Abundance analysis of roAp stars - V. HD 166473

This fifth paper in a sequence on abundance analyses of roAp stars features several improvements and complements over the previous investigations: i. The new VALD-2 atomic data base was used which significantly improves th e analysis of C, N, O, and rare earth elements (REE) and in particular incl udes also some doubly ionized REE species. ii. An individual opacity distribution function table was generated for a s uccessful synthesis of photometric indices of this very peculiar star. iii. The influence of a (rather strong) magnetic field on abundance determi nations is studied and presented for 30 elements. iv. Our investigation of 33 elements (45 ions) is the hitherto most complet e chemical analysis of a chemically peculiar star, using modern tools. Similar to the four roAp stars analysed by us so far (alpha Cir: Kupka et a l. 1996, HD 203932. Gelbmann et al. 1997, gamma Equ: Ryabchikova et al. 199 7a, and KD 24712: Ryabchikova et al. 1997b) we find nearly solar abundances of Fe and Ni, and a definite overabundance of Cr and especially Co. Rare e arth elements have large overabundances, whereas C and O are under-abundant relative to the Sun. This pattern seems to be a common property of the che mically peculiar (CPZ, Ap) stars. A new and most striking result is the discovery of the anomalous line stren gths of the second ions of REE resulting in an abundance increase of up to +1.5 dex, compared to values obtained from lines of the first ions. This an omaly is not found in non-roAp and "normal" stars.