Chemical abundances of the Milky Way thick disk and stellar halo

Abstract

We report the chemical abundances of 97 metal-poor stars likely belonging to the Milky Way thick disk and inner/outer stellar halo. All of the spectra of the sample stars have been obtained with the High Dispersion Spectrograph (HDS) mounted on the Subaru Telescope and have analyzed in a homogeneous manner. We show that the thick disk stars show higher [Na/Fe], [Mg/Fe] and [Si/Fe] ratios with small scatter, while the inner and outer halo stars show lower average abundance ratios of these elements with larger scatter in [Fe/H]>−1.5 [1]. The abundance ratios of many of the neutron-capture elements are more enhanced in the halo stars than the thick disk stars. These results suggest that the thick disk and halo stars were formed under the influences of different degrees of Type II/Type Ia supernovae (SNe) enrichments. The larger scatter in the abundances for the halo stars may further indicate that a sizable fraction of the halo stars have formed within different star forming clumps, that may have various chemodynamical histories.