3-D Photoionization Structure and Distances of Planetary Nebulae IV. NGC   40
  Continuing our series of papers on the 3-D structure and accurate distances of Planetary Nebulae (PNe), we present here the results obtained for the planetary nebula NGC\,40. Using data from different sources and wavelengths, we construct 3-D photoionization models and derive the physical quantitities of the ionizing source and nebular gas. The procedure, discussed in detail in the previous papers, consists of the use of 3-D photoionization codes constrained by observational data to derive the three-dimensional nebular structure, physical and chemical characteristics and ionizing star parameters of the objects by simultaneously fitting the integrated line intensities, the density map, the temperature map, and the observed morphologies in different emission lines. For this particular case we combined hydrodynamical simulations with the photoionization scheme in order to obtain self-consistent distributions of density and velocity of the nebular material. Combining the velocity field with the emission line cubes we also obtained the synthetic position-velocity plots that are compared to the observations. Finally, using theoretical evolutionary tracks of intermediate and low mass stars, we derive the mass and age of the central star of NGC\,40 as $(0.567 \pm 0.06)$M$_{\odot}$ and $(5810 \pm 600)$yrs, respectively. The distance obtained from the fitting procedure was $(1150 \pm 120)$pc. 
Hektor Monteiro and Diego Falceta-Gon\c{c}alves
astro-ph.SR