Yttrium, Barium, and the Lanthanides in AP and AM Stars

Abstract

This paper gives an element-by-element description of the spectra of yttrium, barium, and the lanthanides as they appear on 34 high-resolution spectra of 29 stars. Most of the stars are chemically peculiar (Ap or Am). Possible deviations from the odd--even effect are examined carefully, and two categories of such deviations are discussed. It is concluded that nuclear processes cannot be excluded on the basis of an odd-Z anomaly. An empirical two-component model for the lanthanide abundances is suggested. No resolution of the nuclear versus nonnuclear theories of abundance pecularies is proposed.