1994A&A...291..521S

Atmospheric abundances of copper and zinc are derived for a sample of 40 normal, superficially normal, and HgMn-type main-sequence late-B stars by LTE spectrum-synthesis analysis of co-added high-resolution International Ultraviolet Explorer (IUE) spectra. In the normal and superficially normal stars, the abundances of these elements are generally consistent with their solar values, to within the limits of observational and analytical error. In most (but not all) HgMn stars, copper is found to be overabundant and, moreover, exhibits a pronounced positive correlation with effective temperature similar to that seen for manganese. Zinc is typically deficient in the HgMn stars with underabundances of 2dex or more in many cases, although it is apparently overabundant in three programme stars and present at essentially solar abundance in three others. There appears to be no characteristic distinguishing those HgMn stars which are zinc-rich or zinc-normal from those that are zinc-deficient. These results provide further evidence for the existence of a sub-group of hot, mild HgMn stars characterised, in the context of this work, by relatively moderate overabundances of copper when compared with other `genuine' HgMn stars of similar effective temperature. While the copper abundance correlation with effective temperature would appear to be a possible signature of radiative diffusion in the atmospheres of HgMn stars, the inexplicably dichotomous behaviour of zinc in the same objects could prove difficult to reconcile with existing parameter-free models of this mechanism.