First Detection of Circular Polarization in 4.7 GHz Excited OH Masers

Abstract We report the first detection of circular polarization in 4.7 GHz excited OH masers in star-forming regions made using full Stokes measurements with the Green Bank 100 m telescope. The Zeeman shift between the two circular components provides a measure of the magnetic field pervading these maser spots. Three different methods are used to determine the shift in velocity between the RCP and LCP components. We find fields with B ∼ 100 mG using archival molecular parameters that have limited precision and uncertain values. Reservations of using 1.7 and 6.0 GHz OH masers to estimate magnetic fields in star-forming regions are discussed.