论文标题
使用CN识别M71中的多个人群
Identifying Multiple Populations in M71 Using CN
论文作者
论文摘要
我们已经观察到CN功能在$ \ sim $ 3800〜〜和4120〜Å〜以及CH频段$ \ sim $ 4300〜〜使用多对象光谱仪M71中的145个进化的星星使用多对象光谱仪,hydra,wiyn-3.335m。我们使用这些测量值来创建两个$δ$ CN指数,发现两个分布最适合两个人群,即CN增强和CN-正常。我们发现我们样本中的42 $ \ pm $ 4 \%是CN增强的。 CN增强的百分比为40美元$ \ pm $ 13 \%的AGB,HB星的百分比为33 $ \ pm $ 9 \%,这表明在这些恒星演变的这些阶段,第二代恒星没有缺失。两代人在HB上也分开了大小和颜色,这使我们可以通过安装适当的Zahbs找到两个人群之间的差异。我们样品覆盖的群集中心的距离范围很大,使我们能够研究第一人口恒星与群集中心距离的比例的依赖性,并且我们发现该比率在径向上没有变化,并且两个人群在空间上混合了。最后,我们将多个种群的识别与基于NA-O抗相关和HST紫外线光度法的分类进行了比较,并且我们发现这两种方法都很好。
We have observed the CN features at $\sim$3800 ~Å~ and 4120~ Å~ as well as the CH band at $\sim$4300~Å~ for 145 evolved stars in the Galactic globular cluster M71 using the multi-object spectrograph, Hydra, on the WIYN-3.5m telescope. We use these measurements to create two $δ$CN indices finding that both distributions are best fit by two populations, a CN-enhanced and CN-normal. We find that 42 $\pm$ 4\% of the RGB stars in our sample are CN-enhanced. The percentage of CN-enhanced is 40 $\pm$ 13\% for the AGB and 33 $\pm$ 9\% for the HB stars, which suggests there are no missing second generation stars at these stages of stellar evolution. The two generations also separate in magnitude and color on the HB, which allows us to find the difference in He abundance between the two populations by fitting appropriate ZAHBs. The broad range of distances from the cluster's center covered by our sample allows us to study the dependence of the ratio of the number of first to second population stars on the distance from the cluster's center, and we find that this ratio does not vary radially and that the two populations are spatially mixed. Finally, we compare our identification of multiple populations with the classification based on the Na-O anti-correlation and the HST UV photometry, and we find good agreement with both methods.