Schedule Oct 01, 2008
Chemical Abundances in the Least Evolved Dwarf Galaxies
Josh Simon (Caltech)

We present some of the first high-resolution spectroscopic metallicities of stars in the recently discovered ultra-faint dwarf galaxies around the Milky Way. These galaxies have mean metallicities as low as [Fe/H] = -2.6, more metal-poor than the least-enriched globular clusters. We measure the abundances of Fe, Mg, Ca, Ti, Sc, Sr, Ba, and C and show that the ultra-faint dwarfs have high abundances of alpha elements and low abundances of neutron capture species. At least some of the ultra-faint dwarfs contain large abundance spreads, demonstrating that either these systems do not consist of simple stellar populations or chemical mixing within them was inefficient. We also find similarities between the observed abundance patterns and those seen in halo stars. We discuss these results in the context of the formation of the ultra-faint dwarfs and the origin of metal-poor stars in the halo of the Milky Way.

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