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

Abstract

ABSTRACTWe 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 dwarf spectral types from late K to early M that could be identified by ultra–wide‐field transit surveys such as SuperWASP. These surveys will monitor approximately a million K and M dwarfs with |b|>20° (where blending of sources is not a significant problem) at a level sufficient to detect transits of low‐luminosity companions. We look at the current observational evidence for such systems and suggest that ∼1% of late K and early‐to‐mid M dwarfs could have a very close (∼0.02 AU) brown dwarf companion. With this assumption, and using SuperWASP 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 from radial velocity and follow‐up light curve measurements. By inferring the brown dwarf effective temperature distribution, assuming a uniform age spread and an α = 0.5 companion brown dwarf mass function, the simulation estimates that brown dwarf brightness could also be measurable (at the 10% level) for ∼60 of these binary systems from near‐infrared follow‐up light curves of the secondary eclipse. We consider irradiation of these brown dwarfs by their primary stars and conclude that it would be below the 10% level for ∼70% of them. This means that in these cases, the measured brown dwarf brightnesses should essentially be the same as those of free‐floating counterparts. The predicted age distribution of the primaries is dominated by young systems, and ∼20 binaries could be younger than 1 Gyr. Irradiation will be below the 10% level for ∼80% of these. We suggest that many of these young binary systems will be members of “kinematic moving groups,” allowing their ages to be accurately constrained.