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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[6.06] The Sodium Hydride Line Opacity for Brown Dwarf and Extra-solar Giant Planet Atmospheres

A. Horvath (Lycoming College), P. C. Stancil (University of Georgia), B. K. Taylor (University of Texas at Tyler), T. Leininger, F. X. Gadéa (Université Paul Sabatier)

Atomic sodium is an important opacity in the spectra of brown dwarfs and is the only atmospheric constituent to date that has been detected in an extrasolar giant planet (EGP). For temperatures between ~1000 and 2000~K, NaH and NaCl are the next most abundant sodium species (Lodders, 1999, ApJ, 519, 793). Due to the lack of opacity data for these molecules, they have not been considered in brown dwarf and EGP synthetic spectra models.

In this work, we consider NaH and present comprehensive theoretical molecular line lists for rovibrational transitions in the ground X state and for the electronic transition between the A and X states. The list contains the transition energies and oscillator strengths for all allowed rotational and vibrational transitions. The calculations use hybrid potential curves based on experimental data, the theoretical X state potential and dipole moment function of Taylor & Newman (2003, J. Chem. Phys., 118, 8770), and the theoretical A state potential and X-A transition moment function of Leininger et al. (2000, J. Phys. B, 33, 1805). Using the Numerov-Cooley method, we find that there are 860 and 1824 rovibrational levels in the X and A states, respectively, which give rise to a large number of rotational transitions.

Pure rotational, rovibrational, and AarrowX electronic LTE spectra are presented for temperatures typical of brown dwarfs and EGPs. The bandheads occur at 8.8~\mu and 3990~Å~ for the fundamental vibrational and AarrowX electronic transitions, respectively.

This work was supported in part by the NSF REU Program at UGA and NASA grant NAG5-10551.

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