Mapping Excitation in the Inner Regions of the Planetary Nebula NGC 5189
  using HST WFC3 Imaging
  The planetary nebula (PN) NGC 5189 around a Wolf-Rayet [WO] central star
demonstrates one of the most remarkable complex morphologies among PNe with
many multi-scale structures, showing evidence of multiple outbursts from an AGB
progenitor. In this study we use multi-wavelength Hubble Space Telescope Wide
Field Camera 3 (WFC3) observations to study the morphology of the inner 0.3 pc
$\times$ 0.2 pc region surrounding the central binary that appears to be a
relic of a more recent outburst of the progenitor AGB star. We applied
diagnostic diagrams based on emission line ratios of H$\alpha$ $\lambda$6563,
[O III] $\lambda$5007, and [S II] $\lambda\lambda$6717,6731 images to identify
the location and morphology of low-ionization structures within the inner
nebula. We distinguished two inner, low-ionization envelopes from the ionized
gas, within a radius of 55 arcsec ($\sim$ 0.15 pc) extending from the central
star: a large envelope expanding toward the northeast, and its smaller
counterpart envelope in the opposite direction toward the southwest of the
nebula. These low-ionization envelopes are surrounded by a highly-ionized
gaseous environment. We believe that these low-ionization expanding envelopes
are a result of a powerful outburst from the post-AGB star that created shocked
wind regions as they propagate through the previously expelled material along a
symmetric axis. Our diagnostic mapping using high-angular resolution line
emission imaging can provide a novel approach to detection of low-ionization
regions in other PNe, especially those showing a complex multi-scale
morphology.
