Abstract
We present the spatial and velocity distributions of H[2]O and OH masers in the OH/IR star W43A. These masers have the same systemic velocity and are, therefore, likely to be associated with the common stellar object. However, the OH masers exhibit clear arc-shaped structures and indicate a spherically-expanding shell, while most of the H[2]O masers are extremely collimated spatially and kinematically. The observed angular pattern of the H[2]O masers is well fit by a precessing jet model. We infer that an elongated planetary nebula is formed by such a ``molecular jet'' during the short period (< 1000years) of the transition through the proto-planetary nebula phase.
