P o S ( N I C X I I I ) 0 0 1 Stellar Structure , Evolution and Nucleosynthesis : Key Uncertainties and their Impact

After a brief introduction, we focus on a few key physical ingredients for the evolution of stars and the related nucleosynthesis, namely mass loss, convection and rotation. We first review the current status of their uncertainties and then discuss their impact. Concerning convection, we list key existing and future 3D hydrodynamics simulations needed to constrain prescriptions used in the modelling of convective boundaries in 1D codes. We then discuss the impact of rotation on the s process in both massive and low-mass stars. Massive star models including rotation-induced mixing reproduce much better several observational constraints (e.g. primary nitrogen production and boosted weak s process). AGB models including rotation, on the other hand, fail to produce s process although codes using different prescriptions yield contradictory results. The inclusion of the interaction of rotation with magnetic fields has a positive effect on the predicted spin of white dwarfs. We investigated the impact of this interaction on the 13C-pocket and find that magnetic fields may also help rotating stars produce more (rather than less) s-process. Current uncertainties in the treatment of convection, rotation and magnetic fields limit the predictive power of stellar evolution models and different implementations in codes lead to different results. Combining 3D hydrodynamics simulations and theoretical work with observational constraints will be needed to improve the situation. In this context, nucleosynthetic signatures of these processes will play a key role as they have up to now.