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Title:
The Elemental Abundances in Bare Planetary Nebula Central Stars and the Shell Burning in AGB Stars
Authors:
Werner, Klaus; Herwig, Falk
Affiliation:
AA(Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany; ), AB(Theoretical Astrophysics Group, Los Alamos National Laboratory, Mail Stop B227, Los Alamos, NM 87545; )
Publication:
The Publications of the Astronomical Society of the Pacific, Volume 118, Issue 840, pp. 183-204. (PASP Homepage)
Publication Date:
02/2006
Origin:
UCP
PASP Keywords:
Stars: AGB and Post-AGB, Stars: Abundances, Stars: Atmospheres, Stars: Evolution, Stars: Interiors, nuclear reactions, nucleosynthesis, abundances
Abstract Copyright:
(c) 2006: The Astronomical Society of the Pacific
DOI:
10.1086/500443
Bibliographic Code:
2006PASP..118..183W

Abstract

We review the observed properties of extremely hot, hydrogen-deficient post-asymptotic giant branch (AGB) stars of spectral type [WC] and PG1159. Their H deficiency is probably caused by a (very) late helium-shell flash or an AGB final thermal pulse, laying bare interior stellar regions that are usually kept hidden below the hydrogen envelope. Thus, the photospheric elemental abundances of these stars allow us 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 that simulate AGB evolution and the occurrence of a late He-shell flash. We compare predicted elemental abundances to those determined by quantitative spectral analyses performed with advanced non-LTE model atmospheres. 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.