The Classification of T Dwarfs

Abstract

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.

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