Cosmological Insights into the Early Accretion of r-process-enhanced Stars. I. A Comprehensive Chemodynamical Analysis of LAMOST J1109+0754
Mohammad K. Mardini, Vinicius M. Placco, Yohai Meiron, Marina Ishchenko, Branislav Avramov, Matteo Mazzarini, Peter Berczik, Manuel Arca Sedda, Timothy C. Beers, Anna Frebel, Ali Taani, Martina Donnari, Mashhoor A. Al-Wardat, Gang Zhao
Abstract
Abstract This study presents a comprehensive chemodynamical analysis of LAMOST J1109+0754, a bright ( V = 12.8), extremely metal-poor ([Fe/H] = −3.17) star, with a strong r -process enhancement ([Eu/Fe] = +0.94 ± 0.12). Our results are based on the 7D measurements supplied by Gaia and the chemical composition derived from a high-resolution ( R ∼ 110,000), high signal-to-noise ratio ( optical spectrum obtained by the 2.4 m Automated Planet Finder Telescope at Lick Observatory. We obtain chemical abundances of 31 elements (from lithium to thorium). The abundance ratios ([X/Fe]) of the light elements ( Z ≤ 30) suggest a massive Population III progenitor in the 13.4–29.5 M ⊙ mass range. The heavy-element (30 < Z ≤ 90) abundance pattern of J1109+075 agrees extremely well with the scaled-solar r -process signature. We have developed a novel approach to trace the kinematic history and orbital evolution of J1109+0754 with a cOsmologically deRIved timE-varyiNg Galactic poTential (the ORIENT) constructed from snapshots of a simulated Milky Way analog taken from the Illustris-TNG simulation. The orbital evolution within this Milky Way–like galaxy, along with the chemical abundance pattern, implies that J1109+0754 likely originated in a low-mass dwarf galaxy located ∼60 kpc from the center of the Galaxy, which was accreted ∼6–7 Gyr ago, and that the star now belongs to the outer-halo population.