Early disc accretion as the origin of abundance anomalies in globular clusters
Early disc accretion as the origin of abundance anomalies in globular clusters
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DOI：
10.1093/mnras/stt1745
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发表时间：
2013-12-01
影响因子：
4.8
通讯作者：
Gieles, M.
中科院分区：
文献类型：
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作者：
Bastian, N.;Lamers, H. J. G. L. M.;Gieles, M.
球状星团(GC)曾经被认为是简单的恒星群(即具有相同年龄和化学丰度的所有恒星)，现在已知存在各种反常现象，如颜色-星等图中的多个离散(或扩散)群和轻元素(如Na、O、Al)的丰度变化。已经提出了多种模型来解释观测到的异常，尽管所有模型都有严重的缺陷(例如，要求恒星和GC的初始质量函数不是标准的，最初的质量必须是今天观测的质量的10-100倍)。这些模型也与今天形成的大质量星团的观测结果不符，这些星团没有显示出显著的年龄分布，星团内也没有气体/尘埃。在这里，我们提出了一个气团形成的模型，在这个模型中，低质量的前主序恒星将从相互作用的大质量双星和快速旋转的恒星中释放出来的丰富物质附着到它们的星周圆盘上，并最终到达年轻恒星。正如以前的研究所表明的那样，沉积的物质与在GC中观察到的不寻常的丰度和模式相匹配。提出的模型不需要多代恒星的形成，符合今天形成的大质量星团的已知性质，并解决了“质量预算问题”，而不需要GC在出生时明显更大的质量。对模型的潜在警告以及模型预测进行了讨论。
Globular clusters (GCs), once thought to be well approximated as simple stellar populations (i.e. all stars having the same age and chemical abundance), are now known to host a variety of anomalies, such as multiple discrete (or spreads in) populations in colour-magnitude diagrams and abundance variations in light elements (e.g. Na, O, Al). Multiple models have been put forward to explain the observed anomalies, although all have serious shortcomings (e.g. requiring a non-standard initial mass function of stars and GCs to have been initially 10-100 times more massive than observed today). These models also do not agree with observations of massive stellar clusters forming today, which do not display significant age spreads nor have gas/dust within the cluster. Here we present a model for the formation of GCs, where low-mass pre-main-sequence stars accrete enriched material released from interacting massive binary and rapidly rotating stars on to their circumstellar discs, and ultimately on to the young stars. As was shown in previous studies, the accreted material matches the unusual abundances and patterns observed in GCs. The proposed model does not require multiple generations of star formation, conforms to the known properties of massive clusters forming today and solves the 'mass budget problem' without requiring GCs to have been significantly more massive at birth. Potential caveats to the model as well as model predictions are discussed.