Lanthanide Rare Earths in Stellar Spectra With Emphasis on Chemically Peculiar Stars

This paper deals with stellar abundance patterns of the lanthanides. It is divided into two parts. In Part A we investigate the accuracy with which partition functions may be calculated from known energy levels. Corrections for "missing levels" are made, and current "best estimates" are tabulated. The current values are compared with partition functions built into the ATLAS code. The latter are generally rather good, except for Ce III. An increase of about a factor of two in published cerium abundances in many CP stars is indicated. In Part B, the systematics of the behavior of La II through Tm II are reviewed one-by-one. The emphasis is on CP stars, but late-type giants and dwarfs are also discussed. It is concluded that the overall "typical" pattern is tolerably well described by varying degrees of enhancement of the solar pattern, including the odd-even effect. Definite non-solar patterns do occur, however, such as the neodymium-samarium holes and the positive europium anomaly. From these abundance patterns we infer processes, nuclear or non-nuclear, that are distinct from those responsible for the lanthanide composition of the majority of stellar atmospheres.