Title:

Examples of how to use the Hanle effect to study magnetic fields



Jean Arnaud 
Observatory du Midi-Pyrenees
Toulouse, France


Abstract:

The Hanle effect modifies, in presence of magnetic field, the linear
polarization generated by resonance scattering processes in spectral
lines. One of the first uses of this effect in solar physics, in its
so-called "strong field" regime, was, in the late seventies, the study
of the large scale coronal magnetic fields topology from the
polarization of visible and near infrared emission lines. In this
regime, only the plane-of-the sky magnetic field direction can be
inferred.  At a time where projects are underway to measure the weak
Zeeman-induced Stokes V to constrain the line-of-sky field strength, I
will present the main results of the old linear polarization
observations.