Circular polarization of circumstellar water masers around S Per

We present the first circular polarization measurements of circumstellar H2 O masers. Previously the magnetic field in circumstellar envelopes has been estimated using polarization observations of SiO and OH masers. SiO masers are probes of the high temperature and density regime close to the central star. OH masers are found at much lower densities and temperatures, genera lly much further out in the circumstellar envelope. The detection of the ci rcular polarization of the (6(16)-5(23)) rotational transition of the H2O m aser could be attributed to Zeeman splitting due to the magnetic field in t he intermediate temperature and density regime. The fields inferred here ag ree well with predicted values for a combination of the r(-2) dependence of a solar-type magnetic field, and the coupling of the field to the high den sity masing regions. We also discuss the unexpected narrowing of the circul ar polarization spectrum.