Non-LTE line formation for Fe I and Fe II in the atmospheres of A-F type stars

TL;DR

This study investigates non-LTE effects on Fe I and Fe II line formation in A-F star atmospheres, showing smaller abundance corrections than previous models, with implications for stellar parameter determinations.

Contribution

It provides a comprehensive non-LTE analysis using an improved Fe atom model, quantifying line formation effects across a range of stellar parameters.

Findings

Non-LTE effects cause Fe I lines to be depleted, with abundance corrections up to 0.1 dex for dwarfs.

Fe II lines are slightly strengthened, with corrections around -0.03 dex.

Non-LTE corrections are smaller than previous studies due to a more complete Fe atom model.

Abstract

Non-local thermodynamical equilibrium (non-LTE) line formation for neutral and singly-ionized iron is considered through a range of spectral types when the effective temperature varies from 6500 K up to 8500 K, the gravity from log g = 4 down to log g = 3, and the metallicity is solar one. The non-LTE calculations were performed with a comprehensive model atom for iron which was treated in our earlier paper (Mashonkina et al. 2011, A&A, 528, A87). The departures from LTE lead to systematically depleted total absorption in the Fe I lines and positive abundance corrections, in qualitative agreement with the Rentzsch-Holm (1996, A&A, 312, 966) study. However, our predicted magnitude of the non-LTE effects is significantly smaller compared to the previous results due to the use of rather complete model atom of Fe I. The non-LTE abundance corrections do not exceed 0.1 dex for the dwarf models and 0.20 dex for the giant ones. Non-LTE leads to strengthening the Fe II lines, however, the effect is small, such that the abundance correction is at the level of -0.01 to -0.03 dex over the whole range of stellar parameters being considered. No firm conclusion can be drawn with respect to whether or not the Fe I/Fe II ionization equilibrium is fulfilled in the atmosphere of the Sun and Procyon due to uncertainty in available gf-values for visible lines of Fe I and Fe II.