Kepler observations of the high-amplitude delta Scuti star V2367Cyg

We analyse Kepler observations of the high-amplitude delta Scuti (HADS) star V2367Cyg (KIC9408694). The variations are dominated by a mode with frequency f1= 5.6611d-1. Two other independent modes with f2= 7.1490d-1 and f3= 7.7756d-1 have amplitudes an order of magnitude smaller than f1. Nearly all the light variation is due to these three modes and their combination frequencies, but several hundred other frequencies of very low amplitude are also present. The amplitudes of the principal modes may vary slightly with time. The star has twice the projected rotational velocity of any other HADS star, which makes it unusual. We find a correlation between the phases of the combination frequencies and their pulsation frequencies, which is not understood. Since modes of highest amplitude in HADS stars are normally radial modes, we assumed that this would also be true in this star. However, attempts to model the observed frequencies as radial modes without mode interaction were not successful. For a star with such a relatively high rotational velocity, it is important to consider the effect of mode interaction. Indeed, when this was done, we were able to obtain a model in which a good match with f1 and f2 is obtained, with f1 being the fundamental radial mode.