Sneden Christopher, Cowan John J
Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712, USA.
Science. 2003 Jan 3;299(5603):70-5. doi: 10.1126/science.1077506.
We review the origin and evolution of the heavy elements, those with atomic numbers greater than 30, in the early history of the Milky Way. There is a large star-to-star bulk scatter in the concentrations of heavy elements with respect to the lighter metals, which suggests an early chemically unmixed and inhomogeneous Galaxy. The relative abundance patterns among the heavy elements are often very different from the solar system mix, revealing the characteristics of the first element donors in the Galaxy. Abundance comparisons among several halo stars show that the heaviest neutron-capture elements (including barium and heavier) are consistent with a scaled solar system rapid neutron-capture abundance distribution, whereas the lighter such elements do not conform to the solar pattern. The stellar abundances indicate an increasing contribution from the slow neutron-capture process (s-process) at higher metallicities in the Galaxy. The detection of thorium in halo and globular cluster stars offers a promising, independent age-dating technique that can put lower limits on the age of the Galaxy.
我们回顾了银河系早期历史中重元素（原子序数大于30的元素）的起源与演化。相对于较轻的金属元素，重元素在恒星之间的丰度存在很大的离散，这表明早期银河系在化学上是未混合且不均匀的。重元素之间的相对丰度模式通常与太阳系的混合模式有很大不同，揭示了银河系中首批元素贡献者的特征。对几颗晕星的丰度比较表明，最重的中子俘获元素（包括钡及更重的元素）与按比例缩放的太阳系快速中子俘获丰度分布一致，而较轻的此类元素则不符合太阳系模式。恒星丰度表明，在银河系中金属丰度较高时，慢中子俘获过程（s过程）的贡献在增加。在晕星和球状星团恒星中检测到钍提供了一种有前景的独立测年技术，它可以为银河系的年龄设定下限。
