Manganese abundances in mercury-manganese stars

We use exact curve-of-growth analysis and spectral synthesis to deduce the abundance of Mn from high signal-to-noise ratio visible-region echelle spec tra of selected Mn I and Mn II lines in 24 HgMn stars. The results are comp ared with the Mn abundances derived from UV resonance lines by Smith & Dwor etsky. We find excellent agreement for several unblended Mn lines and confi rm the temperature dependence of the Mn abundance found by Smith & Dworetsk y. The Mn II lines at lambda lambda 4206 and 4326 are much stronger than on e would predict from the mean Mn abundances. The lack of agreement is great est for stars with the strongest Mn II lines. Using ad hoc multicomponent f its to the profiles of sharp-lined stars, we show that most of the discrepa ncies can be explained by hyperfine structure that desaturates the lines, w ith full widths of the order of 0.06-0.09 Angstrom.