Apex and internal structure of the Praesepe open cluster

The results of a study of the internal structure and kinematics of the Praesepe cluster are reported. The “AD-diagram” method is used to determine the position of the cluster apex, which is found to be close to the apex positions of other clusters, in particular to the Hyades apex. The internal morphology of the cluster is also analyzed. The distribution of the Praesepe members in the XY -plane shows that the cluster consists of a homogeneous core and a non-uniform corona. An analysis of stellar radial velocities and parallaxes reveals their weak correlation. This might be due to the axial rotation of the cluster. The inferred rotational velocity is comparable with that of the Hyades within the quoted errors. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)