Electron-capture supernovae as the origin of elements beyond iron

TL;DR

This study investigates electron-capture supernovae as potential sources of elements beyond iron, using advanced 2D models to match observed stellar abundances and estimate their contribution to galactic chemical evolution.

Contribution

It introduces 2D hydrodynamic models revealing neutron-rich convective lumps that produce elements between the iron group and N=50 nuclei, improving understanding of nucleosynthesis in ECSNe.

Findings

ECSNe can produce elements from Zn to Zr in agreement with halo star observations.

ECSNe contribute approximately 4% to all core-collapse supernovae.

Additional low Ye,min ejecta could enable weak r-process nucleosynthesis beyond N=50.

Abstract

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 (2D) hydrodynamic explosion model of an ECSN. We find that neutron-rich convective lumps with an electron fraction down to Ye,min=0.40, which are absent in the one-dimensional (1D) 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 ~4% of all stellar core-collapse events. If tiny amounts of additional material with slightly lower Ye,min down 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.