EDP Sciences
Free access
Volume 442, Number 2, November I 2005
Page(s) 643 - 650
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20053363

A&A 442, 643-650 (2005)
DOI: 10.1051/0004-6361:20053363

Effects of line-blocking on the non-LTE Fe I spectral line formation

R. Collet1, M. Asplund2 and F. Thévenin3

1  Department of Astronomy and Space Physics, Uppsala University, Box 515, 751 20 Uppsala, Sweden
    e-mail: remo@astro.uu.se
2  Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia
3  Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France

(Received 4 May 2005 / Accepted 11 July 2005)

The effects of background line opacity (line-blocking) in statistical equilibrium calculations for $\element{Fe}$ in late-type stellar atmospheres have been investigated using an extensive and up-to-date model atom with radiative data primarily from the IRON Project. The background metal line opacities have been computed using data from the MARCS stellar model atmospheres. While accounting for this line opacity is important at solar metallicity, the differences between calculations including and excluding line-blocking at low metallicity are insignificant for the non-local thermodynamic equilibrium (non-LTE) abundance corrections for $\ion{Fe}{i}$ lines. The line-blocking has no impact on the non-LTE effects of $\ion{Fe}{ii}$ lines. The dominant uncertainty in $\element{Fe}$ non-LTE calculations for metal-poor stars is still the treatment of the inelastic $\ion{H}{i}$ collisions, which here have been included using scaling factors to the classical Drawin formalism, and whether or not thermalisation of the high $\ion{Fe}{i}$ levels to $\ion{Fe}{ii}$ ground state should be enforced. Without such thermalisation, the $\ion{Fe}{i}$ non-LTE abundance corrections are substantial in metal-poor stars: about 0.3 dex with efficient (i.e. Drawin-like) $\ion{H}{i}$ collisions and $\la$0.5 dex without. Without both thermalisation and $\ion{H}{i}$ collisions, even $\ion{Fe}{ii}$ lines show significant non-LTE effects in such stars.

Key words: line: formation -- Sun: abundances -- stars: abundances -- stars: individual: Procyon -- stars: individual: HD 140283 -- stars: individual: G64-12

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© ESO 2005