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There are many Slowly Pulsating B (SPB) stars and gamma Dor stars in theKepler Mission data set. The light curves of these pulsating stars have beenclassified phenomenologically into stars with symmetric light curves and withasymmetric light curves. In the same effective temperature ranges as the gammaDor and SPB stars, there are variable stars with downward light curves thathave been conjectured to be caused by spots. Among these phenomenologicalclasses of stars, some show `frequency groups' in their amplitude spectra thathave not previously been understood. While it has been recognised thatnonlinear pulsation gives rise to combination frequencies in a Fourierdescription of the light curves of these stars, such combination frequencieshave been considered to be a only a minor constituent of the amplitude spectra.In this paper we unify the Fourier description of the light curves of thesegroups of stars, showing that many of them can be understood in terms of only afew base frequencies, which we attribute to g mode pulsations, and combinationfrequencies, where sometimes a very large number of combination frequenciesdominate the amplitude spectra. The frequency groups seen in these stars arethus tremendously simplified. We show observationally that the combinationfrequencies can have amplitudes greater than the base frequency amplitudes, andwe show theoretically how this arises. Thus for some gamma Dor and SPB starscombination frequencies can have the highest observed amplitudes. Among the Bstars are pulsating Be stars that show emission lines in their spectra fromoccasional ejection of material into a circumstellar disk. Our analysis givesstrong support to the understanding of these pulsating Be stars as rapidlyrotating SPB stars, explained entirely by g mode pulsations.

A unifying explanation of complex frequency spectra of gamma Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curves