A long-term high-resolution study of the visual activity curve of the Perseid meteor stream 1953–1983

Abstract

Perseid and sporadic meteor hourly rates and magnitudes observed in 1953–1983 by a team of visual observers at the Onsala Space Observatory, Sweden, are analysed. A high-resolution study of the zenithal hourly rates of bright Perseid meteors ( m⩽2.5) versus solar longitude has been made using a step length of 0.05° in solar longitude. The present study, which is based on 147 Perseid hourly rates, observed between solar longitudes 138.70°–141.65° (equinox 2000) covers the period of maximum Perseid activity. Somewhat surprisingly it reveals a multi-peak structure of the Perseid maximum with at least four separate peaks in the activity curve of bright Perseids. The first peak located at 139.38° corresponds to the crossing of the nodal plane of the parent comet, the second at 139.68° is the so-called “new” Perseid maximum, the third peak at 140.20° is the “old” or “traditional” maximum of the shower, while the fourth peak although less intense than the previous three peaks indicates a well-defined activity maximum centred on 140.78°. It is interesting to note that, for bright Perseids, the nodal maximum is of the same intensity as the “new” and “old” maxima, but is of a somewhat shorter duration than these two maxima. A similar study of the activity curve of all observed Perseid meteors (i.e. independent of apparent magnitude) shows the same multi-peak structure, but with slightly less pronounced peaks. In a previous study of the Perseid activity curve based on 605 photographic Perseid orbits obtained in various two-station programs 1937–1985 the multi-peak structure can be recognised in a number versus solar longitude diagram (Lindblad and Porubcan, 1994. Planet Space Sci. 42, 117–122.). The various peaks in the photographic data are located at the same solar longitudes as in the visual data. This agreement between the results of the present long-term visual study and a long-term photographic study of the Perseid activity curve strongly supports our conclusions as to the multi-peak structure of the Perseid shower.