ИСТИНА

Results of observations of circumstellar maser sources in long-period variable stars are reported. We have monitored a sample of Mira-type and semiregular variables in the H2O (wavelength 1.35 cm) and OH (wavelength 18 cm) radio lines. A comparison with data of optical photometry and spectroscopy have been done. The observations in the H$_2$O line at 1.35 cm were carried out on the RT-22 radio telescope of the Pushchino Radio Astronomy Observatory in 1980--2011. The sample included sixty late-type variable stars with circumstellar envelopes. For most stars twenty to thirty variability cycles (lasting about a year). There is a correlation of the H$_2$O line flux density with the light variations: in general, the maser intensity follows the optical variability with a certain phase lag. Figure 1 illustrates variations in the H$_2$O maser emission versus the optical light curve for the Mira-type star U Her. A model, in which the maser variability is caused by the joint influence of a shock wave propagating in the circumstellar envelope and of the variable radio continuum of the stellar photosphere, is considered. There are indications to a quasiperiodic character of the variations of the integrated H2O line flux and mean radial velocity of the maser emission at a timescale of 14-15 years. Polarimetry of the OH maser emission has allowed us to draw conclusions about circumstellar magnetic field. Results of observations of circumstellar OH masers in the lines at a wavelength of 18 cm are reported. The observations were carried out on the radio telescope of the Nancay Radio Astronomy Observatory (France). In 2007-2011 seventy late-type stars (including Mira-type and semiregular variables) were observed. For 53 of them the emission in at least one of three OH lines (1612, 1665, or 1667 MHz) was detected. Circular and linear polarization of the maser emission was measured; this yielded all four Stokes parameters. The results obtained for the stars T Lep, R LMi, and R Crt are discussed. The emission of T Lep in the 1665 and 1667 MHz OH lines was observed for the first time. In the OH line profiles of all three stars features probably due to Zeeman splitting were detected. Estimates of the magnetic intensity in the maser sources 0.46-2.32 mG) were obtained.