Influence of departures from LTE on determinations of the sulfur abundances in A-K type stars

TL;DR

This study develops a correction grid for sulfur abundance measurements in A-K stars accounting for non-LTE effects, using an advanced atomic model tested on 13 stars, improving accuracy across a wide temperature range.

Contribution

The paper introduces a comprehensive LTE departure correction grid for sulfur lines in stellar spectra, incorporating updated atomic data and ionized sulfur levels, applicable up to 10,000 K.

Findings

The correction grid effectively accounts for non-LTE effects in sulfur line analysis.

Sulfur abundances are consistently determined across different spectral lines and stellar parameters.

Refined wavelengths and oscillator strengths improve sulfur abundance measurements.

Abstract

The influence of departures from local thermodynamic equilibrium (LTE) on neutral sulfur lines is considered. A grid of corrections is proposed to take into account the influence of departures from LTE for neutral sulfur lines in the visible and infrared spectral regions, including the H-band. The grid is calculated using the atomic model of sulfur incorporating the most up-to-date collision rates with electrons and hydrogen. The inclusion of levels and transitions of ionized sulfur in the atomic model made it possible to expand the range of effective temperatures of stellar photospheres in the grid up to 10000 K. The atomic model was tested in determining the sulfur abundance of 13 stars and showed its adequacy in a wide range of fundamental stellar parameters. In the spectra of all test stars, the sulfur lines are fitted with similar abundances of the element, regardless of the degree of influence of the effects of deviation from LTE on a particular spectral line. For lines of several multiplets, the wavelengths and oscillator strengths were refined. A list of S I lines recommended for determining sulfur abundance has been created.