Photoionization modeling of the Galactic planetary nebulae Abell 39 and   NGC 7027
  We estimate distances to the spherical planetary nebula Abell 39 and the bipolar planetary nebula NGC 7027 by interpolating from a wide grid of photoionization models using the 3-D code, MOCASSIN. We find preliminary distances of 1.5 kpc and 0.9 kpc respectively, with uncertainties of about 30%. 
Ashkbiz Danehkar, David J. Frew, Quentin A. Parker, Orsola De Marco
astro-ph.GA