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Dynamo des étoiles de type solaire : impact de la masse et de la rotation

Abstract : Magnetic fields are known to be present in a wide variety of stars, from fully convective low-mass stars to massive stars with external radiative layers. In solar-type stars, the large-scale magnetic field is continuously produced by dynamo processes generated by the interplay between convection and rotation in the convection zone. In spite of fast progress in dynamo modelling and extremely accurate solar observations, some of the physical processes involved in the solar dynamo are still controversial. In the last few years, outstanding improvements of stellar spectropolarimeters have allowed the detection of magnetic fields in cool stars with low activity levels, similar to the Sun. This work aims at analyzing spectropolarimetric data in order to provide new information about solar-type star dynamo, by determining the link between stellar magnetic properties and fundamental stellar parameters, especially mass and rotation. The stellar sample includes 19 stars on the main sequence and probes masses between 0.6 and 1.4 solar mass, and rotation periods between 3.4 and 43 days. The monitoring started in 2007. Spectropolarimetric data analysis allowed the reconstruction of the large-scale magnetic topology thanks to the Zeeman-Doppler Imaging technique. Chromospheric emission, spectral lines asymmetry, and Zeeman broadening of the lines, which are all sensitive to a wider range of spatial scales, have also been studied. Small- and large-scale magnetic field variability have been observed within time intervals ranging from stellar rotation periods to a few years. A number of polarity reversals and magnetic cycles shorter than solar have been identified for several rapid rotators. The occurrence of rapid stellar cycles seems to depend on the stellar rotation period and were only observed for stars with short rotation periods.
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https://tel.archives-ouvertes.fr/tel-00713213
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Submitted on : Friday, June 29, 2012 - 3:45:22 PM
Last modification on : Thursday, October 15, 2020 - 4:07:38 AM
Long-term archiving on: : Thursday, December 15, 2016 - 7:30:37 PM

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  • HAL Id : tel-00713213, version 1

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Audrey Morgenthaler. Dynamo des étoiles de type solaire : impact de la masse et de la rotation. Astrophysique stellaire et solaire [astro-ph.SR]. Université Paul Sabatier - Toulouse III, 2012. Français. ⟨tel-00713213⟩

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