Origin of anomalous Xe-H in nanodiamond stardust

Still today, the nucleosynthesis origin of Xe-II 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 (5) 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 fi to the measured Xe-H abundance ratios Xe-i/Xe-136 can be obtained with the high-S "main" component of a "cold" r-process variant.