Membership determination of stars using proper motions in the region of the open cluster M 11 ^*

¹ Shanghai Observatory, Chinese Academy of Sciences, Shanghai 200030, China
² CCAST(World Laboratory), P.O. Box 8730, Beijing 100080, China

Send offprint request to: Cheng-gang Su

Received: 20 January 1997
Accepted: 26 May 1997

Abstract

Relative proper motions of 872 stars in the open cluster M 11 region are reduced using 10 plate pairs taken over time baselines of years with the double astrograph telescope of Shanghai Observatory. The scale is . The plates were measured with the PDS machines in the Purple Mountain Observatory in Nanjing and the Institute of Technology and Communication in Luoyang, China. The average proper motion accuracy is about 1.1 mas/yr with of the data better than 1 mas/yr.
Membership probabilities of 785 stars within 25′ centred on M 11 are determined based on their proper motions. The method used is suggested by Su et al. (1995) with some improvements of Zhao & He (1990), in which the space distribution and magnitude dependencies for cluster stars are taken into account. The results are significantly good. The total integrated membership probabilities for all these stars is 547 and the number of stars with probabilities higher than 0.7 is 541. It can be found after the membership determination that there exists mass segregation in M 11. Some comparisons and discussion are also given.