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T. R. Geballe (Gemini), S. K. Leggett (UKIRT), X. Fan (Princeton), D. P. Schneider (Penn State), G. K. Knapp, A. McDaniel, J. E. Gunn, R. H. Lupton, M. A. Strauss (Princeton), D. A. Golimowski, T. Henry, E. Peng, Z. I. Tsvetanov, A. Uomoto, W. Zheng (JHU), G. J. Hill (Texas), L.W. Ramsey (Penn State)
We have obtained high quality 1-2.5 microns spectra of three cool brown dwarfs, recently identified in the Sloan Digital Sky Survey and one cool brown dwarf from the Two Micron All Sky Survey. JHK photometry of the three SDSS objects, which had been photometrically selected from their i'-z' colors as likely methane dwarfs, suggested that they could be "transition objects" between the L and T classes of brown dwarfs. Their spectra, obtained by CGS4 on UKIRT, contain both CO and CH4 features, as well as H2O bands. The CH4 bands are weaker than those in all other methane dwarfs reported to date. The strengths of the bands of these three molecules are different in each object, and together the spectra form a sequence linking the late L-type dwarfs and previously observed T dwarfs. We propose that these SDSS objects represent the early subclasses of the T classification. In the 2MASS object, Gl 570D, identified by Burgasser et al. (astro-ph/0001194) as being significantly cooler than other methane dwarfs, the bands of CH4 and H2O are deeper and in some cases broader than in any other known T dwarf, further narrowing the windows short of 3 microns where radiation can easily escape.
The author(s) of this abstract have provided an email address for comments about the abstract: tgeballe@gemini.edu