Variability of the H2O maser associated with the Mira variable RS Virginis

The results of observations of the H2O maser emission (lambda = 1.35 cm) of the Mira-type variable star RS Vir are presented. The observations were ca rried out in 1981-2001 (JD = 2 444 900 2 451 995) on the RT-22 radio telesc ope of the Pushchino Radio Astronomy Observatory (Russia). The variability curve of the H2O maser emission integrated flux F-int(H2O) of RS Vir correl ates with its visual light curve with some phase delay Delta phi = (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 H2O maser RS Vir is caused by periodic action of pulsati on-driven shock waves, the shock travel time from the photosphere to the in ner boundary of the H2O maser shell can be as long as (3-5)P. Another expla nation is that maser variations may be connected with changing gas density in the masering region of the circumstellar envelope. In particular, long-t erm maser variations (the "superperiod") may be caused by changing mass los s rate (M) over dot. M.