A birth and growth of a collimated molecular jet from an AGB star

With the VLBA, we have observed water masers associated with the OH/IR star, W43A, which trace a birth and growth of a molecular jet. The water masers exhibit the collimated distribution (1700 AU: 20 AU) and fast motions (±150 km s). The maser distribution was well fit by a precessing jet model. The jet length has extended by 800 AU within 8 years, indicating that the extension rate is roughly equivalent to the jet speed (150 km s). Very likely the jet was born around the year 1960. An elongated planetary nebula will be formed by such a jet during an extremely short period (<< 1000 yrs) of the transition to form a ptoto-planetary nebula. Then fading of the water maser jet will be observed during our own life.