Evidence for Zeeman Splitting in 1720 MHz OH Line Emission (9)

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 $sup 2$Pi$sub 3$/$sub 2$ F=2$Yields$1 transition. A three-station VLBU experiment was conducted to measure the spatial separation of the emitting regions of the components of opposite sense polarization. The doublets in the 1720-MHz OH spectra of W3(OH), W51, NGC 6334 (N), and NGC 7538 (N) are found to be spatially coincident to within a linear dimension of approx.10$sup 15$ cm (10$sup 2$ 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 10$sup -3$ gauss. (AIP)