On the Line Formation in Stellar Magnetized Atmospheres

Abstract

The line formation process in stellar magnetized atmospheres is studied by observing the wavelength-dependence of Stokes contribution functions. The influence of magnetic field on the escape line photon distribution and line absorption is obtained by comparing with the null magnetic field case. Two models are adopted. One assumes limited distributions of both the line absorption and magnetic field where a hypothetical magneto-sensitive line is formed. The other is a model atmosphere of sunspot umbra in which Mg I 5172.7 forms. It is found that the magnetic field influences the formation region of Stokes I at wavelengths sufficient close to the Zeeman splitting points +/- Delta lambda (H). The formation regions at wavelengths far away from the Zeeman splitting points generally show a non-magnetic behaviour. Further, if the line core is split by the Zeeman effect, the line formation core introduced in the previous paper disappears. On the other hand, Stokes Q, U, V at each wavelength within the line form in the same layers where both the line absorption and magnetic field are present in the models accepted for the lines used. When the line absorption and magnetic field ubiquitously exist, the formation regions of the pi peaks or valleys of Stokes Q, U and those of sigma of Stokes V generally cover the widest depth range. It is pointed out that such a study is instructive in the explanation of solar polarized filtergrams. It can tell us at each observation point where the received line photons of wavelengths within the bandpass come from and where their polarization states are formed or give us the distributions of these photons as well as their polarization intensities. Thus a three-dimensional image can be constructed for a morphologic study of the observed area from serial filtergrams.