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Étude du disque Galactique par marquage chimique de ses populations stellaires

Abstract : Studying both the chemical composition and kinematics of Milky Way stars is essential to understand how big structures of our Galaxy are formed. Indeed, low-mass stars retain in their photosphere the chemical composition of the interstellar medium is which they were born. Additionally, the kinematics are essential to characterize different stellar populations. Galactic Archaeology is based on the observation of a huge number of stars in order to put constraints on a galactic scale. In this thesis, we focus on the galactic disc, a major component of the Milky Way. In the context of the Gaia mission, we have developed an automatic procedure GAUGUIN, devoted to deriving chemical abundances. GAUGUIN is based on a grid of synthetic spectra and a Gauss-Newton algorithm to find the best solution. We first applied our method to the Gaia-ESO Survey (GES) data to derive alpha and iron-peak chemical abundances for 10000 stars. We then derived lithium abundances for 7300 stars from the AMBRE project. GAUGUIN is well adapted to massive spectroscopic surveys, both in terms of computation time and accuracy. GAUGUIN will be soon integrated into the RVS DPAC analysis pipeline of the Gaia mission. We studied the velocity dispersions in the galactic disc as a function of the [Mg/Fe] ratio, used as an age proxy. From the recommended atmospheric parameters and abundances of 6800 GES stars, we detected thick disc stars with cool kinematics and high [Mg/Fe] ratio, so presumably old. In the generally turbulent context of the primitive galactic disc, this thesis places these results in the framework of the different disc formation and evolution scenarios. We also showed that the lithium abundance in the galactic disc increases as a function of the metallicity in the domain -1<[M/H]<+0 dex and decreases at super-solar metallicities. Finally, the thin and the thick discs could be characterized by different lithium abundance evolutions. Our results confirms that chemical abundances are an important diagnostic for understanding the formation and the evolution of the Milky Way stellar populations. Moreover, the development of automatic pipelines of abundance derivation is necessary to face the challenges imposed by current massive spectroscopic surveys.
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https://tel.archives-ouvertes.fr/tel-01261576
Contributor : Guillaume Guiglion <>
Submitted on : Monday, January 25, 2016 - 3:27:28 PM
Last modification on : Tuesday, May 26, 2020 - 6:50:43 PM
Long-term archiving on: : Tuesday, April 26, 2016 - 11:10:29 AM

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  • HAL Id : tel-01261576, version 1

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Guillaume Guiglion. Étude du disque Galactique par marquage chimique de ses populations stellaires. Astrophysique galactique [astro-ph.GA]. Université de Nice Sophia Antipolis, 2015. Français. ⟨tel-01261576⟩

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