Modelling hybrid Beta Cephei/SPB pulsations: Gamma Pegasi

TL;DR

This paper models the hybrid Beta Cephei/SPB pulsations of Gamma Pegasi, showing that opacity enhancements improve the fit to observed frequencies beyond standard models.

Contribution

It introduces opacity enhancements around iron-group element bumps to better match observed pulsation frequencies in Gamma Pegasi.

Findings

Standard models fail to fit observed frequencies accurately.

Opacity increases of 20-50% improve model fits.

Enhanced models better reproduce the observed pulsation spectrum.

Abstract

Recent photometric and spectroscopic observations of the hybrid variable Gamma Pegasi (Handler et al. 2009, Handler 2009) revealed 6 frequencies of the SPB type and 8 of the Beta Cep type pulsations. Standard seismic models, which have been constructed with OPAL (Iglesias & Rogers 1996) and OP (Seaton 2005) 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 200 000 K (Z bump) and 2 million K (Deep Opacity Bump).