arXiv 0708.38482007-08-28astro-ph

第二颗星星

The Second Stars

Falk Herwig

备注：: Biermann award 2004 lecture, AG meeting, Prague
发表信息：: 2005RvMA...18...21

摘要：

第一批可能质量很大的恒星的喷出物污染了大爆炸原始元素与第一批较重元素的混合物。由此产生的超贫金属丰度分布为第二颗恒星提供了初始条件，这些恒星的初始质量范围很广，可以达到中等质量和低质量。这些第二颗恒星对于理解早期宇宙中元素的起源的重要性是多方面的。虽然大质量的第一颗恒星早已消失，但第二颗恒星仍然存在，目前正在观察。它们是关于第一批恒星的信息的载体，但它们本身也能够进行核生产。例如，为了使用超贫金属或极贫金属的恒星作为早期宇宙r过程的探测器，就需要一个可靠的第二恒星s过程模型。最终，第二颗恒星可能会为我们提供重要的线索，从结构形成到恒星如何实际制造元素，不仅在早期，而且在现在的宇宙中。特别是富碳极贫金属的恒星，其中大部分显示的S-过程签名，被认为是与化学产额从进化的巨阶段的中等质量的恒星。现在存在这样的AGB星在极低金属丰度的模型，与观测的比较显示出重要的差异，例如关于氮的合成。这可能暗示了极端贫金属演化恒星的燃烧和混合方面，这些方面尚未包括在演化的标准图像中，例如氢摄入闪光。中等质量的第二颗恒星也可能在通过慢中子俘获反应链（s-过程）形成重元素的过程中发挥了重要作用。模型与观察结果的比较揭示了物理输入和假设的哪些方面需要改进。s过程是一个特别有用的诊断工具，用于探测负责恒星中元素产生的物理过程，例如旋转。随着新的观测技术和策略继续渗透到该领域，例如多目标光谱学或未来的光谱调查，极端贫金属恒星将在解决一些最基本和最具挑战性的天文学问题方面发挥越来越重要的作用。

英文摘要：

The ejecta of the first probably very massive stars polluted the Big Bang primordial element mix with the first heavier elements. The resulting ultra metal-poor abundance distribution provided the initial conditions for the second stars of a wide range of initial masses reaching down to intermediate and low masses. The importance of these second stars for understanding the origin of the elements in the early universe are manifold. While the massive first stars have long vanished the second stars are still around and currently observed. They are the carriers of the information about the first stars, but they are also capable of nuclear production themselves. For example, in order to use ultra or extremely metal-poor stars as a probe for the r-process in the early universe a reliable model of the s-process in the second stars is needed. Eventually, the second stars may provide us with important clues on questions ranging from structure formation to how the stars actually make the elements, not only in the early but also in the present universe. In particular the C-rich extremely metal-poor stars, most of which show the s-process signature, are thought to be associated with chemical yields from the evolved giant phase of intermediate mass stars. Models of such AGB stars at extremely low metallicity now exist, and comparison with observation show important discrepancies, for example with regard to the synthesis of nitrogen. This may hint at burning and mixing aspects of extremely metal-poor evolved stars that are not yet included in the standard picture of evolution, as for example the hydrogen-ingestion flash. The second stars of intermediate mass may have also played an important role in the formation of heavy elements that form through slow neutron capture reaction chains (s-process). Comparison of models with observations reveal which aspects of the physics input and assumptions need to be improved. The s-process is a particularly useful diagnostic tool for probing the physical processes that are responsible for the creation of elements in stars, like for example rotation. As new observational techniques and strategies continue to penetrate the field, for example the multi-object spectroscopy, or the future spectroscopic surveys, the extremely metal-poor stars will play an increasingly important role to address some of the most fundamental and challenging, current questions of astronomy.

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