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Title:
The Spectra of T Dwarfs. I. Near-Infrared Data and Spectral Classification
Authors:
Burgasser, Adam J.; Kirkpatrick, J. Davy; Brown, Michael E.; Reid, I. Neill; Burrows, Adam; Liebert, James; Matthews, Keith; Gizis, John E.; Dahn, Conard C.; Monet, David G.; Cutri, Roc M.; Skrutskie, Michael F.
Affiliation:
AA(Division of Physics, Mathematics, and Astronomy, MS 103-33, California Institute of Technology, Pasadena, CA 91125 ), AB(Infrared Processing and Analysis Center, MS 100-22, 770 South Wilson Avenue, California Institute of Technology, Pasadena, CA 91125 ), AC(Division of Geological and Planetary Sciences, MS 105-21, California Institute of Technology, Pasadena, CA 91125 ), AD(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218; also Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104-6396. ), AE(Steward Observatory, 933 North Cherry Avenue, University of Arizona, Tucson, AZ 85721 ), AF(Steward Observatory, 933 North Cherry Avenue, University of Arizona, Tucson, AZ 85721 ), AG(Division of Physics, Mathematics, and Astronomy, MS 103-33, California Institute of Technology, Pasadena, CA 91125 ), AH(Infrared Processing and Analysis Center, MS 100-22, 770 South Wilson Avenue, California Institute of Technology, Pasadena, CA 91125 ), AI(US Naval Observatory, P.O. Box 1149, Flagstaff, AZ 86002 ), AJ(US Naval Observatory, P.O. Box 1149, Flagstaff, AZ 86002 ), AK(Infrared Processing and Analysis Center, MS 100-22, 770 South Wilson Avenue, California Institute of Technology, Pasadena, CA 91125 ), AL(Five College Astronomy Department, Department of Physics and Astronomy, 619 LGRT B, University of Massachusetts, Amherst, MA 01003 )
Publication:
The Astrophysical Journal, Volume 564, Issue 1, pp. 421-451. (ApJ Homepage)
Publication Date:
01/2002
Origin:
UCP
Astronomy Keywords:
Infrared: Stars, Stars: Fundamental Parameters, Stars: Low-Mass, Brown Dwarfs, Techniques: Spectroscopic
DOI:
10.1086/324033
Bibliographic Code:
2002ApJ...564..421B

Abstract

We present near-infrared spectra for a sample of T dwarfs, including 11 new discoveries made using the 2 Micron All Sky Survey. These objects are distinguished from warmer (L-type) brown dwarfs by the presence of methane absorption bands in the 1-2.5 mum spectral region. A first attempt at a near-infrared classification scheme for T dwarfs is made, based on the strengths of CH4 and H2O bands and the shapes of the 1.25, 1.6, and 2.1 mum flux peaks. Subtypes T1 V-T8 V are defined, and spectral indices useful for classification are presented. The subclasses appear to follow a decreasing Teff scale, based on the evolution of CH4 and H2O bands and the properties of L and T dwarfs with known distances. However, we speculate that this scale is not linear with spectral type for cool dwarfs, due to the settling of dust layers below the photosphere and subsequent rapid evolution of spectral morphology around Teff~1300-1500 K. Similarities in near-infrared colors and continuity of spectral features suggest that the gap between the latest L dwarfs and earliest T dwarfs has been nearly bridged. This argument is strengthened by the possible role of CH4 as a minor absorber, shaping the K-band spectra of the latest L dwarfs. Finally, we discuss one peculiar T dwarf, 2MASS 0937+2931, which has very blue near-infrared colors (J-Ks=-0.89+/-0.24) due to suppression of the 2.1 mum peak. The feature is likely caused by enhanced collision-induced H2 absorption in a high-pressure or low-metallicity photosphere.

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