Superhumps and accretion disk precession in TT Arietis

We have been conducting a long-term (1988-1998) photometric study of the no va-like variable TT Arietis. The main periodic signal in the star's light c urve 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. I n 1997, this signal disappeared and was replaced by a stronger signal 8.5% longer than the orbital period. This new wave strongly resembles the "super humps" commonly seen in SU UMa-type dwarf novae during superoutburst. In su perhump parlance, we could say that a negative superhump was replaced by a positive superhump (P > P-orb). This could signify the development of an ec centric instability in the accretion disk. The two superhumps probably sign ify two types of disk precession: apsidal advance and nodal regression. TT Ari is an excellent candidate for observational studies that probe the orig in of superhumps.