The OH ground-state masers in W3(OH) - I. Results for 1665 MHz

We present observational data and analysis of the OH masers in the star-forming region W3(OH). The observation was performed with the Very Long Baseline Array in 1996 August. 276 masers have been detected, and from these 83 Zeeman pairs identified, allowing the velocity profile and magnetic field structure of the gas to be determined. The bulk of the masers lies in a north-south distribution that contains a clear velocity gradient and indicates ordered rotation, implying a minimum mass for the central star of similar to8 M.. The proper motions suggest there must be an element of expansion in the rotation - possibly the destruction of a disc is being observed. Deviations from Gaussian line shapes were found to be extremely rare; major deviations exist for just two cases.