Origin of anomalous Xe-H in presolar diamonds: Indications of a "cold" r-process

TL;DR

This study investigates the nucleosynthesis origin of Xe-H in presolar nanodiamonds, proposing a 'cold' r-process in supernovae as the most consistent explanation based on updated nuclear physics and astrophysical modeling.

Contribution

The paper introduces a novel 'cold' r-process scenario in supernovae, with detailed modeling of neutron freezeout conditions, to explain Xe-H isotopic anomalies in presolar diamonds.

Findings

A 'cold' r-process with fast freezeout best explains Xe-H data.

Eliminating the 'weak' r-process component improves model agreement.

Pure 'main' or 'strong' r-process scenarios align better with observed isotopic ratios.

Abstract

We report on a concerted effort aimed at understanding the nucleosynthesis origin of Xe-H in presolar nanodiamonds. Previously explored possible explanations have included a secondary neutron-burst process occurring in the He-shell of a type II supernova (SN), as well as a rapid separation, between unstable precursor isobars of a primary r-process, and stable Xe isotopes. Here we present results from the investigation of a rapid neutron-capture scenario in core-collapse SNe with different non-standard r-process variants. Our calculations are performed in the framework of the high-entropy-wind (HEW) scenario using updated nuclear-physics input. We explore the consequences of varying the wind expansion velocity (Vexp) for selected electron fractions (Ye) with their correlated entropy ranges (S), and neutron-freezeout temperatures (T9(freeze)) and timescales (tau-r(freeze). We draw several conclusions: For Xe-H a "cold" r-process with a fast freezeout seems to be the favored scenario. Furthermore, eliminating the low-S range (i.e. the "weak" r-process component) and maintaining a pure "main" or even "strong" r-process leads to an optimum overall agreement with the measured iXe/136Xe abundance ratios. Our results can provide valuable additional insight into overall astrophysical conditions of producing the r-process part of the total SS heavy elements in explosive nucleosynthesis scenarios.