Origin of Anomalous Xe-H in Nanodiamond Stardust

TL;DR

This study investigates the nucleosynthesis origin of Xe-H in presolar nanodiamonds by analyzing r-process nucleosynthesis in supernova ejecta, suggesting a 'cold' r-process as the best fit for observed Xe-H ratios.

Contribution

It explores non-standard r-process variants in supernova models to explain Xe-H isotopic abundances in nanodiamonds, identifying a 'cold' r-process as the most consistent scenario.

Findings

High-S 'main' component fits Xe-H ratios well

Cold r-process variant explains isotopic features

Parameter variations refine nucleosynthesis models

Abstract

Still today, the nucleosynthesis origin of Xe-H in presolar nanodiamonds is far from understood. Historically, possible explanations were proposed by a secondary "neutron-burst" process occurring in the He- or C/O-shells of a type-II supernova (SN-II), which are, however, not fully convincing in terms of modern nucleosynthesis conditions. Therefore, we have investigated Xe isotopic abundance features that may be diagnostic for different versions of a classical, primary r-process in high-entropy-wind (HEW) ejecta of core-collapse SN-II. We report here on parameter tests for non-standard r-process variants, by varying electron abundances (Y$_e$), ranges of entropies (S) and expansion velocities (V$_{exp}$) with their correlated neutron-freezeout times ($\tau$(freeze)) and temperatures (T$_9$(freeze)). From this study, we conclude that a best fit to the measured Xe-H abundance ratios $^i$Xe/$^{136}$Xe can be obtained with the high-S "main" component of a "cold" r-process variant.