Element abundances of 4 metal-poor stars

The relative variations of the chemical compositions between stars is also increasing with decreasing stellar metallicity, allowing to reveal the pure signature of unique nucleosynthesis processes. The study of the r-process is for instance one of the main goals of stellar archaeology, and metal-poor stars show an unexpected complexity in the stellar production of the r-process elements in the early Galaxy.

In this work we report the atmospheric parameter, the main dynamic properties and the abundances of four metal-poor stars: HE 1523-0901, HD 6268, HD 121135, and HD 195636 (-1.5>[Fe/H]>-3.0). The abundances are derived from spectra obtained with the HRS echelle spectrograph at the Southern African Large Telescope, using both LTE and NLTE approaches, with an average error between 0.10 and 0.20dex. Based on their kinematical properties, we show that HE 1523-0901 and HD 195636 are halo stars with typical high velocities; HD 121135 has a peculiar kinematical behaviour making unclear if it is a halo or an accreted star; and HD 6268 is possibly a rare prototype of very metal-poor thick disk stars.