Transfer of Polarized Radiation in Hydrogen Lines in Dense Magnetized Plasmas

Abstract

Polarimetric observations of hydrogen Balmer lines have been frequently used to diagnose the magnetic fields of stars of various types. Such observations have so far been interpreted using a simple description of the line formation, which rests on questionable physical foundations. This may. explain, at least in part, why significant differences exist between field intensities determined through this approach and those obtained by application of other, sounder methods. We present a new theoretical description of the transfer of polarized radiation in hydrogen lines in dense plasmas in the presence of a magnetic field. This is the most realistic treatment ever made of this problem: we take simultaneously into account the Stark effect induced by the charged particles of the plasma, the Zeeman effect created by the magnetic field, and the Lorentz effect corresponding to the electric field seen by the radiating atom as it moves through the magnetic field. We show that if this improved description of the line formation is used to interpret the observations, the derived magnetic field intensities may significantly differ from those determined through the simpler method used in all practical applications so far. The differences depend in a fairly complex way on the physical parameters prevailing in the line forming region, in particular, the temperature, the density, and the magnetic field itself.