New Calculations of Thermal Pulses and s–Process Nucleosynthesis in Agb Stars

Extract

A set of thermal pulse models was computed, for initial stellar masses extending from low (M=1.5, 3 M_⊙) to intermediate (M=5, 7 M_⊙), using the FRANEC evolutionary code and assuming standard mass loss and solar metallicity. The main features are: i) the third dredge–up is naturally found, even for core masses below 0.7–0.8 M_⊙; ii) before the dredge–up occurrence, the main characteristics of the models (convective shell mass, interpulse duration, overlapping between adjacent pulses) are determined solely by the core mass M_H , well reproducing a behaviour which is typical in the current literature (see e.g. Schonberner, 1979): in particular, the shell mass is a decreasing function of M_H ; iii) after dredge–up is started, the evolutionary track is modified and the strength of the pulses is enhanced; iv) the amount of dredge–up increases in time, from ≃ 10⁻⁴ M_⊙ to ≃ 10⁻³ M_⊙.