Burgasser, Adam J. and Kirkpatrick, J. Davy and Reid, I. Neill and Brown, Michael E. and Miskey, Cherie L. and Gizis, John E. (2003) Binarity in Brown Dwarfs: T Dwarf Binaries Discovered with the Hubble Space Telescope Wide Field Planetary Camera 2. Astrophysical Journal, 586 (1). pp. 512-526. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20120926-090054521
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We present the discovery of two T dwarf binaries, 2MASS 1225-2739AB and 2MASS 1534-2952AB, identified in a sample of 10 T dwarfs imaged with the Hubble Space Telescope (HST) Wide Field Planetary Camera 2. Companionship is established by the uniquely red F814W-F1042M colors of the binary components, caused by heavily pressure-broadened K I absorption centered at 7665 and 7699 Å. The separations of the two binary systems are 0."282 ± 0."005 and 0."065 ± 0."007, implying projected separations of 3.17 ± 0.14 and 1.0 ± 0.3 AU, respectively. These close separations are similar to those found in previous brown dwarf binary searches and permit orbital mapping over the coming decade. 2MASS 1225-2739AB has a substantially fainter secondary, with ΔM_(F814W) = 1.59 ± 0.04 and ΔM_(F1042M) = 1.05 ± 0.03; this system is likely composed of a T6 primary and T8 secondary with mass ratio 0.7-0.8. The observed binary fraction of our HST sample, 20^(+17%)_(-1), is consistent with results obtained for late-type M and L field dwarfs and implies a bias-corrected binary fraction of 9^(+15%)_(-4) for α ≳ 1 AU and q ≳ 0.4, significantly lower than the binary fractions of F-G and early-type M dwarf stars. Neither of the T binaries have separations α ≳ 10 AU, consistent with results from other brown dwarf binary searches. Using the statistical models of Weinberg, Shapiro, & Wasserman, we conclude that tidal disruption by passing stars or giant molecular clouds, which limits the extent of wide stellar binaries, plays no role in eliminating wide brown dwarf binaries, implying either disruption very early in the formation process (ages ≾ 1-10 Myr) or a formation mechanism that precludes such systems. We find that the maximum binary separation in the brown dwarf regime appears to scale as M^2_(total), a possible clue to the physical mechanism that restricts wide substellar systems.
|Additional Information:||© 2003 American Astronomical Society. Received 2002 September 12; accepted 2002 November 21. We thank our referee, L. Close, for in-depth criticisms and helpful suggestions for our manuscript, and useful discussions on wide stellar binaries. We also thank A. Ghez, D. Koerner, & J. Liebert for discussions on disks and binary star formation, and D. Koerner and A. Dolphin for useful discussions on PSF fitting. A. J. B. acknowledges support by NASA through Hubble Fellowship grant HST-HF-01137.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. J. D. K. acknowledges the support of the Jet Propulsion Laboratory, California Institute of Technology, which is operated under contract with the National Aeronautics and Space Administration. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with proposal ID 8563. This publication makes use of data from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation.|
|Subject Keywords:||binaries: visual; stars: formation; stars: fundamental parameters; stars: individual (2MASS J12171110–0311131, 2MASS J12255432–2739466, 2MASS J15344984–2952274); stars: low-mass, brown dwarfs|
|Official Citation:||Binarity in Brown Dwarfs: T Dwarf Binaries Discovered with the Hubble Space Telescope Wide Field Planetary Camera 2 Adam J. Burgasser et al. 2003 ApJ 586 512|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||26 Sep 2012 16:33|
|Last Modified:||27 Dec 2012 02:43|
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