The interaction of the halo around the butterfly planetary nebula NGC 650-1 with the interstellar medium

Abstract

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.