Kinematics of the H2O masers in W49N: analysis of the velocity variance-covariance matrix.
Abstract (from CDS):
The proper motions of the H2O 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 H2O 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 H2O 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.
ISM: H II Regions - ISM: individual (W49N) - ISM: Kinematics and Dynamics - Masers - Radio Lines: ISM - Techniques: Interferometric