An orbital motion study of globular cluster NGC6205

The positions and absolute proper motions of 264 stars in the field of about 70′ x 70′ around the globular cluster NGC6205 were determined. In the astrometric reduction, three early and three late epoch plates taken with the 40-cm refractor at Shensan, Shanghai, China, were used, with the epoch span of 73 a. The reduction was done using the central overlapping method, with 5 Hipparcos stars and 38 Tycho-2 stars as reference stars. Based on the reduced data of proper motion, the membership probabilities of the sample stars were determined. An absolute proper motion of the cluster of(1.49±0.36)mas a^-1 in R.A. and (3.06±0.35)mas a^-1 in Decl. was obtained. From this proper motion, together with distance and radial velocity data, we derived the space motion of NGC6205 and the orbit of the cluster in the Galaxy via numerical integration.