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Preprint 12c/08

Abundances in Hot Evolved Stars

Klaus Werner (1), Thomas Rauch (1), Jeffrey W. Kruk (2)

(1) Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, University of Tübingen, 72076 Tübingen, Germany
(2) Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, U.S.A.

To be published in: Proceedings: Future Directions in Ultraviolet Spectroscopy Conference, Annapolis, MD, 2008

Abstract. The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden intershell region. Thus, the photospheric element abundances of these stars allow us to draw conclusions about details of nuclear burning and mixing processes in the precursor AGB stars. We compare predicted element abundances to those determined by quantitative spectral analyses performed with advanced non-LTE model atmospheres. A good qualitative and quantitative agreement is found for many species (He, C, N, O, Ne, F, Si, Ar) but discrepancies for others (P, S, Fe) point at shortcomings in stellar evolution models for AGB stars. Almost all of the chemical trace elements in these hot stars can only be identified in the UV spectral range. The Far Ultraviolet Spectroscopic Explorer and the Hubble Space Telescope played a crucial role for this research.

Preprint (754 kb PDF file including figures)

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