Flux-Tube Model Atmospheres and Stokes [ITAL]V[/ITAL] Zero-crossing Wavelengths

Abstract

First results of the inversion of Stokes I and V profiles from plage regions near disk center are presented. Both low and high spatial resolution spectra of Fe I 6301.5 and Fe I 6302.5 Å obtained with the Advanced Stokes Polarimeter (ASP) have been considered for analysis. The thin flux-tube approximation, implemented in an LTE inversion code based on response functions, is used to describe unresolved magnetic elements. The code allows the simultaneous and consistent inference of all atmospheric quantities determining the radiative transfer with the sole assumption of hydrostatic equilibrium. By considering velocity gradients within the tubes, we are able to match the full ASP Stokes profiles. The magnetic atmospheres derived from the inversion are characterized by the absence of significant motions in high layers and strong velocity gradients in deeper layers. These are essential to reproduce the asymmetries of the observed profiles. Our scenario predicts a shift of the Stokes V zero-crossing wavelengths, which is indeed present in observations made with the Fourier Transform Spectrometer.