ABUNDANCE RATIOS AND GALACTIC CHEMICAL EVOLUTION

Abstract

▪ Abstract  The metallicity of stars in the Galaxy ranges from [Fe/H] = −4 to +0.5 dex, and the solar iron abundance is ε(Fe) = 7.51 ± 0.01 dex. The average values of [Fe/H] in the solar neighborhood, the halo, and Galactic bulge are −0.2, −1.6, and −0.2 dex respectively. Detailed abundance analysis reveals that the Galactic disk, halo, and bulge exhibit unique abundance patterns of O, Mg, Si, Ca, and Ti and neutron-capture elements. These signatures show that environment plays an important role in chemical evolution and that supernovae come in many flavors with a range of element yields. The 300-fold dispersion in heavy element abundances of the most metal-poor stars suggests incomplete mixing of ejecta from individual supernova, with vastly different yields, in clouds of ∼106 M[Formula: see text]. The composition of Orion association stars indicates that star-forming regions are significantly self-enriched on time scales of 80 million years. The rapid self-enrichment and inhomogeneous chemical evolution models are required to match observed abundance trends and the dispersion in the age-metallicity relation.