2015A&A...575A..49C

The active star-forming region W33B is a source of OH and H₂O maser emission located in distinct zones around the central object. The aim was to obtain the complete Stokes pattern of polarised OH maser emission and to trace its variability and to investigate flares and long-term variability of the H₂O maser and evolution of individual emission features. Observations in the OH lines at a wavelength of 18cm were carried out on the Nancay radio telescope (France) at a number of epochs in 2008-2014; H₂O line observations (long-term monitoring) at λ=1.35cm were performed on the 22 m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) between 1981 and 2014. We have observed strong variability of the emission features in the main 1665- and 1667MHz OH lines as well as in the 1612MHz satellite line. Zeeman splitting has been detected in the 1665MHz OH line at 62km/s and in the 1667MHz line at 62 and 64km/s. The magnetic field intensity was estimated to be from 2 to 3mG. The H₂O emission features form filaments, chains with radial-velocity gradients, or more complicated structures including large-scale ones. Long-term observations of the hydroxyl maser in the W33B region have revealed narrowband polarised emission in the 1612MHz line with a double-peak profile characteristic of type IIb circumstellar masers. The 30 year monitoring of the water-vapour maser in W33B showed several strong flares of the H₂O line. The observed radial-velocity drift of the H₂O emission features suggests propagation of an excitation wave in the masering medium with a gradient of radial velocities. In OH and H₂O masers some turbulent motions of material are inferred.