Elemental abundances in normal late-B and HgMn stars from co-added IUE spectra. I: Iron-peak elements

The abundances of five iron-peak elements in a sample of 40 normal, superficially normal, and HgMn-type late-B stars are derived by spectrum-synthesis analysis of co-added high-resolution IUE spectra. Approximately solar abundances of these elements are obtained for the normal stars, with the notable exception of Alpha Lyr which is shown to be mildly metal-deficient in accordance with published analyses of its visual-region spectrum. The superficially normal stars are generally indistinguishable from the normal stars in terms of their Fe-peak elemental abundances. The HgMn stars exhibit a large diversity in Cr and Fe abundances, a striking effective-temperature-dependent Mn enhancement, and substantially subsolar abundances of Co and Ni. Even for Mn, Co, and Ni there are some HgMn stars which depart from the more general behavior of the group as a whole, and thus these results tend to confirm the rather heterogeneous nature of this peculiarity class suspected in previous surveys of their visual-region spectra. By making schematic corrections for the effects on our analysis of atmospheric chemical stratification, we show that the predictions of radiative diffusion theory for Mn are in excellent accord with the observed upper envelope of abundances in the HgMn stars.