Statistical model of meteor streams I. Analysis of the model

A new model has been developed for analyzing the dynamical properties of meteor streams. It is based on the Southworth-Hawkins D-criterion of the similarity of two orbits in terms of the differences in their Keplerian elements. In contrast to the earlier stream searches, the statistical rather than the determinate concept is adopted for the definition of a stream. In particular, the proposed method emphasized the significance of the character of the D-distribution of meteors with respect to the mean orbit of a meteor stream. The mean orbital elements are computed as a weighted mean of the elements of individual meteors with D smaller than a certain limit. This process is iterated until the mean orbit converges. The calculations were performed on a high speed computer by means of a program that solved the iteration procedure and listed the meteors according to increasing D, thus giving the D-distribution to be studied. To test the method, empirical D-distributions were obtained for some major streams from the Harvard- Smithsonian Radio Meteor Project survey of more than 19 000 orbits. We have assumed the empirical D-distribution for each stream to consist of an intrinsic Maxwellian D-distribution of the stream, contaminated by a sporadic-background D-distribution. Eliminating the latter by analyzing artificial samples of meteors with randomly distributed orbits, we have developed a graphical method for determining the intrinsic dispersion, σ, in the stream's D-distribution. Model calculations suggest that as a result of planetary perturbations, σ increases secularly. There is some evidence that σ could serve to estimate the mean age of streams, but more studies on this subject are necessary.