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Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2018

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

Résumé

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).
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hal-02104754 , version 1 (18-11-2020)

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P. François, E. Caffau, P. Bonifacio, M. Spite, F. Spite, et al.. TOPoS. V. Abundance ratios in a sample of very metal-poor turn-off stars. Astronomy and Astrophysics - A&A, 2018, 620, pp.A187. ⟨10.1051/0004-6361/201834375⟩. ⟨hal-02104754⟩
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