The Classification of T Dwarfs
We discuss methods for classifying T dwarfs based on spectral morphological features and indices. T dwarfs are brown dwarfs which exhibit methane absorption bands at 1.6 and 2.2 μm. Spectra at red optical (6300–10100 Å) and near-infrared (1–2.5 μm) wavelengths are presented, and differences between objects are noted and discussed. Spectral indices useful for classification schemes are presented. We conclude that near-infrared spectral classification is generally preferable for these cool objects, with data sufficient to resolve the 1.17 and 1.25 μm K I doublets lines being most valuable. Spectral features sensitive to gravity are discussed, with the strength of the K-band peak used as an example. Such features may be used to derive a two-dimensional scheme based on temperature and mass, in analogy to the MK temperature and luminosity classes.
Additional Information© 2001 Springer-Verlag Berlin Heidelberg. A.J. Burgasser acknowledges S.K. Leggett, B.R. Oppenheimer, and M.A. Strauss for providing useful spectral data for comparison, and D. Saumon for use of unpublished model spectra. Enlightening discussions over the role of H_2 were had with A. Burrows, M. Marley, and D. Saumon. AJB also acknowledges the contributions of the other members of the 2MASS Rare Objects Team: R. Cutri, C. Dahn, J. Gizis, J. Liebert, B. Nelson, and I.N. Reid. Data presented herein were obtained at the W. M. Keck Observatory which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by generous financial support of the W. M. Keck Foundation. This contribution 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.
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