Abundance Patterns in Chemically Peculiar Stars of the Upper Main Sequence

Abstract

Abundance patterns in Chemically peculiar (CP) stars are discussed within the context of nuclear and non-nuclear mechanisms for the origin of the anomalies. Some abundance patterns depart significantly from "solar" but nevertheless show the signature of nuclear systematics. Other abundances are most difficult to reconcile with reasonable nuclear processes. The empirical facts are presently far from being clear. Enormous selection effects influencing abundance systemativs of CP stars have not yet been taken into account. Useful abundances are avialable for elements in the iron group and lighter, but for yttrium and the rare earths, uncertainities, including possible deviations from ionization equilibrium, are very large. An approach via Chaberlain's Multiple Working Hypothesis is afvocated. There is not yet a sound basis for rejecting either nuclear or non-nuclear mechanisms.