研究年轻星团和小星协之间的边界：Bochum1的测试案例
Investigating the borderline between a young star cluster and a small stellar association: a test case with Bochum1
摘要：
通常，一个松散的恒星分布可以分为OB星群、星协或年轻的疏散星团。我们利用与典型的OB协会Vul OB 1的比较。Bochum 1是受上述分类问题影响的天体的一个典型例子，本文讨论了Bochum 1的性质，Bochum 1的场净化CMD显示了主序星（MS）和前主序星（PMS）。我们报告了两个新的小角度大小，紧凑的年轻集群和一个嵌入集群在波鸿1地区。Vul OB 1拥有年轻的疏散星团NGC 6823和非常紧凑的嵌入式星团Cr 404。Vul OB 1星协包括H II区Sh 2 -86，其恒星含量（$\approx3$ Myr）比波鸿1（$\approx9$ Myr）年轻，波鸿1没有气体排放。波鸿1拥有一个新发现的致密星团作为其核心。波鸿1的RDP是不规则的，不能用类似国王的轮廓来拟合，这表明恒星从原始星团中被侵蚀或分散。与Bochum 1相似，NGC 6823的净化CMD呈现出明显的MS和PMS序列。单独来看，MS和PMS恒星的RDP遵循国王般的轮廓。核心显示了一个重要的MS恒星的过剩密度，模仿的配置文件后核心崩溃集群。在如此年轻的年龄，它可以被解释为在突出的核心形成了过多的恒星。目前的研究表明，波鸿1是一个星团化石仍然可能是动态演变成一个OB协会。波鸿1可能是连接早期星团溶解与低质量OB协会形成的缺失环节。
英文摘要：
Usually, a loose stellar distribution can be classified as an OB stellar group, an association, or a young open cluster. We make use of comparisons with the typical OB association Vul OB1. In the present paper we discuss the nature of Bochum 1, a typical example of an object affected by the above classification problem.The field-decontaminated CMD of Bochum 1 presents main sequence (MS) and pre-main sequence (PMS) stars. We report two new small angular-size, compact young clusters and one embedded cluster in the area of Bochum 1. Vul OB1 harbours the young open cluster NGC 6823 and the very compact embedded cluster Cr 404. The Vul OB1 association includes the H II region Sh2-86, and its stellar content is younger ($\approx3$ Myr) than that of Bochum 1 ($\approx9$ Myr), which shows no gas emission. Bochum 1 harbours one of the newly found compact clusters as its core. The RDP of Bochum 1 is irregular and cannot be fitted by a King-like profile, which suggests important erosion or dispersion of stars from a primordial cluster. Similarly to Bochum 1, the decontaminated CMD of NGC 6823 presents conspicuous MS and PMS sequences. Taken separately, RDPs of MS and PMS stars follow a King-like profile. The core shows an important excess density of MS stars that mimics the profile of a post-core collapse cluster. At such young age, it can be explained by an excess of stars formed in the prominent core. The present study suggests that Bochum 1 is a star cluster fossil remain that might be dynamically evolving into an OB association. Bochum 1 can be a missing link connecting early star cluster dissolution with the formation of low-mass OB associations.
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