Scandium Abundance in F-G-K Stars in a Wide Metallicity Range

Abstract

A new Sc II model atom has been constructed using up-to-date atomic data. To test it, we have carried out nonlocal thermodynamic equilibrium (non-LTE) calculations for three stars with reliably determined atmospheric parameters: the Sun, HD 61421 (Procyon), and HD 84937. Allowance for the departures from LTE leads to a decrease in the root-mean-square abundance error compared to the LTE case and agreement, within the limits of this error, of the abundances deduced from different Sc II lines. The solar non-LTE abundance $\log\varepsilon_{\textrm{Sun}}=3.12± 0.05$ exceeds the meteoritic abundance recommended by Lodders (2021) by 0.08 dex. However, agreement within 0.02 dex with the meteoritic abundance has been obtained for Procyon. Based on high-resolution spectra, we have determined the LTE and non-LTE scandium abundances for 56 stars in a wide metallicity range, ${-}2.62≤\textrm{[Fe/H]}≤ 0.24$. The dependence of [Sc/Fe] on [Fe/H] demonstrates a similarity with the behavior of the $α$-process elements: scandium is enhanced relative to iron ([Sc/Fe] $∼$ 0.2) in stars with $\textrm{[Fe/H]}<{-}1$, and [Sc/Fe] decreases with increasing [Fe/H] for a higher metallicity. The scandium abundance correlates with the titanium abundance. The results obtained are important for solving the problem of the origin of scandium.