Physico-chemical spectroscopic mapping of the planetary nebula NGC 40 and the 2D_NEB, a new 2D algorithm to study ionized nebulae

In this paper we present an analysis of the physical and chemical conditions of the planetary nebula NGC 40 through spatially resolved spectroscopic maps. We also introduce a new algorithm -2D_NEB- based on the well-established IRAF nebular package, which was developed to enable the use of the spectroscopic maps to easily estimate the astrophysical quantities of ionized nebulae. The 2D_NEB was benchmarked, and we clearly show that it works properly, since it compares nicely with the IRAF nebular software.

Using this software, we derive the maps of several physical parameters of NGC 40. From these maps, we conclude that T_e[N II] shows only a slight temperature variation from region to region, with its values constrained between ∼8000 and 9500 K. Electron densities, on the other hand, have a much more prominent spatial variation, as N_e[S II] values vary from ∼1000 to 3000 cm^-3. Maps of the chemical abundances also show significant variations. From the big picture of our work, we strongly suggest that analysis with spatial resolution be mandatory for more complete study of the physical and chemical properties of planetary nebulae.