The 18th International Symposium on Origin of Matter and Evolution of Galaxies (OMEG18)

A Na-rich Actinide-boost r-II Candidate: The Chemo-kinematic Origin of LAMOST J015857.38+382834.7

Oct 21, 2026, 6:00 PM

3h

Headquarters Building 2F (RIKEN)

Poster Presentation Poster Session

Speaker

Dayoung Byun (Chungnam National University)

Description

We present a chemo-kinematic study of an extremely metal-poor giant LAMOST J015857.38+382834.7 (hereafter J0158) with [Fe/H] = -3.46. J0158 shows an unusual light-element pattern, with strong Na enhancement but no strong carbon enhancement, consistent with globular cluster-like second-population chemistry. Its high [Eu/Fe] = +1.6, and low Ba abundance classify it as a strongly r-process-enhanced r-II star. The high [Th/Fe] = +2.0 implies [Th/Eu] ≈ +0.4, making J0158 a promising actinide-boost r-II candidate, though further Th/U confirmation is needed. A pair-instability supernova (PISN) origin is disfavored because J0158 is Na-rich and neutron-capture-rich, unlike PISN candidates that show very low Na and weak neutron-capture enrichment. Its orbit places it near the Wukong/LMS-1 substructure, suggesting formation in an accreted dwarf-galaxy system locally enriched by a rare r-process event.