Evidence for Zeeman Splitting in 1720 MHz OH Line Emission (9),
OWENS VALLEY RADIO OBSERVATORY PASADENA CALIF
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A number of 1720-MHz OH maser sources have relatively simple spectra consisting of doublets with opposite senses of circular polarization. Such doublets could be due to the Zeeman splitting of the doublet Pi32F 2 to 1 transition. A 3-station VLBI experiment was conducted to measure the spatial separation of the emitting regions of the components of opposite sense polarization. The doublets in the 1720-MHz OH spectra of W3OH, W51, NGC6334N and NGC7538N are found to be spatially coincident to within a linear dimension of about 100 Au, suggesting that they originate from the same region in space. This is taken to be strong evidence for identifying the doublets as Zeeman components. The magnetic field within the OH maser sources responsible for the observed splitting is typically a few times .001 gauss.