  The majority of the observed planetary nebulae exhibit elliptical or bipolar
structures. Theoretical modeling has indicated that magnetically collimated
jets may be responsible for the formation of the non-spherical planetary
nebulae. The aim of this project is to measure the Zeeman splitting caused by
the magnetic field in the OH and H2O maser regions occurring in the
circumstellar envelope and bipolar outflow of the evolved star W43A. We report
a measured magnetic field of approximately 100 micro-gauss in the OH maser
region of the circumstellar envelope around W43A. The GBT observations reveal a
magnetic field strength B|| of ~30 mG changing sign across the H2O masers at
the tip of the red-shifted lobe of the bipolar outflow. We also find that the
OH maser shell shows no sign of non-spherical expansion and that it probably
has an expansion velocity that is typical for the shells of regular OH/IR
stars. The GBT observations confirm that the magnetic field collimates the H2O
maser jet, while the OH maser observations show that a strong large scale
magnetic field is present in the envelope surrounding the W43A central star.
The magnetic field in the OH maser envelope is consistent with the one
extrapolated from the H2O measurements, confirming that magnetic fields play an
important role in the entire circumstellar environment of W43A.
