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Manganese abundances in Mercury-Manganese stars

C. M. Jomaron, M. M. Dworetsky* and C. S. Allen

Department of Physics and Astronomy, University College London, London WC1E 6BT

Electronic (Web Browser) preprint of a paper submitted 16th July 1998 and accepted for publication by Monthly Notices of the Royal Astronomical Society, 23 October 1998.

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We use exact curve-of-growth analysis and spectrum synthesis to deduce the abundance of Mn from high signal-to-noise visible-region échelle spectra of selected Mn I and Mn II lines in 24 HgMn stars. The results are compared to the Mn abundances derived from UV resonance lines by Smith & Dworetsky [1993]. We find excellent agreement for several unblended Mn lines and confirm the temperature dependence of the Mn abundance found by Smith & Dworetsky. The Mn II lines at 4206 and 4326 are much stronger than one would predict assuming the mean Mn abundances. The lack of agreement is greatest for stars with the strongest Mn II lines. Using ad hoc multicomponent fits to the profiles of sharp-lined stars, we show that the discrepancies can be explained by hyperfine structure that desaturates the lines, with full widths of the order of 0.06--0.09Å.

Key words: stars:abundances - stars:chemically peculiar - line:profiles

*Guest Observer, Lick Observatory