Third spectra of rare earth elements in chemically peculiar stars: IUE spectra

Third spectra of the lanthanides can be identified in IUE spectra of certain chemically peculiar A stars with the help of statistical techniques. These spectra are rather weak. The intrinsically strongest lines are probably only a few tens of mA in equivalent widths, and the detections are perhaps best described as marginal. There is no doubt, even in the lanthanide-strong Ap stars, that the iron group, and not the rare earth spectra, dominate the line absorption in the satellite ultraviolet. Provisional, quantitative estimates of abundances are made that are based on the third spectra, but in view of the severe blending, uncertainties in the stellar model, and the lack of gf-values, definitive results cannot be made at this time. (author)