Time variation of the water maser in ON2

Context. The results of monitoring of the water-vapour maser in the 1.35-cm line toward ON2 in 1995 -2004 are reported. Aims. 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. Methods. The observations were carried out on the RT-22 radio telescope of Pushchino Radio Astronomy Observatory. Results. The emission of the northern component (ON2 N) took place in a broad interval of radial velocities, from -12 to 9 km s(-1). 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 H II region.