Subtle Signatures of Multiplicity in Late-type Dwarf Spectra: The Unresolved M8.5 + T5 Binary 2MASS J03202839-0446358

• Main Authors: Burgasser, Adam J. (Contributor), Liu, Michael C. (Author), Ireland, Michael J. (Author), Cruz, Kelle L. (Author), Dupuy, Trent J. (Author)
• Other Authors: MIT Kavli Institute for Astrophysics and Space Research (Contributor)
• Format: Article
• Language: English
• Published: American Astronomical Society, 2011-12-06T15:15:43Z.
• Subjects: Article
• Online Access: Get fulltext

 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 μ m . 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.