Review: progress in NLTE calculations and their application to large data-sets

TL;DR

This review summarizes recent progress in NLTE line-formation calculations for FGK stars, highlighting their importance for accurate stellar parameter determination in large-scale surveys and discussing current challenges and applications.

Contribution

It provides a comprehensive overview of NLTE modeling advancements, systematic errors in LTE methods, and the integration of NLTE with <3D> models for stellar spectroscopy.

Findings

NLTE calculations improve accuracy of stellar parameters.

Systematic errors in LTE methods can be significant.

NLTE with <3D> models enhances spectroscopic analysis.

Abstract

One of the major tasks in interpretation of data from large-scale stellar surveys is to determine the fundamental atmospheric parameters such as effective temperature, surface gravity, and metallicity. In most on-going and upcoming projects, they are derived spectroscopically, with relying on classical one-dimensional (1D) model atmospheres and the assumption of LTE. This review discusses the present achievements and problems of non-local thermodynamic equilibrium (NLTE) line-formation calculations for FGK-type stars. The topics that are addressed include (i) the construction of comprehensive model atoms for the chemical elements with complex term system, (ii) possible systematic errors inherent in classical LTE spectroscopic determinations of stellar parameters and chemical abundances, (iii) the uncertainties in final NLTE results caused by the uncertainties in atomic data, and (iv) applications of the NLTE line-formation calculations coupled to the spatial and temporal average <3D> models to spectroscopic analyses.