On the Nature of Rotation in the Praesepe Cluster

Abstract

Although a large number of Galactic open clusters (OCs) have been identified, the internal kinematic properties (e.g., rotation) of almost all the known OCs are still far from clear. With the high-precision astrometric data of Gaia EDR3, we have developed a methodology to unveil the rotational properties of the Praesepe cluster. Statistics of the three-dimensional residual motions of the member stars reveal the presence of Praesepe’s rotation and determine its spatial rotation axis. The mean rotation velocity of the Praesepe cluster within its tidal radius is estimated to be 0.2 ± 0.05 km s−1, and the corresponding rotation axis is tilted in relation to the Galactic plane with an angle of 41° ± 12°. We also analyzed the rms rotational velocity of the member stars around the rotation axis, and found that the rotation of the member stars within the tidal radius of Praesepe probably follows Newton’s classical theorems.