The chemical composition of extremely metal-poor stars are expected to reflect a quite small umber of nucleosynthesis processes. Recent abundance analyses for extremely metal-poor stars have provided quite valuable information on the origin of the elements, and the individual nucleosynthesis processes involved.

The rapid neutron capture process (r-process) is known to be responsible, in solar system aterial, for about half of the abundances of elements beyond the iron-peak. However, the site in which this process is occurring is still unclear. In order to clarify the origin of r-process elements, it is important to investigate the abundances of many neutron-capture elements and to obtain their pattern in metal-poor stars.

We observed 22 very metal-poor stars and determined the abundances of r-process elements [1]. From this sample, we selected a bright, r-process element-enhanced star (HD6268) to investigate the detailed abundance pattern of neutron-capture elements. We obtained a very high quality spectrum of this star with the Subaru Telescope High Dispersion Spectrograph, and measured the abundances of light neutron-capture element (Ag, Pd, etc) which have not been determined by previous
analyses, and also estimated the meaningful upper limit of the abundances of the heaviest neutron-capture elements Pb and U.

In studies of neutron-capture elements in metal-poor stars, detailed atomic line data are indispensable. Recent progress in measurements of the transition probabilities including hyperfine splitting effect for neutron-capture elements (La, Eu, Nd, etc) enable us to determine accurate abundances of these elements in metal-poor stars.

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