Systematic motions in the galactic plane found in the Hipparcos catalogue using Herschel's Method

¹ Centro de Investigaciones de Astronomía CIDA, 5101-A Mérida, Venezuela e-mail: abad@cida.ve
² Grupo de Mecánica Espacial, Depto. de Física Teórica, Universidad de Zaragoza. 50006 Zaragoza, España
³ Department of Astronomy, Yale University, PO Box 208101 New Haven, CT 06520-8101, USA e-mail: vieira@astro.yale.edu

Received: 1 November 2003
Accepted: 20 July 2005

Abstract

Two motions in the galactic plane have been detected and characterized, based on the determination of a common systematic component in Hipparcos catalogue proper motions. The procedure is based only on positions, proper motions and parallaxes, plus a special algorithm which is able to reveal systematic trends. Our results come from two stellar samples. Sample 1 has 4566 stars and defines a motion of apex and space velocity  km s^-1. Sample 2 has 4083 stars and defines a motion of apex and space velocity  km s^-1. Both groups are distributed all over the sky and cover a large variety of spectral types, which means that they do not belong to a specific stellar population. Herschel's method is used to define the initial samples of stars and later to compute the common space velocity. The intermediate process is based on the use of a special algorithm to determine systematic components in the proper motions. As an important contribution, this paper sets out a new way to study the kinematics of the solar neighborhood, in the search for streams, associations, clusters and any other space motion shared by a large number of stars, without being restricted by the availability of radial velocities.