S19A0070abst
S19A0070
Surveys of very metal-poor stars and follow-up spectroscopic studies for them in the past decade have revealed diversity of the abundance ratios in the most metal-poor range, providing with rich information on the nature of first stars and early chemical evolution of the Milky Way Galaxy. We here propose to obtain high-resolution, blue spectra with Subaru/HDS for 12 candidates of extremely metal-poor stars ([Fe/H]<β3) selected from our previous study with LAMOST and Subaru. Key elements of this study are C and N, which reflect the CNO cycle and internal mixing in low-mass stars through their evolution from main-sequence to red giants, as well as the distribution of initial abundances presumably provided by first generation massive stars. Correlations of the C and N abundances with Li (for main-sequence turn-off stars) and neutron-capture elements (e.g., Sr, Ba) are investigated. Minor abundance changes of small amount of mass transfer expected in wide binary will be traced in warm EMP stars, which should not have experienced significant mixing in the object itself. This program was approved in S18A, but useful data were obtained only for three stars due to limited weather condition. We here propose the program again to complete the study.
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