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Title:
Circular polarization of interstellar absorption lines at radio frequencies
Authors:
Deguchi, S.; Watson, W. D.
Affiliation:
AA(Illinois, University, Urbana, IL), AB(Illinois, University, Urbana, IL)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 289, Feb. 15, 1985, p. 621-629. (ApJ Homepage)
Publication Date:
02/1985
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
Circular Polarization, Interstellar Gas, Interstellar Magnetic Fields, Interstellar Radiation, Radio Sources (Astronomy), Absorption Spectra, Radiative Transfer, Sobolev Space, Stokes Law Of Radiation
DOI:
10.1086/162925
Bibliographic Code:
1985ApJ...289..621D

Abstract

The formation of linearly and circularly polarized line radiation at radio frequencies is investigated when radiation from a distant continuum source propagates through a diffuse gas such as the interstellar medium. Radiative transfer equations for the Stokes parameters (I, Q, U, and V) are obtained for the commonly encountered circumstance in which the Zeeman splitting of the particle (atoms or molecules) states is much greater than the inverse lifetime of the state, but much less than the breadth of the line. If the particles are partially aligned, magnetorotation converts linear polarized radiation into circularly polarized radiation. Numerical calculations are performed for a static, homogeneous gas with a uniform magnetic field and for a static, homogeneous gas with a twisted magnetic field. When the magnetic field is twisted, circular polarization is produced even when the incident radiation is unpolarized. The antisymmetric (about line center) profile of circular polarization that results from magnetorotation resembles, but is not identical with, a normal Zeeman pattern. The peak circular polarization tends to be only about one-tenth of the linear polarization in the emitted radiation, however.

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