Instabilities of captured shocks in the envelopes of massive stars

The evolution of strange-mode instabilities into the non-linear regime has been followed by a numerical simulation for an envelope model of a massive star with a solar chemical composition, M = 50 M ○. , T eff = 10 4 K and L = 1.17 x 10 6 L ○. . Contrary to previously studied models, for these parameters, shocks are captured in the H-ionization zone and perform rapid oscillations within it. A linear stability analysis is performed to verify that this behaviour is physical. The origin of an instability discovered in this way is identified by the construction of an analytical model. As a result, stratification turns out to be essential for instability. The difference from common stratification instabilities - for example, convective instabilities - is discussed.