疏散星团M11的研究1．自行测定与成员研究

STUDIES OF THE OPEN CLUSTER M11 1. PROPER MOTION MEASUREMENT AND MEMBERSHIP DETERMINATION

本文利用中国科学院上海天文台４０厘米双筒天体照相仪所拍摄得的１０对底片（历元差１６─７０年），经ＰＤＳ测量仪测量，共确定了疏散星团Ｍｌｌ天区８７２颗恒星的相对自行，其中８５％以上恒星的自行测定精度好于±０″．１／百年．利用所测得的相对自行和新的数学模型，确定了不同星等组恒星的分布参数并计算了团中心距ｒ≤２５＇内７８５颗恒星的成员概率，其中成员概率大于０．７的恒星共有５４１颗．详细的讨论表明，新方法不仅在理论上更为严格，实用上也是可行的，可以使星团成员确定取得更为合理的结果．

plate pairs with epoch differences of 16-70 years of the open cluster Mll,which were taken with the 40cm double astrograph of Shanghai Observatory, are measured on the PDS microdensitometers. The relative proper motions of 872 stars in the cluster region are detendned, of which accuracies of 85 percent are better than ±0.″1 per century. The distribution parameters of stars with different magnitudes are reduced on the basis of a new mathematical model. the membership probabilities of all individual stars are calculated,in which the stars with membership probabilities higher than 0.7 being 541. It is shown from detailed discussion that the new approach of membership determination is not only theoretically rigorous, but also practically feasible, based on which the more reasonalbe results can be obtained for membership determination of open star clusters. Furthermore, we have found just from the results of the distribution parameter solutions of Mll that there appears to be some evidances for the effect of space mass segregation and some less significant effect of velocity mass segregation for the cluster.