Magnetic field structure in the outer OH maser envelope of VX Sagittarii

The OH 1612 MHz maser transition from the supergiant star VX Sgr has been i maged in all Stokes parameters using MERLIN. Numerous elliptically polarise d components are distributed in a roughly symmetric envelope of a size simi lar to that measured in total maser intensity. The polarisation vectors are generally tangential to the circumstellar envelope, indicating a globally ordered magnetic field at the distance of about 1400 au from the supergiant . It is suggested that a predominance of projected radial magnetic lines an d a displacement between the red-and blue-shifted parts of the envelope can be explained with a dipole field tilted at 20-30 degrees to the line of si ght.