AAS 203rd Meeting, January 2004
Session 6 Brown Dwarf Stars
Poster, Monday, January 5, 2004, 9:20am-6:30pm, Grand Hall

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[6.05] Alkali Halide Opacity in Brown Dwarf and Cool Stellar Atmospheres: A Study of Lithium Chloride

K. Kirby (ITAMP, Harvard-Smithsonian CfA), P. F. Weck (University of Georgia), A. Schweitzer (Hamburger Sternwarte, Universitaet Hamburg, Germany), P. C. Stancil (University of Georgia), P. H. Hauschildt (Hamburger Sternwarte, Universitaet Hamburg)

Recent thermochemical equilibrium calculations have revealed the important role played by lithium chloride in the lithium chemistry of cool dwarf atmospheres (K. Lodders 1999, ApJ 519, 793). Indeed, LiCl appears to be the dominant Li-bearing gas over an extended domain of the (P,T) diagram, typically for temperatures below 1500 K. LiCl has a large dipole moment in its ground electronic state which can give rise to intense rovibrational line spectra. In addition, LiCl can make dipole transitions to several low-lying unbound excited states, causing dissociation of the molecule. For these reasons, LiCl may be a significant source of line and continuum opacity in brown dwarf and cool stellar atmospheres.

In this work, we report calculations of complete lists of line oscillator strengths and photodissociation cross sections for the low-lying electronic states of LiCl. We have performed single- and double-excitation configuration interaction calculations using the {\tt ALCHEMY} {\em ab initio} package (Mc Lean et al. 1991, MOTECC 91, Elsevier, Leiden) and obtained the potential curves and the corresponding dipole transition moment functions between the X~1\Sigma+ ground state and the B~1\Sigma+ and A~1\Pi excited states.

The resulting line oscillator strengths and molecular photodissociation cross sections have been included in the {\tt PHOENIX} stellar atmosphere code (Hauschildt & Baron 1999, J. Comput. App. Math. 102, 41). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state (EOS).

This work was supported in part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222, and NAG5-10551 as well as NASA/JPL grant 961582.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.