The Remarkable Spectrum of the Brown Dwarf Gliese 229 B

Details The Remarkable Spectrum of the Brown Dwarf Gliese 229 B The Remarkable Spectrum of the Brown Dwarf Gliese 229 B

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.1217s&link_type=abstract

American Astronomical Society, DPS meeting #28, #12.17; Bulletin of the American Astronomical Society, Vol. 28, p.1114

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The discovery a year ago of Gliese 229B (Nakajima et al. 1995 , Nature, 378, 463), the first indisputable brown dwarf, has unveiled a remarkable object. The models of Marley et al. 1996, (Science, 272, 1919) reveal that T_eff= 960 +/- 70K with a gravity between 800 and 2200 m/s(2) , or 30 to 75 times that of Jupiter. The mass is estimated to lie between 30 and 55 Jupiter masses. With T_eff ~ 1000K, Gl229B falls squarely in the intermediate range between Jupiter and the latest stars. Its spectrum shows characteristics of both. Our models confirm the identification of strong CH_4 features in the spectrum of Gl229B. More importantly, they reveal that the near-IR spectrum is dominated by H_2O absorption, a characteristic it shares with very-low mass stars. This is confimed by the high resolution spectrum of Geballe et al. 1996 (Ap. J. Letters, in press). Strong NH_3 features are predicted near 10 mu m. The strong bands of TiO, VO and FeH, so ubiquitous in the spectra of very-low mass stars, are absent. These refractory elements condense at levels below the photosphere (Fegley & Lodders 1996, Ap. J. Letters, in press) and clouds do not appear to play an important role in shaping the infrared spectrum of Gl229B. We have identified diagnostics for the surface gravity which should help reduce the presently large uncertainty on the mass determination. The spectrum of Gl229B is unique and is best described as a hybrid between solar system objects (e.g. Jupiter and Titan) and very-low mass stars. Model atmospheres and synthetic spectra are the most reliable tools to unlock the secrets of this first brown dwarf. We discuss in detail the results from our first generation of models. Complementary posters are presented in this session by Marley et al. and Burrows et al.

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