The Origin of LAMOST J1109+7459
  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.
