Atmospheric shock effects in early B stars.

The proposal that radial motions might explain the observational peculiarities of Beta Cephei variables is examined by generating a series of isothermal radial-shock models in suitable early B star atmospheres. The model atmospheres used as initial equilibrium configurations have (effective temperature, log g) values of (23,000 K, 3.62), (22,500 K, 4.0), and (25,000 K, 4.0). The models are discussed in the context of the radial-velocity 'stillstand' effect and line splitting, as observed in the large-amplitude variable BW Vul. Comparison of models based on the three chosen atmospheres shows that over the length of the Beta Cephei instability strip, temperature differences do not substantially affect the form of the radial-velocity curve. However, it is found that an increase in gravity advances the first strong shock in phase and increases the number of rebound shocks by reducing the time between them. The observed line splitting in BW Vul is identified with the first and stronger shock.