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

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.Comment: 8 pages, 8 figures, accepted for publication in Astronomy & Astrophysics, 2013. arXiv admin note: text overlap with arXiv:1203.619

Chemical composition study of Galactic stellar substructures

Helmi et al. (2006) identified three new coherent groups of stars in the Geneva-Copenhagen survey (GCS) (Nordström et al. 2004) and suggested that those might correspond to remains of disrupted satellites. In this dissertation work we investigate detailed elemental abundances in stars belonging to two of the newly identified GCS kinematic groups. The main aim of the study is to perform a high-resolution spectroscopic analysis of the kinematic groups stars and to compare the results with Galactic thin- and thick-disc dwarfs. The main atmospheric parameters and abundances of 21 chemical elements have been determined. The abundance pattern of programme stars has similar characteristics to those of the Galactic thick disc, which might suggest that their formation histories are linked. We compare our results with other Galactic kinematic substructures studies. The comparison of kinematic and chemical composition patterns in the Galactic substructures, leads us to the conclusion that the origin of the GCS kinematic stellar groups was different from Galactic streams which originated in a course of the resonant interactions between stars in the outer disk and the Galactic bar. We revisited the determination for one of GCS kinematic group stars. The chemical composition together with the kinematic properties and ages of stars in the investigated GCS groups support a gas-rich satellite merger scenario as a possible origin for these kinematic groups

Cheminės sudėties tyrimas Galaktikos žvaigždžių substruktūrose

Helmi et al. (2006) identified three new coherent groups of stars in the Geneva-Copenhagen survey (GCS) (Nordström et al. 2004) and suggested that those might correspond to remains of disrupted satellites. In this dissertation work we investigate detailed elemental abundances in stars belonging to two of the newly identified GCS kinematic groups. The main aim of the study is to perform a high-resolution spectroscopic analysis of the kinematic groups stars and to compare the results with Galactic thin- and thick-disc dwarfs. The main atmospheric parameters and abundances of 21 chemical elements have been determined. The abundance pattern of programe stars has similar characteristics to those of the Galactic thick disc, which might suggest that their formation histories are linked. We compare our results with other Galactic kinematic substructures studies. The comparison of kinematic and chemical composition patterns in the Galactic substructures, leads us to the conclusion that the origin of the GCS kinematic stellar groups was different from Galactic streams which originated in a course of the resonant interactions between stars in the outer disk and the Galactic bar. We revisited the determination for one of GCS kinematic group stars. The chemical composition together with the kinematic properties and ages of stars in the investigated GCS groups support a gas-rich satellite merger scenario as a possible origin for these kinematic groups