Testing stellar models: the red giant stage

The He burning stage of stellar evolution, when stars increase enormously in size and become Red Giants, is of particular importance for the production of C, O, and the s-process abundances in the universe. From observations these stars are known for the efficient transport of freshly synthesised material to the surface and its ejection into the interstellar medium by strong stellar winds. In view of the complexity of this scenario, s-process nucleosynthesis provides a valuable tool for testing and assisting the yet uncertain stellar models in surprising detail. (orig.)