Explaining the Multiple Populations in Globular Clusters by Multiple Episodes of Star Formation and Enrichment without Gas Expulsion from Massive Star Feedback
Explaining the Multiple Populations in Globular Clusters by Multiple Episodes of Star Formation and Enrichment without Gas Expulsion from Massive Star Feedback
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DOI：
10.3847/1538-4357/aaec67
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发表时间：
2018-07
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影响因子：
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通讯作者：
Jenny J. Kim;Young-Wook Lee
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文献类型：
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作者：
Jenny J. Kim;Young-Wook Lee
为了研究在银河系晕和核球中发现的多个恒星种群的起源，我们构建了它们的低质量祖先的化学演化模型。根据最近的理论发展，我们假设超新星爆炸波发生井喷，而不驱逐预富集的环境气体，而相对缓慢的风的大质量恒星（WMS），连同风和喷出物从低到高质量的渐近巨星分支星，都在本地保留在这些质量较小的系统。有趣的是，我们发现，所观察到的Na-O反相关的贫金属GC可以再现时，多个事件的星爆和富集被允许继续在这些子系统。一个特定形式的星星形成历史的连续恒星世代之间的时间间隔减少，但是，需要获得这一结果，这是在良好的协议与合成水平分支模型获得的参数。“质量预算问题”也大大减轻了我们的模型没有特设假设的星星形成效率，初始质量函数，和第一代恒星的优先损失。我们还应用这些模型来研究李等人提出的富金属核球中的超氦富红团星的起源。我们发现，化学富集的WMS可以自然地再现所需的强氦增强富金属子系统。我们的研究结果进一步强调，气体排出或保留是理解GC中多种群的关键因素。
In order to investigate the origin of multiple stellar populations found in globular clusters (GCs) in the halo and bulge of the Milky Way, we have constructed chemical evolution models for their putative low-mass progenitors. In light of recent theoretical developments, we assume that supernova blast waves undergo blowout without expelling the pre-enriched ambient gas, while relatively slow winds of massive stars (WMSs), together with the winds and ejecta from low- to high-mass asymptotic giant branch stars, are all locally retained in these less massive systems. Interestingly, we find that the observed Na–O anti-correlations in metal-poor GCs can be reproduced when multiple episodes of starburst and enrichment are allowed to continue in these subsystems. A specific form of star formation history with decreasing time intervals between the successive stellar generations, however, is required to obtain this result, which is in good agreement with the parameters obtained from synthetic horizontal branch models. The “mass budget problem” is also much alleviated by our models without ad hoc assumptions on star formation efficiency, initial mass function, and the preferential loss of first-generation stars. We also apply these models to investigate the origin of super-He-rich red clump stars in the metal-rich bulge suggested by Lee et al. We find that chemical enrichment by the WMSs can naturally reproduce the required strong He enhancement in metal-rich subsystems. Our results further underscore that gas expulsion or retention is a key factor in understanding the multiple populations in GCs.