A Research on the Evolution of Population III Stars and on the Method of Their Search

这项研究的目的是从理论和观测上讨论寻找第三星族恒星的可能性，这些恒星在我们的宇宙中首先诞生，尚未被发现。这些恒星是由大爆炸核合成处理过的原始物质组成的，因此完全没有碳和重金属元素。只有质量不超过0.8太阳质量的低质量恒星才能以核燃烧恒星的形式存活下来，这种低质量的第三星族恒星会变成氮含量增加的碳星。我们在初始质量和金属丰度的参数范围内扩展了已有的计算，给出了关于碳星演化的一般图象：极低金属丰度碳星的形成机制不同于富金属对应的形成机制，这一结果与观测结果一致，即当[Fe/H]<-2.5.在此基础上，我们提出了一种利用碳、氮分子谱线探测富氮碳星，进而用氮/碳比判别富氮碳星的新方法，并利用木曾天文台的施密特望远镜和2KCCD进行了试验观测。东京大学。

The purpose of this research is to discuss theoretically and observationally the possibility of searching for Population III stars, which have been born first in our Universe and are yet to be discovered. These stars have been composed of the primordial matter processed by the Big-Bang nucleosynthesis, and hence, totally devoid of carbon and heavier metal elements. It is only low-mass stars not heavier than 0.8 solar masses that survive to date as nuclear burning stars.It has been known that such low-mass, population III stars become carbon stars with enhanced nitrogen. We have extended the exsistent computation in the parameter region of initial mass and metallicity to present a general picture concerning the evolution to carbon stars: The formation mechanism of carbon stars with extremely low metallicity is different from those of metal-richer correspondences, which gives a result consistent with the observation that a fraction of carbon stars increases greatly for low-metalliclty of [Fe/H]<-2.5.On the basis of these theoretical results, we propose a new method of search for population III stars to detect nitrogen-rich carbon stars by aid of molecular lines of carbon and nitrogen and further to discriminate them with the nitrogen/carbon ratio.In order to check the validity of this new method, we made test observations by using Schmidt telescope with 2KCCD at Kiso observatory, the Uniersity of Tokyo.