arXiv 1605.028022016-05-09astro-ph.GA

银河系球状星团的范围及其原始云的质量

The realm of the Galactic globular clusters and the mass of their primordial clouds

Guillermo Tenorio-Tagle, Casiana Munoz-Tunon, Santi Cassisi, Sergiy Silich

备注：: 17 pages, 2 figures, accepted for publication in the Astrophysical Journal
DOI：: 10.3847/0004-637X/825/2/118

摘要：

通过对氦增强效应（$ΔY$）、第一代和第二代恒星质量比（$M_{1G}/M_{2G}$）和银河系球状星团实际质量（$M_{GC}$）的经验约束，我们设想了这些恒星系统形成的一种可能方案。我们的方法允许通过蒸发或潮汐相互作用和不同的恒星形成效率的恒星可能的损失。在我们的方法中，第一代恒星的形成效率（$ε_{1G}$）是连接恒星世代的核心因素，因为它不仅定义了第一代恒星的质量和可用于进一步恒星形成的剩余质量，而且还确定了污染第二代恒星所需的物质量。以这种方式，$ε_{1G}$完全由GC中连续代之间的He增强来定义。我们还表明，球状星团适合在$ΔY$ { \it vs} $M_{1G}/M_{2G}$图，表明三种不同的进化路径。中心的一个是没有损失恒星的星团，通过潮汐相互作用，从他们的任何一个恒星世代，因此他们目前的$M_{GC}$值是相同的低质量恒星的数量（$M_* \le$ 1 M $_\odot$），从两个恒星世代。其他可能的演化意味着第一代恒星的损失，或者第二代恒星形成效率低和/或第二代恒星损失的组合。从这些考虑，我们得出了一个下限的质量（$M_{tot}$）的个别原始云的起源球状星团。

英文摘要：

By adopting the empirical constraints related to the estimates of Helium enhancement ($ΔY$), present mass ratio between first and second stellar generations ($M_{1G}/M_{2G}$) and the actual mass of Galactic globular clusters ($M_{GC}$), we envisage a possible scenario for the formation of these stellar systems. Our approach allows for the possible loss of stars through evaporation or tidal interactions and different star formation efficiencies. In our approach the star formation efficiency of the first generation ($ε_{1G}$) is the central factor that links the stellar generations as it not only defines both the mass in stars of the first generation and the remaining mass available for further star formation, but it also fixes the amount of matter required to contaminate the second stellar generation. In this way, $ε_{1G}$ is fully defined by the He enhancement between successive generations in a GC. We also show that globular clusters fit well within a $ΔY$ {\it vs} $M_{1G}/M_{2G}$ diagram which indicates three different evolutionary paths. The central one is for clusters that have not loss stars, through tidal interactions, from either of their stellar generations, and thus their present $M_{GC}$ value is identical to the amount of low mass stars ($M_* \le$ 1 M$_\odot$) that resulted from both stellar generations. Other possible evolutions imply either the loss of first generation stars or the combination of a low star formation efficiency in the second stellar generation and/or a loss of stars from the second generation. From these considerations we derive a lower limit to the mass ($M_{tot}$) of the individual primordial clouds that gave origin to globular clusters.

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