Chemical abundances of very metal-poor stars

Abstract

High-resolution and high signal-to-noise ratio spectra of 32 very metal-poor stars were obtained with the Coudé echelle spectrograph mounted on the 2.16-m telescope at the National Astronomical Observatories (Xinglong, China). Equivalent widths of FeI, FeII, OI, NaI, MgI, AlI, SiI, SiII, KI, CaI, ScII, TiI, VI, CrI, MnI, NiI, CuI and BaII lines were measured. Stellar effective temperatures were determined by colour indices. Stellar surface gravities were calculated from Hipparcos parallaxes and stellar evolutionary tracks. Photospheric abundances of 16 elements were derived by local thermodynamical equilibrium analysis. Stellar space motions (U, V, W) and Galactic orbital parameters were calculated. Based on kinematics, sample stars were separated into dissipative collapse and accretion components of halo population. The global kinematics of the two components were analysed. Element abundances were discussed as functions of metallicities. The results of oxygen and α-elements abundance confirmed the previous works. The [K/Fe] shows a gradual systematic increase toward a lower metallicity, such as in the case of α-elements. The [Ba/Fe] trend suggests that the s-process dominated Ba production at least for the metal-poor stars with [Fe/H]> -2.0.