Stellar substructures in the solar neighbourhood

II. Abundances of neutron-capture elements in the kinematic Group 3 of the Geneva-Copenhagen survey

¹ Institute of Theoretical Physics and Astronomy, Vilnius University, A. Gostauto 12, 01108 Vilnius, Lithuania
e-mail: edita.stonkute@tfai.vu.lt; grazina.tautvaisiene@tfai.vu.lt; renata.zenoviene@tfai.vu.lt
² Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
e-mail: birgitta@nbi.ku.dk

Received: 8 March 2013
Accepted: 18 April 2013

Abstract

Context. 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.

Aims. We determine detailed elemental abundances of s- and r-process elements in stars belonging to Group 3 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.

Methods. 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.

Results. 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.

Conclusions. The chemical composition together with the kinematic properties and ages of stars in Group 3 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 Group 3 and the thick-disc stars might suggest that their formation histories are linked.