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

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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.<i>Aims.<i/> Sixty five...

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Main Authors: François, Patrick (Author) , Caffau, Elisabetta (Author) , Christlieb, Norbert (Author) , Klessen, Ralf S. (Author) , Koch-Hansen, Andreas (Author) , Ludwig, Hans-Günter (Author)
Format: Article (Journal)
Language:English
Published: 14 December 2018
In: Astronomy and astrophysics
Year: 2018, Volume: 620
ISSN:1432-0746
DOI:10.1051/0004-6361/201834375
Online Access:Verlag, Volltext: http://dx.doi.org/10.1051/0004-6361/201834375
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Author Notes: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, and S. Zaggia
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Summary: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.<i>Aims.<i/> 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.<i>Methods.<i/> We analysed medium-resolution spectra (<i>R<i/> ≃ 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.<i>Results.<i/> 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).
Item Description:Gesehen am 16.10.2020
Physical Description:Online Resource
ISSN:1432-0746
DOI:10.1051/0004-6361/201834375

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