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Title:
The Element Abundances in Bare Planetary Nebula Central Stars and the Shell Burning in AGB Stars
Authors:
Werner, K.; Herwig, F.
Journal:
eprint arXiv:astro-ph/0512320
Publication Date:
12/2005
Origin:
ARXIV
Comment:
Review, accepted for publication in PASP, Febr. 06 issue. For high resolution versions of Figures 1 and 6 see preprint on http://astro.uni-tuebingen.de/publications/paper_05_05.shtml
Bibliographic Code:
2005astro.ph.12320W

Abstract

We review the observed properties of extremely hot hydrogen-deficient post-AGB stars of spectral type [WC] and PG1159. Their H-deficiency is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse, laying bare interior stellar regions which are usually kept hidden below the hydrogen envelope. Thus, the photospheric element abundances of these stars allow to draw conclusions about details of nuclear burning and mixing processes in the precursor AGB stars. We summarize the state-of-the-art of stellar evolution models which simulate AGB evolution and the occurrence of a late He-shell flash. 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. Future work can contribute to an even more complete picture of the nuclear processes in AGB stars.

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Title:
Evolution of Asymptotic Giant Branch Stars
Authors:
Herwig, Falk
Journal:
Annual Review of Astronomy & Astrophysics, vol. 43, Issue 1, pp.435-479 (Annual Reviews Homepage)
Publication Date:
09/2005
Origin:
ARAA
Bibliographic Code:
2005ARA&A..43..435H

Abstract

The current status of modeling the evolution and nucleosynthesis of asymptotic giant branch (AGB) stars is reviewed. The principles of AGB evolution have been investigated in recent years leading to improved and refined models, for example with regard to hot-bottom burning or the third dredge-up. The postprocessing s-process model yields quantitative results that reproduce many observations. However, these and most other processes in AGB stars are intimately related to the physics of stellar mixing. Mixing in AGB stars is currently not well-enough understood for accurate yield predictions. Several constraints and methods are available to improve the models. Some regimes of AGB evolution have not yet been studied in sufficient detail. These include the super-AGB stars and AGB stars at extremely low or ultra low metallicity.