Speaker
Description
Type Ia supernovae (SNIa) are fundamental probes of cosmic expansion and major contributors to Galactic chemical evolution, yet the nature of their progenitors remains unsettled. Two main progenitor classes can be identified: the explosion of a near-Chandrasekhar-mass or a sub-Chandrasekhar-mass white dwarf. In recent work (Battino et al. 2025), complemented by earlier studies (Battino et al. 2020), we performed the first full nucleosynthesis calculations during the formation of near-Chandrasekhar white dwarfs in two key scenarios: slow merger of CO white dwarfs and H-accretion from a non-degenerate companion. We demonstrated that, in both cases, pre-explosive nuclear burning in the outer layers activates the $^{22}$Ne($\alpha$,n)$^{25}$Mg neutron source, efficiently producing trans-Fe elements like Rb, Sr, and Kr (exceeding their initial abundance by 1000 times), which will be ejected by the following explosion.
In this contribution, I present new theoretical results covering the last remaining channel able to form a near-Chandrasekhar SNIa progenitor: rapidly He-accreting white dwarfs ($\dot{M} \sim 10^{-6}\,M_{\odot}\,\mathrm{yr}^{-1}$). Also in this case, the $^{22}$Ne($\alpha$,n)$^{25}$Mg neutron source is activated during recurrent He-flashes along the accretion process, producing a thick surface layer highly enriched in trans-Fe species. Additionally, we discuss the case of slowly He-accreting white dwarfs ($10^{-8} < \dot{M}/(M_{\odot}\,\mathrm{yr}^{-1}) < 10^{-7}$), which are likely to end in a sub-Chandrasekhar explosion. While our preliminary results show that some trans-Fe production could also take place in this case, the heavy-element-enriched layer is very thin. This would severely limit the trans-Fe ejected yields from sub-Chandrasekhar explosions, likely to values at least 100 times lower than the yields from near-Chandrasekhar explosions.
We therefore confirm that a significant production of trans-Fe elements in SNIa progenitors can only be hosted by near-Chandrasekhar systems. This provides strong support for the use of trans-Fe species as a previously unexplored spectroscopic signature to discriminate between near- and sub-Chandrasekhar explosions.