Impact of 3D Macrophysics and Nuclear Physics on the <i>p</i> -nuclei in O–C Shell Mergers

Abstract O–C shell mergers in massive stars are a site for producing the p- nuclei by the γ process, but 1D stellar models rely on mixing length theory (MLT), which does not match the radial velocity profiles of 3D hydrodynamic simulations. We investigate how 3D macrophysics-informed mixing impacts the nucleosynthesis of p- nuclei. We postprocess the O shell of the M ZAMS = 15 M ⊙ , Z = 0.02 model from the NuGrid stellar data set. Applying a downturn to velocities at the boundary and increasing velocities across the shell as obtained in previous results, we find a nonlinear, nonmonotonic increase in p -nuclei production with a spread of 0.96 dex and find that isotopic ratios can change. Reducing C-shell ingestion rates as found in 3D simulations suppresses production, with spreads of 1.22–1.84 dex across MLT and downturn scenarios. Applying dips to the diffusion profile to mimic quenching events also suppresses production, with a 0.51 dex spread. We analyze the impact of varying all photodisintegration rates of unstable n -deficient isotopes from Se to Po by a factor of 10 up and down. The nuclear physics variations for the MLT and downturn cases have a spread of 0.56–0.78 dex. We also provide which reaction rates are correlated with the p- nuclei and find few correlations shared between mixing scenarios. Our results demonstrate that uncertainties in mixing arising from uncertain 3D macrophysics are as significant as nuclear physics and are crucial for understanding p -nuclei production during O–C shell mergers quantitatively.