The physical foundations of stellar magnetic field diagnosis from polarimetric observations of hydrogen lines

We have completed a new study of the formation of hydrogen lines in dense magnetized plasmas. We have developed a global formalism including the effects of the magnetic field and of the motional electric field. The latter, resulting from the motion of the radiating hydrogen atom in the magnetic field, modifies the structure of the matrices appearing in the equation of transfer of the Stokes vector and introduces a coupling between microscopic (“intrinsic”) and macroscopic (Doppler) contributions to the line profiles. We have used this new treatment of line formation to revisit the interpretation of photopolarimetric (Stokes I and V ) observations of Balmer lines in terms of mean longitudinal magnetic field.