VELOCITY-FIELDS ASSOCIATED WITH THE MAGNETIC COMPONENT OF SOLAR FACULAE

The Stokes V asymmetries observed in solar faculae can be interpreted by invoking the presence of magnetic and velocity fields variations along the line-of-sight. By means of a perturbative approach, we develop the theoretical dependence on magnetic and velocity fields of the Stokes V profile around its zero-crossing point. We find that the empirical curves of growth for the V zero-crossing point and the slope, as well as the curve of growth for the integral (previously derived by Sánchez Almeida et al., 1989, through the same approach), are reproduced quite well with a single atmosphere which assumes such simultaneous variations. The depth dependence of the fields that give the best fit in our model presents several striking properties which cannot be released without totally compromising the goodness of the fit. Namely, the magnetic field strength increases towards the observer while the downflowing velocity field decreases. Both variations must occur co-spatially, in the same atmospheric layers. This fact seems to contradict theoretical models for the fanning out parts of magnetic concentrations which foresee a sharp separation between a static magnetic layer and a deep zone with velocity fields. We discuss a possible solution of such contradiction in terms of a finite optical thickness of the boundary layer between zones with and without magnetic field in faculae. © 1990 Kluwer Academic Publishers.