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arXiv 1707.00744astro-ph.GAastro-ph.SR
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银河系星团的结构和质量分离

Structure and mass segregation in Galactic stellar clusters

Sami Dib, Stefan Schmeja, Richard J. Parker

备注：
Accepted to MNRAS
发表信息：
MNRAS 473, 849 (2018)
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摘要：

我们量化了大量银河系疏散星团的结构，并寻找星团中质量最大的恒星的质量分离的证据。我们计算了银河系星团（MWSC）目录中1276个星团的结构和质量分离比，每个星团至少包含40颗恒星，它们距离太阳的距离可达$\approx 2$ kpc。我们使用一种基于计算簇的最小生成树的方法，并且对于每个簇，我们计算结构参数\Q\和质量分离比$Λ_{\rm MSR}$。我们的研究结果表明，大多数集群具有一个\Q\参数，在0.7 - 0.8的范围内，因此既不强烈集中，也没有显示出显着的子结构。只有27%的\Q值为$> 0.8$，可视为集中。在1276个簇中，只有14\ %显示出显著的质量分离（$Λ_{\rm MSR} > 1.5$）。此外，星系团的结构或质量分离程度与它们在银河系中的位置之间没有相关性。比较测量的年轻疏散星团在MWSC的\Q\值的N体数值模拟，遵循的\Q\参数的演变超过前10个百万年的集群的生活表明，在MWSC目录中发现的年轻集群最初拥有本地平均体积密度$ρ_{*} \approx 10-100$ M $_{\odot}$ pc $^{-3}$。

英文摘要：

We quantify the structure of a very large number of Galactic open clusters and look for evidence of mass segregation for the most massive stars in the clusters. We characterise the structure and mass segregation ratios of 1276 clusters in the Milky Way Stellar Cluster (MWSC) catalogue containing each at least 40 stars and that are located at a distance of up to $\approx 2$ kpc from the Sun. We use an approach based on the calculation of the minimum spanning tree of the clusters, and for each one of them, we calculate the structure parameter \Q\ and the mass segregation ratio $Λ_{\rm MSR}$. Our findings indicate that most clusters possess a \Q\ parameter that falls in the range 0.7-0.8 and are thus neither strongly concentrated nor do they show significant substructure. Only 27\% can be considered centrally concentrated with \Q\ values $> 0.8$. Of the 1276 clusters, only 14\% show indication of significant mass segregation ($Λ_{\rm MSR} > 1.5$). Furthermore, no correlation is found between the structure of the clusters or the degree of mass segregation with their position in the Galaxy. A comparison of the measured \Q\ values for the young open clusters in the MWSC to N-body numerical simulations that follow the evolution of the \Q\ parameter over the first 10 Myrs of the clusters life suggests that the young clusters found in the MWSC catalogue initially possessed local mean volume densities of $ρ_{*} \approx 10-100$ M$_{\odot}$ pc$^{-3}$.

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