Transition masses (M_O1, M_O2, M_HeF) as a function of metallicity in the case of no rotation. The red and green lines indicate M_O1 and M_O2, respectively; the blue line indicates M_HeF. The red area indicates models with a radiative core without convective overshooting. The yellow area delineates the region of growing overshooting efficiency, while full overshooting efficiency occurs in the region above the green line. The vertical dotted grey lines mark the six computed initial metallicities. The solar metallicity is Z_⊙ = 0.01524, from Caffau et al. (2011).