Asteroid Families. I. Identification by Hierarchical Clustering and Reliability Assessment

It is shown here that an entirely automatic procedure, applied to a large set of asteroid proper elements and taking their finite accuracy into account, can lead to a reliable asteroid family classification. The method allows (1) the statistical significance and robustness to be assessed for each family, (2) discrimination between members of dense family 'cores' and peripheral objects, (3) the complex large-scale structure of the asteroid belt to be taken into account, and (4) to give a rough estimate of the relative velocities needed to separate 'neighboring' family members. A preliminary analysis using the method is made of the properties of 21 families. Agreements and discrepancies of the results of the present classification with respect to those from previous classifications are pointed out.