tokens: ID34) or (ID02, ID29), where one star is a Sct pulsator, but the other one is not pulsating (ID29) or pulsating only in the low-frequency domain (ID34). All the Sct stars in our sample are Sct/Dor hybrids, confirming the already known result that over 98percent of Sct stars are hybrids (Balona 2018c ). For all stars, most peaks in the low-frequency region are independent modes. In a number of stars, some of the peaks in the low-frequency region are among those of highest amplitude. Hence, the definition of a Dor star is simply a Sct star where no significant frequencies are present above 5d 1 . There appears to be no real difference between the two classes of stars. Dor, Sct, and constant stars are to be found within the same small region at the cool end of the instability strip (Balona 2018c ). Many of the Sct stars discussed above seem to exhibit rotational modulation (Table 1 ), as shown by the presence of a low-frequency peak and its harmonic, both of which tend to be variable in amplitude. This is an indication on the existence of stellar activity, either through star-spots or any other corotating surface inhomogeneity. These rotational peaks are, in many cases, among the peaks with the largest amplitudes. Moreover, rotational modulation dominates the photometric variability of some Dor stars in our sample. We detect rotation in nine out of 16 Sct stars, i.e. 56percent of the sample. In six of them the rotational peaks are among the 20 largest amplitude peaks. Moreover, we detect rotation peaks in 26 out of 34 main-sequence stars (76percent) or 16 out of 24 main-sequence stars falling within the general location of the Kepler Sct instability region (Fig. 1 ). In some cases, it seems that more than one spot could be present on the stellar surface (e.g. ID11). In other cases, like ID14, rotation seems to be almost synchronized with the orbital period in a binary system, similar to the cool rotating variable ID06. One star, ID28, seems to be a ROTD-type variable similar to those detected by Balona ( 2013 ): most likely, the sharp peak is the rotational frequency, and the hump is due to Rossby modes (Saio etal. 2018 ). There is a clear indication of activity and star-spots on the surface of the A-type stars, as previously found by Balona ( 2011 , 2013 ). This suggests the presence of magnetic fields on the stellar surfaces that are not expected in such hot stars with very thin convective envelopes. The dynamo mechanism, which is thought to be responsible for magnetic activity in cool stars, cannot operate in stars with predominantly radiative envelopes. Star-spots seem to be also common among the much hotter B stars (Balona 2016 ; Balona etal. 2019 ). This is not surprising since there is no difference in the envelope structure between the A and B stars. Amplitude variations are found among the frequencies of highest amplitude in all four stars belonging to GroupIII (see last column of Table 1 ). They show a diversity of behaviours, including
ner_tags: B-CelestialObject O B-CelestialObject B-CelestialObject O O O O O O O O O O O O O O B-CelestialObject O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O B-CelestialObject O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O B-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O