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Highly r-process enhanced metal-poor stars (MP r-II, $rm [Eu/Fe]>1$ and $rm [Fe/H]lesssim-1.5$) have been observed in ultra-faint dwarf (UFD) galaxy, specifically in Reticulum~II (Ret~II). The fact that only a few UFDs contain such stars implies that the r-process site may reflect very rare, but individually prolific events, such as neutron star mergers (NSMs). Considering the relatively short star formation history (SFH) of UFDs, it is puzzling how they could experience such a rare phenomenon. In this work, we show the results of cosmological hydrodynamic zoom-in simulations of isolated UFDs ($M_{vir}approx10^7-10^8$ solar mass and $M_{ast}approx10^3-10^4$ solar mass at $z=0$) to explain the formation of MP r-II stars in UFDs. We employ a simple toy model for NSM events, adopting parameters consistent with observations, such as the NSM rate (1 per $M_{ast}approx10^5$ solar mass) and europium (Eu) mass ($M_{Eu}approx10^{-5}$ solar mass). We identify only one simulated galaxy ($ M_{vir}approx4.6times10^7$, $M_{ast}approx 3.4times 10^3$ solar mass at $z=0$) with abundances similar to Ret~II in a simulation volume that hosts $sim30$ UFD analogs, indicating that such abundances are possible but rare. By exploring a range of key parameters, we demonstrate that the most important factor in determining the formation of MP r-II stars in UFDs is how quickly subsequent stars can be formed out of r-process enriched gas. We find that it takes between 10 to 100~Myr to form the first and second burst of MP r-II stars. Over this period, Eu-polluted gas maintains the required high abundance ratios of $rm [Eu/Fe]>1$.
We present a chemical abundance analysis of four additional confirmed member stars of Tucana III, a Milky Way satellite galaxy candidate in the process of being tidally disrupted as it is accreted by the Galaxy. Two of these stars are centrally locat
We search for RR Lyrae stars in 27 nearby ($<100$ kpc) ultra-faint dwarf satellite galaxies using the Gaia DR2 catalog of RR Lyrae stars. Based on proper motions, magnitudes and location on the sky, we associate 47 Gaia RR Lyrae stars to 14 different
CEMP-no stars, a subset of carbon enhanced metal poor (CEMP) stars ($rm [C/Fe]geq0.7$ and $rm [Fe/H]lesssim-1$) have been discovered in ultra-faint dwarf (UFD) galaxies, with $M_{rm vir} sim 10^8$ Msun and $M_{ast}sim10^3-10^4$ Msun at $z=0$, as well
The discovery of Ultra-Faint Dwarf (UFD) galaxies in the halo of the Milky Way extends the faint end of the galaxy luminosity function to a few hundred solar luminosities. This extremely low luminosity regime poses a significant challenge for the pho
The ultra-faint dwarf galaxy Reticulum 2 (Ret 2) was recently discovered in images obtained by the Dark Energy Survey. We have observed the four brightest red giants in Ret 2 at high spectral resolution using the Michigan/Magellan Fiber System. We pr