Abstract

The history of the early chemical evolution of the Universe and the formation of galaxies is imprinted in the chemistry of old stellar populations. The bulge is the oldest component of the Milky Way and the Galaxy’s oldest stars are likely metal-poor stars in the inner bulge with small apocenters. In the past, stars with these properties have been impossible to find due to extreme reddening and extinction along the line of sight to the inner bulge. We have used the mid-infrared metal-poor star selection of Schlaufman & Casey (2014) to find some of the most metal-poor stars in the Galaxy. An orbit analysis using Gaia DR2 astrometry and our measured radial velocities confirms that these stars are tightly bound inner bulge stars. We found a distinctively different chemical pattern in the most metal-poor star we analyzed. We propose that the distinct abundance signature we detect is a product of nucleosynthesis in the Chandrasekhar-mass thermonuclear supernova of a CO white dwarf accreting from a helium star, a distinct event not yet observed through Milky Way halo abundances. I will also show results from an upcoming work on the Magellanic Clouds. These two galaxies lie in the mass range between the very well-studied Milky Way and the dwarf spheroidal galaxies. Even with the proximity of the Magellanic Clouds the details of their chemical evolution are still largely unexplored, especially at the low metallicity end. We used the same selection method to identify some of the most metal-poor stars found to date in the LMC and SMC. We show that their chemistry is consistent with the distinctive slow evolution previously observed in the Magellanic Clouds. We report a strikingly high percentage of r-process enhanced stars (9 out of 11 stars, or∼ 81%), including the identification of up to seven r-II stars. We show that the chemistry of the Clouds is more similar to that of lower mass dwarf galaxies than that of more massive dwarf galaxies or the Milky Way, possibly a result of their isolation.