Instabilities And Pulsations In Models Of The B-Type Supergiant Kappa Cassiopeiae (Hd 2905)

For the B-type supergiant kappa Cassiopeiae (HD 2905), variabilities with periods between several hours and a few days have been observed both photometrically and spectroscopically. A recent study of this star by SimOn-Diaz et al. has revealed variability with a dominant period of 2.7 d. To understand this variability, we present a linear non-adiabatic stability analysis with respect to radial perturbations for models of kappa Cassiopeiae. Instabilities associated with the fundamental mode and the first overtone are identified for models with masses between 27 and 44 M-circle dot. For selected models, the instabilities are followed into the nonlinear regime by numerical simulations. As a result, finite amplitude pulsations with periods between 3 and 1.8 d are found. The model with a mass of 34.5 M-circle dot exhibits a pulsation period of 2.7 d consistent with the observations. In the nonlinear regime, the instabilities may cause a substantial inflation of the envelope.