The stability of massive stars and its dependence on metallicity and opacity

Abstract

Following a similar investigation based on the LAOL opacities, the stability of massive stars is re-examined using the latest available OPAL opacity tables. Two groups of dynamical strange-mode and mode-coupling instabilities are identified, one associated with He ionization and the other with the enhancement of opacity due to heavy elements. In the Hertzsprung–Russell diagram, the stability boundary of the first group closely resembles the observed Humphreys–Davidson limit, while the second group provides a strongly metallicity-dependent instability domain that covers the range of observed luminous blue variables for solar chemical composition. Relations to instabilities on the upper main sequence and in the β Cepheid regime are discussed, and the significance of these strong instabilities for stellar and galactic evolution is stressed.