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Abteilung Astronomie

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Preprint 01b/97

Abundance Patterns of Iron and Nickel in sdO Stellar Atmospheres

Stefan Haas(1), Ulrich Heber(1), Stefan Dreizler(2), Klaus Werner(3)

(1)Dr. Remeis-Sternwarte, Sternwartstr. 7, D-96049 Bamberg, Germany
(2)Institut für Astronomie und Astrophysik, Universität Kiel, D-24098 Kiel, Germany
(3)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany

Contribution to the 3rd Conference on Faint Blue Stars, Schenectady USA, October 13-17, 1996

Abstract. The UV spectra of sdO stars show many weak lines of mainly iron and nickel. The quantitative analyses of these lines is rendered difficult because non-LTE effects need to be accounted for. We present an investigation of the impact of iron group line blanketing on non-LTE model atmospheres of sdO stars. We discuss its influence on the atmospheric structure, on diagnostic line profiles and on the emergent UV and EUV spectrum. The computation of model atmospheres is based on the 'Accelerated Lambda Iteration' technique in combination with a statistical approach for the inclusion of millions of lines from iron group elements. We applied our models successfully to abundance analyses of iron and nickel lines in the high resolution IUE spectra of sdO stars. The derived abundance patterns of iron and nickel are of special interest since they can give direct hints to the primordial metallicity and can be used as an indicator for diffusion/radiative acceleration processes.

Paper (27k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de)
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