Kinematics of the H2O masers in W49N: Analysis of the velocity variance-covariance matrix

The proper motions of the H2O masers in W49N have been measured with multie poch very long baseline interferometry (VLBI) by Gwinn, Moran, & Reid. The number of motions derived is large (105), and the spatial coverage of the s ource by maser spots is excellent, making W49N a natural candidate for anal ytic tools based on diagonalization of the velocity variance-covariance mat rix (VVCM). The velocity dispersions (or internal relative velocities) used in VVCM analysis are the quantities directly determined by VLBI proper mot ion experiments, which lack an absolute phase reference. I apply the VVCM d iagonalization procedure to the H2O masers in W49N, deriving in an objectiv e, 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 H2O masers, and with the axis of the large-scale outflow seen in molecular emi ssion. I also present kinematic evidence not revealed by previous modeling for pronounced asymmetry of the collimating mechanism that channels the mas er outflow, and propose an explanation in terms of magnetic drag.