2005ApJ...622L.125I

We report Very Long Baseline Array and Very Large Array observations of 22 GHz H₂O and 43 GHz SiO (v=1, J=1-0) maser emission as well as 7 mm continuum emission in W43A, which exhibits a highly collimated jet of molecular gas and a spherically expanding envelope very similar to that of an OH/IR star. The spatiokinematical structure of the H₂O masers is well fitted to a precessing jet model with an expansion velocity of 150 km/s and a dynamical age of ∼50 yr. The spatiokinematical structure of the SiO masers is well fitted to a biconically expanding flow model, whose axis is parallel to the direction of the collimated jet. Astrometry of the H₂O and SiO masers suggests that these maser sources have a common dynamical center, possibly as part of a binary system, within 70 AU. The SiO masers may be excited on the surface of the cone that has significant deceleration and interacts with the jet. A 7 mm continuum emission source is located ∼1300 AU away from these maser sources at a position angle of about -60° from the jet axis. The physical relation of the continuum to the maser sources is still unclear.