**Meteor Streams Identification: a New Approach**

**Cl. Froeschlé (Obs. Côte d'Azur), T. J. Jopek (Posnan Obs.), G. B. Valsecchi (I.A.S.)**

The orbital similarity criterion by Southworth and Hawkins is a generalized distance in the 5-dimensional space of orbital elements (perihelion distance, eccentricity, inclination, argument of perihelion, longitude of node). Meteor orbits, however, are characterized by only 4 indepentently measured quantities, since a meteor can be observed only at one of the nodes, and at a heliocentric distance of 1 AU.

We have therefore looked for a set of 4 variables, possibly directly deducible from observed quantities, that would allow meteor stream identification without passing through the computation of orbital elements. In fact, some of the quantities that are used in the geometric setup of Opik's theory of close encounters are ideally suited for the task. Thus, we have established and tested a stream identification criterion based on the geocentric unperturbed velocity and three angles, of which the first two are related in a simple way to the radiant, and the third is the longitude of node.

The new criterion has been applied to a sample of 865 precisely reduced photographic meteor orbits, and the outcomes have been compared to those obtained, on the same sample, with the criterion by Southworth and Hawkins. All the high-inclination, high-velocity streams are successfully recovered by the new criterion; significant differences exist, on the other hand, for the low-velocity, near-ecliptical streams.