摘要
利用上海天文台 40cm天体照相仪底片资料所提供的疏散星团M1 1天区 (团心距r≤2 5′)内的 785颗恒星的相对自行和成员概率 ,讨论了M1 1的CM图、年龄、距离、半径、光度函数、质量和分层效应 ,得到M1 1的距离为 1 659pc ,年龄为 (1 .8— 2 .2 )× 1 0 8年 ,半径约为 2 4 .5pc ,光度质量 4354M⊙ ,位力质量 50 0 0M⊙ ,在确定光度函数时 ,提出了一种考虑样本天区不完备的修正办法 ,以便从观测光度函数导出现时光度函数 .分析表明 ,作为一个中等年龄的疏散星团 ,M 1 1中的团星已表现出较明显的空间质量分层效应 ;而另一方面 ,尽管存在速度质量分层效应 。
Using the relative proper motions and the membership probabilities of 785 stars in the M11 region within a distance of 25′ from the cluster center, which are derived from the plates taken with the 40 cm astrograph of the Shanghai Observatory, we discuss the CM diagram, distance, age, luminosity function (LF) and segregation effects for the cluster, from which it is found that the distance of M11 is 1659 pc, its age (1.8-2.2) ×10 8 yrs, the luminosity mass 4354 M ⊙, and the virial mass some 5000 M ⊙. To determine the LF, an approach is developed to account for the incompleteness of the sample region in order to arrive at the present day LF of the cluster from what is observed. It is shown from our analysis that there appears to be a relatively significant mass segregation in M11 as an intermediate age open cluster, while there seems to be also a subtle velocity segregation in the cluster.
基金
国家自然科学基金
上海天文台青年实验室基金资助
关键词
疏散星团
CM图
光度函数
分层效应
星系团
open cluster M11——CM diagram——luminosity function——segregation effect
