Issue |
A&A
Volume 399, Number 3, March I 2003
|
|
---|---|---|
Page(s) | L31 - L34 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20030080 | |
Published online | 14 February 2003 |
Letter to the Editor
Multi-level 3D non-LTE computations of lithium lines in the metal-poor halo stars HD 140283 and HD 84937
1
Research School of Astronomy, Mt. Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia
2
Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern, N-0315 Oslo, Norway
Corresponding author: M. Asplund, martin@mso.anu.edu.au
Received:
16
December
2002
Accepted:
13
January
2003
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 Li i 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 Li i 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 HD 140283 and HD 84937, which
is a consequence of the dominance of the radiation in determining
the population density of Li i. Although 3D non-LTE can be
expected to give results rather close (≈
dex)
to 1D non-LTE for this reason,
there may be systematic trends with metallicity
and effective temperature.
Key words: line: formation / radiative transfer / stars: abundances / stars: atmospheres / stars: Population II
© ESO, 2003
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