Speaker
Description
Very metal-poor (VMP) stars record the signatures of early accreted galaxies, making them essential tools for unraveling the early Galaxy formation. Meanwhile, understanding the origin of VMP stars requires comprehensive studies of their chemical compositions and kinematics, which are currently lacking. We cluster the dynamically tagged groups for ~6000 VMP stars and conduct a chemodynamical analysis on 352 of them with uniform detailed chemical abundances derived from the high-resolution spectra. We find stars associated with Gaia-Sausage-Enceladus (GSE), Thamnos, Helmi streams, Sequoia, Wukong/LMS-1, Pontus, and the very metal-poor disk (VMPD). In general, there is little significant difference in the abundance trends for different elements between VMP substructures and non-clustered VMP halo stars. However, several interesting features are found: (i) a subgroup in GSE exhibits a very high fraction of $r$-process enhanced stars, with four out of five showing $\mathrm{[Eu/Fe]>+1.0}$, providing us an opportunity to unveiling the $r$-process nucleosynthesis in GSE; (ii) the VMPD shows lower Zn abundances than the rest, which indicates that it could be a relic of small stellar systems; (iii) Helmi streams show deficiencies in carbon and light neutron-capture elements, suggesting a potential lack of rotating massive stars; and (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, which can be used to constrain the properties of their progenitor dwarf galaxies.
