EVN maps of 5 cm line OH emission from star-forming regions

Abstract

We have used three antennas of the EVN (Effelsberg, Medicina and Jodrell Bank) to observe in W3(OH) and in five other star-forming regions, simultaneously, and for the first time, the two main lines of the ${}^2\text{φ}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, $\text{J}\text{=}\text{5}\text{2}$ excited state of OH with right and left circularly polarized feeds. The data were correlated with the MkIII MPIfR correlator in Bonn and processed with the AIPS package at the Observatoire de Bordeaux. In W3(OH) we made cleaned maps of all individual channels for each line and polarization. These maps made with a 5×6.5 mas beam reveal complex kinematics and spatial structure with both extended emission and unresolved features. This fact and polarization properties demon-strate the masing nature of the emission. Maser features are identified by searching for emission over adjacent channels, and adjacent positions (within about one synthesized beam) in both polarizations after we had mapped and selected one channel as a phase reference. We have been able to identify OH Zeeman pairs and to estimate the magnetic field strength across W3(OH); the field varies from about 1 to 10 mG. At the time of this conference, three other star-forming regions (M17, ON1 and W51) show fringes while two other regions are still incompletely processed.