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Astron. Astrophys. 317, L67-L70 (1997)


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Letter to the Editor

Detection of compact water maser spots around late-type stars

H. Imai 1, 2, T. Sasao 2, O. Kameya 2, M. Miyoshi 2, K. M. Shibata 2, Y. Asaki 2, T. Omodaka 3, M. Morimoto 3, N. Mochizuki 3, 4, T. Suzuyama 5, S. Iguchi 6, S. Kameno 7, T. Jike 3, K. Iwadate 2, S. Sakai 2, T. Miyaji 7, N. Kawaguchi 7 and K. Miyazawa 7

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 Department of Physiscs, Faculty of Science, Kagoshima University, Korimoto 1-21-3, Kagoshima, 890, Japan
5 Faculty of Engineering, Kagoshima University, Korimoto 1-21-3, Kagoshima, 890, Japan
6 Department of Electronic Engineering, The University of Electro-Communications, Chôfugaoka 1-5-1, Chôfu, Tokyo, 182, Japan
7 Nobeyama Radio Observatory, National Astronomical Observatory, Nobeyama, Minamimaki, Minamisaku, Nagano, 384-13, Japan

Received 20 August 1996 / Accepted 22 October 1996

Abstract

We observed water masers around 21 late type stars using very long baseline interferometry (VLBI) composed of 6-m telescope at Kagoshima and 10-m telescope at Mizusawa, Japan. Despite the fairly long baseline (1300 km) and the low sensitivity, we detected compact water masers around three semiregular variables R Crt, RT Vir and RX Boo and two supergiants VY CMa and VX Sgr. Detection of the stellar water masers around nearby semiregular variables at about 100 pc implies the very compact size of these maser spots of the order of [FORMULA] cm, considerably smaller than the widely accepted typical size for stellar water masers. Almost all the line profiles of the water masers detected at the first epoch changed dramatically at the second epoch after six months. However, some strong emission peaks were detected in the same velocity at both epochs, suggesting that the lifetime of the strong maser spots is longer than six months.

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

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

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998

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