A small fraction of metal-poor stars in the Galactic halo have remarkable low abundance ratios of α elements ([α/Fe] < 0). The abundance pattern of such low-α stars could be produced by nucleosynthesis from very massive (> 100M⊙) first-generation stars, which contribute excess iron into the interstellar medium. On the other hand, many of low-α stars have been found in dwarf galaxies, suggesting low-α stars in the Galactic halo might be the remnants of infalling dwarf galaxies. We propose to obtain high-resolution spectra with Subaru/HDS for 50 such objects from LAMOST survey for exploring their multiple origins. The detailed abundance measurements for these low-α halo stars will provide unique opportunities to study the enrichment by very massive stars and the assembly history of the Galaxy.
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