Influence of the vertical and horizontal magnetic field inhomogeneity on the Stokes parameters of the magnetically sensitive Fe I line 525.02 nm

Abstract

Based on calculations of the Stokes parameters for the Holweger-Mliller model atmosphere, we study sensitivity of the Fe I 525.02 nm line to some kinds of vertical and horizontal magnetic field inhomogeneity. A noticeable asymmetry is shown to appear in the V profile peaks when the vertical gradient is -0.4 mT/km, which is typical of some theoretical flux tube models. The asymmetry is most pronounced in a pure longitudinal magnetic field and at a low macroturbulent velocity. A similar effect is observed for the Q profile in nonlongitudinal fields as well. The Fe I 525.02 nm line is sensitive also to subtelescopic fields of mixed polarity like those observed by Stenflo in IR lines. We argue that the Wilson depression in small-scale flux tubes renders strong-field areas invisible at heliocentric angles greater than 60--65 degrees, since they are screened by surroundings with weaker magnetic fields.