THE STABILITY OF MASSIVE MAIN-SEQUENCE STARS

The stability of massive main-sequence stars with respect to radial pe rturbations is re-examined using recently provided opacity tables, Thr ee types of instability are identified: (1) dynamical instabilities as sociated with the occurrence of strange modes; (2) instability of the first overtone caused by the kappa-mechanism; and (3) instability of t he fundamental mode due to a mixture of the kappa- and epsilon-mechani sms. Critical masses as a function of metallicity are determined for t he various instabilities. With respect to both range and strength, ins tabilities driven by the kappa- and epsilon-mechanisms are negligible when compared with strange-mode instabilities.