摘要：Context.Maser emission is a strong tool for studying high-mass star-forming regions and their evolutionary stages. OH masers in particular can trace the circumstellar material around protostars and determine their magnetic field strengths at milliarcsecond resolution.Aims.We seek to image OH maser emission towards high-mass protostellar objects to determine their evolutionary stages and to locate the detected maser emission in the process of high-mass star formation.Methods.In 2007, we surveyed OH maser emission towards 217 high-mass protostellar objects to study its presence. In this paper, we present follow-up MERLIN observations of a ground-state OH maser emission towards one of these objects, IRAS 19092+0841.Results.We detect emissions from the two OH main spectral lines, 1665 and 1667 MHz, close to the central object. We determine the positions and velocities of the OH maser features. The masers are distributed over a region of~ 5′′corresponding to 22 400 AU (or~0.1 pc) at a distance of 4.48 kpc. The polarization properties of the OH maser features are determined as well. We identify three Zeeman pairs from which we inferred a magnetic field strength of~4.4 mG pointing towards the observer.Conclusions.The relatively small velocity spread and relatively wide spacial distribution of the OH maser features support the suggestion that this object could be in an early evolutionary state before the presence of disk, jets or outflows.
