All Hipparcos stars within the range and have been considered. The sample is essentially complete to 1 M . Members have been selected on the basis of the space motion of the cluster, taking into account all three components of the space velocity of the considered stars and the full covariance matrix of the observational errors. Within the cluster, the kinematical structure is fully consistent with parallel space motion of the member stars with an internal velocity dispersion of about 0.3 km s .
Mass segregation is clearly visible.
The three-dimensional structure of the cluster is derived from the individual distances to members, determined from the Hipparcos absolute trigonometric parallaxes. These discrepancies are explained in Perryman et al.