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2MASS J20261584–2943124: an Unresolved L0.5 + T6 Spectral Binary
We identify the L dwarf 2MASS J20261584–2943124 as an unresolvedspectral binary, based on low-resolution, near-infrared spectroscopyfrom IRTF/SpeX. The data reveal a peculiar absorption feature at 1.6?m, previously noted in the spectra of other very low-mass spectralbinaries, which likely arises from overlapping FeH and CH4absorption bands in the blended light of an L dwarf/T dwarf pair.Spectral template matching analysis indicates component types of L0.5and T6, with relative brightness ?H = 4.2 ± 0.6. Laserguide star adaptive optics imaging observations with Keck/NIRC2 fail toresolve the source, indicating a maximum separation at the observingepoch of 0farcs25, or a projected separation of 9 AU assuming a distanceof 36 ± 5 pc. With an age that is likely to be relatively older(gsim5 Gyr) based on the system's large V tan and mass ratioarguments, the relative motion of the potentially "massive" (0.06-0.08 Msun) components of 2MASS J2026–2943 may be detectablethrough radial velocity variations, like its earlier-type counterpart2MASS J03202839–0446358 (M8+T5), providing dynamical massmeasurements that span the hydrogen burning limit.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
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