1997A&A...319L...1I

We performed VLBI monitoring observations of water masers around a semiregular variable RT Vir and detected for the first time systematic shifts of line-of-sight velocities in time for several spatially distinguished water maser spots. In some strong water maser spots, the line-of-sight velocities linearly increased or decreased through successive observing sessions during four months. The rates of the velocity shifts ranged from -3.55 to 1.76km/s/yr. We also noted that the blue-shifted and red-shifted maser components with respect to the stellar velocity are clearly separated in the celestial plane. If mass-loss process of the evolved star is described with simple kinematic models like bipolar flow or rotation disk, we should find one-to-one correspondence between acceleration/deceleration and blue-shift/red-shift of the maser spots. However, we did not find such a clear correspondence. The fact is likely to imply the more complicated nature of the real mass-loss process of the evolved star.