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Title:
A Method for Determining the Physical Properties of the Coldest Known Brown Dwarfs
Authors:
Burgasser, Adam J.; Burrows, Adam; Kirkpatrick, J. Davy
Affiliation:
AA(Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Building 37, Cambridge, MA 02139-4307 ), AB(Department of Astronomy, University of Arizona, Tucson, AZ 85721 ), AC(Infrared Processing and Analysis Center, Mail Stop 100-22, California Institute of Technology, Pasadena, CA 91125 )
Publication:
The Astrophysical Journal, Volume 639, Issue 2, pp. 1095-1113. (ApJ Homepage)
Publication Date:
03/2006
Origin:
UCP
Astronomy Keywords:
Stars: Fundamental Parameters, Stars: Individual: Alphanumeric: 2MASS J09373487+2931409, stars: individual (2MASS J09393548-2448279), stars: individual (2MASS J11145133-2618235), Stars: Individual: Name: Gliese 570D, Stars: Low-Mass, Brown Dwarfs
DOI:
10.1086/499344
Bibliographic Code:
2006ApJ...639.1095B

Abstract

We present a method for measuring the physical parameters of the coldest T-type brown dwarfs using low-resolution near-infrared spectra. By comparing H2O and H2-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 0939-2448 and 2MASS 1114-2618, both appear to be >~50 K cooler than the latest type T dwarf, 2MASS 0415-0935, 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 Teff/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.
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