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Paper: Abundance Trends in the Milky Way Disk as Observed by SEGUE
Volume: 458, Galactic Archaeology: Near-Field Cosmology and the Formation of the Milky Way
Page: 105
Authors: Cheng, J. Y.; Rockosi, C. M.; Morrison, H. L.; Schönrich, R. A.; Lee, Y. S.; Beers, T. C.
Abstract: Detailed observations of the Galaxy can be used to test predictions made by models of disk formation and evolution, and they serve to complement large surveys that study galaxies at high redshift. The observed radial and vertical metallicity distribution of old stars in the Milky Way disk provides powerful constraints on the chemical enrichment and dynamical history of the disk. We present trends in [Fe/H] and [α/Fe] as a function of Galactocentric radius R and height above the plane |Z| using 7010 main sequence turnoff stars observed by the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. The sample consists of mostly old thin and thick disk stars, with a minimal contribution from the stellar halo, in the region 6 < R < 16 kpc, 0.15 < |Z| < 1.5 kpc. We find that the radial metallicity gradient Δ[Fe/H]/Δ R becomes flat at heights |Z| > 1 kpc. In addition, we find that the high-α population, which dominates at large heights |Z| in the inner disk (R < 10 kpc), makes up a small fraction of stars in the outer disk (R > 10 kpc). The chemical and kinematic properties of high-α stars in the outer disk differ from those in the inner disk, consistent with the high-α population having a short scale length. Our observations are consistent with the predictions for a thick disk formed in situ at high redshift, and the lack of high-α stars at large R and |Z| provides a strong constraint on the strength of radial migration induced by transient spiral arms.
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