Spatial mapping of the Hanle and Zeeman effects on the Sun


Spatial mapping of the Hanle and Zeeman effects on the Sun has been done for the first time, through Stokes vector imaging with a narrow- band (0.2 ̊A) universal filter. It is shown how the polarization signatures of the Hanle and Zeeman effects can be cleanly distinguished from each other by comparing the Stokes images recorded at different, specially selected wavelengths within the Na I D$_2$-D$_1$ line system. Examples of the polarization signatures of sunspots, faculae, the supergranulation network, and large-scale canopy fields are shown. The most striking result of our observations is that the scattering polarization has an extremely intermittent structure rather than being a simple function of limb distance. These intermittent scattering polarization signals are cospatial with the facular and supergranulation network seen both in intensity and circular polarization. The observed pattern can be explained in terms of magnetic enhancement of the scattering polarization in the network and/or Hanle depolarization of the scattering polarization outside the network. Since however no magnetic fields are seen in circular polarization outside the network, the relative absence of linear scattering polarization there may be explained by Hanle depolarization only if the volume filling, depolarizing magnetic field has mixed polarities on a subarcsec scale that is not resolved.

Astronomy & Astrophysics