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Preprint 04/04

Identification of neon in FUSE and VLT spectra of extremely hot hydrogen-deficient (pre-) white dwarfs

K. Werner (1), T. Rauch (1,2), E. Reiff (1), J.W. Kruk (3) and R. Napiwotzki (4)

(1) Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
(2) Dr.-Remeis-Sternwarte, Universität Erlangen-Nürnberg, Sternwartstraße 7, D-96049 Bamberg, Germany
(3) Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, U.S.A.
(4) Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK

To be published in: A&A

Abstract. One of the strongest absorption lines observed in far-ultraviolet FUSE spectra of many PG1159 stars remained unidentified up to now. We show that this line, located at 973.3 Å, stems from Ne-VII. We also present new optical high-resolution spectra of PG1159 stars, obtained with the ESO VLT, which cover the Ne-VII ~3644Å line and a newly identified Ne-VII multiplet in the 3850 - 3910Å region. We compare the observed neon lines with NLTE models and conclude a substantial neon overabundance in a number of objects. Although a detailed analysis is still to be performed in order to compare quantitatively the abundances with evolutionary theory predictions, this corroborates the idea that the PG1159 stars and their immediate progenitors, the [WC]-type nuclei of planetary nebulae, display intershell matter of their precursor AGB stars. Possibly as the consequence of a late He-shell flash, H-deficient and (s-processed) Fe-depleted matter, that is strongly enriched by 3-alpha-processed elements (C, O, Ne), is dredged up to the surface. Hence, a detailed study of the element abundance patterns in these peculiar stars gives the unique possibility to probe mixing and nucleosynthesis processes in the precursor AGB stars.
 
Key words: stars: abundances - stars: atmospheres - stars: evolution - stars: AGB and post-AGB - stars: white dwarfs

Preprint (847 kb PDF file including figures)
Astrophysics (astro-ph): astro-ph/0407356

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