Evolution of the H2O maser emission in S252A during 1981-1995

A catalog of the H2O maser emission spectra of the source S252A is presented, The spectra, with radial velocity resolution 0.101 km/s, were obtained ih 1981-1995 on the RT-22 radio telescope of the Radio Astronomy Station of the Lebedev Institute of Physics in Pushchino. It appears that, in addition to the two main components of total flux variability-long-period (6 years) and flaring (similar to 2 years)-there are variations on a much longer timescale, i.e., a superperiod (30-40 years). A regular drift in the radial velocity of the maser emission of in total similar to 3 km/s for the period from 1977-1994 was detected. Possible models for the H2O maser source are discussed. The most plausible model has the maser condensations located in a toroid with a radius of similar to 10(17) cm. In the center of the toroid rs a star In the process of forming, the luminosity of which, like the H2O maser emission, may have three types of variability.