Rotation of open clusters based on Gaia data. Praesepe

Abstract High–precision trigonometric parallaxes, proper motions, and radial velocities of the Gaia DR2 catalog allow us to investigate the problem of open clusters rotation. Such a study could naturally be started with the clusters closest to the Sun, so we chose Praesepe as an object of our study. We selected 908 probable cluster members up to the apparent magnitude G = 19 mag based on their trigonometric parallaxes and proper motions, within 10° distance from the cluster center. We estimated the cluster distance modulus to be 6.36 mag and 6.02 mag using the trigonometric parallaxes of the probable cluster members and by fitting the theoretical isochrone to the cluster hertzsprung‐russell (HR) diagram, respectively. The cluster rotation velocity was estimated to be 0.4 km s −1 at the periphery of the cluster, using three different methods. In the future, we will continue the study of clusters rotation, with several nearby open clusters.