Abundance Ratios in Metal-Rich Halo and Thick-Disk Stars

Recent determinations of precise abundance ratios for nearby halo and thick disk stars in the metallicity range −1.3 < Fe/H] < −0.5 have revealed a significant cosmic spread in the abundances of oxygen, magnesium, sodium, nickel, s-process and r-process elements relative to iron. Possible explanations of these variations are reviewed. In particular, it is discussed if the differences in abundance ratios are correlated with the kinematics of the stars, and hence can be used to identify stellar populations in the Galaxy. This revised version was published online in July 2006 with corrections to the Cover Date.