2MASS J00101758-1735387: Journey Across the Cosmos from an R-processed Ultra Faint Dwarf Galaxy to the Milky Way Halo

While the lighter elements (Z < 30) are known to be forged during the lifetime of stars, the elements heavier than strontium are thought to be formed by events following their deaths. Metal-poor stars enhanced with the rapid-neutron-capture (or r-) process are pristine objects that have formed from gas enriched by a single or few r-process events and provide the perfect opportunity to study the origins of the r-process. Neutron star mergers are the most likely candidates for the astrophysical sites of the r-process. Older, metal-poor stars provide the perfect opportunity to constrain these sites. We present a detailed abundance analysis of a metal-poor r-process enhanced star, 2MASS J00101758-1735387, with [Fe/H]= -2.4 dex. We detect Thorium from which we estimate a preliminary age of about 14 Gyrs, from [Th/Eu]= -0.507 using nucleo-cosmo chronometry. Early analysis of this halo star’s chemical abundances shows that the traces of its α-elements are systematically lower than what would be expected of stars in the Milky Way Halo. Its [Mg/Eu] ratio, is however consistent with the Ultra Faint Dwarf Galaxy Reticulum II, which is an old and less chemically evolved system than the Milky Way. Further comparisons to other UFDs can help elucidate into the accretion origin of J0010-1735. Moreover, the age of J0010-1735 itself allows us to age the system in which it was born. Thus our star may present a unique opportunity to place a preliminary age for the oldest galaxies in the universe.