More pieces of the puzzle

Chemistry and substructures in the galactic thick disk

Amina Helmi, Mary Williams, K. C. Freeman, J. Bland-Hawthorn, G. De Silva

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

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 < epsilon < 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.
Original languageEnglish
Article number135
Number of pages6
JournalAstrophysical Journal
Volume791
Issue number2
DOIs
Publication statusPublished - 20 Aug 2014
Externally publishedYes

Keywords

  • Galaxy: disk
  • Galaxy: formation
  • stars: abundances

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