  We present the first direct measurements of the magnetic field strength and
direction in a collimated jet from an evolved star on its way to become a
planetary nebula. Very Long Baseline Array (VLBA) observations of the linear
and circular polarization of the water masers in the collimated jet of W43A
reveal a strong toroidal magnetic field, indicating that the jet is
magnetically collimated. The magnetic field strength in the jet extrapolated
back to the stellar surface yields a surface field of several Gauss, consistent
with the measurements of maser polarization in a large sample of evolved stars.
The origin of the magnetic field is yet unknown, although the jet precession
might point to the existence of a heavy planet or stellar companion. This is
the first direct observational evidence for magnetic collimation in the jets,
that likely play an important role in shaping planetary nebulae.
