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Session 26 - Neutrinos & Stellar Abundances.
Oral session, Wednesday, January 07
Jefferson,
The spectrum of Gl 229B in the 4.5-5.1 \mum interval shows evidence for CO at mole fractions of qCO > 50 ppm. Molecular line opacity limits the depth to which we can see at these wavelengths to the T \approx 800 K level. At this temperature, the predicted equilibrium abundance of CO (Fegley and Lodders, ApJ 472, L37 [1996]) is more than 1600 times lower than the lower limit we determine. Dynamical quenching of CO-CH_4 equilibrium is one mechanism that can lead to enhanced CO at low temperatures, but this mechanism requires convection in the T \approx 800-1250 K, P \approx 1-8 bar region of Gl 229B's atmosphere, a region in which a detached convection zone is predicted by some models of Gl 229B (Marley et al. Science 272, 1919 [1996]). The presence of disequilibrium abundances of CO in Gl 229B's upper atmosphere reduces the emergent flux in the 4-5 \mum interval and may make searches for new brown dwarfs using this band less sensitive.
