Bibcode
Delgado Mena, E.; Tsantaki, M.; Adibekyan, V. Zh.; Sousa, S. G.; Santos, N. C.; González Hernández, J. I.; Israelian, G.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 606, id.A94, 20 pp.
Fecha de publicación:
10
2017
Revista
Número de citas
159
Número de citas referidas
149
Descripción
Aims: To understand the formation and evolution of the different
stellar populations within our Galaxy it is essential to combine
detailed kinematical and chemical information for large samples of
stars. The aim of this work is to explore the chemical abundances of
neutron capture elements which are a product of different
nucleosynthesis processes taking place in diverse objects in the Galaxy,
such as massive stars, asymptotic giant branch (AGB) stars and
supernovae (SNe) explosions. Methods: We derive chemical
abundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Eu for a large sample
of more than 1000 FGK dwarf stars with high-resolution (R 115 000) and
high-quality spectra from the HARPS-GTO program. The abundances are
derived by a standard local thermodynamic equilibrium (LTE) analysis
using measured equivalent widths (EWs) injected to the code MOOG and a
grid of Kurucz ATLAS9 atmospheres. Results: We find that thick
disc stars are chemically disjunct for Zn and Eu and also show on
average higher Zr but lower Ba and Y than the thin disc stars. We also
discovered that the previously identified high-α metal-rich
population is also enhanced in Cu, Zn, Nd, and Eu with respect to the
thin disc but presents lower Ba and Y abundances on average, following
the trend of thick disc stars towards higher metallities and further
supporting the different chemical composition of this population. By
making a qualitative comparison of O (pure α), Mg, Eu (pure
r-process), and s-process elements we can distinguish between the
contribution of the more massive stars (SNe II for α and r-process
elements) and the lower mass stars (AGBs) whose contribution to the
enrichment of the Galaxy is delayed, due to their longer lifetimes. The
ratio of heavy-s to light-s elements of thin disc stars presents the
expected behaviour (increasing towards lower metallicities) and can be
explained by a major contribution of low-mass AGB stars for s-process
production at disc metallicities. However, the opposite trend found for
thick disc stars suggests that intermediate-mass AGB stars play an
important role in the enrichment of the gas from where these stars
formed. Previous works in the literature also point to a possible
primary production of light-s elements at low metallicities to explain
this trend. Finally, we also find an enhancement of light-s elements in
the thin disc at super-solar metallicities which could be caused by the
contribution of metal-rich AGB stars. Conclusions: This work
proves the utility of homogeneous and high-quality data of modest sample
sizes. We find some interesting trends that might help to differentiate
thin and thick disc population (such as [Zn/Fe] and [Eu/Fe] ratios) and
that can also provide useful constraints for Galactic chemical evolution
models of the different populations in the Galaxy.
Based on observations collected at the La Silla Observatory, ESO
(Chile), with the HARPS spectrograph at the 3.6 m ESO telescope (ESO
runs ID 72.C—0488, 082.C—0212, and 085.C—0063).Full
Tables 1 and 3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/A94
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Israelian