R-Process Alliance：2MASS J22132050-5137385，已知 [Eu/Fe] = +2.45 的最高 r 过程增丰恒星
The R-Process Alliance: 2MASS J22132050-5137385, the Star with the Highest-known r-process Enhancement at [Eu/Fe] = +2.45
AI总结：
R-Process Alliance 团队发现 2MASS J22132050-5137385 是已知 [Eu/Fe] = +2.45 的最高 r 过程增丰恒星，通过钍铀衰变测定其 r 过程物质年龄为 13.6 Gyr，并提出利用超铀裂变碎片特征评估 r 过程产量的新方法。
摘要：
我们报告了在明亮（V = 11.63）且极度贫金属（[Fe/H] = -2.20 +- 0.12）的恒星 2MASS J22132050-5137385 中探测到的 47 种元素的恒星参数与化学丰度。我们使用 Magellan Inamori Kyocera Echelle 光谱仪观测了这颗恒星，这是 R-Process Alliance 持续工作的一部分。2MASS J22132050-5137385 的光谱表现出异常强的铁族以上元素谱线，我们的分析表明这些元素由快中子捕获（r 过程）核合成产生。我们得出其铕增丰 [Eu/Fe] = +2.45 +- 0.08，高于目前已知的任何其他 r 过程增丰恒星。这颗恒星仅是第八颗同时探测到钍和铀的 r 过程增丰恒星，我们根据这些同位素的放射性衰变计算出 r 过程物质的年龄为 13.6 +- 2.6 Gyr。该恒星含有相对较高的可能作为超铀裂变碎片产生的元素增丰，我们提出了一种利用该特征来评估 r 过程增丰恒星样本中 r 过程产量与气体稀释的新方法。我们得出结论，2MASS J22132050-5137385 表现出高水平的 r 过程增丰，因为它形成于 r 过程物质稀释程度低于平均水平的环境中。假设标准重子迷你晕质量为 10^6 M_sun 且金属保留率为 1%，该恒星形成于仅约 600 M_sun 的云团中。
英文摘要：
We present stellar parameters and chemical abundances of 47 elements detected in the bright (V = 11.63) very metal-poor ([Fe/H] = -2.20 +- 0.12) star 2MASS J22132050-5137385. We observed this star using the Magellan Inamori Kyocera Echelle spectrograph as part of ongoing work by the R-Process Alliance. The spectrum of 2MASS J22132050-5137385 exhibits unusually strong lines of elements heavier than the iron group, and our analysis reveals that these elements were produced by rapid neutron-capture (r-process) nucleosynthesis. We derive a europium enhancement, [Eu/Fe] = +2.45 +- 0.08, that is higher than any other r-process-enhanced star known at present. This star is only the eighth r-process-enhanced star where both thorium and uranium are detected, and we calculate the age of the r-process material, 13.6 +- 2.6 Gyr, from the radioactive decay of these isotopes. This star contains relatively large enhancements of elements that may be produced as transuranic fission fragments, and we propose a new method using this characteristic to assess the r-process yields and gas dilution in samples of r-process-enhanced stars. We conclude that 2MASS J22132050-5137385 exhibits a high level of r-process enhancement because it formed in an environment where the r-process material was less diluted than average. Assuming a canonical baryonic minihalo mass of 10^6 M_sun and a 1 percent metal retention rate, this star formed in a cloud of only ~ 600 M_sun.
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