3D hydrodynamic simulations of C ingestion into a convective O shell

Interactions between convective shells in evolved massive stars have been linked to supernova impostors, to the production of the odd-Z elements Cl, K, and Sc, and they might also help generate the large-scale asphericities that are known to facilitate shock revival in supernova explosion models. We investigate the process of ingestion of C-shell material into a convective O-burning shell, including the hydrodynamic feedback from the nuclear burning of the ingested material. Our 3D hydrodynamic simulations span almost 3 dex in the total luminosity L-tot. All but one of the simulations reach a quasi-stationary state with the entrainment rate and convective velocity proportional to L-tot and L-tot(1/3) tot, respectively. Carbon burning provides 14-33 per cent of the total luminosity, depending on the set of reactions considered. Equivalent simulations done on 768(3) and 1152(3) grids are in excellent quantitative agreement. The flow is dominated by a few large-scale convective cells. An instability leading to large-scale oscillations with Mach numbers in excess of 0.2 develops in an experimental run with the energy yield from C burning increased by a factor of 10. This run represents most closely the conditions expected in a violent O-C shell merger, which is a potential production site for odd-Z elements such as K and Sc and which may seed asymmetries in the supernova progenitor. 1D simulations may underestimate the energy generation from the burning of ingested material by as much as a factor 2 owing to their missing the effect of clumpiness of entrained material on the nuclear reaction rate.