Typical Masses of First Stars and the Origin of the Peculiar Elemental Abundances in the Early Universe

第一代恒星，称为第三星族星，在宇宙中不包含重元素。当前天文学的主要焦点之一是它们的典型质量是多少，即，它们的质量函数，因为这些质量决定了第一批恒星是否是宇宙再电离的来源，以及中等质量和超大质量黑洞的起源。在这项研究中，我们模拟了第一批恒星的演化和超新星爆炸，并试图通过核合成与观测到的极贫金属（EMP）恒星的化学丰度之间的比较来估计它们的典型质量和爆炸能量。我们研究了EMP星与太阳丰度不同的特殊丰度模式，计算了经历质量吸积并从1个太阳质量开始增加质量的第三星族（PopIII）星的演化。计算是通过引力坍缩阶段进行的。我们的研究结果概括如下：1）首先，我们采用了第一颗星星形成的三维宇宙学模拟中估计的吸积率。Pop III.1恒星的质量增加到1000太阳质量，并形成中等质量的黑洞。这样的中等质量黑洞可能是超大质量黑洞的种子，因此是非常有趣的对象。2）接下来，我们研究了Pop III.2恒星，其质量吸积被Pop III.1恒星的反馈效应阻止。我们发现这些恒星的质量增加了50-100个太阳质量。这些恒星经历引力坍缩和核合成，产生在EMP星中观察到的丰度模式。

The first generation of stars, called Population III stars, in the Universe do not contain heavy elements. It is one of the main focus of current astronomy that how much are their typical masses, i.e., their mass function, because those masses determine whether the first stars are the source of cosmic re-ionization, and the origin of intermediate and super-massive black holes. In this study, we modeled the evolution and supernova explosions of the first stars, and tried to estimate their typical masses and explosion energies from the comparison between nucleosynthesis and the observed chemical abundances of extremely metal-poor (EMP) stars. We focus on the peculiar abundance pattern of EMP stars, which is very different from the solar abundance.We have calculated the evolution of Population III (Pop III) stars that undergo mass accretion and increase their masses from 1 solar mass. The calculation has been conducted through the phase of gravitational collapse. Our findings are summarized as follows.1) First we adopted the accretion rate as estimated from the 3 dimensional cosmological simulation of the first star formation. The mass of the Pop III.1 stars increase through 1000 solar mass, and intermediate mass black holes are formed. Such intermediate mass black holes can be the seeds of super-massive black holes, thus being very interesting objects.2) Next we studied Pop III.2 stars whose mass accretion is stopped by the feedback effect of Pop III.1 stars. We found that those stars increase their masses through 50-100 solar mass. These stars undergo gravitational collapse and nucleosynthesis to produce the abundance pattern observed in EMP stars.