Speaker
Description
We present a detailed chemical abundance analysis of LAMOST J122216.86−063345.26 (J1222), an actinide-boost r-I star observed with Gemini-S/GHOST. J1222 is a very metal-poor giant with [Fe/H] = −2.45 and is dynamically associated with the I’itoi substructure, making it a valuable tracer of early chemical enrichment in a system accreted into the Milky Way. From 43 measured elements, we find [Eu/Fe] = +0.61 and [Ba/Eu] = −0.52, classifying J1222 as an r-I star. Despite its moderate Eu enhancement, it shows a clear actinide-boost signature, with [Th/Dy] = −0.74. We also derive upper limits for U and Pb, which further constrain its neutron-capture abundance pattern. This combination suggests that actinide production is not simply set by the overall level of r-process enhancement. We interpret the abundance pattern of J1222 in relation to compact-object merger enrichment, including NSM and NS–BHM scenarios, focusing on neutron-rich ejecta, post-merger outflows, and the enriched gas from which the star formed. As a fossil record within the I’itoi substructure, J1222 connects the nucleosynthetic conditions of early r-process enrichment to the chemical evolution of an accreted system, and ultimately to the assembly history of the Milky Way halo.
| Category | Observation |
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