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Space Telescope Science Institute
Gliese 229B: A Really Cool Brown Dwarf

S. R. Kulkarni
California Institute of Technology
Pasadena, CA

For the past five years we have been carrying out a coronagraphic survey of nearby stars using the Johns Hopkins Tip-Tilt Coronagraph. Last year we have identified a common proper motion companion to the nearby star Gliese 229. This companion has very peculiar colors (blue in the near-IR and very red in the optical). We report broad-band photometry of the object from 0.7 micron to 10 microns. The bolometric luminosity is 6¥10 -6 LSun. Strong absorption features and bands due to methane and water (steam) are seen. We conclude that this is a brown dwarf with an effective temperature of 900 K. Strong bands of refractory oxides and hydrides (TiO, VO, FeH) are conspicuously missing from the Keck optical spectrum - similar to the situation in Jupiter. We conclude that the metals have rained out of the atmosphere.