The problem of the circular polarization of emission from interstellar OH molecules

The degree of circular polarization for all four maser lines of the ground state of interstellar OH molecules is calculated on the basis of the Boltzmann distribution of populations of Zeeman sublevels. It is shown that considerable circular polarization should be observed in the main lines, and that the degree of circular polarization should be low in the satellite lines. Ranges of magnetic field strength, OH concentration, and cloud kinetic temperature are determined for which the circular polarization of OH emission is possible.