Volume 542, June 2012
|Number of page(s)||26|
|Published online||13 June 2012|
Accurate and homogeneous abundance patterns in solar-type stars of the solar neighbourhood: a chemo-chronological analysis⋆
INPE, Divisão de Astrofísica, Av. dos Astronautas,
1758 São José dos Campos,
2 UFRJ, Observatório do Valongo, Ladeira do Pedro Antônio 43, 20080-090 Rio de Janeiro, Brazil
3 Observatório Nacional, Rua Gal. José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro, Brazil
Accepted: 22 April 2012
Aims. We report the derivation of abundances of C, Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Sm in a sample of 25 solar-type stars of the solar neighbourhood, correlating the abundances with the stellar ages, kinematics, and orbital parameters.
Methods. The spectroscopic analysis, based on data of high resolution and high signal-to-noise ratio, was differential to the Sun and applied to atomic line equivalent widths supplemented by the spectral synthesis of C and C2 features. We also performed a statistical study by using the method of tree clustering analysis, searching for groups of stars sharing similar elemental abundance patterns. We derived the stellar parameters from various criteria, with average errors of 30 K, 0.13 dex, and 0.05 dex, respectively, for Teff, log g, and [Fe/H]. The average error of the [X/Fe] abundance ratios is 0.06 dex. Ages were derived from theoretical HR diagrams and membership of the stars in known kinematical moving groups.
Results. We identified four stellar groups: one having, on average, over-solar abundances (⟨[X/H]⟩ = +0.26 dex), another with under-solar abundances (⟨ [X/H] ⟩ = −0.24 dex), and two with intermediate values (⟨ [X/H] ⟩ = −0.06 and +0.06 dex) but with distinct chemical patterns. Stars sharing solar metallicity, age, and Galactic orbit possibly have non-solar abundance ratios, a possible effect either of chemical heterogeneity in their natal clouds or migration. A trend of [Cu/Fe] with [Ba/Fe] seems to exist, in agreement with previous claims in the literature, and maybe also of [Sm/Fe] with [Ba/Fe]. No such correlation involving C, Na, Mn, and Zn is observed. The [X/Fe] ratios of various elements show significant correlations with age. [Mg/Fe], [Sc/Fe], and [Ti/Fe] increase with age. [Mn/Fe] and [Cu/Fe] display a more complex behaviour, first increasing towards younger stars up to the solar age, and then decreasing, a result we interpret as possibly related to time-varying yields of SN Ia and the weak s-process in massive stars. The steepest negative age relation is due to [Ba/Fe], but only for stars younger than the Sun, and a similar though less significant behaviour is seen for Zr, Ce, and Nd. [Sr/Fe] and [Y/Fe] show a linearly increasing trend towards younger stars. The [Cu/Ba] and [Sm/Ba] therefore decrease for younger stars. We found that [Ba/Mg], [Ba/Zn], and [Sr,Y,Ba/Sm] increase but only for stars younger than the Sun, whereas the [Sr/Mg], [Y/Mg], [Sr/Zn], and [Y/Zn] ratios increase linearly towards younger stars over the whole age range.
Key words: stars: solar-type / stars: fundamental parameters / stars: abundances
© ESO, 2012
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