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  TOPoS. IV. Chemical abundances from high-resolution observations of seven extremely metal-poor stars

Bonifacio, P., Caffau, E., Spite, M., Spite, F., Sbordone, L., Monaco, L., et al. (2018). TOPoS. IV. Chemical abundances from high-resolution observations of seven extremely metal-poor stars. Astronomy and Astrophysics, 612.

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Item Permalink: https://hdl.handle.net/21.11116/0000-0005-CEC2-8 Version Permalink: https://hdl.handle.net/21.11116/0000-0005-CEC3-7
Genre: Journal Article

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https://ui.adsabs.harvard.edu/abs/2018A&A...612A..65B (Any fulltext)
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 Creators:
Bonifacio, P.1, Author
Caffau, E.1, Author
Spite, M.1, Author
Spite, F.1, Author
Sbordone, L.1, Author
Monaco, L.1, Author
François, P.1, Author
Plez, B.1, Author
Molaro, P.1, Author
Gallagher, A. J.1, Author
Cayrel, R.1, Author
Christlieb, N.1, Author
Klessen, R. S.1, Author
Koch, A.1, Author
Ludwig, H. -G.1, Author
Steffen, M.1, Author
Zaggia, S.1, Author
Abate, C.1, Author
Affiliations:
1Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners, ou_2421692              

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Free keywords: stars: population II stars: abundances Galaxy: abundances Galaxy: formation Galaxy: halo cosmology: observations Astrophysics - Solar and Stellar Astrophysics Astrophysics - Cosmology and Nongalactic Astrophysics Astrophysics - Astrophysics of Galaxies
 Abstract: Context. Extremely metal-poor (EMP) stars provide us with indirect information on the first generations of massive stars. The TOPoS survey has been designed to increase the census of these stars and to provide a chemical inventory that is as detailed as possible.
Aims: Seven of the most iron-poor stars have been observed with the UVES spectrograph at the ESO VLT Kueyen 8.2 m telescope to refine their chemical composition.
Methods: We analysed the spectra based on 1D LTE model atmospheres, but also used 3D hydrodynamical simulations of stellar atmospheres.
Results: We measured carbon in six of the seven stars: all are carbon-enhanced and belong to the low-carbon band, defined in the TOPoS II paper. We measured lithium (A(Li) = 1.9) in the most iron-poor star (SDSS J1035+0641, [Fe/H] <-5.2). We were also able to measure Li in three stars at [Fe/H] -4.0, two of which lie on the Spite plateau. We confirm that SDSS J1349+1407 is extremely rich in Mg, but not in Ca. It is also very rich in Na. Several of our stars are characterised by low α-to-iron ratios.
Conclusions: The lack of high-carbon band stars at low metallicity can be understood in terms of evolutionary timescales of binary systems. The detection of Li in SDSS J1035+0641 places a strong constraint on theories that aim at solving the cosmological lithium problem. The Li abundance of the two warmer stars at [Fe/H] -4.0 places them on the Spite plateau, while the third, cooler star, lies below. We argue that this suggests that the temperature at which Li depletion begins increases with decreasing [Fe/H]. SDSS J1349+1407 may belong to a class of Mg-rich EMP stars. We cannot assess if there is a scatter in α-to-iron ratios among the EMP stars or if there are several discrete populations. However, the existence of stars with low α-to-iron ratios is supported by our observations. Based on observations obtained at ESO Paranal Observatory, Programmes 189.D-0165,090.D-0306, 093.D-0136, and 096.D-0468.

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 Dates: 2018
 Publication Status: Issued
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Title: Astronomy and Astrophysics
Source Genre: Journal
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Pages: - Volume / Issue: 612 Sequence Number: - Start / End Page: - Identifier: -