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Title: More pieces of the puzzle: chemistry and substructures in the galactic thick disk

We present a study of the chemical abundances of solar neighborhood stars associated with dynamical structures in the Milky Way's (thick) disk. These stars were identified as an overdensity in the eccentricity range 0.3 < ε < 0.5 in the Copenhagen-Geneva Survey by Helmi et al. We find that stars with these dynamical characteristics do not constitute a homogeneous population. A relatively sharp transition in dynamical and chemical properties appears to occur at a metallicity of [Fe/H] ∼ –0.4. Stars with [Fe/H] > –0.4 have mostly lower eccentricities, smaller vertical velocity dispersions, are α-enhanced, and define a rather narrow sequence in [α/Fe] versus [Fe/H], clearly distinct from that of the thin disk. Stars with [Fe/H] < –0.4 have a range of eccentricities, are hotter vertically, and depict a larger spread in [α/Fe]. We also found tentative evidence of a substructure possibly associated with the disruption of a metal-rich star cluster. The differences between these populations of stars is also present in, e.g., [Zn/Fe], [Ni/Fe], and [SmII/Fe], suggesting a real physical distinction.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen (Netherlands)
  2. Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Germany (Germany)
  3. Research School of Astronomy and Astrophysics The Australian National University, Cotter Road Weston Creek, ACT 2611 (Australia)
  4. Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006 (Australia)
  5. Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia)
Publication Date:
OSTI Identifier:
22365274
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 791; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CONCENTRATION RATIO; DISPERSIONS; ELEMENT ABUNDANCE; METALLICITY; METALS; MILKY WAY; STAR CLUSTERS; STARS; VELOCITY