mass and radius measurements. By inferring the brown dwarf effective temperature distribution, assuming a uniform age spread and an alpha=0.5 companion brown dwarf mass function, the simulation estimates that brown dwarf brightness could also be measurable (at the 10% level) for about 60 of these binary systems from the secondary eclipse. Irradiation of the brown dwarfs will be below the 10% level for about 70% of these systems, meaning that the measured brown dwarf brightnesses should generally be the same as those of free-floating counterparts. The predicted age distribution of the primaries is dominated by young systems, and about 20 binaries could be younger than 1Gyr. We suggest that many of these young binary systems will be members of ``kinematic moving groups'', allowing their ages to be accurately constrained.