揭开疏散星团的等级结构：英仙座双星团
Unveiling the Hierarchical Structure of Open Star Clusters: the Perseus Double Cluster
摘要：
介绍了一种新的研究疏散星团结构的运动学方法。我们采用了一种层次聚类算法，使用天体坐标和自行的恒星在该领域的集群的视野估计代理的成对的恒星的结合能，并安排他们在一个二叉树。根据$σ$ -平台方法，通过在两个阈值处修剪树来识别聚类子结构及其成员。在100个模拟星表上测试该算法表明，平均而言，所识别的星团的成员是$(91.5\pm 3.5)$ \%完整的，不相关的恒星的比例是$(10.4\pm 2.0)$ \%。我们将该算法应用于从盖亚数据发布2的英仙座双集群的视野中的恒星。该方法识别单个结构Sub1，其分为两个子结构Sub1-1和Sub1-2。这些子结构与$h$ Per和$χ$ Per一致：Sub1-1和Sub1-2的自行分布和成员的色星等图与文献报道的$h$ Per和$χ$ Per完全一致。这些结果表明，我们的层次聚类算法可以是一个强大的工具，揭示复杂的星团运动学信息。
英文摘要：
We introduce a new kinematic method to investigate the structure of open star clusters. We adopt a hierarchical clustering algorithm that uses the celestial coordinates and the proper motions of the stars in the field of view of the cluster to estimate a proxy of the pairwise binding energy of the stars and arrange them in a binary tree. The cluster substructures and their members are identified by trimming the tree at two thresholds, according to the $σ$-plateau method. Testing the algorithm on 100 mock catalogs shows that, on average, the membership of the identified clusters is $(91.5\pm 3.5)$\% complete and the fraction of unrelated stars is $(10.4\pm 2.0)$\%. We apply the algorithm to the stars in the field of view of the Perseus double cluster from the Data Release 2 of Gaia. This approach identifies a single structure, Sub1, that separates into two substructures, Sub1-1 and Sub1-2. These substructures coincide with $h$ Per and $χ$ Per: the distributions of the proper motions and the color-magnitude diagrams of the members of Sub1-1 and Sub1-2 are fully consistent with those of $h$ Per and $χ$ Per reported in the literature. These results suggest that our hierarchical clustering algorithm can be a powerful tool to unveil the complex kinematic information of star clusters.
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