Electron-Capture Supernovae as the Origin of Elements Beyond Iron

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 Y e,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 Y e,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.

Explosive Nucleosynthesis of Ultra-Stripped Type Ic Supernovae

“…This figure indicates large abundance ratios in elements Zn-Mo, i.e., the abundance ratio of the first-peak r-process elements is large. The similar trend has been found in electron capture SNe [9]. An ultra-stripped SN has only thin Si and O/Ne-layers on the Fe core.…”

Nucleosynthesis in Supernovae, Hypernovae/Gamma-ray Bursts and Compact Binary Mergers

“…Electron capture supernovae, do not produce much Fe/Ni, thus, the non-correlation with r-elements would hold, but this mass range in the IMF leads to frequent events, and simulations (e.g. [77]) also indicate that at most a weak r-process can be obtained. 3.…”

“…EC supernovae produce small amounts of alpha-and Fe-peak elements (see e.g. [77]). 10 -90 M ⊙ stars undergo Fecore collapse.…”

Evolution and Nucleosynthesis of Low and Intermediate-Mass Stars

“…The nucleosynthesis yields of super-AGB stars is uncertain: they go through HBB but their contribution to heavy element production is currently unclear. Electron capture supernova may produce r process elements [37,38], and super-AGB stars may be a site of the i process [21].…”