2001A&A...376..928L

The results of observations of the H₂O maser emission (λ=1.35cm) of the Mira-type variable star RS Vir are presented. The observations were carried out in 1981-2001 (JD=2444900-2451995) on the RT-22 radio telescope of the Pushchino Radio Astronomy Observatory (Russia). The variability curve of the H₂O maser emission integrated flux F_int(H2_O) of RS Vir correlates with its visual light curve with some phase delay Δφ=(0.05-0.35)P (P is the star's period). The delay variations seem to be periodic at a timescale of 19-20 years (``superperiod'' of the maser variations). If the variability of the H<sub>2</sub>O maser RS Vir is caused by periodic action of pulsation-driven shock waves, the shock travel time from the photosphere to the inner boundary of the H<sub>2</sub>O maser shell can be as long as (3-5)P. Another explanation is that maser variations may be connected with changing gas density in the masering region of the circumstellar envelope. In particular, long-term maser variations (the ``superperiod'') may be caused by changing mass loss rate {dot}(M).