2025/06/09 by Xie, Renjing, Li, Haining, Zhang, Ruizhi +5 · 1 citation
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2506.07758
The main-sequence turnoff (MSTO) stars well preserve the chemical properties where they were born, making them ideal tracers for studying the stellar population. We perform a detailed chemo-dynamical analysis on moderately metal-poor (-2.0<[Fe/H]<-1.0) MSTO stars to explore the early accretion history of the Milky Way. Our sample includes four stars observed with high-resolution spectroscopy using CFHT/ESPaDOnS and 163 nearby MSTO stars selected from the SAGA database with high-resolution results. Within the action-angle spaces, we identified Gaia-Sausage-Enceladus (GSE, 35), stars born in the Milky Way (in situ, 31), and other substructures (21). We find that both GSE and in-situ stars present a similar Li plateau around A(Li)∼ 2.17. GSE shows a clear α-knee feature in Mg at [Fe/H]∼-1.60± 0.06, while the α-elements of in-situ stars remain nearly constant within the metallicity range. The iron-peak elements show little difference between GSE and in-situ stars except for Zn and Ni, which decrease in GSE at [Fe/H]>-1.6, while they remain constant in in-situ stars. Among heavy elements, GSE shows overall enhancement in Eu, with [Ba/Eu] increasing with the metallicity, while this ratio remains almost constant for in-situ stars, suggesting the contribution of longer time-scale sources to the s-process in GSE. Moreover, for the first time, we present the r-process abundance pattern for an extremely r-process enhanced (r-II) GSE star, which appears consistent with the solar r-process pattern except for Pr. Further investigation of larger GSE samples using high-resolution spectra is required to explore the reason for the significantly higher Pr in the GSE r-II star.