Tests of the pulsation and starspot models for the periodic Be stars

We review the correlation between the projected rotational velocity and the periods of the periodic Be stars (λ Eri variables). By estimating the radius from the spectral type and assuming that the photometric period is the same as the period of rotation, the equatorial rotational velocity can be derived. We discuss and revise the spectral type/radius calibration. The resulting distribution of equatorial velocities is not significantly different from that of a statistical deconvolution of a large number of Be stars assuming random orientation of the axes of rotation. We conclude that the photometric period is the same as the rotation period within 5 per cent. It follows that the pulsation and starspot models for these stars are practically indistinguishable because the pulsational velocity is restricted to very low values. We then derive an expression for the radial velocity to light amplitude ratio. The observed ratios are much higher than predicted from the pulsation/starspot model. There are several other reasons why the pulsation/starspot model needs to be abandoned. A velocity field of unknown origin of several tens of km s−1 is required to explain the observations.