1997A&A...317L..67I

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 (1300km) 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 100pc implies the very compact size of these maser spots of the order of 10¹²cm, 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.