Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. III. Dynamically Tagged Groups and Chemodynamical Properties
arxiv(2024)
摘要
Very metal-poor (VMP) stars record the signatures of early accreted galaxies,
making them essential tools for unraveling the early stages of Galaxy
formation. Understanding the origin of VMP stars requires comprehensive studies
of their chemical compositions and kinematics, which are currently lacking.
Hence, we conduct a chemodynamical analysis of 352 VMP stars selected from one
of the largest uniform high-resolution VMP star samples, jointly obtained from
LAMOST and Subaru. We apply a friends-of-friends clustering algorithm to the
master catalog of this high-resolution sample, which consists of 5778 VMP
stars. It results in 131 dynamically tagged groups with 89 associated with
known substructures in the Milky Way, including Gaia-Sausage-Enceladus (GSE),
Thamnos, Helmi streams, Sequoia, Wukong, Pontus, and the very metal-poor disk
(VMPD). Our findings are: (i) the VMPD shows lower Zn abundances than the rest,
which indicates that it could be a relic of small stellar systems; (ii) Sequoia
shows moderately high r-process abundances; (iii) Helmi streams show
deficiencies in carbon and light neutron-capture elements; (iv) the fraction of
carbon-enhanced metal-poor stars with no enhancement in heavy elements (CEMP-no
stars) seems low in the VMPD and the Helmi streams; and (v) a subgroup in GSE
exhibits a very high fraction of r-process enhanced stars, with four out of
five showing [Eu/Fe]> +1.0. The abundance patterns of other elements in VMP
substructures largely match the whole VMP sample. We also study large-scale
correlations between abundance ratios and kinematics without classifying stars
into substructures, but it does not yield significant correlations once the
overall chemical evolution is considered for most elements.
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