  Recent three-dimensional simulations have suggested that convective seed
perturbations from shell burning can play an important role in triggering
neutrino-driven supernova explosions. Since isolated simulations cannot
determine whether this perturbation-aided mechanism is of general relevance
across the progenitor mass range, we here investigate the pertinent properties
of convective oxygen and silicon burning shells in a broad range of
presupernova stellar evolution models. We find that conditions for
perturbation-aided explosions are most favourable in the extended oxygen shells
of progenitors between about 16 and 26 solar masses, which exhibit large-scale
convective overturn with high convective Mach numbers. Although the highest
convective Mach numbers of up to 0.3 are reached in the oxygen shells of
low-mass progenitors, convection is typically dominated by small-scale modes in
these shells, which implies a more modest role of initial perturbations in the
explosion mechanism. Convective silicon burning rarely provides the high Mach
numbers and large-scale perturbations required for perturbation-aided
explosions. We also find that about $40\%$ of progenitors between 16 and 26
solar masses exhibit simultaneous oxygen and neon burning in the same
convection zone as a result of a shell merger shortly before collapse.

Solar and Stellar Astrophysics