ChJAA Vol 2, No 3 (2002) / Wu

Determination of the Proper Motions and Membership of the Globular Cluster M3 and of its Orbit in the Galaxy

Zhen-Yu Wu, Jia-Ji Wang, Li Chen

Abstract

We examine 14 plates of the globular cluster M3 (NGC 5272) taken with the 40 cm refractor at the Sheshan station of Shanghai Astronomical Observatory. The plates span over a period of about 77 years. The positions and absolute proper motions of eight stars in the Hipparcos Catalogue and of 49 stars in the Tycho-2 Catalogue are used as the reference frame. The astrometric reduction is made with the central overlapping principle. The absolute proper motions of 534 stars in a region of about 100'×100' around the cluster are measured. With the new proper motion data the membership probabilities of the stars are determined. The average absolute proper motion obtained for the cluster is -0.06±0.30 mas yr-1 in R.A. and -2.6±0.30 mas  yr-1 in Decl. By combining this result with the known distance and radial velocity of the cluster, we also obtained the Galactic orbit of M3 for a chosen three-component Galactic potential.

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