| Abstract * |
: |
The weak-field approximation (WFA) gives a quick and a conceptually simple way to compute a solution of the polarized radiative transfer equation for Stokes parameters Q, U and V. These solutions are given by the derivatives of the observed Stokes I profile along the spectral direction. The WFA is well suited for chromospheric lines that are sensitive to the Zeeman effect like the Ca II 8542 Å spectral line. We have focused on this line, since is sensitive to the lower part of the chromosphere and the WFA can be used regularly to derive B from observations. The WFA is applied to observations by defining a merit penalty function and trying to minimize it. We have also considered a modified version of the normal WFA formula imposing spatial constrain with the nearest neighbour pixels by minimizing the difference with them with a certain weight. The problem becomes global and the solution has to be found for the entire observations simultaneously: it will be a sparse linear system of equations. So, this method is expected to help with noisy data and in situations where the derivative of I is very shallow, which introduces a large uncertainty in non-coupled estimates. Then, the purpose of this project will be to apply this method also to other lines and study the stratification of the magnetic field in the solar photosphere and chromosphere. |
