We calculate a grid of models with and without the effects of axial rotation for massive stars in the range of 9 to 60 M _ { \odot } and metallicity Z = 0.004 appropriate for the SMC .
Remarkably , the ratios \Omega / \Omega _ { \mathrm { crit } } of the angular velocity to the break–up angular velocity grow strongly during the evolution of high mass stars , contrary to the situation at Z = 0.020 .
The reason is that at low Z , mass loss is smaller and the removal of angular momentum during evolution much weaker , also there is an efficient outward transport of angular momentum by meridional circulation .
Thus , a much larger fraction of the stars at lower Z reach break–up velocities and rotation may thus be a dominant effect at low Z .
The models with rotation well account for the long standing problem of the large numbers of red supergiants observed in low Z galaxies , while current models with mass loss were predicting no red supergiants .
We discuss in detail the physical effects of rotation which favour a redwards evolution in the HR diagram .
The models also predict large N enrichments during the evolution of high mass stars .
The predicted relative N–enrichments are larger at Z lower than solar and this is in very good agreement with the observations for A–type supergiants in the SMC .
tars : evolution – Stars : rotation – supergiant – Magellanic Clouds