English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We employ measurements of the [alpha/Fe] ratio derived from low-resolution(R~2000) spectra of 17,277 G-type dwarfs from the SEGUE survey to separate theminto likely thin- and thick-disk subsamples. Both subsamples exhibit stronggradients of orbital rotational velocity with metallicity, of opposite signs,-20 to -30 km/s/dex for the thin-disk and +40 to +50 km/s/dex for thethick-disk population. The rotational velocity is uncorrelated withGalactocentric distance for the thin-disk subsample, and exhibits a small trendfor the thick-disk subsample. The rotational velocity decreases with distancefrom the plane for both disk components, with similar slopes (-9.0 {\pm} 1.0km/s/kpc). Thick-disk stars exhibit a strong trend of orbital eccentricity withmetallicity (about -0.2/dex), while the eccentricity does not change withmetallicity for the thin-disk subsample. The eccentricity is almost independentof Galactocentric radius for the thin-disk population, while a marginalgradient of the eccentricity with radius exists for the thick-disk population.Both subsamples possess similar positive gradients of eccentricity withdistance from the Galactic plane. The shapes of the eccentricity distributionsfor the thin- and thick-disk populations are independent of distance from theplane, and include no significant numbers of stars with eccentricity above 0.6.Among several contemporary models of disk evolution we consider, radialmigration appears to have played an important role in the evolution of thethin-disk population, but possibly less so for the thick disk, relative to thegas-rich merger or disk heating scenarios. We emphasize that more physicallyrealistic models and simulations need to be constructed in order to carry outthe detailed quantitative comparisons that our new data enable.

Formation and Evolution of the Disk System of the Milky Way: [alpha/Fe] Ratios and Kinematics of the SEGUE G-Dwarf Sample