DETECTION OF COMPACT WATER MASER SPOTS AROUND LATE-TYPE STARS

We observed water masers around 21 late type stars using very long bas eline 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 aro und three semiregular variables R Crt, RT Vir and RX 1300 and two supe rgiants VY CMa and VX Sgr. Detection of the stellar water masers aroun d nearby semiregular variables at about 100 pc implies the very compac t size of these maser spots of the order of 10(12)cm considerably smal ler than the widely accepted typical size for stellar water masers. Al most all the line profiles of the water masers detected at the first e poch changed dramatically at the second epoch after six months. Howeve r, some strong emission peaks were detected in the same velocity at bo th epochs, suggesting that the lifetime of the strong maser spots is l onger than six months.