Speaker
Description
High-dispersion spectroscopic observations have been conducted using the Subaru Telescope for metal-poor star candidates detected by China's spectroscopic survey telescope LAMOST, determining the chemical composition of about 400 objects [1, 2]. We have determined detailed abundances of heavy elements for objects that show excesses of elements heavier than iron, with analyzing the kinematics (orbital motions of these stars) in the Milky Way Galaxy. We report on the results of our series of studies on the r-process. (1) 65 objects showing excess of the r-process ([Eu/Fe]$>0.3$) are identified, among which 20 objects showing particularly large excess ([Eu/Fe]$>0.7$) are estimated based on the kinematics to have been formed in low-mass dwarf galaxies that accreted into the Galactic halos [3]. (2) Within the main substructure of the Galactic halo, the Gaia-Sausage-Enceladus (GSE), there is a group of r-process element-enhanced objects exhibiting similar orbital motion [4]. (3) One of these objects is an actinide-boost star showing an excess of the actinoid element Th, marking the example identified in GSE [5]. (4)A very metal-poor ([Fe/H] = -2.9) star that shows a large r-process excess also exhibits a large excess of Zn, suggesting that its origin is related to a supernova with high explosive energy [3].
[1] Aoki et al. 2022, ApJ, 931, 146
[2] Li et al. 2022, ApJ, 931, 147
[3] Lin et al. et al. 2026, ApJ 1003, 75
[4] Zhang et al. 2024, ApJ 966, 174
[5] Lin et al. 2025, ApJ 984, L43
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