Asteroseismology of hybrid pulsators made possible: simultaneous MOST space photometry and ground-based spectroscopy of [gamma] PEG

Abstract

We have acquired simultaneous high-precision space photometry and radial velocities of the bright hybrid [beta] Cep/Slowly Pulsating B pulsator [gamma] Peg. Frequency analyses reveal the presence of six gravity (g) modes of high radial order together with eight low-order [beta] Cep oscillations in both data sets. Mode identification shows that all pulsations have spherical degrees = 0–2. An 8.5M[circle dot] model reproduces the observed pulsation frequencies; all theoretically predicted modes in the [beta] Cep domain are detected. We suggest, contrary to previous authors, that [gamma] Peg is a single star; the claimed orbital variations are due to g-mode pulsation. [gamma] Peg is the first hybrid pulsator for which a sufficiently large number of high-order g modes and low-order pressure (p) and mixed modes have been detected and identified to be usable for in-depth seismic modeling.