Towards understanding rapid line-profile and light variations of early-type stars 3. Some thoughts and reflections

The current situation in the research of rapid line-profile and light varia tions of early-type stars is critically reviewed. It is suggested that the ultimate understanding of the physical processes causing these variations c an only come from an open-minded and complex approach to the problem and fr om systematic observational effort. It is argued that the results of the se arch for periodicities in the complicated variations of these objects depen d critically on whether the method used is appropriate to the real physical situation. The danger of detection of a false multiperiodicity is pointed out for two particular situations: (i) a single-periodic signal which under goes slow periodic change, e.g., due to the light time effect in a binary s ystem, and (ii) a single-periodic signal with a complicated phase curve (a model of not exactly equidistant corotating spokes). It is argued that the observed rapid variations need not be due to classical non-radial pulsation s but may arise from more complicated velocity fields in the stellar atmosp heres and/or mantles. Two early-type stars, epsilon Per and zeta Oph, are discussed in detail. It is argued that both may be the cases where the variations are caused by co rotating structures slightly above the stellar photosphere. For epsilon Per , the pattern of the variations can also be affected by the motion of the s tar in a binary orbit. For zeta Oph, a double-wave light curve with the cor otation period of 0.(d)64 (suggested by the author earlier for the line-pro file variations) was found from Hipparcos V photometry and its presence can also be suspected in other existing photometric data and in the recurrence times of the narrow features seen in the UV spectra.