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

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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.