Synthetic super-AGB stars

We describe our first attempt at modelling nucleosynthesis in massive AGB stars which have undergone core carbon burning, the super-AGB stars. We fit a synthetic model to detailed stellar evolution models in the mass range 9< M/M_⊙<11.5 (Z=0.02), and extrapolate these fits to the end of the AGB. We determine the number of thermal pulses and AGB lifetime as a function of mass and mass-loss prescription. Our preliminary nucleosynthesis calculations show that, for a reasonable mass-loss rate, the effect of hot-bottom burning in super-AGB stars on the integrated yield of a stellar population is not large. There are many uncertainties, such as mass-loss and convective overshooting, which prevent accurate yield calculations. However, as potential progenitors of electron-capture supernovae, these stars may contribute 7% of non-type-Ia supernovae.