From correlations between orbital parameters, several new coherent groups of
stars were recently identified in the Galactic disc and suggested to correspond
to remnants of disrupted satellites. To reconstruct their origin at least three
main observational parameters - kinematics, chemical composition and age - must
be known. We determine detailed elemental abundances in stars belonging to the
so-called Group 2 of the Geneva-Copenhagen Survey and compare the chemical
composition with Galactic thin- and thick-disc stars, as well as with the
Arcturus and AF06 streams. The aim is to search for chemical signatures that
might give information about the formation history of this kinematic group of
stars. High-resolution spectra were obtained with the FIES spectrograph at the
Nordic Optical Telescope, La Palma, and were 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 32 stars of Group 2 is -0.42 +-
0.10 dex. The investigated group consists mainly of two 8- and 12-Gyr-old
stellar populations. Abundances of oxygen, alpha-elements, and
r-process-dominated elements are higher than in Galactic thin-disc dwarfs. This
elemental abundance pattern has similar characteristics as that of the Galactic
thick-disc. The similarity in chemical composition of stars in Group 2 with
that in stars of the thick-disc might suggest that their formation histories
are linked. The chemical composition together with the kinematic properties and
ages of stars in the investigated stars provides evidence of their common
origin and possible relation to an ancient merging event. A gas-rich satellite
merger scenario is proposed as the most likely origin. Groups 2 and 3 of the
Geneva-Copenhagen Survey might have originated in the same merging event.Comment: 17 pages, 13 figures, accepted for publication in Astronomy &
Astrophysics, 201
