2MASS J20261584–2943124: an Unresolved L0.5 + T6 Spectral Binary

Creators: Gelino, Christopher R.; Burgasser, Adam J.

Abstract

We identify the L dwarf 2MASS J20261584–2943124 as an unresolved spectral binary, based on low-resolution, near-infrared spectroscopy from IRTF/SpeX. The data reveal a peculiar absorption feature at 1.6 μm, previously noted in the spectra of other very low-mass spectral binaries, which likely arises from overlapping FeH and CH4 absorption bands in the blended light of an L dwarf/T dwarf pair. Spectral template matching analysis indicates component types of L0.5 and T6, with relative brightness ΔH = 4.2 ± 0.6. Laser guide star adaptive optics imaging observations with Keck/NIRC2 fail to resolve the source, indicating a maximum separation at the observing epoch of 0".25, or a projected separation of 9 AU assuming a distance of 36 ± 5 pc. With an age that is likely to be relatively older (≳ 5 Gyr) based on the system's large V_(tan) and mass ratio arguments, the relative motion of the potentially "massive" (0.06-0.08 M_⊙) components of 2MASS J2026–2943 may be detectable through radial velocity variations, like its earlier-type counterpart 2MASS J03202839–0446358 (M8+T5), providing dynamical mass measurements that span the hydrogen burning limit.

Additional Information

© 2010 The American Astronomical Society. Received 2010 March 31; accepted 2010 April 29; published 2010 May 26. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors acknowledge telescope operators Bill Golisch, Paul Sears, and Eric Volquardsen, and instrument specialist John Rayner at IRTF; and Hien Tran and Jason McIlroy at Keck, for their assistance during the observations. We also thank the referee, Kevin Luhman, for his very prompt and helpful review. This publication makes use of data from the Two Micron All Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, and funded by the National Aeronautics and Space Administration and the National Science Foundation. 2MASS data were obtained from the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has benefitted from the M, L, and T dwarf compendium housed at http://DwarfArchives.org and maintained by Chris Gelino, Davy Kirkpatrick, and Adam Burgasser; the Very-Low-Mass Binaries Archive housed at http://www.vlmbinaries.org and maintained by Nick Siegler, Chris Gelino, and Adam Burgasser; and the SpeX Prism Spectral Libraries, maintained by Adam Burgasser at http://www.browndwarfs.org/spexprism. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: IRTF (SpeX), Keck:II (NIRC2,LGS)

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