Fe I in metal-poor stars

The deduced iron abundance is found to depend on the excitation potential of the line used, higher excitation lines generally indicating higher abundances. This could be caused by departures from the local thermodynamic equilibrium (LTE) or by temperature inhomogeneities in the stellar atmospheres.

The dependency of this effect on the stellar atmospheric parameters is investigated. From the comparison of iron lines with lines of other elements, it is concluded that the low excitation Fe I lines are much more affected than the high excitation lines. The consequences of these effects for the classical abundance analyses are examined.