We report the results of 67 h of CCD photometry of the recently discovered dwarf nova SDSS J210014.12+004446.0 (SDSS J2100). The data were obtained on 24 nights spanning a month. During this time, we observed four ordinary outbursts lasting about 2–3 days and reaching an amplitude of ∼1.7 mag. On all nights, our light curve revealed persistent modulation with the stable period of 0.081 088(3) days (116.767 ± 0.004 min) and large amplitude of 0.5–0.6 mag in quiescence reduced to 0.1‐0.2 mag during outbursts. These humps were already observed on one night by Tramposch et al., who additionally observed superhumps during a superoutburst. Remarkably, from scant evidence at their disposal they were able to discern them as negative and positive (common) superhumps, respectively. Our period in quiescence clearly different from their superhump period confirmed this. Our discovery of an additional modulation, attributed by us to the orbital wave, completes the overall picture. Lack of superhumps in our data indicates that all eruptions we observed were ordinary outbursts. The earlier observation of the superhumps combined with the presence of the ordinary outbursts in our data enables classification of SDSS J2100 as an active SU UMa dwarf nova with two types of outbursts. Additionally, we have promoted SDSS J2100 to the select group of cataclysmic variables exhibiting three periodic modulations of light from their accretion discs. We updated available information on positive and negative superhumps and thus provided enhanced evidence that their properties are strongly correlated mutually as well as with the orbital period. By recourse to these relations, we were able to remove an alias ambiguity and to identify the orbital period of SDSS J2100 of 0.083 304(6) days (119.958 ± 0.009 min). SDSS J21000 is only third SU UMa dwarf nova showing both positive and negative superhumps. Their respective period excess and deficit equal to 4.99 ± 0.03 and −2.660 ± 0.008 per cent, yielding the mass ratio q≈ 0.24.

We report the first quiescent detection of KV UMa, the optical counterpart of XTE J1118 + 480, in the near-infrared. The observed magnitudes and colours are consistent with a K7-M0 V star, at the distance of 1.4 ± 0.2 kpc. The light curve shows strong orbital modulation with possible contamination from a superhump detected in the quiescent optical light curves.

Context.We report an analysis of photometric behaviour of DI UMa, an extremely active dwarf nova. The observational campaign (completed in 2007) covers five superoutbursts and four normal outbursts. Aims. We examined principal parameters of the system to understand peculiarities of DI UMa, and other active cataclysmic variables. Methods. Based on precise photometric measurements, temporal light curve behaviour, O−C analysis, and power spectrum analysis, we investigated physical parameters of the system. Results. We found that the period of the supercycle now equals 31.45 ± 0.3 days. Observations during superoutbursts infer that the period of superhumps equals P sh = 0.055318(11) days (79.66 ± 0.02 min). During quiescence, the light curve reveals a modulation of period P orb = 0.054579(6) days (78.59 ± 0.01 min), which we interpret as the orbital period of the binary system. The values obtained allowed us to determine a fractional period excess of 1.35% ± 0.02%, which is surprisingly small compared to the usual value for dwarf novae (2%-5%). A detailed O−C analysis was performed for two superoutbursts with the most comprehensive coverage. In both cases, we detected an increase in the superhump period with a mean rate ofṖ/P sh = 4.4(1.0) × 10 −5 . Conclusions. Based on these measurements, we confirm that DI UMa is probably a period bouncer, an old system that reached its period minimum a long time ago, has a secondary that became a degenerate brown dwarf, the entire system evolving now toward longer periods. DI UMa is an extremely interesting object because we know only one more active ER UMa star with similar characteristics (IX Dra).

We report results of an extensive world-wide observing campaign devoted to the recently discovered dwarf nova SDSS J162520.29+120308.7 (SDSS J1625). The data were obtained during the July 2010 eruption of the star and in August and September 2010 when the object was in quiescence. During the July 2010 superoutburst SDSS J1625 clearly displayed superhumps with a mean period of P sh = 0.095942(17) days (138.16 ± 0.02 min) and a maximum amplitude reaching almost 0.4 mag. The superhump period was not stable, decreasing very rapidly at a rate of Ṗ = −1.63(14) • 10 −3 at the beginning of the superoutburst and increasing at a rate of Ṗ = 2.81(20)•10 −4 in the middle phase. At the end of the superoutburst it stabilized around the value of P sh = 0.09531(5) day.During the first twelve hours of the superoutburst a low-amplitude double wave modulation was observed whose properties are almost identical to early superhumps observed in WZ Sge stars. The period of early superhumps, the period of modulations observed temporarily in quiescence and the period derived from radial velocity variations are the same within measurement errors, allowing us to estimate the most probable orbital period of the binary to be P orb = 0.09111(15) days (131.20 ± 0.22 min). This value clearly indicates that SDSS J1625 is another dwarf nova in the period gap. Knowledge of the orbital and superhump periods allows us to estimate the mass ratio of the system to be q ≈ 0.25. This high value poses serious problems both for the thermal and tidal instability (TTI) model describing the behaviour of dwarf novae and for some models explaining the origin of early superhumps.