VLA line observations of OH/IR stars.

The VLA was used in a spectral line mode at 1612 MHz to investigate the structure of eleven OH/IR stars. Ten objects have large radial velocities and are expected to be close to their tangential points. For six resolved sources very accurate distances could be derived by combining the angular radii of the OH shell with available phase lag diameters. A comparison of these geometric distances with kinematic distances gives a determination of the distance to the Galactic center of 9.2 + or - 1.2 kpc. The OH shells appear to be fairly symmetric, with deviations from spherical symmetry of less than 20 percent, and rather thin, the thickness being at most 20 percent of the radius. The OH density falls off as 1/r squared, or slightly steeper.