Decomposition of the Galactic Disk: Abundances and Kinematics

Abstract To this contribution we present a brief review of our recent abundance surveys (Reddy et al. 2003; Reddy et al. 2006) of the Milky Way galaxy. Survey focussed on controlled samples of stars selected based on their kinematic properties to belong either thin disk, thick disk or halo components of the Galaxy. Abundance and kinematic results were obtained for about 400 F-, G- and K- dwarfs. Abundances for 22 elements representing different production mechanisms (α-process, p-capture, Fe-peak, s- and r-process) and sites (AGB, SNIa, SNII) were obtained using high quality and high resolution echelle spectra. Results showed thin and thick disk components are distinct stellar populations with different chemical history. The ratios of α-elements and a few other elements (like Al, V, and Co) are clearly enhanced for stars in the thick disk compared to thin disk stars at given metallicity. Abundance ratios for halo and thick disk stars are very similar. Dispersion in [X/Fe] ratios at given metallicity is comparable to measurement errors inferring lack of cosmic' scatter. Thick disk stars are older (10-13 Gyrs) compared to their counter parts (1-10 Gyrs) in the thin disk. Abundance results for thin and thick disk stars favor the models of hierarchical formation of the galaxy.