Variability of the H2O maser emission in S255

The paper reports the results of observations of the H2O maser in S255 carr ied out in 1982-1985 and 1990-2000 on the 22-meter telescope of the Pushchi no Radio Astronomy Observatory. The H2O maser emission extends from -2 to 1 4 km/s and is mainly concentrated in three radial-velocity intervals. The v elocity of the central group of emission features coincides with that of th e molecular cloud, while the two lateral groups (blueshifted and redshifted ) are positioned in the spectrum more or less symmetrically relative to the central feature. During the monitoring of S255, two phenomena were observe d. First, the integrated flux of the H2O maser emission varied in a cyclic manner with a period of two to four years; this may be connected with activ ity of the protostar. Second, the fluxes of emission features (or groups of features) were anticorrelated. The emission of the three groups of feature s noted above dominated in succession. In some time intervals, a triplet sp ectral structure with anticorrelation between the fluxes of the lateral com ponents and of the central and lateral components was observed. The flux an ticorrelation between groups of features and individual features could be d ue to competition between spatial emission pumping modes in a nonuniform Ke plerian disk. (C) 2001 MAIK "Nauka/Interperiodica".