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Continuing our series of papers on the 3-D structure and accurate distancesof Planetary Nebulae (PNe), we present here the results obtained for theplanetary nebula NGC\,40. Using data from different sources and wavelengths, weconstruct 3-D photoionization models and derive the physical quantitities ofthe ionizing source and nebular gas. The procedure, discussed in detail in theprevious papers, consists of the use of 3-D photoionization codes constrainedby observational data to derive the three-dimensional nebular structure,physical and chemical characteristics and ionizing star parameters of theobjects by simultaneously fitting the integrated line intensities, the densitymap, the temperature map, and the observed morphologies in different emissionlines. For this particular case we combined hydrodynamical simulations with thephotoionization scheme in order to obtain self-consistent distributions ofdensity and velocity of the nebular material. Combining the velocity field withthe emission line cubes we also obtained the synthetic position-velocity plotsthat are compared to the observations. Finally, using theoretical evolutionarytracks of intermediate and low mass stars, we derive the mass and age of thecentral star of NGC\,40 as $(0.567 \pm 0.06)$M$_{\odot}$ and $(5810 \pm600)$yrs, respectively. The distance obtained from the fitting procedure was$(1150 \pm 120)$pc.

3-D Photoionization Structure and Distances of Planetary Nebulae IV. NGC 40