Abstract

We present a detailed chemical abundance and kinematic analysis of a chemically peculiar Milky Way (MW) halo field, metal-poor ([Fe/H] = -2.4), highly enhanced r-process star ([Eu/Fe] = 1.22), 2MASS J00101758-1735387 (hereafter J0010-1735, also known as HE0007-1752 discovered as part of the R-Process Alliance. Analysis of its chemical abundances shows that its light (C, Na, Al, K), alpha (Mg, Si, Ti),  as well as Fe-peak (Sc, Cr, Mn, Co, Ni and Zn) elements, except for Ca, are sub-solar, and are systematically deficient as compared to field MW halo stars. We then investigate possible origins and chemical enrichment scenarios that could explain J0010-1735's observed chemical abundance pattern. Its kinematic analysis based on Gaia EDR3, supplemented by its unusual abundance pattern indicates a likely accretion origin from an old stellar system, such as the MW or Large Magellanic Cloud (LMC) dwarf satellite galaxies, which have previously undergone an r-process enrichment event. Moreover, we detect Th in J0010-1735 from which we determine a cosmochronometric age of 12.5 pm 4.2 Gyrs. This allows us to place an observational age constraint on the UFD systems from which stars such as J0010-1735 were born and accreted, as well as the r-process enrichment event itself.