1997A&A...322..493T

We investigate the optical line-profile variability of the prototype of the β Cephei stars. From more than 600 spectra, with a typical signal to noise ratio of over 200 and high spectral resolution, we deduce that the variations show periodicity with at least five different frequencies. We find variability at the previously known frequencies f₁=5.25cycles/day (radial pulsation) and f₂=5.38c/d and f₃=4.92c/d. Additionally, we report two new frequencies f₄=5.08c/d and f₅=5.42c/d. These five frequencies are present in periodograms of the velocity moments of all of the absorption lines considered (SiIII λ 4552, 4567, 4574 and OII λ 4591), and also in periodograms of the intensity variations in these lines. The variations at frequencies f₁ and f₂ can be successfully modelled by a radial and a non-radial (l=2 or l=1, m=1) pulsation, respectively. Following results of studies of the UV resonance lines of β Cep, we interpret the frequency spacings f₁-f₃≃0.33c/d, f₁-f₄≃0.17c/d, f₅-f₁≃0.17c/d as multiples of the rotation frequency of the star. We discuss the influence of the presence of a (surface) magnetic field on the apparent modulation of the line-profile variability of the radial pulsation mode.