Linear and circular polarization for masers with weak zeeman splittings

Abstract

Theory is reviewed for the linear and circular polarization of radiation from astrophysical masers in which the Zeeman splitting g-Omega is much less than the spectral linewidth Delta omega. ^When g-Omega is greater than about Gamma (the decay rate for the molecular states), polarization - mainly linear - can be generated. ^New results are presented that describe the generation of circular polarization by intensity-dependent (or 'false') Zeeman effects. ^As a result, the magnetic field strengths inferred from the circular polarization of circumstellar SiO masers may be smaller than previous estimates by a factor of 100 or more. ^(Author (revised))