Detailed abundances in a sample of very metal-poor stars

Abstract

Context. Unevolved metal-poor stars bore witness to the early evolution of the Galaxy, and the determination of their detailed chemical composition is an important tool to understand its chemical history. The study of their chemical composition can also be used to constrain the nucleosynthesis of the first generation of supernovae that enriched the interstellar medium. Aims. We aim to observe a sample of extremely metal-poor star (EMP stars) candidates selected from the Sloan Digital Sky Survey data release 12 (SDSS DR12) and determine their chemical composition. Methods. We obtained high-resolution spectra of a sample of five stars using HDS on Subaru telescope and used standard 1D models to compute the abundances. The stars we analysed have a metallicity [Fe/H] of between −3.50 and −4.25 dex. Results. We confirm that the five metal-poor candidates selected from low-resolution spectra are very metal poor. We present the discovery of a new ultra metal-poor star (UMP star) with a metallicity of [Fe/H] = −4.25 dex (SDSS J1050032.34−241009.7). We measured in this star an upper limit of lithium (log(Li/H) ≤ 2.0. We found that the four most metal-poor stars of our sample have a lower lithium abundance than the Spite plateau lithium value. We obtain upper limits for carbon in the sample of stars. None of them belong to the high carbon band. We measured abundances of Mg and Ca in most of the stars and found three new α-poor stars.