A PROTOSTELLAR JET MODEL FOR THE WATER MASERS IN W49N

Observations by Gwinn, Moran, & Reid of the proper motions of water ma sers in W49N show that they have an elongated distribution expanding f rom a common center. Features with high space velocity only occur far from the center, while low-velocity features occur at all distances. W e propose that these observations can be interpreted in terms of a she ll of shocked molecular gas that is driven by the expanding cocoon of a high-velocity protostellar jet. We present three-dimensional numeric al simulations in support of this interpretation and argue that this s ource provides a unique opportunity for a detailed study of jet-driven cocoons.