Testing convective mixing in massive stars

Stellar evolution sequences are presented for stars in the mass range 5-21 M ⊙ with initial metallicity Z = 0.002 and initial helium abundance Y = 0.25 resembling average composition of the Small Magellanic Cloud. The stellar models are calculated with different treatment of convective mixing in regions of varying molecular weight gradient. The stellar sequences are used to study the morphology of the well-observed star cluster NGC 330 in the SMC. We argue that convective mixing should be inhibited in inhomogeneous stellar regions in order to understand the morphology of NGC 330. In other words, our contribution emphasizes the important role of semi-convection in the evolution of massive stars.