Non-LTE abundances of Mg and K in extremely metal-poor stars and the evolution of [O/Mg], [Na/Mg], [Al/Mg] and [K/Mg] in the Milky Way

TL;DR

This study derives non-LTE abundances of magnesium and potassium in extremely metal-poor stars, improving the precision of elemental ratios to better inform models of Galactic chemical evolution and supernova yields.

Contribution

It provides the first non-LTE abundance measurements of Mg and K in EMP stars, refining previous LTE estimates and enhancing constraints on Galactic chemical evolution models.

Findings

NLTE corrections align with existing literature

Abundance ratios show reduced scatter, increasing precision

Magnesium confirmed as a reliable reference element

Abstract

LTE abundances of light elements in extremely metal-poor (EMP) stars have been previously derived from high quality spectra. New derivations, free from the NLTE effects, will better constrain the models of the Galactic chemical evolution and the yields of the very first supernovae. The NLTE profiles of the magnesium and potassium lines have been computed in a sample of 53 extremely metal-poor stars with a modified version of the program MULTI and adjusted to the observed lines in order to derive the abundances of these elements. The NLTE corrections for magnesium and potassium are in good agreement with the works found in the literature. The abundances are slightly changed, reaching a better precision: the scatter around the mean of the abundance ratios has decreased. Magnesium may be used with confidence as reference element. Together with previously determined NLTE abundances of sodium and aluminum, the new ratios are displayed, for comparison, along the theoretical trends proposed by some models of the chemical evolution of the Galaxy, using different models of supernovae.