International Summer Institute for Modeling in Astrophysics

We investigate local radiative hydrodynamic instabilities in the envelopes of massive stars. Two different stellar models are considered, a simple polytropic model and a more realistic stellar evolution code model. For both cases, we compare the local optical depth and radiative flux with analytically derived instability criteria. Only a thin outer shell of the star, containing a mass of about 10^-6 M_star to 10^-5 M_star, can be subjected to this instability. However, the growth rate of the instability is relatively fast (about 10,000s) indicating a possible run-away effect.