出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We have obtained high resolution (R=60,000), high quality (S/N >100) spectroscopy using Subaru/
HDS for 20 candidate extremely metal-poor stars ([Fe/H]<−3) to determine their chemical
abundance patterns. In the observing program we found HE1327-2326, which has [Fe/H]= −5.4,
the lowest Fe abundance known in normal stars. This star shows extremely large excesses of C
and N, and also excesses of other light elements (e.g. O, Na). The low iron abundance and the
peculiar abundance pattern provide a signature of the nucleosynthesis by the first generation stars
in the Universe. We also present the preliminary results for other stars: (1) The iron abundances
of our sample, except for HE 1327−2326, are higher than [Fe/H]= −4. There is a gap of iron
abundance between [Fe/H]= −4 and −5. This would indicate that the nucleosynthesis, or formation
processes that are responsible for the stars with [Fe/H]< −5 and others are quite different.
(2) Six stars of our sample, including HE1327-2326, show clear excesses of carbon. Only two
of them show excesses of the heavy neutron-capture element Ba, suggesting a large contribution
of AGB nucleosynthesis. The origin of carbon-excesses in other stars are still unclear, but the
existence of these stars is a remarkable feature only found at the extremely low metallicity.
