Physics
Scientific paper
Jan 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003phdt.........4p&link_type=abstract
PhD Thesis, Observatoire Midi-Pyrenees, 14 avenue Edouard Belin, 31400 Toulouse, France
Physics
Stars: Activity, Stars: Magnetic Fields, Stars: Rotation, Stars: Cool Spots, Stars: Binaries: Close, Stars: Imaging, Instrumentation: Polarimeters
Scientific paper
Magnetic fields are involved in many stellar physics issues through their ability to impact various mechanisms operating in stellar interiors and environment, among which convection, diffusion, rotation, accretion and mass-loss. The present work is a contribution to the investigation of stellar magnetic activity through the development of instrumental and modeling tools and through the interpretation of observations in the framework of dynamo theories.
1- An experimental procedure was developed to measure and improve the achromaticity of Fresnel rhombs used in ESPaDOnS (new generation spectropolarimeter designed for the Canada-France-Hawaii Telescope).
2- In order to improve surface differential rotation measurements on active stars, an original method was developed and validated through numerical simulation, significantly increasing the number of targets adapted to this type of investigation. An unsually weak surface shear was detected on a component of a close binary system, suggesting that tidal forces can significantly impact the dynamics of convective envelopes.
3- The photospheric magnetic field of a sample of active fast-rotating stars was investigated by means of Zeeman-Doppler Imaging, confirming that the surface field of these objects usually features an important azimuthal component. The temporal evolution of photospheric structures was monitored on timescales ranging from a few days to several years, providing important information on the dynamo processes at the origin of the reconstructed magnetic topologies.
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