A hybrid β Cephei-SPB star in a binary system: γ  Pegasi

Observatoire de la Côte d'Azur, Département GEMINI – UMR 6203, BP 4229, 06304 Nice Cedex 4, France e-mail: chapellier@obs-nice.fr

Received: 12 July 2005
Accepted: 24 October 2005

Abstract

High resolution and high signal to noise ratio spectroscopic observations of the classical β Cephei star γ Peg were obtained between 1991 and 2005. The analysis of these data combined with previously published results shows that γ Peg is a spectroscopic binary with an orbital period of 370.5 d. We discovered three new frequencies in addition to the well-known 6.5897 d^-1 (0.15175 d) one. That at 6.01 d^-1 is a typical β Cephei frequency. The two others at 0.68 and 0.87 d^-1 are similar to the high degree g-mode frequencies found in SPB stars. Thus, γ Peg is a hybrid β Cephei-SPB star. Its position in the HR diagram is compatible with such a status. 
In addition, a small increase of the main period has been detected between the 1995 and 2005 observations.