Kinematic structure of the corona of the Ursa Major flow found using proper motions and radial velocities of single stars

Institute of Astronomy of the Russian Academy of Sciences, 48 Pyatnitskaya Str., 119017 Moscow, Russia e-mail: svv@inasan.ru

Received: 8 August 2005
Accepted: 5 January 2006

Abstract

Aims.We study the kinematic structure of peripheral areas of the Ursa Majoris stream (Sirius supercluster).

Methods.We use diagrams of individual stellar apexes developed by us and the classical technique of proper motion diagrams generalized to a star sample distributed over the sky.

Results.Out of 128 cluster members we have identified three corona (sub)structures comprised of 13, 13 and 8 stars. The substructures have a spatial extension comparable to the size of the corona. Kinematically, these groups are distinguished by their proper motions, radial velocities and by the directions of their spatial motion. Coordinates of their apexes significantly differ from those of the apexes of the stream and its nucleus. Our analysis shows that these substructures do not belong to known kinematic groups, such as Hyades or Castor. We find kinematic inhomogeneity of the corona of the UMa stream.