2005A&A...442..643C

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