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Processus dynamos dans les étoiles entièrement convectives

Abstract : In solar-type stars, the generation of magnetic field through dynamo effect concentrates in the tachocline, a thin layer of strong shear located at the interface between the radiative core and the convective envelope. Below 0.35 solar mass, main sequence stars are fully convective and thus do not possess a tachocline. And yet, some fully-convective dwarfs are very active, and strong photospheric magnetic fields have been detected. The generation of magnetic field in these objects therefore relies on non-solar dynamo processes. In spite of recent theoretical advances, dynamo processes in fully convective dwarfs remain poorly understood. The observational part of this work has consisted in a spectropolarimetric survey of a small sample of M dwarfs located on both sides of the fully-convective divide. Large-scale magnetic topologies and their dependency on main stellar parameters - mass and rotation period - have been investigated with Zeeman-Doppler Imaging techniques. This study reveals a sharp transition in magnetic topologies of M dwarfs close to the fully convective boundary. The presence of an unexpected behaviour below 0.2 solar mass is also evidenced : stars with similar parameters host radically different large-scale magnetic fields.
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https://tel.archives-ouvertes.fr/tel-00480428
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Submitted on : Tuesday, May 4, 2010 - 11:06:38 AM
Last modification on : Monday, April 5, 2021 - 2:26:13 PM
Long-term archiving on: : Thursday, September 16, 2010 - 12:41:18 PM

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  • HAL Id : tel-00480428, version 1

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Julien Morin. Processus dynamos dans les étoiles entièrement convectives. Planète et Univers [physics]. Université Paul Sabatier - Toulouse III, 2009. Français. ⟨tel-00480428⟩

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