Five-colour optical photometry of AE Aquarii.

Five-color (Walraven system) observations of the cataclysmic variable AE Aquarii were made in 1984 and 1985. During the observations, the source was quite active, showing rapid flares during about one third of the time. These flares are superposed on a quiescent ellipsoidal light curve, which reflects the tidal and rotational deformation of the secondary star. During quiescence, mass transfer is not absent as is indicated by the quiescent spectral energy distribution which contains a blue accretion component. If it is assumed that the spectrum of the latter is similar to that emitted during the flares, the spectral type of the secondary is K3. The optical flux emitted in the flares is about 3 times the quiescent accretion flux. This, and the rather short rise times of the flares, suggest that the flares are due to an accretion instability that occurs within a few white-dwarf radii, perhaps as a result of magnetospheric gating of the inflowing matter at the inner edge of the accretion disk.