Formation of MnI lines in the solar atmosphere

TL;DR

This study performs a comprehensive NLTE analysis of 39 MnI lines in the solar spectrum to improve manganese abundance measurements and understand NLTE effects on line formation in the solar atmosphere.

Contribution

It provides the first detailed NLTE analysis of manganese lines in the solar spectrum, including hyperfine structure effects and the impact of NLTE on abundance determinations.

Findings

NLTE effects significantly influence manganese line formation.

Hyperfine structure causes strong line broadening.

NLTE analysis improves accuracy of manganese abundance in the Sun.

Abstract

We present a detailed NLTE analysis of 39 MnI lines in the solar spectrum. The influence of NLTE effects on the line formation and element abundance is investigated. Our goal is the derivation of solar log gfe values for manganese lines, which will later be used in differential abundance analysis of metal-poor stars. The method of spectrum synthesis is employed, which is based on a solar model atmosphere with initially specified element abundances. A manganese abundance of 5.47 dex is used with the theoretical line-blanketed model atmosphere. Statistical equilibrium calculations are carried out for the model atom, which comprises 245 and 213 levels for MnI and MnII, respectively. Photoionization cross-sections are assumed hydrogenic. For line synthesis van der Waals broadening is calculated according to Anstee & O'Mara's formalism. It is shown that hyperfine structure of the Mn lines also has strong broadening effects, and that manganese is prone to NLTE effects in the solar atmosphere. The nature of the NLTE effects and the validity of the LTE approach are discussed in detail. The role of photoionization and collisional interaction is investigated.