The r-process Pattern of a Bright, Highly r-process-enhanced Metal-poor Halo Star at [Fe/H] ∼ −2
The r-process Pattern of a Bright, Highly r-process-enhanced Metal-poor Halo Star at [Fe/H] ∼ −2
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[Fe/H] ~ −2 处明亮、高度 r 过程增强的贫金属晕星的 r 过程模式
DOI：
10.3847/2041-8213/aaa9b4
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
D. Yong
中科院分区：
文献类型：
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作者：
C. Sakari;V. Placco;T. Hansen;E. Holmbeck;T. Beers;A. Frebel;I. Roederer;K. Venn;G. Wallersteín;C. E. Davis;E. M. Farrell;D. Yong
高解析度光谱分析显示了一颗新的高度r过程增强（[Eu/Fe] = 1.27，[Ba/Eu] = −0.65），非常贫金属（[Fe/H] = −2.09）的逆行晕星星RAVE J153830.9-180424，它是R过程联盟巡天的一部分。在V = 10.86时，这是银河系晕中已知的最明亮和最富含金属的r-II星星。它的亮度使得能够对主要由r过程产生的各种化学物质进行高S/N检测，包括Ru，Pd，Ag，Tm，Yb，Lu，Hf和Th等元素的一些不常检测到的线，上限为Pb和U。这是对贫金属r-II星星中最完整的r过程普查。J1538-1804的[Ba/Eu]和[Pb/Fe]较低，因此没有显示出S过程污染的迹象。与许多其他r过程增强的恒星一样，J1538-1804的r过程模式与太阳的第一、第二和第三峰之间的元素相匹配，并且没有表现出锕系元素的增强。宇宙年代测定法显示r过程物质相当古老。这个强大的主要r-过程模式是一个必要的约束r-过程形成的情况下（特别感兴趣的是在最近的中子星星合并，GW 170817），并有重要的后果的起源r-II星。R-Process Alliance将在不久的将来报告更多的r-I和r-II恒星。
A high-resolution spectroscopic analysis is presented for a new highly r-process-enhanced ([Eu/Fe] = 1.27, [Ba/Eu] = −0.65), very metal-poor ([Fe/H] = −2.09), retrograde halo star, RAVE J153830.9–180424, discovered as part of the R-Process Alliance survey. At V = 10.86, this is the brightest and most metal-rich r-II star known in the Milky Way halo. Its brightness enables high-S/N detections of a wide variety of chemical species that are mostly created by the r-process, including some infrequently detected lines from elements like Ru, Pd, Ag, Tm, Yb, Lu, Hf, and Th, with upper limits on Pb and U. This is the most complete r-process census in a very metal-poor r-II star. J1538–1804 shows no signs of s-process contamination, based on its low [Ba/Eu] and [Pb/Fe]. As with many other r-process-enhanced stars, J1538–1804's r-process pattern matches that of the Sun for elements between the first, second, and third peaks, and does not exhibit an actinide boost. Cosmo-chronometric age-dating reveals the r-process material to be quite old. This robust main r-process pattern is a necessary constraint for r-process formation scenarios (of particular interest in light of the recent neutron star merger, GW170817), and has important consequences for the origins of r-II stars. Additional r-I and r-II stars will be reported by the R-Process Alliance in the near future.