THE NODAL, THE NEW AND THE OLD MAXIMUM OF THE PERSEID METEOR STREAM

Visual observations of Perseid meteors carried out in 1953-83 at the O nsala Space Observatory are analyzed to study the fine structure of th e Perseid meteor stream maximum. Observed hourly rates are corrected f or weather conditions and to a zenithal value. The Perseid activity cu rve is studied (1) for all observed Perseids, (2) for Perseids of app. magnitude 2.0 or brighter. The activity curve for both data sets show s two main peaks, one at solar long. 138.65 degrees (1950.0), very nea r to the node of the parent comet (Swift-Tuttle), and a second peak at 139.42 degrees, corresponding to the ''traditional'' maximum of the s hower. A third, less conspicuous peak at 138.96 degrees is also eviden t in the data. This peak could possibly be an early indication of the so-called ''new'' maximum of the Perseid stream. The detection of a we ll-defined peak in rates very near to the node of the parent comet,is important since the position of the Perseid visual maximum usually quo ted in the literature deviates from the cometary node by almost 1 degr ees in solar longitude. (C) 1998 Elsevier Science Ltd. All rights rese rved.