New ultra metal-poor stars from SDSS: follow-up GTC medium-resolution spectroscopy

• Published in: Astronomy and astrophysics (Berlin) Vol. 604; p. A9
• Main Authors: Aguado, D. S., Allende Prieto, C., González Hernández, J. I., Rebolo, R., Caffau, E.
• Format: Journal Article
• Language: English
• Published: Heidelberg EDP Sciences 01.08.2017
• Subjects: Astrophysics; Carbon; Dwarf stars; Galactic evolution; Galaxies; galaxies: formation; galaxies: halos; Galaxy: abundances; Interstellar chemistry; Interstellar matter; Iron; Metallicity; Metals; Organic chemistry; Physics; Sciences of the Universe; Spectra; Spectral resolution; Spectroscopy; Stars; stars: abundances; stars: Population II; Stellar atmospheres
• ISSN: 0004-6361; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/201731320

Context. The first generation of stars formed in the Galaxy left behind the chemical signatures of their nucleosynthesis in the interstellar medium, visible today in the atmospheres of low-mass stars that formed afterwards. Sampling the chemistry of those low-mass provides insight into the first stars. Aims. We aim to increase the samples of stars with extremely low metal abundances, identifying ultra metal-poor stars from spectra with modest spectral resolution and signal-to-noise ratio (S/N). Achieving this goal involves deriving reliable metallicities and carbon abundances from such spectra. Methods. We carry out follow-up observations of faint, V > 19, metal-poor candidates selected from SDSS spectroscopy and observed with the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at GTC. The SDSS and follow-up OSIRIS spectra were analyzed using the FERRE code to derive effective temperatures, surface gravities, metallicities and carbon abundances. In addition, a well-known extremely metal-poor star has been included in our sample to calibrate the analysis methodology. Results. We observed and analyzed five metal-poor candidates from modest-quality SDSS spectra. All stars in our sample have been confirmed as extremely metal-poor stars, in the [Fe/H] < −3.3 regime. We report the recognition of J173403+644632, a carbon-enhanced ultra metal-poor dwarf star with [Fe/H] = −4.3 and [C/Fe] = + 3.1.