Search for Population III Stars and study on Stars in Down of the Universe

本研究是在发现一颗铁丰度仅为太阳1/20万的巨型HE 0107-5240后开始的，旨在系统地探索其表面丰度的特征，并讨论寻找在银河系形成过程中形成的极贫金属恒星，特别是由完全无金属物质构成的第一代恒星的幸存者III族恒星。经过3年的研究，我们从形成、演化、核合成和光谱研究的角度，在理论和观测上对这些早期宇宙遗迹的性质有了较大的了解。在理论方面，我们发现在极贫金属的恒星中，中子捕获反应发生在氢混合引起的氦壳闪光期间，不仅产生从碳到钠，镁和铝的轻元素，而且还产生重的s-pr…我们还阐明了在无金属条件下它们的演化和超新星核合成的特殊方面，并证明如果考虑到非球对称的影响，超新星爆炸可以产生各种碳铁比的产率，包括所观察到的如此大的碳铁比。此外，研究还表明，在极贫金属的大质量恒星中，在碳燃烧过程中会产生奇核（如钠和铝）的增强。对于恒星的形成，我们提出了在原始云中考虑到大质量恒星的辐射和超新星爆炸的影响下，产生可以存活至今的低质量恒星的情景。在观测研究方面，我们根据本研究项目参与者组织的斯巴鲁HDS的光谱数据，阐明了极金属贫星在碳富集和中子捕获元素增强方面的性质。尤其值得注意的是，他们与美国和德国的研究团队合作，发现了金属含量最低的亚巨星HE 1327-232。这是第二颗金属丰度低于太阳10万分之一的恒星，随着理论的发展，可以作为一个探测器来刺激早期宇宙研究的未来进展。少

This study started after the discovery a giant HE 0107-5240 with the iron abundance as small as 1/200,000 of the solar value and aimed at exploring the characteristics of surface abundances systematically and discussing the search for of the extremely metal-poor stars, formed during the formation of the Galaxy, and in particular, the population III stars that are the survivors of first generation stars made of matter completely devoid of metals. Through the 3 years research, we have made considerable progress in understanding the properties of these relics from the early Universe both theoretically and observationally from the viewpoints of their formation, evolution and nucleosynthesis and from the spectroscopic study.For the theoretical side, we find that in the extremely metal-poor stars, neutron capture reactions occur during the helium shell-flashes invoked by hydrogen mixing and yield not only the light elements from carbon, to sodium, magnesium, and aluminum but also, heavy s-pr … More ocess elements such as strontium as observed form extremely metal-poor stars.We also elucidate the peculiar aspects of their evolution and supernova nucleosynthesis of under the devoid of metals and demonstrate that supernova explosion can produce the yields of various ratio between carbon to iron including such a large ratio as observed if the effect of non-spherical-symmetry is taken into account. In addition it is shown that the enhancement of odd nuclei such as sodium and aluminum can be produced during the carbon-burning in extremely metal-poor massive stars. As for the star formation, we proposed a scenario to give birth to low-mass stars that can survive to date under with the effect of irradiation and supernova explosion of massive stars taken into account in the primordial clouds.For the observational research, we clarify the nature of extremely metal poor-stars as to the carbon-enrichment and also to the enhancement of neutron-capture elements on the basis of the spectroscopic data from Subaru HDS of the projects organized by participants of this research program. In particular, most remarkable is the discovery of sub-giant HE 1327-232 of the metal-poorest star known t data in collaboration with USA and German research teams. This is the second star below metallicity below 1/100,000 of solar value and along the theoretical development, may serve as a probe to stimulate future progress in the study of the early Universe. Less