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 Ltot. All but one of the simulations reach a quasi-stationary state with the entrainment rate and convective velocity proportional to Ltot and L1tot/3, respectively. Carbon burning provides 14-33 per cent of the total luminosity, depending on the set of reactions considered. Equivalent simulations done on 7683 and 11523 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.
Bibliographical noteFunding Information:
RA, who completed most of this work as a CITA (Canadian Institute for Theoretical Astrophysics) national fellow, acknowledges support from CITA and from the Klaus Tschira Stiftung. PW acknowledges NSF (National Science Foundation) grants 1413548 and 1515792. FH acknowledges support from a NSERC (National Sciences and Engineering Research Council) Discovery grant. This research was conducted as part of the JINA (Joint Institute for Nuclear Astrophysics) Center for the Evolution of the Elements (NSF grant PHY-1430152). NCSA’s (National Center for Supercomputing Applications’) Blue Waters and Compute Canada/WestGrid provided the computing and data processing resources for this project. We thank two anonymous referees for their comments, which improved the quality of this paper. This work benefited from the use of a large amount of free software, most importantly the MESA stellar-evolution code, IPYTHON/JUPYTER notebooks, PYTHON libraries MATPLOTLIB and PYSHTOOLS, the FFMPEG software suite, Subversion revision control system, or the LaTeX document preparation system.
- Stars: evolution
- Stars: interiors
- Stars: massive