Description
We obtained high signal-to-noise intermediate-resolution (R~6000-11000) optical (600-1000nm) and near-infrared (1000-2480nm) spectra of each component of the the closest brown dwarf binary, Luhman 16AB, with X-Shooter on the Very Large Telescope (VLT). We classify the primary and secondary as L6-L7.5 and T0+/-1, respectively, in agreement with previous measurements. We present measurements of the lithium pseudo-equivalent widths, which appears of similar strength on both components. The presence of lithium (^7^Li) in both components imply masses below 0.06M_{sun} while comparison with models suggests lower limits of 0.04M_{sun}. The detection of lithium in the T component is the first of its kind. Similarly, we assess the strength of other alkali lines (e.g. 6-7{AA} for RbI and 4-7{AA} for CsI features) and compare them with estimates for L and T dwarfs. We also derive effective temperatures and luminosities of each component of the binary (-4.66dex, 1305K) and (-4.68dex, 1320K) for the L and T dwarf, respectively. Using our radial velocity determinations, the binary does not appear to belong to any of the well-known moving group. Our preliminary theoretical analysis of the optical and J-band spectra indicates that the L- and T-type spectra can be reproduced with a single temperature and gravity but different relative chemical abundances which impact strongly the spectral energy distribution of L/T transition objects.
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