Superhumps and accretion disk precession in TT Arietis

We have been conducting a long-term (1988-1998) photometric study of the nova-like variable TT Arietis. The main periodic signal in the star's light curve normally occurs at a period that varies but averages similar to 0.1329 days, which is about 3.5% shorter than the orbital period of the binary. In 1997, this signal disappeared and was replaced by a stronger signal 8.5% longer than the orbital period. This new wave strongly resembles the "superhumps" commonly seen in SU UMa-type dwarf novae during superoutburst. In superhump parlance, we could say that a negative superhump was replaced by a positive superhump (P > P-orb). This could signify the development of an eccentric instability in the accretion disk. The two superhumps probably signify two types of disk precession: apsidal advance and nodal regression. TT Ari is an excellent candidate for observational studies that probe the origin of superhumps.