A non-local thermodynamic equilibrum study of scandium in the Sun

Abstract

Aims. We investigate the formation of neutral and singly ionized scandium lines in the solar photospheres. The research is aimed at derive solar (Sc) values for scandium lines, which will later be used in differential abundance analyses of metal-poor stars.Methods. Extensive statistical equilibrium calculations were carried out for a model atom, which comprises 92 terms for Sc I and 79 for Sc II. Photoionization cross-sections are assumed to be hydrogenic. Synthetic line profiles calculated from the level populations according to the NLTE departure coefficients were compared with the observed solar spectral atlas. Hyperfine structure (HFS) broadening is taken into account.Results. The statistical equilibrium of scandium is dominated by a strong underpopulation of Sc I caused by missing strong lines. It is nearly unaffected by the variation in interaction parameters and only marginally sensitive to the choice of the solar atmospheric model. Abundance determinations using the ODF model lead to a solar Sc abundance of between = 3.07 and , depending on the choice of values. The long known difference between photospheric and meteoritic scandium abundances is confirmed for the experimental -values. © 2008 ESO.