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Formation and Evolution of the Disk System of the Milky Way: [alpha/Fe] Ratios and Kinematics of the SEGUE G-Dwarf Sample | | Young Sun Lee
; Timothy C. Beers
; Deokkeun An
; Zeljko Ivezic
; Andreas Just
; Constance M. Rockosi
; Heather L. Morrison
; Jennifer A. Johnson
; Ralph Schonrich
; Jonathan Bird
; Brian Yanny
; Paul Harding
; Helio J. Rocha-Pinto
; | | Date: |
15 Apr 2011 | | Abstract: | We employ measurements of the [alpha/Fe] ratio to separate them into likely
thin- and thick-disk subsamples. Both subsamples exhibit strong gradients of
orbital rotational velocity with metallicity, but with opposite signs (-20 to
-30 km/s/dex for the thin-disk population, and +40 to +50 km/s/dex for the
thick-disk population). We find that the rotational velocity decreases with the
distance from the plane for both disk components. The mean rotational velocity
is uncorrelated with Galactocentric distance for the thin-disk subsample, and
exhibits only a marginally significant correlation for the thick-disk
subsample. Thick-disk stars exhibit a very strong trend of orbital eccentricity
with metallicity (-0.2 dex^-1), while the eccentricity does not change with
metallicity for the thin-disk subsample. The eccentricity is almost independent
of Galactocentric radius for the thin-disk stars, while a marginal gradient of
the eccentricity with distance exists for the thick-disk population. Both
subsamples possess similar trends of increasing eccentricity with distance from
the Galactic plane. The shapes of the overall distributions of orbital
eccentricity for the thin- and thick-disk populations are quite different from
one another, independent of distance from the plane; neither subsample has
significant numbers of stars with eccentricity above 0.6. These observational
results provide strong new constraints on models for the formation and
evolution of the Milky Way’s disk system. | | Source: | arXiv, 1104.3114 | | Services: | Forum | Review | PDF | Favorites | |
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