The shaping of planetary nebulae through
interaction with the ISM
Wareing C.J., O'Brien T.J.O., Zijlstra A.A., Kwitter K.B., Irwin J.,
Wright N., Greimel R., Drew J.E., 2006, MNRAS, 366, 387
Abstract
Sh 2-188 is an example of strong interaction between a planetary nebula and
the ISM. It shows a single arc-like structure, consisting of several
filaments, which is postulated to be the result of motion through the ISM.
We present new IPHAS H-alpha images which reveal structure behind the
filamentary limb. A faint, thin arc is seen opposite the bright limb, in
combination forming a closed ring. Behind the faint arc a long, wide tail
is detected, doubling the size of the nebula. The nebula extends 15 arcmin
on the sky in total. We have developed a `triple-wind' hydrodynamical
model, comprising of the initial `slow' AGB wind and the later `fast'
stellar wind (the interacting stellar wind model), plus a third wind
reflecting the motion through the ISM. Simulations at various velocities of
the central star relative to the ISM find that a high velocity of 125 km/s
is required to reproduce the observed structure. We find that the bright
limb and the tail already form during the AGB phase, prior to the formation
of the PN. The closure of the ring arises from the slow--fast wind
interaction. Most of the mass lost on the AGB has been swept downstream,
providing an explanation of the missing mass problem in PNe. We report a
proper motion for the central star of 30.0+/-10.0 mas/yr in the
direction of the bright limb. Assuming the central star is moving at
125+/-25 km/s, the distance to the nebula is estimated to be
855+500-420 pc, consistent with a spectroscopic
distance to the
star. At this distance Sh 2-188 is one of the largest planetary nebulae
known, with an extent of 2.8 pc. The model shows that this size was already
set during the AGB phase.
paper (pdf, preprint, 7.5M)