观测最古老恒星中的r过程签名
Observing the r-Process Signature in the Oldest Stars
摘要：
贫金属恒星的丰度模式为我们提供了关于银河系化学演化各个阶段的丰富化学信息。特别是，这些恒星使我们能够研究元素的形成和演化以及所涉及的核合成过程。贫金属星是高红移宇宙的局部等价物，因此对早期宇宙的各种问题提供了关键的观测约束。本文介绍了贫金属星及其作为研究中子俘获核合成过程，特别是r-过程的“宇宙实验室”的作用。贫金属恒星HE 1523-0901就是这类天体的一个例子。它的光谱显示出与r过程有关的中子俘获元素的最强过剩。测量了Eu、Os和Ir等重中子捕获元素，以及放射性元素Th和U。Th和U的丰度与稳定元素的丰度相结合，使核年代学成为可能，即，恒星年龄的测定HE 1523-0901似乎约为13 Gyr。年龄不确定性范围从2-5 Gyr的个别计时器，很大程度上是由于理论上的不确定性，在初始生产率的就业计时器。放射性元素铅的衰变产物可以用来限制r过程的计算。目前只有少数这样的恒星被探测到U。然而，这些物体对于研究这种核合成过程至关重要。
英文摘要：
The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of the chemical evolution of the Galaxy. In particular, these stars allow us to study the formation and evolution of the elements and the involved nucleosynthesis processes. Metal-poor stars are the local equivalent of the high-redshift Universe, and thus offer crucial observational constraints on a variety of issues regarding the early Universe. This review presents an introduction to metal-poor stars and their role as "cosmic lab" for the study of neutron-capture nucleosynthesis processes, particularly that of the r-process. The metal-poor star HE 1523-0901 serves as an example for this group of objects. It displays in its spectrum the strongest overabundance of neutron-capture elements associated with the r-process. Heavy neutron-capture elements such as Eu, Os, and Ir were measured, as well as the radioactive elements Th and U. Abundance of Th and U, in conjunction with those of stable elements make possible nucleo-chronomtery, i.e., the determination of stellar ages. HE 1523-0901 appears to be ~13 Gyr old. Age uncertaintites range from 2-5 Gyr for individual chronometers, and are largly due to theoretical uncertainties in the initial production ratio of the employed chronometers. The decay product of the radioactive elements, lead, can be used to constrain r-process calculations. Only few such stars are currently known with detected U. These objects, however, are crucial for the study of this nucleosynthesis process.
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