Bibcode
Adibekyan, V. Zh.; Santos, N. C.; Sousa, S. G.; Israelian, G.
Bibliographical reference
Astronomy and Astrophysics, Volume 535, id.L11
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11
2011
Journal
Citations
133
Refereed citations
124
Description
We performed a uniform and detailed analysis of 1112 high-resolution
spectra of FGK dwarfs obtained with the HARPS spectrograph at the ESO
3.6 m telescope (La Silla, Chile). Most stars have effective
temperatures 4700 K ≤ Teff ≤ 6300 K and lie in the
metallicity range of -1.39 ≤ [Fe/H] ≤ 0.55. Our main goal is to
investigate whether there are any differences between the elemental
abundance trends (especially [α/Fe] ratio) for stars of different
subpopulations. The equivalent widths of spectral lines are
automatically measured from HARPS spectra with the ARES code. The
abundances of three α elements are determined using a differential
LTE analysis relative to the Sun, with the 2010 revised version of the
spectral synthesis code MOOG and a grid of Kurucz ATLAS9 atmospheres.
The stars of our sample fall into two populations, clearly separated in
terms of [α/Fe] up to super-solar metallicities. In turn,
high-α stars are also separated into two families with a gap in
both [α/Fe] ([α/Fe] ≈ 0.17) and metallicity ([Fe/H] ≈
-0.2) distributions. The metal-poor high-α stars (thick disk) and
metal-rich high-α stars are on average older than chemically
defined thin disk stars (low-α stars). The two α-enhanced
families have different kinematics and orbital parameters. The
metal-rich α-enhanced stars, such as thin disk stars have nearly
circular orbits, close to the Galactic plane. We put forward the idea
that these stars may have been formed in the inner Galactic disk, but
their exact nature still remains to be clarified.
Tables 1 and 2 are available in electronic form at http://www.aanda.org
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