Jeudi 24 Mars - 11 h 00
Salle Manuel Forestini - IPAG
When an intermediate mass star is evolving off the main sequence, its radius increases and its rotational velocity is reduced, and a convective envelope is created which deepens. The red giant branch therefore appears as crucial to study the interplay of the magnetic fields and stellar evolution, since parameters directly connected to the production of surface magnetic fields are greatly modified.
I will present a survey of about 40 RGB and AGB stars which appeared good candidates to host surface magnetic fields detectable with the new generation spectro-polarimeters NARVAL (@TBL) and ESPaDOnS (@CFHT) . More than 30 evolved stars have been magnetically detected so far, and Zeeman Doppler Images are being obtained for several of them, which enlightens our knowledge of the magnetic properties of red giant stars.
I will illustrate this study by presenting results obtained for a fast rotating star (V390 Aur : magnetic field driven by a solar-type dynamo), for the descendant of an Ap star (EK Eri), and for Pollux (very weak magnetic field discovered : driven by a non solar-type dynamo ?).
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