论文标题
M22中的五个恒星种群（NGC 6656）
Five Stellar Populations in M22 (NGC 6656)
论文作者
论文摘要
我们介绍金属复合物球状簇（GC）M22（NGC 6656）的CA-CN-CN光度法。由于平均金属性的差异，我们的光度法清楚地显示了M22红色巨型分支（RGB）恒星中离散的双CN-CH反相关性。两个主要组之间的人口数比为n（g1）：n（g2）= 63：37（+/- 3），而G1则更多的金属罚款。此外，G1可以分为两个亚群，其数值比为n（cn-w）：n（cn-s）= 51:49（+/- 4），而G2则可以分为三个亚群，分别为n（cn-w）：n（cn-s-i）：n（cn-s）：n（cn-s）= 24：32:44（cn-s）= 24：32:44（+-444444444444444444444444444444444444岁）。簇中各个恒星的正确运动显示出内部旋转的证据，显示了G2的旋转速度更快，证实了我们先前的径向速度结果。单个亚群的累积径向分布（CRD）在以下方面引人入胜：（1）在两个主要组中，CN-S亚群的CRD比其他亚种群更为集中。 （2）G1 CN-S和G2 CN-S的CRD非常相似。 （3）同样，G1 CN-W和G2 CN-W和CN-I几乎具有相同的CRD。我们还通过比较了单个亚群的相对氦气丰度，通过比较其RGB凸起幅度，发现在G1中没有氦丰度变化，而G2中需要Delta y = 0.03〜0.07的显着增强氦气的增强。我们的结果支持了M22通过两个GC合并形成的想法。
We present the Ca-CN-CH photometry of the metal-complex globular cluster (GC) M22 (NGC 6656). Our photometry clearly shows the discrete double CN-CH anticorrelations in M22 red giant branch (RGB) stars, due to the difference in the mean metallicity. The populational number ratio between the two main groups is n(G1):n(G2) = 63:37(+/-3), with the G1 being more metal-poor. Furthermore, the G1 can be divided into two subpopulations with the number ratio of n(CN-w):n(CN-s) = 51:49 (+/-4), while the G2 can be divided into three subpopulations with n(CN-w):n(CN-i):n(CN-s) = 24:32:44 (+/-5). The proper motion of individual stars in the cluster shows an evidence of internal rotation, showing the G2 with a faster rotation, confirming our previous results from radial velocities. The cumulative radial distributions (CRDs) of individual subpopulations are intriguing in the following aspects: (1) In both main groups, the CRDs of the CN-s subpopulations are more centrally concentrated than other subpopulations. (2) The CRDs of the the G1 CN-s and the G2 CN-s are very similar. (3) Likewise, the G1 CN-w and the G2 CN-w and CN-i have almost identical CRDs. We also estimate the relative helium abundance of individual subpopulations by comparing their RGB bump magnitudes, finding that no helium abundance variation can be seen in the G1, while significant helium enhancements by Delta Y = 0.03 ~ 0.07 are required in the G2. Our results support the idea that M22 formed via a merger of two GCs.
