Toward spectral classification of L and T Dwarfs: Infrared and optical spectroscopy and analysis

T. R. Geballe, G. R. Knapp, S. K. Leggett, X. Fan, D. A. Golimowski, S. Anderson, J. Brinkmann, I. Csabai, J. E. Gunn, S. L. Hawley, G. Hennessy, T. J. Henry, G. J. Hill, R. B. Hindsley, Ž Ivezić, R. H. Lupton, A. McDaniel, J. A. Munn, V. K. Narayanan, E. PengJ. R. Pier, C. M. Rockosi, D. P. Schneider, J. Allyn Smith, M. A. Strauss, Z. I. Tsvetanov, A. Uomoto, D. G. York, W. Zheng

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We present 0.6-2.5 μm, R ≳ 400 spectra of 27 cool, low-luminosity stars and substellar objects. Based on these and previously published spectra, we develop a preliminary spectral classification system for L and T dwarfs. For late L and T types the classification system is based entirely on four spectral indices in the 1-2.5 μm interval. Two of these indices are derived from water absorption bands at 1.15 and 1.4 μm, the latter of which shows a smooth increase in depth through the L and T sequences and can be used to classify both spectral types. The other two indices make use of methane absorption features in the H and K bands, with the X-band index also applicable to mid-to-late L dwarfs. Continuum indices shortward of l μm used by previous authors to classify L dwarfs are found to be useful only through mid-L subclasses. We employ the 1.5 μm water index and the 2.2 μm methane index to complete the L classification through L9.5 and to link the new system with a modified version of the 2MASS "color-d" index. By correlating the depths of the methane and water absorption features, we establish a T spectral sequence from T0 to T8, based on all four indices, that is a smooth continuation of the L sequence. We reclassify two 2MASS L8 dwarfs as L9 and L9. 5 and identify one SDSS object as L9. In the proposed system methane absorption appears in the K band approximately at L8, two subclasses earlier than its appearance in the H band. The L and T spectral classes are distinguished by the absence and presence, respectively, of H-band methane absorption.

Original languageEnglish (US)
Pages (from-to)466-481
Number of pages16
JournalAstrophysical Journal
Issue number1 I
StatePublished - Jan 1 2002

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Infrared: stars
  • Stars: low-mass, brown dwarfs
  • Surveys


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