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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

369 Citations (Scopus)

Abstract

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
Pages (from-to)466-481
Number of pages16
JournalAstrophysical Journal
Volume564
Issue number1 I
DOIs
Publication statusPublished - 1 Jan 2002
Externally publishedYes

Keywords

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

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