Long-term variations in β Cephei stars

In Sect. 1, we investigate pulsation periods of the beta Cephei stars for which sufficient data have accumulated. We discover the following dichotomy: either there is a constant, positive rate of period change, or the period variation is complex. We discuss the sole exception in Sect. 2. In Sect. 3, we consider the amplitudes of the three strongest pulsation modes of 16 (EN) Lac. The first two amplitudes vary on time scales of 70 and 50 yr, respectively. Since these numbers are close to the reciprocal pulsation growth-rates, we conclude that the variations are due to resonant mode coupling. For the third amplitude, we derive a period of 1.855 yr, which we attribute to interference of two close-frequency modes of constant amplitude.