Use of the highly sensitive Hokupa'a curvature wavefront sensor has allowed for the first time direct adaptive optics (AO) guiding on brown dwarfs and VLM stars (SpT=M7-L2). An initial survey of 9 such objects discovered one 0.15" binary (2MASSJ 1426316+155701). The companion is about half as bright as the primary (Delta K = 0.61+/-0.05$, Delta H = 0.70+/-0.05) and has even redder colors H-K=0.59+/-0.14 than the primary. The blended spectrum of the binary has been previously determined to be M9.0. We modeled a blend of an M8.5 template and a L1-L3 template reproducing a M9.0 spectrum in the case of Delta K = 0.61+/-0.05,Delta H = 0.70\pm0.05$. These spectral types also match the observed H-K colors of each star. Based the previously observed low space motion and $H_{ \alpha}$ activity we assign an age of $0.8^{ +6.7}_{ -0.3} Gyr$. Utilizing this age range and the latest DUSTY models of the Lyon group we assign a photometric distance of $18.8^{ +1.44}_{ -1.02} pc$ and masses of $M_{ A}=0.074^{ +0.005}_{ -0.011} M_\odot$ and $M_{ B}=0.066^{ +0.006}_{ -0.015} M_\odot$. We therefore estimate a system separation of $2.92_{ +0.22}^{ -0.16}AU$ and a period of $13.3{ +3.18}^{ -1.51} yr$ respectively. Hence, 2M1426 is among the smallest separation brown dwarf binaries resolved to date.
Categories: astro-ph