Discovery of a 0.̋15 Binary Brown Dwarf, 2MASS J1426316+155701, with Gemini/Hokupa’a Adaptive Optics

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Abstract
Use of the highly sensitive Hokupa'a curvature wave front sensor has allowed for the first time direct adaptive optics (AO) guiding on brown dwarfs and very low mass stars (spectral type M7-L2). An initial survey of nine such objects discovered one 015 binary (2MASS J1426316+155701). The companion is about half as bright as the primary (ΔK = 0.61 ± 0.05, ΔH = 0.70 ± 0.05) and has even redder colors, H-K = 0.59 ± 0.14, than the primary. The blended spectrum of the binary has been previously determined to be M9.0. We modeled a blend of an M8.5 template and an L1-L3 template, reproducing a M9.0 spectrum in the case of ΔK = 0.61 ± 0.05, ΔH = 0.70 ± 0.05. These spectral types also match the observed H-K colors of each star. Based the previously observed low space motion and Hα activity, we assign an age of 0.8 Gyr. Utilizing this age range and the latest DUSTY models of the Lyon group, we assign a photometric distance of 18.8 pc and masses of MA = 0.074 M☉ and MB = 0.066 M☉. We therefore estimate a system separation of 2.92 AU and a period of 13.3 yr. Hence, 2MASS J1426316+155701 is among the smallest-separation brown dwarf binaries resolved to date.
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