S-process nucleosynthesis - Classical approach and asymptotic giant branch models for low-mass stars

A critical comparison is made between the results of s-process nucleosynthesis obtained with the phenomenological classical approach and a stellar model for helium shell burning in low-mass stars. For the first time, close agreement is found between the abundances determined by the classical analysis and the results of a stellar model. The calculated abundances are found in good agreement with the s-process yields observed in solar material, and the corresponding quantities characterizing the neutron exposure are outlined in detail. Emphasis is laid on the information deduced from the abundance patterns in s-process branchings, i.e., neutron density and temperature. Despite the conceptual differences between the steady flow approximation of the classical approach and the dynamical environment of thermal pulses in low-mass stars, the results of both models are quite similar, but still obscured by the present uncertainties of the nuclear input data; further improvements are required to quantify the trends of the true physical conditions during the s-process which start to emerge from the above studies.