South African Astronomical Observatory (SAAO), South Africa
Date & Time :
Kepler photometry shows that most non-pulsating A-type stars vary with periodstypical of the expected rotation periods. The periodogram is simple and usually consists of a peak and its harmonic with amplitudes typically smaller than 50 ppm. We presume that the variation is rotational modulation caused by spots or some other co-rotating obscuration. This is supported by the distribution of equatorial velocities derived from the photometric periods. From the broadening of the peaks in the periodogram, we estimate that differential rotation in A-type stars is very similar to that in the Sun. Flares on A-type stars have been recently discovered in Kepler data. We show that such flares cannot be attributed to a late-type companion but must originate on the A star itself or an interaction between the A star and a close companion. We also discuss activity in B-type stars and argue that Be stars, in particular, are magnetically active. We present a simple model which explains all major characteristics of Be stars.