2003/05/08 by Adam J. Burgasser, J. Davy Kirkpatrick, James Liebert +1 · 2 citations
Chemistry · Physics and Astronomy · #Absorption (acoustics) #Absorption band #Absorption spectroscopy #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Brown dwarf #Infrared #Near-infrared spectroscopy #Optics #Physics #Spectral line #Spectroscopy and Laser Applications #Stars #Stellar classification #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/376756
published as Astrophys.J. 594 (2003) 510-524 · 22 pages including 9 figures, accepted to ApJ v594 Sept. 2003
arxiv created 2003/05/08 · openalex publication_date 2003/08/20 · arxiv updated 2016/08/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
We present 6300-10100 Å spectra for a sample of 13 T dwarfs observed using LRIS mountedtpdel 99 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 H 2 O absorption; and a possible weak CH 4 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 H 2 O 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.