The results of monitoring the water-vapor maser at λ=1.35 cm in Sgr B2 are presented. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) in 1982–1992. A strong flare of the maser radiation associated with Sgr B2(N) was detected in this period. The absolute strength of this flare is comparable to the megamaser emission observed in Orion in 1979–1987. The flare is probably due to a strengthening of the flow of material from the rotating accretion disk, in which are embedded the three ultracompact HII regions K1, K2, and K3. A subsequent excitation of emission features at increasingly higher radial velocities was observed, associated with a gradient of V LSR along the direction of the outflow. The large width of the lines (>0.86 km/s) could reflect a complex structure for the maser spots, such as a chain or filamentary structure, as has been observed in Orion and S140.

Water maser emission from star forming regions has been monitored for several decades using the Puschino radio telescope, showing radial velocity variations consistent with material in Keplerian orbit around protostars. MERLIN and the EVN are now being used to image the 22 GHz emission on au scales and measure proper motions. This will distinguish discs from outflows, and provide an estimate of the central mass and possibly orbiting; condensations.

The results of observations of the S128 H 2 O maser carried out from February 1995 to March 2001 on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory are presented. Two activity cycles of the H 2 O maser with a period of about 10 years were observed during the total monitoring interval (1981–2001). This may be connected either with cyclic activity of the central star in S128 during its formation or with the influence on the H 2 O masering region of shocks arising near an ionization front at the interface of two colliding CO clouds. The emission at radial velocities from −73 to −70 km/s consists of four emission features. The emission feature at −71.8 km/s exhibits a flux dependence on linewidth that is typical of an unsaturated maser.

The paper reports the results of observations of the H2O maser in S255 carried out in 1982–1985 and 1990–2000 on the 22-meter telescope of the Pushchino Radio Astronomy Observatory. The H2O maser emission extends from −2 to 14 km/s and is mainly concentrated in three radial-velocity intervals. The velocity of the central group of emission features coincides with that of the 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 observed. 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 activity of the protostar. Second, the fluxes of emission features (or groups of features) were anticorrelated. The emission of the three groups of features noted above dominated in succession. In some time intervals, a triplet spectral structure with anticorrelation between the fluxes of the lateral components and of the central and lateral components was observed. The flux anticorrelation between groups of features and individual features could be due to competition between spatial emission pumping modes in a nonuniform Keplerian disk.

Results of observations of the H2O maser in S269 carried out from October 1980 to February 2001 on the 22-m telescope (RT-22) of the Pushchino Radio Astronomy Observatory are presented. During the monitoring of S269, variability of the integrated flux of the maser emission with a cyclic character and an average period of 5.7 years was observed. This may be connected with cyclic activity of the central star during its formation. Emission at radial velocities of 4–7 km/s was detected. Thus, the H2O maser emission in S269 extends from 4 to 22 km/s, and is concentrated in three radial-velocity intervals: 4–7, 11–14, and 14–22 km/s. In some time intervals, the main group of emission features (14–22 km/s) had a triplet structure. The central velocity of the total spectrum is close to the velocity of the CO molecular cloud and HII region, differing from it by an amount that is within the probable dispersion of the turbulent gas velocities in the core of the CO molecular cloud. A radial-velocity drift of the component at VLSR≈20 km/s with a period of ≈26 years has been detected. This drift is likely due to turbulent (vortical) motions of material.

H2O line observations at lambda = 1.35 cm of the Mira Ceti-type variable star U Ori are reported. The observations cover the time interval from March, 1980, to September, 1999, Variations of the integral flux and velocity centroid of the H2O line are analysed. The flux in general correlates with the visual light curve, following it with some phase delay Delta phi similar to 0.2 - 0.4P (P is the period of the star). The maser emission is generated in a quasistationary layer of gas and dust at a distance of about 10(14) cm from the stellar centre, The maser variability is explained by the action of periodic shocks, driven by stellar pulsation and arriving to the maser in each stellar cycle. The shocks provide the maser Dumping, whereas the sink of the waste energy is controlled by the dust, periodically heated by the stellar radiation near the light maximum; this accounts for the correlation of tho maser radiation maximum with the descending branch of the light curve. Temporary weakness of the maser emission may be due to decay of the quasi-stationary layer, which is then rebuilt LS a powerful shuck, carrying an ay from the star a portion of the lost mass, once per a few stellar periods - the "superperiod". Ill its turn, the superperiod may reflect multiperiodic pulsation of tie star or the presence of a long-term activity cycle, connected with restructuring of the stellar magnetic field, which is known to be strong in U Ori.

Abstract We present the results of observations of the M-type semiregular supergiant VX Sgr in the water-vapour line at λ = 1.35 cm. The observations were carried out on the 22-metre radio telescope RT-22 in Pushchino in 1981–1996. The profiles of the H2O line have a complex structure typical for H2O masers associated with late-type supergiants. We reveal some features persistent during the last 15 years; we suggest that they arise from masering H2O molecules located in the circumstellar disk and the bipolar outflows from the disk poles. The parameters of the outflow are estimated.

