Bibcode
Adibekyan, V. Zh.; Figueira, P.; Santos, N. C.; Hakobyan, A. A.; Sousa, S. G.; Pace, G.; Delgado Mena, E.; Robin, A. C.; Israelian, G.; González-Hernández, J. I.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 554, id.A44, 8 pp.
Fecha de publicación:
6
2013
Revista
Número de citas
144
Número de citas referidas
133
Descripción
Aims: We analyzed chemical and kinematical properties of about
850 FGK solar neighborhood long-lived dwarfs observed with the HARPS
high-resolution spectrograph. The stars in the sample have log g ≥ 4
dex, 5000 ≤ Teff ≤ 6500 K, and - 1.39 ≤ [Fe/H] ≤
0.55 dex. The aim of this study is to characterize and explore the
kinematics and chemical properties of stellar populations of the Galaxy
in order to understand their origins and evolution. Methods: We
applied a purely chemical analysis approach based on the [α/Fe]
vs. [Fe/H] plot to separate Galactic stellar populations into the thin
disk, thick disk, and high-α metal-rich (hαmr). Then, we
explored the population's stellar orbital eccentricity distributions,
their correlation with metallicity, and rotational velocity gradients
with metallicity in the Galactic disks to provide constraints on the
various formation models. Results: We identified a gap in the
[α/Fe]-[Fe/H] plane for the α-enhanced stars, and by
performing a bootstrapped Monte Carlo test we obtained a probability
higher than 99.99% that this gap is not due to small-number statistics.
Our analysis shows a negative gradient of the rotational velocity of the
thin disk stars with [Fe/H] (-17 km s-1 dex-1),
and a steep positive gradient for both the thick disk and hαmr
stars with the same magnitude of about +42 km s-1
dex-1. For the thin disk stars we observed no correlation
between orbital eccentricities and metallicity, but observed a steep
negative gradient for the thick disk and hαmr stars with
practically the same magnitude (≈-0.18 dex-1). The
correlations observed for the nearby stars (on average 45 pc) using
high-precision data, in general agree well with the results obtained for
the SDSS sample of stars located farther from the Galactic plane.
Conclusions: Our results suggest that radial migration played an
important role in the formation and evolution of the thin disk. For the
thick disk stars it is not possible to reach a firm conclusion about
their origin. Based on the eccentricity distribution of the thick disk
stars only their accretion origin can be ruled out, and the heating and
migration scenario could explain the positive steep gradient of
Vφ with [Fe/H]. When we analyzed the hαmr stellar
population we found that they share properties of both the thin and
thick disk population. A comparison of the properties of the hαmr
stars with those of the subsample of stars from the N-body/SPH
simulation using radial migration suggest that they may have originated
from the inner Galaxy. Further detailed investigations would help to
clarify their exact nature and origin.
Based on observations collected at the La Silla Paranal Observatory, ESO
(Chile) with the HARPS spectrograph at the 3.6-m telescope (ESO runs ID
72.C-0488, 082.C-0212, and 085.C-0063).
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