Tracer particles for core-collapse supernova nucleosynthesis: The advantages of moving backward

TL;DR

This study compares backward and forward tracer particle reconstruction methods in multi-dimensional supernova simulations, finding backward integration more accurately reproduces nucleosynthesis yields, especially for rare isotopes, when inline tracers are unavailable.

Contribution

It demonstrates that backward integration of tracer particles better matches inline results for nucleosynthesis, especially after nuclear statistical equilibrium, improving post-processing accuracy.

Findings

Backward integration aligns closely with inline particle results.

Differences are larger for rare isotopes produced by few particles.

Backward method is recommended when inline tracers are not available.

Abstract

After decades, the theoretical study of core-collapse supernova explosions is moving from parameterized, spherically symmetric models to increasingly realistic multi-dimensional simulations. Obtaining nucleosynthesis yields based on such multi-dimensional core-collapse supernova (CCSN) simulations, however, is not straightforward and frequently tracer particles are employed. Tracer particles may be tracked in situ during the simulation, but often they are reconstructed in a post-processing step based on the information saved during the hydrodynamics simulation. Reconstruction can be done in a number of ways and here we compare the approaches of backward and forward integration of the equations of motion to the results based on inline particle trajectories. We find that both methods agree reasonably well with the inline results for isotopes for which a large number of particles contribute. However, for rarer isotopes that are produced only by a small number of particle trajectories, deviations can be large. For our setup, we find that backward integration leads to a better agreement with the inline particles by more accurately reproducing the conditions following freeze-out from nuclear statistical equilibrium, because the establishment of nuclear statistical equilibrium erases the need for detailed trajectories at earlier times. Based on our results, if inline tracers are unavailable, we recommend backward reconstruction, to the point when nuclear statistical equilibrium last applied, with an interval between simulation snapshots of at most 1 ms for nucleosynthesis post-processing.