2011MNRAS.415.3531B

Visual classification of over 10 000 stars in the Kepler data base has revealed a class of stars with almost monoperiodic light variations and characteristic beating. A subset of these stars have a larger light amplitude and asymmetric light curves with larger variation in maximum brightness than in minimum brightness. The beating is mostly a result of two dominant, closely spaced frequencies. A third group of stars shows multiple low frequencies of comparable amplitudes. All three types of star fall in the region of the Hertzsprung–Russell diagram where γ Dor stars are found and we therefore identify them as γ Dor variables. However, stars with migrating star-spots also have symmetric light curves with beats, so it is likely that the sample is contaminated by non-pulsating stars of this type. If we assume that the dominant frequency in stars with beats is the rotational frequency, the resulting distribution of equatorial rotational velocities matches that of field stars of similar temperature and luminosity. We therefore conclude that the pulsation periods of these stars must be close to their rotational periods. The third group with multiple frequencies may be slowly rotating γ Dor stars. This investigation is closely related to the presence of low frequencies in δ Scuti stars which we briefly discuss.