Multiwavelength Studies of β Cephei Stars
Pulsation, Rotation and Mass Loss in Early-Type Stars
As first pointed out by Moskalik and Dziembowski (1992) all β Cephei stars lie within the domain of H-R diagram where κ-mechanism effectively drives pulsations in the stellar layers with Τ « 2xl0 5 K. For most of these objects a chemical composition described by X = 0.70 and Ζ = 0.02 is sufficient to account for the pulsations, cf. Dziembowski and Pamyatnykh (1993) . Recently, Cugier, Dziembowski and Pamyatnykh (1993) have investigated how the present knowledge about nonadiabatic observables of
... β Cephei stars affects methods of identification of the spherical harmonic degree, /. They found that good photometric and radial velocity data should result in unambiguous identification of /. Cugier, Dziembowski and Pamyatnykh also concluded that nonadiabatic observables can be used to obtain mean stellar parameters of pulsating stars. We report here, as examples, the studies of δ Ceti and BW Vulpeculae. The above mentioned analysis of the ground-based photometric data of δ Cet taken from Jerzykiewicz et al. (1988) indicates: / -0, Ρ2, logT e ff = 4.346 and log # = 3.73. Figure 1 shows that indeed only a model with / = 0 is able to explain the observed flux behaviour of δ Cet in the satellite ultraviolet region. Futhermore, the observed phases of flux maximum as a function of wavelength offer the possibility to determine the effective temperature of β Cephei stars with high precision as Fig. 2 shows for δ Cet. In Fig. 3 the observed light ranges for BW Vul are compared with the nonadiabatic model (/ = 0, pi, logT e ff = 4.29 and logg = 3.71). As one can see, a very good agreement exists even for this star, which is rather extreme case among β Cephei stars considering its large light and radial-velocity amplitudes.