The circumstellar envelopes around OH/IR stars

High spatial resolution observations of the 1612-MHz OH maser emission from five OH/IR stars have been conducted using MERLIN in its spectral-line mode. The observations yield the angular radii of the circumstellar envelopes. These can be combined with the linear radii obtained from phase-lag techniques to calculate source distances. Single-baseline observations have also been conducted to determine the absolute positions of nine OH/IR objects, and it is found that they are coincident with the optical positions of the stars, where these positions are available. All published 1612-MHz OH maser maps of OH/IR stars have been collated in order to study the shell structure. (author)