Kinematics of the H2O Masers in W49N: Analysis of the Velocity Variance‐Covariance Matrix

The proper motions of the H 2 O masers in W49N have been measured with multiepoch very long baseline interferometry (VLBI) by Gwinn, Moran, & Reid. The number of motions derived is large (105), and the spatial coverage of the source by maser spots is excellent, making W49N a natural candidate for analytic tools based on diagonalization of the velocity variance-covariance matrix (VVCM). The velocity dispersions (or internal relative velocities) used in VVCM analysis are the quantities directly determined by VLBI proper motion experiments, which lack an absolute phase reference. I apply the VVCM diagonalization procedure to the H 2 O masers in W49N, deriving in an objective, model-independent way the kinematic axes of the outflow. I then compare these local axes with various geometrical axes suggested by the morphology of an apparent "ring" of H II regions that accompany the one containing H 2 O masers, and with the axis of the large-scale outflow seen in molecular emission. I also present kinematic evidence not revealed by previous modeling for pronounced asymmetry of the collimating mechanism that channels the maser outflow, and propose an explanation in terms of magnetic drag.