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Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition

Burgasser, Adam J. and Kirkpatrick, J. Davy and Cruz, Kelle L. and Reid, I. Neill and Leggett, Sandy K. and Liebert, James and Burrows, Adam and Brown, Michael E. (2006) Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition. Astrophysical Journal Supplement Series, 166 (2). pp. 585-612. ISSN 0067-0049.

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We present the results of a Hubble Space Telescope NICMOS imaging survey of 22 T-type field brown dwarfs. Five are resolved as binary systems with angular separations of 0".05-0".35, and companionship is established on the basis of component F110W - F170M colors (indicative of CH_4 bsorption) and low probabilities of background contamination. Prior ground-based observations show 2MASS 1553+1532AB to be a common proper-motion binary. The properties of these systems—low multiplicity fraction (12^(+7)_(-4)% resolved, as corrected for sample selection biases), close projected separations (ρ = 1.8-5.0 AU) and near-unity mass ratios—are consistent with previous results for field brown dwarf binaries. Three of the binaries have components that span the poorly understood transition between L dwarfs and T dwarfs. Spectral decomposition analysis of one of these, SDSS 1021-0304AB, reveals a peculiar flux reversal between its components, as its cooler T5 secondary is ~30% brighter at 1.05 and 1.27 μm than its T1 primary. This system, 2MASS 0518-2828AB, and SDSS 1534+1615AB all demonstrate that the J-band brightening observed between late-type L to mid-type T dwarfs is an intrinsic feature of this spectral transition, albeit less pronounced than previously surmised. We also find that the resolved binary fraction of L7 to T3.5 dwarfs is twice that of other L and T dwarfs, an anomaly that can be explained by a relatively rapid evolution of brown dwarfs through the L/T transition, perhaps driven by dynamic (nonequilibrium) depletion of photospheric condensates.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Burgasser, Adam J.0000-0002-6523-9536
Kirkpatrick, J. Davy0000-0003-4269-260X
Cruz, Kelle L.0000-0002-1821-0650
Burrows, Adam0000-0002-3099-5024
Brown, Michael E.0000-0002-8255-0545
Additional Information:© 2006 The American Astronomical Society. Received 2006 March 30; accepted 2006 May 22. The authors would like to thank Santiago Arribas and Patricia Royle at STScI for their technical support of HST program GO-9833, and David Sprayberry and Meg Whittle at Keck for their support during the NIRC observations of 2MASS 1553+1532. A. J. B. acknowledges useful discussions with Antonin Bouchez, Randy Campbell, Michael Liu (who gave our original manuscript a careful read), Mark McCaughrean, and Frederick Vrba. We also thank our referee, Brian Patten, for his prompt critique of our manuscript and helpful suggestions. K. L. C. acknowledges support by a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship under AST-0401418. A. B. acknowledges support under NASA grant NNG04GL22G and through the NASA Astrobiology Institute under Cooperative Agreement CAN-02-OSS-02 issued through the Office of Space Science. This work is 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 proposals GO-9833 and GO-10247. 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, 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 publication has benefitted from the M, L, and T dwarf compendium housed at and maintained by Chris Gelino, Davy Kirkpatrick, and Adam Burgasser; and the VLM Binary Archive maintained by N. Siegler (see footnote 9). The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawai’ian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: HST(NICMOS), IRTF(SpeX), Keck:I(NIRC)
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NSF Astronomy and Astrophysics FellowshipAST-0401418
NASANAS 5-26555
Subject Keywords:binaries: visual; stars: fundamental parameters; stars: individual (SDSS J042348.57-041403.5, 2MASS J05185995-2828372, SDSS J092615.38+584720.9, SDSS J102109.69-030420.1, 2MASS J15530228+1532369); stars: low-mass, brown dwarfs
Issue or Number:2
Record Number:CaltechAUTHORS:20110218-115640485
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Official Citation:Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition Adam J. Burgasser, J. Davy Kirkpatrick, Kelle L. Cruz, I. Neill Reid, Sandy K. Leggett, James Liebert, Adam Burrows, and Michael E. Brown doi: 10.1086/506327
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22385
Deposited By: Ruth Sustaita
Deposited On:18 Feb 2011 23:30
Last Modified:03 Mar 2020 13:01

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