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Effects of metallicity, star-formation conditions, and evolution on the B and Be stars populations in the Magellanic Clouds.

Effets de la métallicité, des conditions de formation et de l'évolution sur les populations d'étoiles B et Be des Nuages de Magellan.

Abstract : If in the Milky Way, the B & Be star populations are relatively well known, this is not the same case in the Magellanic Clouds. The Large and Small Magellanic Clouds are galaxies satellites of our proper Galaxy and they are known for having a low metallicity. In order to study the effects of metal under abundances in the hot stars, we have observed large samples of stars in the Magellanic Clouds with the multifibers spectrograph GIRAFFE at the VLT. In this thesis, we present the creation of astrometric and photometric catalogues and the process of B & Be stIf in the Milky Way, the B & Be star populations are relatively well known, this is not the same case in the Magellanic Clouds. The Large and Small Magellanic Clouds are galaxies satellites of our proper Galaxy and they are known for having a low metallicity. In order to study the effects of metal under abundances in the hot stars, we have observed large samples of stars in the Magellanic Clouds with the multifibers spectrograph GIRAFFE at the VLT. In this thesis, we present the creation of astrometric and photometric catalogues and the process of B & Be stars selection. Then, we present the fundamental parameters determination and we examine the consequences of the metallicity on the rotational velocities. For the first time, we show the ZAMS rotational velocities distributions of Be stars and their implications on their behaviour. Afterwards, we compare the evolutionary status of Be stars in the Magellanic Clouds with the Milky Way and we give answers to understand the differences seen. Finally, we give an estimate of the surface carbon abundances and we show differences between the fast rotators like the Be stars and the slow rotators like B stars.ars selection. Then, we present the fundamental parameters determination and we examine the consequences of the metallicity on the rotational velocities. For the first time, we show the ZAMS rotational velocities distributions of Be stars and their implications on their behaviour. Afterwards, we compare the evolutionary status of Be stars in the Magellanic Clouds with the Milky Way and we give answers to understand the differences seen. Finally, we give an estimate of the surface carbon abundances and we show differences between the fast rotators like the Be stars and the slow rotators like B stars.
In the second part of this manuscript, we expose some complementary studies like : the mapping of emission line objects in the Magellanic clouds with the ESO WFI in spectrographic mode; the study of hot stars in young open clusters of the Milky Way. The discovery of short-term photometric variability in Be stars and binaries in the Magellanic clouds and a study of nebular lines are also shown in this latter part.