Long-Period Meteor Streams and the Dispersion of Semimajor Axes of Meteor Orbits

The present work is based on an analysis of a large statistical sample of meteor orbits collected in the Japanese shower catalogue (SonotaCo 2009, WGN, 37, 55) of 114280 video observed meteors. The shower meteor data were selected and analysed with the aim of determining the orbits' distribution in major meteor streams with heliocentric velocities close to the parabolic limit, in which the errors in the velocity determination correspond to large differences in the reciprocal semimajor axis, 1/a. The contribution of the real dispersion of the semimajor axes, a, can be deduced from the high proportion of hyperbolic orbits in the analysed streams, where an excess over the parabolic value can be regarded as being entirely due to measurement errors. The orbital dispersion described by the median absolute deviation in terms of 1/a was found to be +/- 0.083 AU(-1) for the Leonids and +/- 0.080 AU(-1) for the Orionids, and slightly smaller for the Perseid and Lyrid meteor streams (+/- 0.055 and +/- 0.047 AU(-1)). The proximity of the parabolic limit caused a strong influence of observational effects; however, a significant contribution of the real dispersion is involved.