ON NONRADIAL OSCILLATIONS OF B-TYPE STARS

The excitation mechanisms behind the slow pulsations - with periods of the order of one day - of OB stars are discussed on the basis of numerical computations. Non-radial, non-adiabatic stability analysis is performed on a set of evolutionary models with masses between 5.2 M. and 12.1 M.. The long-period oscillations in stellar models below the newly recovered beta Cephei region are found to be excited by the iron bump in the newly available OPAL opacities. For more massive stars exhibiting oscillations with periods of the order of one day, however, another excitation mechanism must be sought.