R-process Elements in the First Generation Stars and High-redshift Objects and the Galactic-and Cosmic-Age Problem.

r过程元素的观测研究是这个项目的最终目的之一，它在2000年刚刚开始，在kea山顶建造了配备高色散光谱仪（HDS）的SUBARU TELESCOPE。我们已经对SUBARU-HDS进行了几次测试观察，证明其工作效果与我们设计的非常好。利用这台摄谱仪，已经观测到几个金属缺乏的晕星，以便探测到来自Th232（半衰期14.1 Gy）、U238 （4.5 Gy）、Re187 （43.5 Gy）和许多其他恒星的金属吸收线。数据分析正在进行中。对超新星爆炸中的r过程核合成也进行了理论研究，以深入了解核合成机制。锕系元素是理想的重放射性原子核，其半衰期为宇宙年龄数量级。在这个项目中，理论上澄清了大多数重r过程元素，包括一些数量的放线素，是在与II型SN爆炸相关的爆炸核合成中产生的。详细研究了这些元素的计算产额与恒星环境物理条件的关系，阐明了r过程丰度产额与来自原中子星中心的中微子通量、中子星质量和半径、熵和动态时间尺度等与中微子驱动风中中微子加热过程密切相关的物理参数之间的关系。

Observational study of the r-process elements was one of the utlimate purposes in this project, and it has just started in the year 2000 with the construction of SUBARU TELESCOPE which is equipped with High-Dispersion-Spectrograph (HDS) at the top of Mt.Kea. We have already carried out several test observations of SUBARU-HDS, which proves to work very well as we designed. Using this spectrograph, several metal-deficient halo stars have already been observed in order to detect metal absorption lines from Th232 (half life 14.1 Gy), U238 (4.5 Gy), Re187 (43.5 Gy), and many others. Data analysis is now underway. Theoretical studies of the r-process nucleosynthesis in supernova explosions also have been carried out to reach deep understanding of the nucleosynthesis mechanism. Actinoids are ideal heavy radioactive nuclei whose half life is of order of cosmic age. In this project, it was theoretically clarified that most heavy r-process elements, including some amounts of actinoids, are produced in explosive nucleosynthesis associated with Type II SN explosions. Dependence of the calculated yields of these elements on the physical conditions of stellar environments were studied in detail : It was clarified the relation between r-process abundance yields and physical parameters such as neutrino flux from the center of proto-neutron star, mass and radius of the neutron star, entropy and dynamic time scale which are closely related to the neutrino heating proceses in the neutrino-driven winds.