The interaction of the halo around the butterfly planetary nebula
  NGC650-1 with the interstellar medium
  With its bright and wide equatorial waist seen almost edge-on (the butterfly
body) and the faint and broad bipolar extensions (the butterfly wings),
NGC650-1 is the archetypical example of bipolar planetary nebula (PN) with
butterfly morphology. We present here deep high-resolution broad- and
narrow-band optical images that expose the rich and intricate fine structure of
this bipolar PN, with small-scale bubble-like features and collimated outflows.
A SHAPE spatio-kinematical model indicates that NGC650-1 has a broad central
torus with an inclination angle of 75 degrees with respect to the line of
sight, whereas that of the bipolar lobes, which are clearly seen in the
position-velocity maps, is 85 degrees. Large field of view deep images show,
for first time, an arc-like diffuse envelope in low- and high-excitation
emission lines located up to 180 arcsec towards the East-Southeast of the
central star, well outside the main nebula. This morphological component is
confirmed by Spitzer MIPS and WISE infrared imaging, as well as by long-slit
low- and high-dispersion optical spectroscopic observations. HST images of
NGC650-1 obtained at two different epochs (14 yrs apart), reveal the proper
motion of the central star along this direction. We propose that this motion of
the star through the interstellar medium compresses the remnant material of a
slow Asymptotic Giant Branch wind, producing this bow-shock-like feature.
