Short-period variability in Be stars

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Abstract
A highly significant correlation is found between the projected rotational velocities and the photometric periods of Be stars. We show that this correlation may be readily understood if the photometric period is equated with the rotational period. If the nonradial pulsation hypothesis (NRP) is correct, we show that g-modes with radial order exceeding 50 must be involved, and that half the Be stars are pulsating with azimuthal spherical harmonic order m = −1, the other half with m = −2. According to current NRP theory, these results indicate that the Be stars rotate like solid bodies. On the basis of some recent observations which show that considerable magnetic activity is present and a particular episode in the Be star K CMa, we suspect that NRP is unlikely to be the cause of low-order periodic variations in Be stars. We suggest a model of rotational modulation caused by active areas. These are speculated to be the footprints of open magnetic field lines along which enhanced mass loss is occurring.

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