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Evolutionary Scenarios and Chemical Inhomogeneities of Extended Horizontal Branch Stars
|Solar and stellar modelling|
|Auteur(s) supplémentaire(s)||Lisa Esch, Pierre Demarque, and Sarbani Basu|
|Institution(s) supplémentaire(s)||Yale University, P.O. Box 208101, New Haven, CT 06520, USA|
|Extended Horizontal Branch (EHB) stars are observed in many|
globular clusters and as field stars in the Galactic halo. They
belong to old stellar populations of the halo and the old disk.
Their evolutionary status is unclear, and still a current subject of
debate. Current interest in these stars arise from their
association with the discoveries of helium abundance inhomogeneities in the globular clusters $omega$ Cen and NGC 2808. The origin of the inhomogeneities is not yet understood, but there are many interpretations.
In order to better understand EHB stars, we explore the evolution
of standard blue HB models using up-to-date physics. We present several grids of post-ZAHB evolutionary models to include both canonical and non-canonical evolutionary scenarios, as well as to compare models that contain semi-convection to models without semi-convection. We follow the models to the termination of nuclear helium burning. The detailed properties of the models, including shell flashes and breathing pulses, are described.