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A Method for Determining the Physical Properties of the Coldest Known Brown Dwarfs

Burgasser, Adam J. and Burrows, Adam and Kirkpatrick, J. Davy (2006) A Method for Determining the Physical Properties of the Coldest Known Brown Dwarfs. Astrophysical Journal, 639 (2). pp. 1095-1113. ISSN 0004-637X. doi:10.1086/499344.

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We present a method for measuring the physical parameters of the coldest T-type brown dwarfs using lowresolution near-infrared spectra. By comparing H_(2)O and H_2-sensitive spectral ratios between empirical data and theoretical atmosphere models, and calibrating these ratios to measurements for the well-characterized 2–5 Gyr companion brown dwarf Gliese 570D, we derive estimates of the effective temperatures and surface gravities for 13 mid- and late-type field T dwarfs. We also deduce the first quantitative estimate of subsolar metallicity for the peculiar T dwarf 2MASS 0937+2931. Derived temperatures are consistent with prior estimates based on parallax and bolometric luminosity measurements, and examination of possible systematic effects indicate that the results are robust. Two recently discovered late-type T dwarfs, 2MASS 09392448 and 2MASS 11142618, both appear to be ≳50 K cooler than the latest type T dwarf, 2MASS 04150935, and are potentially the coldest and least luminous brown dwarfs currently known. We find that, in general, higher surface gravity T dwarfs have lower effective temperatures and luminosities for a given spectral type, explaining previously observed scatter in the T_(eff) /spectral type relation for these objects. Masses, radii, and ages are estimated for the T dwarfs in our sample using the evolutionary models of Burrows et al.; we also determine masses and radii independently for eight T dwarfs with measured luminosities. These two determinations are largely consistent, lending support to the validity of evolutionary models at late ages. Our method is well suited to large samples of faint brown dwarfs and can ultimately be used to directly measure the substellar mass function and formation history in the Galaxy.

Item Type:Article
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URLURL TypeDescription
Burgasser, Adam J.0000-0002-6523-9536
Burrows, Adam0000-0002-3099-5024
Kirkpatrick, J. Davy0000-0003-4269-260X
Additional Information:© 2006 American Astronomical Society. Received 2005 March 4; accepted 2005 October 20. We thank our telescope operators, Dave Griep and Paul Sears, and instrument specialist John Rayner, for their support during the SpeX observations. We also acknowledge extremely helpful comments from our referee, Gibor Basri, and editor, James Liebert, which allowed us to substantially improve on our original manuscript. A. Burgasser thanks P. Hauschildt for making electronic versions of the COND models available for analysis. A. Burrows acknowledges support under NASA grant NNG 04-GL22G. This publication makes use of data from 2MASS, 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. 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. The theoretical material is based on work enabled by the National Aeronautics and Space Administration through the NASA Astrobiology Institute, under cooperative agreement CAN-02-OSS-02 issued through the Office of Space Science. 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 Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this sacred mountain. Facilities: IRTF(SpeX)
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:stars : fundamental parameters; stars : individual (2MASS J09373487+2931409, 2MASS J09393548-2448279, 2MASS J11145133-2618235; Gliese 570D); stars : low-mass, brown dwarfs
Issue or Number:2
Record Number:CaltechAUTHORS:20110211-113311253
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Official Citation:Adam J. Burgasser et al. 2006 ApJ 639 1095 doi: 10.1086/499344
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22141
Deposited On:11 Feb 2011 21:18
Last Modified:09 Nov 2021 16:03

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