2006A&A...456..145L

The results of monitoring of the water-vapour maser in the 1.35-cm line toward ON2 in 1995-2004 are reported. The main goal was to study variations of the H₂O maser emission on a long (10-years) time interval, in particular, velocity drifts and correlation between fluxes in various spectral features. The observations were carried out on the RT-22 radio telescope of Pushchino Radio Astronomy Observatory. The emission of the northern component (ON2N) took place in a broad interval of radial velocities, from -12 to 9km/s. The total H₂O emission has two variability components: slow and flaring. The period of the former component is most likely between 25 and 30-years. The flaring component has a cyclic character with a period from 1.1 to 2.6-years. The alternation of the activity cycles was accompanied by changes in the velocity structure of the H₂O spectra. There is good correlation between the variations in the integrated flux and velocity centroid, as well as between the emissions in various segments of the H₂O spectrum. We suggest that long-term variations and oscillations of the water-maser emission can be related to the non-stationarity and anisotropy of bipolar molecular outflow from the B-type star in the ultracompact HII region.