Kippenhahn diagrams showing the post-MS phases for the four models computed with an initial mass of 15 M_⊙. The vertical axis shows the mass coordinate, and the numbered lines show isoradius levels. Left column: Schwarzschild models. Right column: Ledoux models. Upper row: non-rotating models. Lower row: rotating models. The intermediate convective zone above the H-burning shell is clear in the Schwarzschild models and is associated with the slower expansion of the envelope.