114.05 CEMP Stars in the Halo and Their Origin in Ultra-Faint Dwarf Galaxies (Timothy C. Beers)

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Jun 4th at 3:52 PM until 4:06 PM




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Author(s): Timothy C. Beers1
Institution(s): 1. University of Notre Dame
The very metal-poor (VMP; [Fe/H] < 2.0) and extremely metal-poor (EMP; [Fe/H] < 3.0) stars provide a direct view of Galactic chemical and dynamical evolution; detailed spectroscopic studies of these objects are the best way to identify and distinguish between various scenarios for the enrichment of early star-forming gas clouds soon after the Big Bang. It has been recognized that a large fraction of VMP (15-20%) and EMP stars (30-40%) possess significant over-abundances of carbon relative to iron, [C/Fe] > +0.7. This fraction rises to at least 80% for stars with [Fe/H] < 4.0. Recent studies show that the majority of CEMP stars with [Fe/H] < 3.0 belong to the CEMP-no sub-class, characterized by the lack of strong enhancements in the neutron-capture elements (e.g., [Ba/Fe] < 0.0). The CEMP-no abundance signature is commonly observed among stars ultra-faint dwarf spheroidal galaxies such as SEGUE-1. In addition, kinematic studies of CEMP-no stars strongly suggest an association with the outer-halo population of the Galaxy, which was likely formed from the accretion of low-mass mini-halos. These observations, and other lines of evidence, indicate that the CEMP-no stars of the Milky Way were born in low-mass dwarf galaxies, and later subsumed into the halo.