The Rare Earths in the Peculiar A Stars: A Test Case for the Magnetic Diffusion Hypothesis

Abstract

SummaryA brief formulation and an overview of the magnetic diffusion mechanism is presented. The atomic physics of the rare earth spectra is considered. It is demonstrated that basic differences among these elements contribute to the observed abundance anomalies of rare earth elements. The ion fractions of the rare earth display very different behaviour with temperature and pressure. In the atmospheres of Ap stars, europium tends to have the greatest degree of ionization. While previous studies on the diffusion mechanism with model atmospheres have maintained chemical homogeneity, we argue that this is an unrealistic approach to the Ap stars and present the consequences in the light of the diffusion picture.