A search for streams and associations in meteor databases. Method of Indices

Abstract

A new method of searching for minor meteor streams and associations is presented and discussed. The procedure, based only on mathematical statistics, enables a parallel separation of major and minor streams or associations. The approach utilizes a division of the ranges of examined parameters into equidistant intervals. The method is tested on the IAU Meteor Data Center Lund catalogue of precise photographic orbits representing the most extensive set of photographic meteor orbits. Besides the five orbital elements incorporated in the Southworth–Hawkins D-criterion, we have also included in the procedure the coordinates of the radiant which belong to the most accurately known parameters and the geocentric velocity as a significant parameter characteristic for physically related orbits. The basic idea of the procedure is a division of the observed ranges of parameters into a number of equidistant intervals and assignment of indices to a meteor according to the intervals pertinent to its parameters. The meteors with equal indices are regarded as mutually related. Since various parameters listed in the catalogue contain various relative errors, it is necessary to use several intervals in the division of each parameter to obtain a good fit with the real orbital distribution. The relative ratios, approximated by small integers, corresponding to the reciprocal values of the relative errors, were applied as the basic numbers for the division of the parameters. To test the quality of this method, the first step presented in this paper is aimed at wider intervals providing a less detailed classification (a smaller branching). In this step all the major streams (except of the northern branch of δ-Aquarids) were identified, confirming the efficiency of the procedure. After combining the related groups, 16 streams were identified. The search program also identifies widely spread Taurids. There are separated orbits pertinent to some minor streams such as the o-Draconids, κ-Cygnids, October Draconids, Pegasids and December Monocerotids. Rather surprisingly, even at this strict level, a pair of meteors in orbits similar to the Lyrids with the maximum on April 8 (Arter and Williams, 1995. Earth, Moon, Planets 68, 141–153) are identified. In the next steps the search will be concentrated on the separation of minor streams and eventually some so far unknown associations.