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Etude de l'évolution de la structure interne et du champ magnétique des étoiles pré-séquence principale de masse intermédiaire

Abstract : The angular momentum evolution of intermediate mass stars, and the impact of the magnetic field on this evolution, especially during the pre-main sequence (PMS) phase of stellar evolution, are poorly understood. In this framework, the aims of my thesis work was on one hand to provide observational constraints to this problem, and on the other hand to take the first steps toward a full modeling of PMS evolution at intermediate mass, taking into account rotation and magnetic field.

First, I used the eclipsing binary system RS Cha to test the physics of the PMS stellar evolution models. I redetermined masses and radii of both components of this binary and I measured the metallicity of the system, using spectroscopic data. Our knowledge of the fundamental parameters of this system is therefore now complete. I then tested the current PMS stellar evolutionary models, by matching the observed fundamental parameters of RS Cha to those calculated by the models. I conclude that these models are able to reproduce the observations, provided that the new solar mixture of Asplund et al. (2004) is used. This work confirms independently the results of Asplund and co-authors, in the general context of wide discussion on the validity of this mixture.

The second part of my thesis is dedicated to the study of the magnetism of a sample of 50 Herbig Ae/Be stars, i.e. PMS stars of intermediate mass. Using the new ESPaDOnS spectropolarimeter located at CFHT, we have detected 4 magnetic stars in this sample. We first conclude that the proportion of magnetic stars among Herbig Ae/Be stars is very close to the proportion of magnetic stars among main sequence A and B stars. Secondly, using a very simple oblic rotator model, I showed that the structure of these magnetic fields is very close to a global dipolar structure, as is the magnetic field of the Ap/Bp stars. These results bring strong arguments in favour of the fossil field hypothesis, proposed to explain the origin of the magnetic field of Ap/Bp stars.
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https://tel.archives-ouvertes.fr/tel-00124785
Contributor : Evelyne Alecian <>
Submitted on : Tuesday, January 16, 2007 - 10:31:10 AM
Last modification on : Tuesday, December 15, 2020 - 1:48:03 PM
Long-term archiving on: : Tuesday, April 6, 2010 - 8:00:56 PM

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  • HAL Id : tel-00124785, version 1

Citation

Evelyne Alecian. Etude de l'évolution de la structure interne et du champ magnétique des étoiles pré-séquence principale de masse intermédiaire. Astrophysique [astro-ph]. Université Paris-Diderot - Paris VII, 2006. Français. ⟨tel-00124785⟩

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