Kippenhahn diagrams of two 16 M_⊙ models computed with a convective core reduction parameter of f = 1.12 (top) and f = 1.20 (bottom). Convective (green) and semiconvective (red) regions are shown as a function of mass coordinate and time. Thermonuclear energy generation or loss is colour-coded as shown on the scale on the right-hand side. The evolutionary tracks of both models in the HR diagram are shown in Fig. 2.