THE STABILITY OF MASSIVE STARS AND ITS DEPENDENCE ON METALLICITY AND OPACITY

Following a similar investigation based on the LAOL opacities, the sta bility of massive stars is re-examined using the latest available OPAL opacity tables. Two groups of dynamical strange-mode and mode-couplin g instabilities are identified, one associated with He ionization and the other with the enhancement of opacity due to heavy elements. In th e Hertzsprung-Russell diagram, the stability boundary of the first gro up closely resembles the observed Humphreys-Davidson limit, while the second group provides a strongly metallicity-dependent instability dom ain that covers the range of observed luminous blue variables for sola r chemical composition. Relations to instabilities on the upper main s equence and in the beta Cepheid regime are discussed, and the signific ance of these strong instabilities for stellar and galactic evolution is stressed.