Asteroseismology of hybrid pulsators made possible: simultaneous MOST space photometry and ground-based spectroscopy of Gamma Peg

TL;DR

This study combines space photometry and ground spectroscopy to analyze Gamma Peg, revealing multiple pulsation modes and providing detailed seismic modeling, marking a significant step in hybrid pulsator research.

Contribution

It presents the first comprehensive detection and identification of high-order g modes and low-order p modes in Gamma Peg, enabling advanced seismic modeling of this hybrid pulsator.

Findings

Detection of six high-order g modes and eight low-order Beta Cep oscillations.

All predicted pulsation modes are observed and identified.

Gamma Peg is confirmed as a single star, not a binary.

Abstract

We have acquired simultaneous high-precision space photometry and radial velocities of the bright hybrid Beta Cep/SPB pulsator Gamma Peg. Frequency analyses reveal the presence of six 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 l = 0 - 2. An 8.5 solar mass model reproduces the observed pulsation frequencies; all theoretically predicted modes 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 p and mixed modes have been detected and identified to be usable for in-depth seismic modeling.