Multi-level 3D non-LTE computations of lithium lines in the metal-poor halo stars HD 140283 and HD 84937

Abstract

\n The lithium abundances in metal-poor halo stars are of \nimportance for cosmology, galaxy evolution and stellar structure. \nIn an attempt to study possible systematic errors in the \nderived Li abundances, the line formation of Li <sc>i</sc> lines\nhas been investigated by means of \nrealistic 3D hydrodynamical model atmospheres of halo\nstars and 3D non-LTE radiative transfer calculations.\nThese are the first detailed 3D non-LTE computations reported employing \na multi-level atomic model showing that such problems are now\ncomputationally tractable.\nThe detailed computations reveal that the Li <sc>i</sc> population\nhas a strong influence from the radiation field rather than the local\ngas temperature, indicating that the low derived Li abundances found by Asplund\net al. (1999) \nare an artifact of their assumption of LTE.\nRelative to 3D LTE, the detailed calculations \nshow pronounced over-ionization.\nIn terms of abundances the 3D non-LTE values are within 0.05 dex\nof the 1D non-LTE results for the particular cases\nof HD 140283 and HD 84937, which \nis a consequence of the dominance of the radiation in determining\nthe population density of Li <sc>i</sc>. Although 3D non-LTE can be\nexpected to give results rather close (≈\n $\\pm 0.1$ dex) \nto 1D non-LTE for this reason,\nthere may be systematic trends with metallicity\nand effective temperature. \n \n

Keywords

Affiliated Institutions

• University of Oslo
• Mount Stromlo Observatory AU

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