HANLE DIAGNOSTICS OF SOLAR MAGNETIC-FIELDS - THE SR-II 4078 ANGSTROM LINE

The Hanle depolarization and rotation effects in the Sr Ir 4078 Angstr om line have been explored with the instrumentation at IRSOL (Istituto Ricerche Solari Locarno) by recording the Stokes I, Q, and U line pro files with high spectral resolution and polarimetric accuracy in a lar ge number of regions across the solar disk. From the extracted line pa rameters we have constructed ''Hanle histograms'' showing the statisti cal distributions of the Hanle rotation and depolarization effects. Co mparison with theoretical calculations allow these histograms to be un derstood in terms of magnetic fields with a strength of about 5-10 G, which is similar to the field strengths previously found through analy sis of Q/I Hanle depolarization in the Ca I 4227 Angstrom line. While small-scale magnetic fields with spatially unresolved angular distribu tions contribute to the observed Hanle depolarization effects, the obs erved Hanle rotation effects in Stokes U are due to spatially resolved fields with net large-scale orientations (e.g. global or canopy-type fields). We have also for the first time determined empirical ''Hanle efficiency profiles'', derived independently for the Hanle rotation an d depolarization effects. They show how the Hanle efficiency has its m aximum in the Doppler core of the line and then rapidly decreases to b ecome zero in the line wings.