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

Abstract

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 micron. 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 pseudo-continuum 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.

19 pages, 8 figures; accepted for publication to ApJ (submitted 4 January 2008)

References in corpus (14)

• Meeting the Cool Neighbors. IX. The Luminosity Function of M7-L8 Ultracool Dwarfs in the Field
• Discovery of Two T Dwarf Companions with the Spitzer Space Telescope
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• Mapping the Shores of the Brown Dwarf Desert I.: Upper Scorpius
• Discovery of 11 New T Dwarfs in the Two Micron All-Sky Survey, Including a Possible L/T Transition Binary
• Physical and Spectral Characteristics of the T8 and Later-Type Dwarfs
• The Physical Properties of HD 3651B: An Extrasolar Nemesis?
• Multiepoch Radial Velocity Observations of L Dwarfs
• Discovery of a High Proper Motion L Dwarf Binary: 2MASS J15200224-4422419AB
• Dynamical Mass of GJ 802B: a brown dwarf in a triple system
• SDSS J080531.84+481233.0: An Unresolved L Dwarf/T Dwarf Binary
• Discovery of a nearby L-T transition object in the Southern Galactic plane
• Discovery of a 66 mas Ultracool Binary with Laser Guide Star Adaptive Optics
• On the Nature of the Unique H$\alpha$-Emitting T Dwarf 2MASS J12373919+6526148

Cited by in corpus (8)

• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• Discovery of a T Dwarf Binary with the Largest Known J-Band Flux Reversal
• Measuring tiny mass accretion rates onto young brown dwarfs
• Keck Laser Guide Star Adaptive Optics Monitoring of the M8+L7 Binary LHS 2397aAB: First Dynamical Mass Benchmark at the L/T Transition
• An Infrared High Proper Motion Survey Using 2MASS and SDSS: Discovery of M, L and T Dwarfs
• An Age Constraint for the Very Low-Mass Stellar/Brown Dwarf Binary 2MASS J03202839-0446358AB
• Proper motions of field L and T dwarfs -II
• LGS AO Science Impact: Present and Future Perspectives