2MASS 22344161+4041387AB: A WIDE, YOUNG, ACCRETING, LOW-MASS BINARY IN THE LkHα233 GROUP

We report the discovery of a young, 0 ''.16 binary, 2M2234+4041AB, found as the result of a Keck laser guide star adaptive optics imaging survey of young field ultracool dwarfs. Spatially resolved near-infrared photometry and spectroscopy indicate that the luminosity and temperature ratios of the system are near unity. From optical and near-infrared spectroscopy, we determine a composite spectral type of M6 for the system. Gravity-sensitive spectral features in the spectra of 2M2234+4041AB are best matched to those of young objects (similar to 1 Myr old). A comparison of the T(eff) and age of 2M2234+4041AB to evolutionary models indicates that the mass of each component is 0.10(-0.04)(+0.075) M(circle dot). Emission lines of H alpha in the composite optical spectrum of the system and Br gamma in spatially resolved near-IR spectra of the two components indicate that the system is actively accreting. Both components of the system have IR excesses, indicating that they both harbor circumstellar disks. Though 2M2234+4041AB was originally identified as a young field dwarf, it lies 1'.5 from the well-studied Herbig Ae/Be star, LkH alpha 233. The distance to LkH alpha 233 is typically assumed to be 880 pc. It is unlikely that 2M2234+4041AB could be this distant, as it would then be more luminous than any known Taurus objects of similar spectral type. We re-evaluate the distance to the LkH alpha 233 group and find a value of 325(-50)(+72) pc, based on the Hipparcos distance to a nearby B3-type group member (HD 213976). 2M2234+4041AB is the first low-mass star to be potentially associated with the LkH alpha 233 group. At a distance of 325 pc, its projected physical separation is 51 AU, making it one of the growing number of wide, low-mass binaries found in young star-forming regions.