Resonance line polarization for arbitrary magnetic fields in optically thick media. I - Basic formalism for a 3-dimensional medium.
Résumé
We present in this paper a general formalism to describe resonance line polarization for a two-level atom in an optically thick three-dimensional medium embedded in a magnetic field of arbitrary strength and irradiated by an arbitrary radiation field. The results contained in the present paper generalize those derived in a previous paper (Landi Degl'Innocenti et al. 1990) that were restricted to weak magnetic fields (νL ≪ ΔνD, with νL the Larmor frequency and ΔνD the Doppler broadening of the line). Here the restriction νL ≪ ΔνD is released, which makes the present formulation capable of describing, in a unified framework, resonance polarization, the Hanle effect and the Zeeman effect. Analogously to our previous paper, neglecting atomic polarization in the lower level and stimulated emission, we derive an integral equation for the multipole moments of the density matrix of the upper level by coupling the statistical equilibrium equations for the density matrix with the radiative transfer equations for polarized radiation. The final equation accounts for the effect of the magnetic field and for the role of inelastic and elastic (or depolarizing) collisions. Obviously, in the limiting case of weak magnetic fields (νL ≪ ΔνD), the results of our previous paper are recovered.
Mots clés
Linear Polarization
Optical Thickness
Radiative Transfer
Resonance Lines
Solar Magnetic Field
Atomic Energy Levels
Doppler Effect
Inelastic Collisions
Larmor Precession
Magnetic Fields
Polarized Radiation
lines formation
line polarization
Hanle effect
Zeeman effect
radiation transfer
solar magnetic fields
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