S19B0042abst
S19B0042
Stellar halo of the Milky Way is believed to have formed through hierarchical merger of small stellar systems such as dwarf galaxies. By studying the orbits and chemistry of very metal-poor (VMP) halo stars, we can decode the merger history of the Milky Way. Here we propose to use the high dispersion spectrograph to determine the detailed abundances of heavy elements for βΌ 12 VMP stars in two dynamical substructures. These substructures are newly discovered from our cluster-finding analysis applied to the largest bright VMP star catalog complied from the LAMOST DR3 VMP catalog and Gaia DR2. Judging from their metallicities, these substructures are probably the remnants of tidally disrupted low-mass dwarf galaxies or ultra faint dwarf galaxies. One of the substructures, dubbed Group2, is confirmed to be dynamically associated with a well-studied strongly r-process element enhanced star (r-II star), and thus there is a high probability that many stars in Group2 are also r-II stars. In such a case, Group2 would be the first convincing example of the disrupted ultra-faint dwarf galaxy that accreted to the inner halo of the Milky Way. Our project will be the first attempt to reconstruct the spatially incoherent, ancient tidal remnants and to constrain their progenitor mass.
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