Shock Phenomena in Β Cephei Stars

In this paper, we present new observations of β Cephei stars made with the CFHT coudé Reticon. Spectral sequences of the extreme star BW Vulpeculae show large velocity and line profile changes in Ha and in the CII doublet (λλβ578,6582) over 0.04 of a cycle, during three different cycles on three different nights. In fact, there are two such phases of line doubling where the velocities are nearly discontinuous before and after the so-called velocity "stillstand" (near maximum light). Also, the line doubling phases coincide with pronounced peaks in the Ha core residual intensity. The most straightforward interpretation of these observations is that there are two shock waves, separated by about 50 minutes, which generate double absorption components. For ν Eridani and 7 Pegasi, there are no discernible changes in the Ha profiles, despite rather regular velocity variations. This argues against the shock-wave interpretation for "classical" β Cephei stars.