Examinando por Autor "Salvadori, S."

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    The CEMP star SDSS J0222–0313: The first evidence of proton ingestion in very low-metallicity AGB stars?
    (Astronomy and Astrophysics, 2019) E., Caffau; L., Monaco; P., Bonifacio; S., Korotin; S., Andrievsky; S., Cristallo; M., Spite; F., Spite; Sbordone, L.; François, P.; Cescutti, G.; Salvadori, S.
    Context. Carbon-enhanced metal-poor (CEMP) stars are common objects in the metal-poor regime. The lower the metallicity we look at, the larger the fraction of CEMP stars with respect to metal-poor stars with no enhancement in carbon. The chemical pattern of CEMP stars is diversified, strongly suggesting a different origin of the C enhancement in the different types of CEMP stars. Aims. We selected a CEMP star, SDSS J0222–0313, with a known high carbon abundance and, from a low-resolution analysis, a strong enhancement in neutron-capture elements of the first peak (Sr and Y) and of the second peak (Ba). The peculiarity of this object is a greater overabundance (with respect to iron) of the first s-process peak than the second s-process peak. Methods. We analysed a high-resolution spectrum obtained with the Mike spectrograph at the Clay Magellan 6.5 m telescope in order to derive the detailed chemical composition of this star. Results. We confirmed the chemical pattern we expected; we derived abundances for a total of 18 elements and significant upper limits. Conclusions. We conclude that this star is a carbon-enhanced metal-poor star enriched in elements produced by s-process (CEMP-s), whose enhancement in heavy elements is due to mass transfer from the more evolved companion in its asymptotic giant branch (AGB) phase. The abundances imply that the evolved companion had a low main sequence mass and it suggests that it experienced a proton ingestion episode at the beginning of its AGB phase.
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    TOPoS: III. An ultra iron-poor multiple CEMP system ?
    (EDP Sciences, 2016-11) Caffau, E.; Bonifacio, P.; Spite, M.; Spite, F.; Monaco, L.; Sbordone, L.; François, P.; Gallagher, A.J.; Plez, B.; Zaggia, S.; Ludwig, H.-G.; Cayrel, R.; Koch, A.; Steffen, M.; Salvadori, S.; Klessen, R.; Glover, S.; Christlieb, N.
    Aims. One of the primary objectives of the TOPoS survey is to search for the most metal-poor stars. Our search has led to the discovery of one of the most iron-poor objects known, SDSS J092912.32+023817.0. This object is a multiple system, in which two components are clearly detected in the spectrum. Methods. We have analysed 16 high-resolution spectra obtained using the UVES spectrograph at the ESO 8.2 m VLT telescope to measure radial velocities and determine the chemical composition of the system. Results. Cross correlation of the spectra with a synthetic template yields a double-peaked cross-correlation function (CCF) for eight spectra, and in one case there is evidence for the presence of a third peak. Chemical analysis of the spectrum obtained by averaging all the spectra for which the CCF showed a single peak found that the iron abundance is [Fe/H] = −4.97. The system is also carbon enhanced with [C/Fe] = +3.91 (A(C) = 7.44). From the permitted oxygen triplet we determined an upper limit for oxygen of [O/Fe] < +3.52 such that C/O > 1.3. We are also able to provide more stringent upper limits on the Sr and Ba abundances ([Sr/Fe] < +0.70, and [Ba/Fe] < +1.46, respectively).