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S18B0131abst

S18B0131

A small fraction of metal-poor stars in the Milky Way halo have low abundance ratios of Ξ±-elements, e.g. [Mg/Fe]<0. Such "Ξ±-deficient stars" are frequently found in satellite dwarf galaxies. This suggests that Ξ±-deficient stars in the field halo could be results of late accretion of small stellar systems like dwarf galaxies currently observed. On the other hand, a small number of such stars might be objects that record nucleosynthesis yields of supernova explosions of very massive (>100MβŠ™) objects that produced large amount of Fe. In order to examine the origins of Ξ±-deficient stars, we here propose to obtain high-resolution, blue spectra with Subaru/HDS for 10 such objects having a wide distribution of metallicity found by our previous study with LAMOST and Subaru. Key elements of this study are C, Si, Sc, Mn, Co, Zn and heavy neutron-capture elements. The detailed abundance measurements for this unique sample will provide new constraints on frequency of late accretion of small stellar systems into the halo and on the contribution of supernova explosions of very massive objects.

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