Alpha Cygnids - a possible July minor meteor shower

Abstract

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 18 (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 $\Delta\alpha=+0.6$ $\Delta\delta=+0.2$. Center of the radiant for the moment 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 velocity distributions of 754 possible $\alpha$-Cygnids and 4339 sporadic events by $\chi^2$ and Kolmogorov-Smirnov 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.