We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of the superhump period is found to be composed of three distinct stages: an early evolutionary stage with a longer superhump period, a middle stage with systematically varying periods, and a final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods of less than 0.08 d show positive period derivatives. We present observational characteristics of these stages and give greatly improved statistics. Contrary to an earlier claim, we found no clear evidence for a variation of period derivatives among different superoutbursts of the same object. We present an interpretation that the lengthening of the superhump period is a result of the outward propagation of an eccentricity wave, which is limited by the radius near the tidal truncation. We interpret that late-stage superhumps are rejuvenated excitation of a 3:1 resonance when superhumps in the outer disk are effectively quenched. The general behavior of the period variation, particularly in systems with short orbital periods, appears to follow a scenario proposed in Kato, Maehara, and Monard (2008, PASJ, 60, L23). We also present an observational summary of WZ Sge-type dwarf novae. Many of them have shown long-enduring superhumps during a post-superoutburst stage having longer periods than those during the main superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to be strongly correlated with the fractional superhump excess, or consequently with the mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with multiple rebrightenings tend to have smaller period derivatives, and are excellent candidates for those systems around or after the period minimum of evolution of cataclysmic variables.

Abstract. We report on time-series photometric observations in the earliest stages of superoutbursts of the extreme dwarf novae, AL Com and WZ Sge, which started on 2001 May after the 6 years quiescence and on 2001 July after the 23 years quiescence, respectively. We detected the growth of "early superhumps" during the each rising stage. Our observations reject the mass transfer instability for the trigger of the superoutburst of WZ Sge stars, and show the existence of some relations between the "early superhumps" and the spiral structure, which gives a hint of the origin of the "early superhumps."

Aims. About thirty new times of minimum light recorded with photoelectric or CCD photometers were obtained for four earlytype eccentric-orbit eclipsing binaries CW Cep (P = 2. Their O−C diagrams were analysed using all reliable timings found in the literature, and elements of apsidal motion were improved. Results. We confirm relatively short periods of apsidal motion of about 46, 27, 76, and 124 years for CW Cep, V478 Cyg, AG Per, and IQ Per, respectively. The corresponding internal structure constants, log k 2 , are then found to be -2.12, -2.25, -2.15, and -2.36, under the assumption that the component stars rotate pseudosynchronously. The relativistic effects are negligible, being up to 8% of the total apsidal motion rate in all systems. Using the light-time effect solution, we have predicted a faint third component orbiting with a period of about 39 years for CW Cep.

Abstract. The 2000 outburst of the recurrent nova CI Aql was followed by optical photometry and spectroscopy. Our time-resolved photometry revealed its intraday variations during the outburst. The orbital modulation of the light curve appeared after entering the plateau stage. We found that primary eclipses were ∼0.6 mag in depth, but the profile of the eclipse was significantly different from that in the quiescent phase. The folded orbital light curve was represented by a wide wing of a primary eclipse and it suggests the existence of the accretion disk at the plateau stage. In this outburst, we obtained accurate determination of several minima of primary eclipses, and found that the timings of minima showed a substantial delay compared to the previously reported ephemeris. However, no significant evidence of a change in the orbital period was observed since the discovery of the eclipsing nature of this object. We examined the evolution of optical spectra through the outburst, which reconfirmed the nova nature of this object. A spectrum taken on 2000 October 10 showed the Hα in emission and indicated that the object had not yet reached quiescence. The overall light curve and late-stage spectroscopy have revealed that the plateau is the longest one among recurrent novae.