Modifications to the relationship between the magnetic field and weak Zeeman features in the spectra of astrophysical masers

Numerical solutions are presented for the equations of radiative transfer for astrophysical masers in a magnetic field to describe the observed weak circular polarization of H2O and SiO masers. Previously unrecognized intensity-dependent effects are found to produce circular polarization which resembles that of the usual Zeeman effect. Astrophysical H2O, SiO, and perhaps other masers are likely to be radiatively saturated with rates for stimulated emission that are within 1-2 orders of magnitude of the Zeeman frequency. Under these conditions, the circular polarization found here tends to be larger (but can be smaller) and may be of opposite sign from that given by the standard treatment for polarized Zeeman spectra.