Geballe, Tom R.

Contact Email: tgeballe@gemini.edu
Institute: Gemini Observatory, Hilo, Hawaii
First Coauthor: G. R. Knapp
Institute: Princeton University Observatory
Second Coauthor: S. K. Leggett
Institute: Joint Astronomy Centre, Hilo, Hawaii
Research URL:http://www.gemini.hawaii.edu
Subject Area: Brown Dwarfs & Extrasolar Planets
Waveband: Infrared
Technique: Spectroscopy
Presentation: Poster Display
Title: Towards Spectral Classification of L and T Dwarfs: Infrared and Optical Spectroscopy and Analysis
Abstract: We use near infrared spectroscopy to develop a 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 $\mu$m interval. Two indices are derived from water absorption bands at 1.15 $\mu$m and 1.4 $\mu$m, the latter of which shows a smooth increase in depth through the L and T sequences. The other two indices make use of the methane absorptions in the H and K bands, with the latter of these indices also having applicability to L dwarfs. Continuum indices shortward of 1 $\mu$m used by previous authors to classify L dwarfs are found to be useful only through mid-L. We employ the 1.4 $\mu$m index and the K band "methane" index to complete the L classification through L9. By correlating the depths of the methane and water absorption features, we establish a T spectral sequence from types T0 to T8, smoothly attached to the L sequence. In the propose scheme spectral types L and T are distinguished by the absence and presence, respectively, of H band methane absorption and K band methane absorption is first observed at L8.