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Issue A&A
Volume 409, Number 2, October II 2003
Page(s) L1 - L4
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20031199



A&A 409, L1-L4 (2003)
DOI: 10.1051/0004-6361:20031199

Letter

Inelastic H+Li and H -+Li + collisions and non-LTE Li I line formation in stellar atmospheres

P. S. Barklem1, A. K. Belyaev2 and M. Asplund3

1  Department of Astronomy and Space Physics, Uppsala University, Box 515, 751 20 Uppsala, Sweden
2  Department of Theoretical Physics, A. I. Herzen University, St. Petersburg 191186, Russia
3  Research School of Astronomy, Mt. Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia

(Received 17 July 2003 / Accepted 4 August 2003 )

Abstract
Rate coefficients for inelastic collisions between Li and H atoms covering all transitions between the asymptotic states Li(2s,2p,3s,3p,3d,4s,4p,4d,4f)+H(1s) and Li ++H - are presented for the temperature range 2000-8000 K based on recent cross-section calculations. The data are of sufficient completeness for non-LTE modelling of the Li I 670.8 nm and 610.4 nm features in late-type stellar atmospheres. Non-LTE radiative transfer calculations in both 1D and 3D model atmospheres have been carried out for test cases of particular interest. Our detailed calculations show that the classical modified Drawin-formula for collisional excitation and de-excitation ( $\rm Li^*+H\rightleftharpoons Li^{*\prime}+H$) over-estimates the cross-sections by typically several orders of magnitude and consequently that these reactions are negligible for the line formation process. However, the charge transfer reactions collisional ion-pair production and mutual neutralization ( $\rm Li^*+H\rightleftharpoons Li^++H^-$) are of importance in thermalizing Li. In particular, 3D non-LTE calculations of the Li I 670.8 nm line in metal-poor halo stars suggest that 1D non-LTE results over-estimate the Li abundance by up to about 0.1 dex, aggrevating the discrepancy between the observed Li abundances and the primordial Li abundance as inferred by the WMAP analysis of the cosmic microwave background.


Key words: atomic data -- line: formation -- stars: abundances

Offprint request: P. S. Barklem, barklem@astro.uu.se




© ESO 2003

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