OBSERVATIONS OF LATE-TYPE STARS IN THE WATER-VAPOR RADIO LINE - II - THE LONG-PERIOD VARIABLE RR AQUILAE

Results of observations of the Mira Ceti variable RR Aql in the 1.35-c m 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 observatio ns are compared with published data on the visual light curve of RR Aq l 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 emis sion 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 intensi ty again faded to a level <100 Jy. As in a number of other Mira variab les, RR Aql shows a correlation of the H2O line flux density with its brightness variations: in general, the maser intensity follows the opt ical 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 va riability is the result of the joint influence of a shock wave propaga ting in the circumstellar envelope and variability of the radio contin uum of the stellar photosphere. There are indications that the variati ons of the integrated H2O line flux and mean radial velocity of the ma ser emission have a quasi-periodic character over a time scale of 14-1 5 years. Estimates of the distance to RR Aql are critically re-examine d. A new estimate is obtained based on the M-V-P relationships: r = 40 0 pc.