The Spectra Of T Dwarfs. II. Red Optical Data

Adam J. Burgasser, J. Davy Kirkpatrick, James Liebert, Adam S. Burrows

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We present 6300-10100 Å spectra for a sample of 13 T dwarfs observed using LRIS mounted on the Keck I 10 m Telescope. A variety of features are identified and analyzed, including pressure-broadened K I and Na I doublets; narrow Cs I and Rb I lines; weak CaH, CrH, and FeH bands; strong H2O absorption; and a possible weak CH4 band. Hα emission is detected in three of the T dwarfs, strong in the previously reported active T dwarf 2MASS 1237+6526 and weak in SDSS 1254-0122 and 2MASS 1047+2124. None of the T dwarfs exhibit Li I absorption. Guided by the evolution of optical spectral features with near-infrared spectral type, we derive a parallel optical classification scheme, focusing on spectral types T5 to T8, anchored to select spectral standards. We find general agreement between optical and near-infrared types for nearly all the T dwarfs so far observed, including two earlier type T dwarfs, within our classification uncertainties (∼1 subtype). These results suggest that competing gravity and temperature effects compensate for each other over the 0.6-2,5 μm spectral region. We identify one possible means of disentangling these effects by comparing the strength of the K I red wing to the 9250 Å H2O band. One of our objects, 2MASS 0937+2931, exhibits a peculiar spectrum with a substantial red slope and relatively strong FeH absorption, both consequences of a metal-deficient atmosphere. On the basis of its near-infrared properties and substantial space motion, this object may be a thick disk or halo brown dwarf.

Original languageEnglish (US)
Pages (from-to)510-524
Number of pages15
JournalAstrophysical Journal
Issue number1 I
StatePublished - Sep 1 2003

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Stars: Activity
  • Stars: Fundamental parameters
  • Stars: Low-mass, brown dwarfs

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