出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We have been determining abundances of the actinide element Th, as well as of other heavy neutron-capture elements, based on high resolution spectroscopy with Subaru Telescope High Dispersion Spectrograph (HDS) and Gunma Astronomical Observatory Echelle Spectrograph (GAOES). Our sample covers wide metallicity range (−2.5<[Fe/H]<+0.3). The Th abundances are determined mostly using the Th 5989 Å line, which is less affected by blending of other elements than the 4019 Å one that has been used in previous studies of very metal-poor stars. The preliminary results of our measurements are presented. The Th/Eu abundance ratios of our sample show no significant scatter, and the average is slightly lower than the solar-system value. This result suggests that the actinide production by the r-process does not show large dispersion, or mixing of interstellar matter before formation of these metal-poor stars is very efficient. The Th/Eu ratios in relatively metal-rich ([Fe/H]> −1) stars show some scatter, and the average is higher than found in metal-poor stars. This suggests that these metal-rich stars include young objects where decay of Th is less significant.
