On separation of major meteoroid streams from the sporadic background

The paper deals with a search for chosen photographic meteoroid streams compiled from the IAU Meteor Data Center Lund catalogue from which less than 2% of the orbits had to be removed due to internal inconsistency among the orbit parameters. Additional 35 orbits were removed due to extremely high hyperbolic velocities. The final set consists of 3411 orbits. Members of the Quadrantids, Lyrids, Perseids and Geminids were searched for, firstly, by a stream-search procedure utilizing the Southworth-HawkinsD-criterion. This choice, as a rule, represents the most abundant filament of the stream. Secondly, rate distribution histograms ofD were divided into region of shower meteors and region of sporadic background meteors. The searched database with a relatively low abundance of sporadic meteors in the analyzed periods simplified this choice, and followingly, fitting the obtained values by means of power and exponential functions, the limitingD _s for particular showers were derived. The derivedD _s appears as the optimum value, as for higherD, the number of sporadic meteors included in the stream sample increases more rapidly than the number of additional shower meteors, and for smallerD, the number of shower meteors decreases quicker than the number of omitted sporadic meteors. The following counts of shower meteorsN and limitingD _s were found: Quadrantids (39, 0.22), Lyrids (11, 0.15), Perseids (595, 0.53) and Geminids (224, 0.32). Efficiency of the procedure was tested comparing the number of sporadic meteors in the region of radiant area and the neighbouring regions of the same size.