(Proposal ID) S14A-112

(PI) Aoki Wako

(Proposal Title)
 Subaru/HDS study of extremely/ultra metal-poor stars found with LAMOST

(Abstract)
We propose to obtain R ~ 36, 000 spectra of candidate metal-poor stars ([Fe/H] 
< -3.5) found with LAMOST (22 stars) to search for ultra metal-poor (UMP) 
stars ([Fe/H]< -4.0) and to investigate the chemical properties of objects in 
[Fe/H]< -3.5. Four UMP stars that have [Fe/H] clearly lower than -4 are known 
so far, and three of them are carbonrich. Further discovery and measurements 
for a few such stars have strong impact on the understanding of nucleosynthesis
 by first generations of stars and low-mass star formation in gas clouds with 
lowest metallicity. The second purpose of this program is to measure the light 
and heavy neutron-capture elements Sr and Ba for more than half of our sample. 
This will examine the suggestion by previous studies that Sr/Ba ratios in 
objects with [Fe/H]< -3.5 are as low as the solar value, while many stars with 
[Fe/H]> -3.5 show very high Sr/Ba. If such difference of abundance 
distributions of Sr and Ba is real, the sources of heavy elements at the 
earliest stage of the Galactic chemical evolution could be significantly 
different from those in the later phases. The LAMOST survey for Galactic halo 
stars has been providing a large sample of candidate EMP/UMP stars, which are 
ideal sample to investigate the above problems.