  The evolution of chemical elements in a galaxy is linked to its star
formation history. Variations in star formation history are imprinted in the
relative abundances of chemical elements produced in different supernova events
and asymptotic giant branch stars. We determine detailed elemental abundances
of s- and r-process elements in stars belonging to Group3 of the
Geneva-Copenhagen survey and compare their chemical composition with Galactic
disc stars. The aim is to look for possible chemical signatures that might give
information about the formation history of this kinematic group of stars, which
is suggested to correspond to remnants of disrupted satellites. 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.
Abundances of chemical elements produced mainly by the s-process are similar to
those in the Galactic thin-disc dwarfs of the same metallicity, while
abundances of chemical elements produced predominantly by the r-process are
overabundant. The similar elemental abundances are observed in Galactic
thick-disc stars. The chemical composition together with the kinematic
properties and ages of stars in Group3 of the Geneva-Copenhagen survey support
a gas-rich satellite merger scenario as the most likely explanation for the
origin. The similar chemical composition of stars in Group3 and the thick-disc
stars might suggest that their formation histories are linked.
