OH maser polarization

Abstract

The mechanism to produce circular polarization has been reinvestigated under conditions with radiative pumping and the Faraday rotation due to electrons. ^A new radiative pump mechanism is proposed for the OH main line masers. ^A parity propensity for the OH collisional excitation, which has recently been found by laboratory experiments, prohibits the collisional pumping of the main line masers. ^It is shown that the inversion can be created when the radiation temperature is higher than the kinetic temperature. ^The anisotropic radiative pump can produce unequal magnetic sublevel populations. ^In addition to the line overlap between the Zeeman triplet of the OH main lines, a modest amount of the Faraday rotation due to electrons can increase the degree of circular polarization of OH masers even when the angle to the magnetic field is near pi/2. ^(Author (revised))