A selfconsistent hydrodynamic calculation of a very massive star (MZAMS = 2OOM⊙) including turbulent pressure and energy has been performed. In the contraction phase after core hydrogen exhaustion, the star moves towards cool surface temperatures in the HR diagram (cf. Fig. 1). Consequently, (at Teff ⋍ 8000K) an envelope convection zone developes, and its inner boundery moves inwards with time. First, the envelope remains in hydrostatic equilibrium, with radiation pressure correspondingly decreasing as turbulent pressure increases (gas pressure is small). However, due to the fact, that the gradient of the turbulent pressure is directed inwards at the bottom of the convective zone, this part of the star rapidly contracts. Due to the released contraction energy, the luminosity locally exceeds the Eddington-luminosity. It cannot be transported outwards by convection in the upper part of the convection zone, where convective energy transport is inefficient (▽c ⋍ ▽r) . Thus, the local super-Eddington luminosity leads to the ejection of the overlying layers.
Convectively Generated Turbulent Pressure: A Possible Cause for η Car - Type Shell Ejections