This paper continues the earlier work (Mendoza– Torres et al. 1997) on single-dish 22-GHz observations of the H2O maser associated with the semiregular variable (SRb-type) RT Vir. New spectra, obtained in 1996–1998, are presented, and an analysis of the emission of individual spectral features during the interval of 1986–1998 is performed. All the observations have been carried out on the RT–22 radio telescope of the Pushchino Radio Astronomy Observatory, Lebedev Institute of Physics, Russian Academy of Sciences. As a result of longterm monitoring, the character of variability of multiple spectral components was traced in detail. For many features, a drift in radial velocity was found. There are time intervals with preferential drift direction of the majority of the spectral features. This trend was the most pronounced at velocities<15.5 km s. Possible causes of the drift observed are discussed. From a superposition of all the spectra and from the mean spectrum for 1984–1998, stellar velocity V∗ was determined. It is estimated as 17.3 ± 0.2 km s. The time interval from March to June 1998 is considered as the period of maximum activity of the H2O maser RT Vir during the entire timespan of its observations.

The results of observations of the circumstellar maser emission in the 1.35-cm water vapor line of the variable M-giant W Hya are presented. The observations were carried out in 1980-1998 on the RT-22 radio telescope in Pushchino. A comparison with the data on W Hya at optical wavelengths and in other molecular lines is performed. The H2O line flux variations correlate with the visual light curve. The structure of the H2O emission line profiles of W Hya is discussed. The H2O maser emission of W Hya has a distinct flaring character with a flare recurrence period of 0.8-1.8 years. The activity cycle length varies in a sine-wave-like manner with a superperiod of about 15-16 years. A time delay of the H2O maser emission maxima with respect to visual maxima was observed. The value of this delay is not constant but smoothly varies between 0 and 2.1P (P is the period of stellar activity). To explain the effects observed, a model of shock-wave pumping of the H2O maser is considered.

Some models for H2O maser sources are considered. For S252A and W31A, a model with a circumstellar gas-dust disk explains the data best. The disk precesses in the gravitational field of a rotating external torus. Maser condensations are located on the inner surface of the torus, The main arguments in favor of this model are the absence of nearby compact H II regions, the regular radial-velocity drift of the H2O maser emission, and the asymmetric shape of the radial-velocity distributions of the maser condensations.

Results of observations of the Mira Ceti variable RR Aql in the 1.35-cm water-vapor line are presented. The observations were carried out on the 22-m radio telescope of the Pushchino Radio astronomy Observatory in 1980-1997 (JD 2444306-2445689 and 2446587-2450631). The observations are compared with published data on the visual light curve of RR Aql and its emission in the OH and H2O lines. Sixteen variability cycles of RR Aql (P = 394.78(d)) are covered. Profiles of the H2O maser emission lines for 81 epochs are presented. Beginning from 1989, a rise of the H2O maser activity in RR Aql was observed, especially soon after its visual maximum in September 1992, when the peak Bur density in the H2O line exceeded 500 Jy. By the beginning of 1994, the maser intensity again faded to a level <100 Jy. As in a number of other Mira variables, RR Aql shows a correlation of the H2O line flux density with its brightness variations: in general, the maser intensity follows the optical variability with some phase lag. However, the delay (up to 200(d), or nearly 0.(p)5) is longer than in other H2O-maser Mira variables (on average 0.(p)1-0.(p)3). A model is considered in which the maser variability is the result of the joint influence of a shock wave propagating in the circumstellar envelope and variability of the radio continuum of the stellar photosphere. There are indications that the variations of the integrated H2O line flux and mean radial velocity of the maser emission have a quasi-periodic character over a time scale of 14-15 years. Estimates of the distance to RR Aql are critically re-examined. A new estimate is obtained based on the M-V-P relationships: r = 400 pc.

We present a catalog of the 22 GHz H2O maser profiles of the semiregular variable RT Vir. The observations were made from 1985 to 1996 at the RT-22 radio telescope of the Radio Astronomical Station at Pushchino, Russia. Results obtained after the analysis of the integrated fluxes, the average spectra, the centroid velocity and the superposition of the spectra are reported.Anticorrelation of the integrated fluxes of two spectral intervals (V-LSR < 15.5 and V-LSR > 21 km s(-1)) was found. The characteristic time variation of the maser emission at each of these groups was about 5-6 years. This phenomenon may be explained by a variation of the outflow of the matter from the star. The outflow is weakly bipolar. We can suppose that in such a model the enhancement of the outflow occured alternately with a period of about 5-6 years. The anticorrelation of the integrated fluxes of two groups of maser features, located symmetrically relative to the star, may be a result of this alternation.

Results of investigation of flare activity in the S252A H2O maser are presented. Five flares separated by a mean time of two years were detected. Individual spectral features are distinguished, and their evolution is traced. For some features, there is a correlation between variations of flux and radial velocity. Bulk drift of the main peaks with a reversal of the drift direction is observed. Possible origins of the observed phenomena are discussed.

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.

Results of observations of the H2O maser source NGC 2071 carried out between 1982 and 1993 with the RT-22 radio telescope at the Radioastronomy Station of the Lebedev Physical Institute in Pushchino are presented. The data obtained are analyzed, as are the published H2O data for NGC 2071. The source experienced a few strong outbursts, with various spectral features showing correlated variability. The observations are interpreted in terms of a model of a gas and dust circumstellar disk containing the region of maser generation of the H2O line. The maser variability may be associated with activity of the central star, notably, with stellar-wind variability or precession of a small inclined circumstellar (protoplanetary) disk.