ELECTRON-CAPTURE SUPERNOVAE AS THE ORIGIN OF ELEMENTS BEYOND IRON

We examine electron-capture supernovae (ECSNe) as sources of elements heavier than iron in the solar system and in Galactic halo stars. Nucleosynthesis calculations are performed on the basis of thermodynamic histories of mass elements from a fully self-consistent, two-dimensional hydrodynamic explosion model of an ECSN. We find that neutron-rich convective lumps with an electron fraction down to Y-e,Y-min = 0.40, which are absent in the one-dimensional counterpart, allow for interesting production of elements between the iron group and N = 50 nuclei (from Zn to Zr, with little Ga) in nuclear (quasi-) equilibrium. Our models yield very good agreement with the Ge, Sr, Y, and Zr abundances of r-process-deficient Galactic halo stars and constrain the occurrence of ECSNe to similar to 4% of all stellar core-collapse events. If tiny amounts of additional material with slightly lower Y-e,Y-min down to similar to 0.30-0.35 were also ejected-which presently cannot be excluded because of the limitations of resolution and two dimensionality of the model-a weak r-process can yield elements beyond N = 50 up to Pd, Ag, and Cd as observed in the r-process-deficient stars.