TOPoS: V. Abundance ratios in a sample of very metal-poor turn-off stars

P. François, E. Caffau, P. Bonifacio, M. Spite, F. Spite, R. Cayrel, N. Christlieb, A. J. Gallagher, R. Klessen, A. Koch, H. G. Ludwig, L. Monaco, B. Plez, M. Steffen, S. Zaggia

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Resumen

Context. Extremely metal-poor stars are keys to understand the early evolution of our Galaxy. The ESO large programme TOPoS has been tailored to analyse a new set of metal-poor turn-off stars, whereas most of the previously known extremely metal-poor stars are giant stars. Aims. Sixty five turn-off stars (preselected from SDSS spectra) have been observed with the X-shooter spectrograph at the ESO VLT Unit Telescope 2, to derive accurate and detailed abundances of magnesium, silicon, calcium, iron, strontium and barium. Methods. We analysed medium-resolution spectra (R 10 000) obtained with the ESO X-shooter spectrograph and computed the abundances of several α and neutron-capture elements using standard one-dimensional local thermodynamic equilibrium (1D LTE) model atmospheres. Results. Our results confirms the super-solar [Mg/Fe] and [Ca/Fe] ratios in metal-poor turn-off stars as observed in metal-poor giant stars. We found a significant spread of the [α/Fe] ratios with several stars showing subsolar [Ca/Fe] ratios. We could measure the abundance of strontium in 12 stars of the sample, leading to abundance ratios [Sr/Fe] around the Solar value. We detected barium in two stars of the sample. One of the stars (SDSS J114424-004658) shows both very high [Ba/Fe] and [Sr/Fe] abundance ratios (>1 dex).

Idioma originalInglés
Número de artículoA187
PublicaciónAstronomy and Astrophysics
Volumen620
DOI
EstadoPublicada - 1 dic 2018

Áreas temáticas de ASJC Scopus

  • Astronomía y astrofísica
  • Ciencias planetarias y espacial

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    François, P., Caffau, E., Bonifacio, P., Spite, M., Spite, F., Cayrel, R., Christlieb, N., Gallagher, A. J., Klessen, R., Koch, A., Ludwig, H. G., Monaco, L., Plez, B., Steffen, M., & Zaggia, S. (2018). TOPoS: V. Abundance ratios in a sample of very metal-poor turn-off stars. Astronomy and Astrophysics, 620, [A187]. https://doi.org/10.1051/0004-6361/201834375