The Origin of LAMOST J1109+7459

TL;DR

This paper presents a detailed chemo-dynamical analysis of the extremely metal-poor star LAMOST J1109+0754, revealing its likely origin in a low-mass dwarf galaxy and its association with the Galactic outer halo, based on chemical and orbital data.

Contribution

It provides the first comprehensive chemo-dynamical characterization of LAMOST J1109+0754, including chemical abundances, orbital history, and origin inference using cosmological simulations.

Findings

Star is extremely metal-poor with [Fe/H] = -3.17.

Star shows strong r-process enhancement with [Eu/Fe] = +0.94.

Likely originated in a low-mass dwarf galaxy and belongs to the outer halo.

Abstract

We report a comprehensive Chemo-dynamical analysis of LAMOST J1109+0754, a relatively bright (V = 12.8), extremely metal-poor ([Fe/H] = $-3.17$), and prograde ($J_\phi$ and $V_\phi$ $> 0$) star, with a strong \textit{r}-process enhancement ([Eu/Fe] = $+$0.94 $\pm$ 0.12, [Ba/Fe] = $-$0.52 $\pm$ 0.15). 31 chemical abundances (from Lithium to Thorium) were derived. We suggest a possible progenitor with stellar mass of 13.4-29.5 M$_\odot$. We argue that J1109+0754 is representative of the main \textit{r}-process component due to the well agreement with the scaled-solar \textit{r}-process component. We analyze the orbital history of this star in a {\it time-varying Galactic potential}, based on a Milky-Way analogue model extracted from \texttt{Illustris-TNG} simulations. Using this model, we carry out a statistical estimation of the phase-space coordinates of J1109+0754 at a young cosmic age. Collectively, the calculated motions, the derived chemistry, and the results from the cosmological simulations suggest that LAMOST J1109+0754 most likely formed in a low-mass dwarf galaxy, and belongs to the Galactic outer-halo population.