Sh2-188: a model for a speedy PN
  Sh2-188 is thought to be an ancient planetary nebula in the galactic disk. It appears to be one-sided with recent observations revealing structure behind the filamentary limb. We postulate that Sh2-188 is interacting with the ISM and simulate it in terms of a ``triple-wind'' model comprising of the usual ``fast'' and ``slow'' interacting stellar winds plus the wind due to motion through the ISM. We have run simulations at various velocities of the central star relative to the ISM and find that a high velocity of 125 km/s best approximates the observed structure. We also suggest that Sh2-188 is younger than previously thought and that much of the mass lost on the AGB has been swept downstream. 
C. J. Wareing, T. J. O'Brien, A. A. Zijlstra, J. E. Drew