Astrophys. J., 681, 579-593 (2008/July-1)
Subtle signatures of multiplicity in late-type dwarf spectra: the unresolved M8.5 + T5 binary 2MASS J03202839-0446358.
BURGASSER A.J., LIU M.C., IRELAND M.J., CRUZ K.L. and DUPUY T.J.
Abstract (from CDS):
Evidence is presented that 2MASS J03202839-0446358, a late-type dwarf with discrepant optical (M8:) and near-infrared (L1) spectral types, is an as-yet unresolved stellar/brown dwarf binary with late-type M dwarf and T dwarf components. This conclusion is based on low-resolution, near-infrared spectroscopy that reveals a subtle but distinctive absorption feature at 1.6 µm. The feature, which is also present in the combined light spectrum of the M8.5 + T6 binary SCR 1845-6357, arises from the combination of FeH absorption from an M8.5 primary and pseudocontinuum flux from a T5±1 secondary, as ascertained from binary spectral templates constructed from empirical data. The binary templates provide a far superior match to the overall near-infrared spectral energy distribution of 2MASS J0320-0446 than any single comparison spectra. Laser guide star adaptive optics (LGS AO) imaging observations, including the first application of LGS AO aperture mask interferometry, fail to resolve a faint companion, restricting the projected separation of the system to less than 8.3 AU at the time of observation. 2MASS J0320-0446 is the second very low mass binary to be identified from unresolved, low-resolution, near-infrared spectroscopy, a technique that complements traditional high-resolution imaging and spectroscopic methods.
Stars: Binaries: General - Stars: Fundamental Parameters - Stars: Individual - Stars: Low-Mass, Brown Dwarfs
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