The lithium abundances in metal-poor halo stars are of importance for
cosmology, galaxy evolution and stellar structure. In an attempt to study
possible systematic errors in the derived Li abundances, the line formation of
LiI lines has been investigated by means of realistic 3D hydrodynamical model
atmospheres of halo stars and 3D non-LTE radiative transfer calculations. These
are the first detailed 3D non-LTE computations reported employing a multi-level
atomic model showing that such problems are now computationally tractable. The
detailed computations reveal that the LiI population has a strong influence
from the radiation field rather than the local gas temperature, indicating that
the low derived Li abundances found by Asplund et al. (1999) are an artifact of
their assumption of LTE. Relative to 3D LTE, the detailed calculations show
pronounced over-ionization. In terms of abundances the 3D non-LTE values are
within 0.05 dex of the 1D non-LTE results for the particular cases of HD140283
and HD84937, which is a consequence of the dominance of the radiation in
determining the population density of LiI. Although 3D non-LTE can be expected
to give results rather close (+/-0.1 dex) to 1D non-LTE for this reason, there
may be systematic trends with metallicity and effective temperature.Comment: A&A, in press (Letters to the editors), 5 page