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Preprint 01c/02

Temperature Scale and Iron Abundances of Very Hot Central Stars of Planetary Nebulae

Klaus Werner (1), Jochen L. Deetjen (1), Stefan Dreizler (1), Thomas Rauch (1), Jeff W. Kruk (2)

(1) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
(2) Department of Physics and Astronomy, JHU, Baltimore MD, U.S.A.

in: M. Dopita et al. (eds.): Planetary Nebulae: Their Evolution and Role in the Universe. ASP Conference Series, Vol. 2XX (2002)

Abstract. The determination of effective temperatures of very hot central stars (T_eff > 70.000 K) by model atmosphere analyses of optical H and He line profiles is afflicted with considerable uncertainty, primarily due to the lack of neutral helium lines. Ionization balances of metals, accessible only with UV lines, allow more precise temperature estimates. The potential of iron lines is pointed out. At the same time iron and other metal abundances, hardly investigated until today, may be derived from UV spectra. We describe recent HST spectroscopy performed for this purpose.

A search for iron lines in FUV spectra of the hottest H-deficient central stars (PG1159-type, T_eff > 100.000 K) taken with FUSE was unsuccessful. The derived deficiency is interpreted in terms of iron depletion due to n-capture nucleosynthesis in intershell matter, which is now exposed at the stellar surface as a consequence of a late He shell flash.

Key words: -

Paper (56k gzip'ed Postscript including figures)

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