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Astron. Astrophys. 348, 940-944 (1999)

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The iron abundance in hot central stars of planetary nebulae derived from IUE spectra *

J.L. Deetjen, S. Dreizler, T. Rauch and K. Werner

Institut für Astronomie und Astrophysik, Universität Tübingen, Waldhäuser Strasse 64, D-72076 Tübingen, Germany

Received 11 June 1999 / Accepted 5 July 1999

Abstract

We present the first attempt to determine the iron abundance in hot central stars of planetary nebulae. We perform an analysis with fully metal-line blanketed NLTE model atmospheres for a sample of ten stars ([FORMULA] [FORMULA] 70 000 K) for which high-resolution UV spectra are available from the IUE archive. In all cases lines of FeVI or FeVII can be identified. As a general trend, the iron abundance appears to be subsolar by 0.5-1 dex, however, the S/N of the IUE spectra is not sufficient to exclude a solar abundance in any specific case. Improved spectroscopy by either FUSE or HST is necessary to verify the possibility of a general iron deficiency in central stars. The suspected deficiency may be the result of gravitational settling in the case of three high-gravity objects. For the other stars with low gravity and high luminosity dust fractionation during the previous AGB phase is a conceivable origin.

Key words: stars: abundances – stars: atmospheres – stars: evolution – stars: AGB and post-AGB – stars: white dwarfs – ultraviolet: stars

* Based on observations with the International Ultraviolet Explorer (IUE) satellite

Send offprint requests to: J.L. Deetjen

Correspondence to: deetjen@astro.uni-tuebingen.de

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© European Southern Observatory (ESO) 1999

Online publication: August 13, 199
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