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

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

Abstract

The effects of background line opacity (line-blocking) in statistical equilibrium calculations for 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 lines. The line-blocking has no impact on the non-LTE effects of lines. The dominant uncertainty in non-LTE calculations for metal-poor stars is still the treatment of the inelastic collisions, which here have been included using scaling factors to the classical Drawin formalism, and whether or not thermalisation of the high levels to ground state should be enforced. Without such thermalisation, the non-LTE abundance corrections are substantial in metal-poor stars: about 0.3 dex with efficient (i.e. Drawin-like) collisions and 0.5 dex without. Without both thermalisation and collisions, even lines show significant non-LTE effects in such stars.