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We have analysed a selected sample of 36 Kepler short-cadence stars in the field of NGC 6811. The results reveal that all the targets are variable: 2 red-giant stars with solar-like oscillations, 21 main-sequence pulsators (16 δ Sct and 5 γ Dor stars) and 13 rotating variables. Three new γ Dor variables (one is a hot γ Dor star) are detected in the present work together with five new rotating variables. An in-depth frequency analysis of the δ Scuti and γ Doradus stars in the sample shows that the frequency spectra are very rich, in particular for the δ Sct-type variables. They present very dense frequency distributions and wide diversity in frequency patterns, even for stars being members of the cluster and with very similar location in the H-R diagram. Rotational modulation is found for a high percentage of these main-sequence pulsating stars, which is an indication of stellar activity being common on the surfaces of these hot stars. In some cases, activity dominates the luminosity variations. Significant amplitude variability is also detected in at least some of the pulsation modes of highest amplitude in almost all the δ Sct stars. One of the δ Sct pulsators is a member of a binary system with the pulsating component tidally distorted. This system also shows strong stellar activity, including several flares which probably originate in the δ Sct component.

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