Kinematic studies of ultracompact HII region/molecular cloud interfaces

Abstract

An exciting application of masers as an astrophysical tool is the study of proper motions through multi-epoch VLBI, which has the potential to reveal details of source kinematics on an unprecedented spatial scale. OH masers are particularly interesting, as they are typically situated in the high-density region of molecular gas lying at the interface between ultracompact HII regions and molecular clouds. We discuss OH-maser proper motion measurements we have made of W3(OH), and show that modelling methods developed in the past for H2O maser motions may not be appropriate to this source. We then present new and fairly general analytic techniques that may be used to detect and interpret asymmetric proper motion patterns.