Stellar substructures in the solar neighbourhood. I. Kinematic group 3
  in the Geneva-Copenhagen survey
  Galactic Archeology is a powerful tool for investigating the formation and
evolution of the Milky Way. We use this technique to study kinematic groups of
F- and G-stars in the solar neighbourhood. From correlations between orbital
parameters, three new coherent groups of stars were recently identified and
suggested to correspond to remnants of disrupted satellites. We determine
detailed elemental abundances in stars belonging to one of these groups and
compare their chemical composition with Galactic disc stars. The aim is to look
for possible chemical signatures that might give information about the history
of this kinematic group of stars. High-resolution spectra were obtained with
the FIES spectrograph at the Nordic Optical Telescope, La Palma, and analysed
with a differential model atmosphere method. Comparison stars were observed and
analysed with the same method. The average value of [Fe/H] for the 20 stars
investigated in this study is -0.69 +- 0.05 dex. Elemental abundances of oxygen
and alpha-elements are overabundant in comparison with Galactic thin-disc
dwarfs and thin-disc chemical evolution models. This abundance pattern has
similar characteristics as the Galactic thick-disc. The homogeneous chemical
composition together with the kinematic properties and ages of stars in the
investigated Group 3 of the Geneva-Copenhagen survey provides evidence of their
common origin and possible relation to an ancient merging event. The similar
chemical composition of stars in the investigated group and the thick-disc
stars might suggest that their formation histories are linked.
