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