Observations of Magnetically Split Lines in Ap Stars)

Ap stars whose spectral lines are resolved in several magnetically split components are of particular interest, because their magnetic field can be diagnosed with unrivalled precision, in an essentially approximation-free manner. We are pursuing a systematic programme of search and study of such stars. At present 25 of them are known, of which 13 have been discovered in the course of the present project (Mathys 1990, hereafter Paper I; Mathys & Lanz 1992, hereafter Paper II; this paper).Up to now, we have obtained observations of 22 of these Ap stars with resolved magnetically split lines. We have recorded high-resolution spectra of a region containing, among others, the three lines Cr ɪɪ λ6147.154, Fe ɪ λ6147.741, and Fe II λ 6149.258. The Zeeman patterns of these three lines are, respectively, close to a triplet, close to a quadruplet, and a doublet. The doublet Fe ɪɪ λ 6149.258 is particularly interesting, because of its large Landé factor (2.7): it can be resolved even in stars with fairly modest fields.