6. Concluding remarks
We have analysed a data set of 620 high-quality high-resolution spectra of Cep, taken on a time base of 33 days. With a data set as extensive as this one, we were able to study the line-profile variations of Cep in great detail.
We have shown that the optical line-profile variations of Cep show periodicity with at least five different frequencies. The splitting between four of these frequencies can be reconciled with a period of 6 days; this period is also detected in the periodograms.
The analysis of our data set has shown that a frequency search by means of the CLEAN algorithm can in some circumstances lead to better results than a PDM analysis. We used a technique to partially CLEAN the periodograms resulting from Fourier transformations of the data. This method helps to suppress one-day aliases, but can only be applied if the frequencies in the signal are already known.
We analysed the intensity variations in the line profiles as well as the variations in the moments of the line profiles. The line-profile variations with frequencies and can successfully be modelled with a radial and a non-radial mode respectively. The retrograde non-radial pulsation is best described with spherical wave numbers =2, m =1; the combination =1, m =1 gives the second best description.
We have argued that the variations with frequencies , , and in the spectra of Cep can be described as the result of a modulation effect caused by the combination of the radial pulsation, the rotation, and the presence of a magnetic field. The similarities between the equivalent width variations of UV wind lines and optical lines suggest that a common phenomenon in the stellar wind and in the photosphere (e.g. a magnetic field) causes these similarities. Further theoretical studies are needed in order to be able to draw more definite conclusions on the physical conditions in the photosphere of Cep.
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998