LMC-N66: a close binary system?
M. Peña1, W.-R.
Hamann and M.T. Ruiz
1Instituto de Astronomia, UNAM, Mexico
The planetary nebula LMC-N66 is an extraordinary object, as it is the
only
confirmed PN where the central star is a Wolf-Rayet star of type [WN].
Moreover, the star showed a dramatic brightness outburst in 1993-1994.
In
a previous papers we analyzed the changing stellar spectra and found
evidence
that
the central star is most likely a binary system where a white dwarf
presently
accretes matter from a non-degenerate companion at a high rate. Thus
the
object
is a candidate for a future type Ia supernova in our cosmic
neighborhood. We
have also analyzed the morphology and kinematics of the nebula, using
images
and
high-resolution spectra obtained with the HST. The object presents a
complex
multipolar structure, dominated by very bright lobes located at both
sides
of
the central star and separated by a narrow waist. In addition there is
a
pair
of very extended and twisted loops, also pointing in opposite
directions;
their
symmetry axis and collimation angle differs from those of the bright
lobes.
High resolution spectroscopy reveals two main velocity components,
"approaching" material at an average systemic radial velocity of V =
-50
km/s and similarly bright "receding" material at V= 50 km/s. Opposite
lobes
and
loops possess opposite velocities. Furthermore there are knots and
filaments
of complex structure and kinematics. The morphology and kinematics of
LMC-N66
can be explained as the result of episodic bipolar ejections with
changing
axis.
The bipolar structures could have been produced by collimated streams
ejected
from a precessing central source. The precession could have been
produced
by
an external torque, possibly due to a binary companion.