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The Composition of the Sagittarius Dwarf Spheroidal Galaxy, and Implications for Nucleosynthesis and Chemical Evolution Andrew McWilliam Abstract The metal-rich red giant stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph) show strong enrichment of heavy neutron-capture elements, which correlates with [Fe/H]. The abundance ratios indicate s-process nucleosynthesis from stars with significantly lower metallicities than the metal-rich stars in which the ratios are seen. This rules out mass transfer and self-pollution scenarios, and suggests that the metal-rich Sgr dSph stars formed from s-process enriched gas, dominated by low-metallicity AGB nucleosynthesis products. The low alpha/Fe ratios and unusual iron-peak ratios might be explained by low-metallicity type Ia SN. We can understand these
abundance ratios as the result of extended chemical enrichment in a galaxy which has experienced significant mass-loss; this
mass-loss leads to reduced star formation at high metallicity, with a composition dominated by the products of old, low-mass,
low-metallicity stars. This scenario should be generally applicable to all low-mass systems, modulated by mass loss and star
formation. Thus, we expect to find similar abundance patterns in other dwarf galaxies. This is supported by the chemical
composition of stars in several local systems.
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