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A B S T R A C TNumerical simulations of the evolution of strange-mode instabilities into the non-linear regime have been performed for massive objects and Wolf-Rayet stars. Velocity amplitudes above 10 2 km s ¹1 can be reached which exceed the escape velocity and imply mass loss for massive objects. Although for Wolf-Rayet stars direct mass loss is not observed, the velocity field established by the instability may be sufficient to initiate a line-driven wind. The results are sensitive to the numerical treatment of the problem.

Strange -Mode Instabilities in Luminous StarsIf radiation pressure contributes signijicantly to the total pressure in models f o r the envelopes of hot and luminous stars, such as massive objects and Wolf -Rayet stars, strangemode instabilities with growth rates in the dynamical range do occur. T h e properties of these mechanical instabilities are reviewed and a n intuitive model of t h e underlying in.sta.bility mechanism i s discussed. Adopting spherical geometry the evolution of the instabilities has been followed into the nonlinear regime by numerical simulation. Multiple shocks are formed and velocity amplitudes above lo2 km/sec are reached which can imply direct mass loss of the objects.2 GLATZEL, w.: On the origin of strange modes and the mechanism of related instabilities; MNRAS 271