Superhumps and their Evolution during Superoutbursts

Light curves of superhumps and their evolution during superoutbursts are analyzed by decomposing them into their Fourier components, including the fundamental mode and the first three overtones. The amplitudes of the fundamental mode are found to decrease significantly during superoutburst while those of the overtones remain practically constant. The phases of maxima of the fundamental mode {\it increase} systematically during superoutburst while those of the overtones -- systematically {\it decrease}. The combination of the two effects is responsible for the characteristic evolution of superhump light curves: the appearance and growth of the secondary humps and the spurious phase jumps in the (O-C) diagrams. Two intrepretations are possible. Either that instead of just one superhump period $P_{sh}$ there are four periods $P_k$ which resemble -- but are significantly different from -- the fundamental mode and the first three overtones of $P_{sh}$. Or -- more likely -- that those time-dependent phase shifts are genuine.