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After off-center C ignition in the cores of super-AGB stars the C flamepropagates all the way down to the center, trailing behind it the C-shellconvective zone, and thus building a degenerate ONe core. This standard pictureis obtained in stellar evolution simulations if the bottom C-shell convectionboundary is assumed to be a discontinuity associated with a strictinterpretation of the Schwarzschild condition for convective instability.However, this boundary is prone to additional mixing processes, such asthermohaline convection and convective boundary mixing. Using hydrodynamicsimulations we show that, contrary to previous results, thermohaline mixing istoo inefficient to interfere with the C-flame propagation. However, even asmall amount of convective boundary mixing removes the physical conditionsrequired for the C-flame propagation all the way to the center. This resultholds even if we allow for some turbulent heat transport in the CBM region. Asa result, super AGB stars build in their interiors hybrid C-O-Ne degeneratecores composed of a relatively large CO core (M_CO ~ 0.2 M_sun) surrounded by athick ONe zone (M_ONe ~ 0.85 M_sun) with another thin CO layer above. Ifexposed by mass loss, these cores will become hybrid C-O-Ne white dwarfs.Otherwise, the ignition of C-rich material in the central core, surrounded bythe thick ONe zone, may trigger a thermonuclear supernova explosion. Thequenching of the C-flame may have implications for the ignition mechanism of SNIa in the double-degenerate merger scenario.

The C-flame Quenching by Convective Boundary Mixing in Super-AGB Stars and the Formation of Hybrid C/O/Ne White Dwarfs and SN Progenitors