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Theses

Étude du vent solaire à grande échelle

Abstract : Since the first measurements of the solar wind in 1960, the properties of this plasma outflow from the Sun has been intensively studied, theoretically and by in situ measurements. However, some features still remain not understood, as the transport of the energy in collisionless plasmas like the solar wind. Measuring the temperature of the electrons and their nonthermal properties can give important clues to understand the transport properties. Quasi-thermal noise spectroscopy is a reliable tool for measuring accurately the electron density and temperature since it is less sensitive to the spacecraft perturbations than particle detectors. This noise is produced by the quasi-thermal fluctuations of the particles and allow to measure the moments of their velocity distributions. This method, using a sum of Maxwellian as the electron velocity distribution, has produced a large amount of results with the Ulysses mission. Nevertheless, some limitations on the radio receiver on board Ulysses prevent an accurate measurement of the total temperature of the electrons with a sum of Maxwellian. A new method using kappa distribution is proposed to improved the accuracy of the electron temperature measurements. Its application on the Ulysses data allows to yield the radial evolution of the electron temperature and their nonthermal properties. A preliminary comparison with exospheric models shows the following agreements: a variation of the temperature between an adiabatic and isothermal behaviour, and a constant kappa parameter. The solar wind interacts also with all the objects of the Solar System. Two examples of plasma-dust interactions are studied in the second part of this thesis: the acceleration of nano dust by the solar wind and their detection in the solar wind at one astronomic unit; and the interplanetary magnetic field enhancements possibly due to an interaction between the solar wind and cometary dust. Finally, a more global point of view is taken. The energy flux of the solar wind is almost constant, nearly independent on wind speed and solar activity. A comparison of the energy flux of a spread of stellar winds is made. A shared process at the origin and acceleration of the main-sequence stars and cool giants' winds is suggested. T-Tauri stars' winds show a possible result of an accretion powered wind.
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Submitted on : Thursday, December 16, 2010 - 4:35:05 PM
Last modification on : Monday, December 14, 2020 - 9:45:43 AM
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  • HAL Id : tel-00547571, version 1

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Gaétan Le Chat. Étude du vent solaire à grande échelle. Astrophysique [astro-ph]. Université Paris-Diderot - Paris VII, 2010. Français. ⟨tel-00547571⟩

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