Curious Variables Experiment (CURVE). CCD photometry of active dwarf nova DI UMa

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. We examined principal parameters of the system to understand peculiarities of DI UMa, and other active cataclysmic variables. Based on precise photometric measurements, temporal light curve behaviour, O-C analysis, and power spectrum analysis, we investigated physical parameters of the system. 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 of dot_P/P_sh = 4.4(1.0)*10^{-5}. 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).Comment: Accepted for publication in Astronomy & Astrophysic

Alpha Cygnids: a possible July minor meteor shower

We present a comprehensive study of a possible $\alpha$-Cygnid meteor shower. Based on visual and telescopic observations made by Polish observers we estimate basic parameters of the stream. Activity of $\alpha$-Cygnids lasts from around June 30 to July 31 with clear maximum near July 16-17 (solar longitude $\lambda_\odot=116.5^\circ$). Maximal Zenithal Hourly Rates (ZHRs) are equal to $3.6\pm1.2$. The structure of the radiant analyzed by {\sc radiant} software is most compact for geocentric velocity of the events equal to 41 km/s, and for the drift of the radiant (in units $^\circ$/day) equal to of maximum is $\alpha=302.5^\circ$ $\delta=+46.3^\circ$.We derive population index $r$ equal to $2.55\pm0.14$ from magnitude distribution of 738 possible members of the stream. Comparing the veloctity distributions of 754 possible tests we conclude that both distributions are different with probability very close to 1.0. Telescopic observations strictly confirm the results obtained from visual observations. The smallest values of $\chi^2$ parameter we obtained for the geocentric velocity equal to 40 km/s and for the drift of the radiant (in units $^\circ$/day) equal to $\Delta\alpha=+0.6$ $\Delta\delta=+0.2$. The center of the radiant for moment of maximum is $\alpha=304.9^\circ$ $\delta=+46.2^\circ$. In spite of making many photographic exposures we still have no photographic or video confirmation of the existence of this stream