Envelope structures and optical/radio positions of cool stars

Results are presented from 18-cm VLA observations of OH masers associated with the Mira variables IK Tau, U Her, R Aql, RR Aql, and the supergiant S Per. The linear radii of the OH shells range from about 35 AU to 450 AU. Evidence for axisymmetric structures are found for virtually all of the shells. A model to describe the observations is proposed in which material is flowing from the star in a radially expanding ellipsoidal configuration. It is concluded that axisymmetric outflow is common for red giants and supergiants and that the large magnetic field strength observed for these stars may influence the geometry and initiation of mass loss.