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Tuesday, 24th November at 2.00pm at the JAC
Nikta Amiri
Leiden Observatory/Joint Institute for VLBI in Europe
"The magnetic field of the evolved star W43A"
ABSTRACT:
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(perp) 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.
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