On the Nucleosynthetic Origin of Presolar Silicon Carbide X-Grains

Abstract

In this paper we present an extension of our nucleosynthesis parameter study within the classical neutrino-driven wind scenario of core-collapse supernovae (ccSNe). The principal aim of this decade-old study was to shine light on the production of the historical ‘p-only’ isotopes of the light trans-Fe elements in the Solar System (S.S.). One of our earliest key findings was the co-production of neighbouring classical ‘s-only’ and ‘r-only’ isotopes between Zn (Z = 30) and Ru (Z = 44), alongside the synthesis of light p-isotopes, under similar conditions of a moderately neutron-rich, low-entropy, charged-particle component of Type II SNe wind ejecta. We begin this analysis by expressing the need for nuclear-structure input from detailed spectroscopic experiments and microscopic models in the relevant shape-transition mass region between N = 50 and N = 60. Then, we focus on the unique nucleosynthetic origin of the anomalous isotopic compositions of Zr (Z = 40), Mo (Z = 42) and Ru (Z = 44) in presolar silicon carbide X-grains. In contrast to the interpretation of other studies, we show that these grains do not reflect the signature of a ‘clean’ stellar scenario but are mixtures of an exotic rapid (r-process like) nucleosynthesis component and different fractions of S.S. material. Thus, the synthesis of these light isotopes through a ‘primary’ production mode provides further means to revise the abundance estimates of the light trans-Fe elements in the S.S., reducing our dependence on still favoured ‘secondary’ scenarios like Type Ia SNe or neutron-bursts in exploding massive stars.