Modelling Hybrid Β Cephei / Spb Pulsations: Γ Pegasi

Recent photometric and spectroscopic observations of the hybrid variable γ Pegasi [6, 5] revealed 6 frequencies of the SPB type and 8 of the β Cep type pulsations. Standard seismic models, which have been constructed with OPAL [7] and OP [12] opacities by fitting three frequencies (those of the radial fundamental and two dipole modes), do not reproduce the frequency range of observed pulsations and do not fit the observed individual frequencies with a satisfactory accuracy. We argue that better fitting can be achieved with opacity enhancements, over the OP data, by about 20-50 percent around the opacity bumps produced by excited ions of the iron-group elements at temperatures of about 2× 105 K (Z bump) and 2×106 K (Deep Opacity Bump).