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Éléments lourds et anomalies d'abondance dans les étoiles d'amas globulaires

Abstract : High resolution and high S/N spectra have been acquired with UVES on the VLT-Kueyen telescope (ESO, Chile) for several MS turnoff stars and subgiants at the base of the RGB (V > 16 mag) in 3 globular clusters at different metallicities (NGC6397, NGC6752 and 47Tuc, resp. at [Fe/H] = -2.0, -1.5 and -0.7). Spectra have also been taken for 25 field halo stars. I have used these data to determine the abundances of several n-capture elements in these stars : Sr, Y, Ba, and Eu. This work has been done in the framework of the first programme devoted to studying the chemical composition of scarcely involved globular cluster stars. This is the first determination of abundance for n-capture elements in such stars. These abundances, together with the [Ba/EU] and [Sr, Y/Ba] ratios, have been used to test the self-enrichment scenario in globular clusters. I have compared our data to other well known Galactic globular clusters in which n-capture elements have already been detected in the past, at least in bright giants (V < 12). My results show that the n-capture element abundances are constant in a given cluster, and that this is independent of the evolutionary phase of the observed stars (dwarves, subgiants, or giants). I have also showed that these abundances are not linked to the “abundance anomalies” that are found for the light metals (O, Na, …) in globular clusters. Another important results is that globular clusters seem to have been uniformly enriched by r- and s- process syntheses, which discards the “classical” self-enrichment scenario for the origin of the metallicity and of the n-capture elements in globular clusters.
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Gaël James. Éléments lourds et anomalies d'abondance dans les étoiles d'amas globulaires. Astrophysique stellaire et solaire [astro-ph.SR]. Observatoire de Paris, 2004. Français. ⟨NNT : 2004OBSP0120⟩. ⟨tel-02167406⟩

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