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Astron. Astrophys. 319, L1-L4 (1997)

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Letter to the Editor

Measurement of shifts in line-of-sight velocities of stellar water masers using VLBI

H. Imai 1, 2, K. M. Shibata 2, T. Sasao 2, M. Miyoshi 2, O.Kameya 2, T. Omodaka 3, M. Morimoto 3, T. Iwata 4, 5, T. Suzuyama 6, N. Mochizuki 3, 7, T. Miyaji 8 and M. Takeuti 1

1 Astronomical Institute, Graduate School of Science, Tôhoku University, Aoba, Sendai, 980-77, Japan
2 Mizusawa Astrogeodynamics Observatory, National Astronomical Observatory, 2-12, Hoshigaoka, Mizusawa, Iwate, 023, Japan
3 Department of Physics, College of Liberal Arts, Kagoshima University, 1-21-3, Korimoto, Kagoshima, 890, Japan
4 Kashima Space Research Center, Communications Research Laboratory, 893-1, Hirai, Kashima, Ibaraki, 314, Japan
5 Office of Satellite Systems, National Space Development Agency of Japan, 1-29-6, Hamamatsu-cho, Minato-ku, Tokyo, 105, Japan
6 Faculty of Engineering, Kasoshima University, 1-21-3, Korimoto, Kagoshima, 890, Japan
7 Department of Physics, Faculty of Science, Kagoshima University, 1-21-3, Korimoto, Kagoshima, 890, Japan
8 Nobeyama Radio Observatory, National Astronomical Observatory, Nobeyama, Minamimaki, Minamisaku, Nagano, 384-13, Japan

Received 3 December 1996 / Accepted 7 January 1997


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 1.76 km s-1 yr-1. 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.

Key words: Masers – stars:late-type – stars:mass-loss

Send offprint requests to: H. Imai(E-mail: imai@miz.nao.ac.jp)

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998