A B S T R A C TWe use exact curve-of-growth analysis and spectral synthesis to deduce the abundance of Mn from high signal-to-noise ratio visible-region echelle spectra of selected Mn i and Mn ii lines in 24 HgMn stars. The results are compared with the Mn abundances derived from UV resonance lines by Smith & Dworetsky. We ®nd excellent agreement for several unblended Mn lines and con®rm the temperature dependence of the Mn abundance found by Smith & Dworetsky. The Mn ii lines at ll4206 and 4326 are much stronger than one would predict from the mean Mn abundances. The lack of agreement is greatest for stars with the strongest Mn ii lines. Using ad hoc multicomponent ®ts to the pro®les of sharp-lined stars, we show that most of the discrepancies can be explained by hyper®ne structure that desaturates the lines, with full widths of the order of 0.06±0.09 A Ê .

High-resolution spectra have been obtained for the regions of the Ðve strongest optical lines of Pt II in the spectrum of the cool HgMn star HR 7775, which is one of the sharpest-lined HgMn stars known. Model lines have been constructed from the isotopic and hyperÐne structure laboratory analysis of Engleman. Abundances of the individual isotopes have been determined from spectrum synthesis. The total abundance of Pt is 4.46 dex greater than the adopted solar abundance. The isotopic composition is clearly nonterrestrial, with a pronounced relative enhancement of the heaviest isotope, 198Pt, and deÐ-ciencies of isotopes lighter than 196Pt. The pattern of isotopic composition does not follow the widely assumed fractionation formalism ; the lighter isotopes are far more deÐcient than a single-parameter fractionation pattern would predict.

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