Scandium abundances of F-G-K dwarf stars in a wide metallicity range

TL;DR

This study constructs a new model atom for Sc II, performs non-LTE calculations on select stars, and analyzes scandium abundances across a wide metallicity range, revealing its behavior relative to iron and titanium.

Contribution

The paper introduces a new model atom for Sc II and provides detailed non-LTE abundance analysis for a large sample of stars across various metallicities.

Findings

Non-LTE calculations reduce abundance errors.

Scandium behaves like alpha-process elements, being enhanced at low metallicity.

A potential correlation exists between scandium and titanium abundances.

Abstract

A new model atom of Sc II was constructed using the most up-to-date atomic data. For the testing purpose, the non-local thermodynamic equilibrium (non-LTE) calculations were carried out for three stars with reliably determined atmospheric parameters: the Sun, HD~61421 (Procyon), and HD~84937. Accounting for deviations from LTE leads to smaller abundance errors compared with the LTE case and consistent within the error bars abundances obtained from different Sc II lines. Solar non-LTE abundance log eps_Sun = 3.12+-0.05 exceeds the meteoritic abundance recommended by Lodders (2021), by 0.08~dex. But agreement within 0.02~dex with the meteoritic abundance is obtained for Procyon. Using high-resolution spectra, we determined the scandium LTE and non-LTE abundances for 56 stars in the metallicity range -2.62 <= [Fe/H] <= 0.24. The dependence of [Sc/Fe] on [Fe/H] demonstrates a similarity with the behavior of the alpha-process elements: scandium is enhanced relative to iron ([Sc/Fe] ~ 0.2) for [Fe/H] < -1, and [Sc/Fe] decreases with increasing [Fe/H] for the higher metallicity. There is a hint of a tight relation between abundances of scandium and titanium. The results obtained provide observational constraints to the scenarios of scandium origin.