X-Shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars

Abstract

The extremely metal-poor stars are the direct descendants of the first generation stars. They carry the chemical signature of the pristine Universe at the time they formed, shortly after the Big Bang. We aim to derive information about extremely metal-poor stars from their observed spectra. Four extremely metal-poor stars were selected from the Sloan Digital Sky Survey (SDSS) and observed during the guaranteed observing time of X-Shooter. The X-Shooter spectra were analysed using an automatic code, MyGIsFOS, which is based on a traditional analysis method. It makes use of a synthetic grid computed from one-dimensional, plane-parallel, hydrostatic model atmospheres. The low metallicity derived from the SDSS spectra is confirmed here. Two kinds of stars are found. Two stars are confirmed to be extremely metal-poor, with no evidence of any enhancement in carbon. The two other stars are strongly enhanced in carbon. We could not derive iron abundance for one of them, while [Ca/H] is below -4.5. Two of the stars are members of the rare population of extremely metal-poor stars low in alpha elements.

A&A in press

References in corpus (7)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Nucleosynthetic signatures of the first stars
• An extremely primitive halo star
• The SEGUE Stellar Parameter Pipeline. III. Comparison with High-Resolution Spectroscopy of SDSS/SEGUE Field Stars
• HE 1327-2326, an unevolved star with [Fe/H]<-5.0. II. New 3D-1D corrected abundances from a VLT/UVES spectrum
• First Stars XI. Chemical composition of the extremely metal-poor dwarfs in the binary CS 22876--032
• Extremely metal-poor stars from the SDSS

Cited by in corpus (32)

• The Pristine survey I: Mining the Galaxy for the most metal-poor stars
• TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies
• JINAbase: A database for chemical abundances of metal-poor stars
• High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey
• Four-hundred Very Metal-Poor Stars Studied with LAMOST and Subaru. II. Elemental abundances
• The Best and Brightest Metal-Poor Stars
• TOPoS: IV. Chemical abundances from high-resolution observations of seven EMP stars
• TOPoS: I. Survey design and analysis of the first sample
• Metal-Poor Stars Observed with the Magellan Telescope II. Discovery of Four Stars with [Fe/H] < -3.5
• Probing the existence of very massive first stars
• Chemical Abundance Analysis of Three $\alpha$-Poor, Metal-Poor Stars in the Ultra-Faint Dwarf Galaxy Horologium I
• Ultra metal-poor stars: Spectroscopic determination of stellar atmospheric parameters using iron Non-LTE line abundances
• Evidence for the accretion origin of halo stars with an extreme r-process enhancement
• WHT follow-up observations of extremely metal-poor stars identified from SDSS and LAMOST
• The origin of low [alpha/Fe] ratios in extremely metal-poor stars
• A CEMP-no star in the ultra-faint dwarf galaxy Pisces II
• Low-metallicity star formation: Relative impact of metals and magnetic fields
• The chemical abundance pattern of the extremely metal-poor thin disk star 2MASS J1808-5104 and its origins
• The R-Process Alliance: Fifth Data Release from the Search for R-Process-Enhanced Metal-poor Stars in the Galactic Halo with the GTC
• Pre-supernova mixing in CEMP-no source stars
• Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. III. Dynamically Tagged Groups and Chemodynamical Properties
• Abundance analysis of SDSS J134338.67+484426.6; an extremely metal-poor star from the MARVELS pre-survey
• Investigation of a sample of carbon-enhanced metal-poor stars observed with FORS and GMOS
• Chemical analysis of very metal-poor turn-off stars from SDSS-DR12
• Detailed abundances in a sample of very metal poor stars
• SDSS J102915.14+172927.9: Revisiting the chemical pattern
• Exploring the SDSS Dataset with Linked Scatter Plots: I. EMP, CEMP, and CV Stars
• TOPoS V: Abundance ratios in a sample of very metal-poor turn-off stars
• Deep SDSS Optical Spectroscopy of Distant Halo Stars. III. Chemical analysis of extremely metal-poor stars
• CD -24_17504 revisited: a new comprehensive element abundance analysis
• Searching for Low-mass Population III Stars Disguised as White Dwarfs
• Detailed Abundance Determination of Metal-Poor Stars with X-Shooter I. Unusual Chemistry in Halo Stars