The kinematics of water masers in the stellar molecular outflow source, IRAS 19134+2131

Using the Very Large Array (VLA) and the Very Long Baseline Array (VLBA), we have observed water maser emission in the proto-planetary nebula candidate IRAS 19134+2131, in which the water maser spectrum has two groups of emission features separated in radial velocity by ~100 km s-1. The blue-shifted and red-shifted clusters of maser features are clearly separated spatially by ~150 mas, indicative of a fast collimated flow. However, not all of the maser features are aligned along the axis of the flow, as is seen in the similar high-velocity water maser source, W43A. Comparing the VLA and VLBA maps of the water maser source, we find 4 maser features that were active for 2 years. Using only VLBA data, we identified proper motions for 8 maser features. The full 3D outflow velocity is estimated to be ~130 km s-1, indicating that the dynamical age of the flow is only ~50 yr. On the basis of the relative positions with respect to the nearby extragalactic reference source, J1925+2106, we also obtain a secular motion of IRAS 19134+2131of $\mu_{l}=-4.6\pm0.7$ mas yr-1 along the Galactic plane toward the Galactic centre. This indicates a “far distance" (≥16 kpc) for IRAS 19134+2131 if the Galactic rotation curve remains flat at 220 km s-1.