Abstract
Density distributions of four planetary nebulae have been calculated in cylindrical coordinates (r,z,ϕ) using the iterative deprojection algorithm by Bremer (1995). Narrowband filter CCD images of NGC 2346, NGC 6563, NGC 6826 and NGC 7009 in the Hα line (6562.8 å) were corrected for cosmic ray hits, background/foreground stars were removed, and the position angles PA of their symmetry axes were determined with a maximum correlation criterion. For NGC 6563, the axis was shifted manually to the south-east to put it on the central ridge (the PA was conserved). For deprojections in cylindrical coordinates, an inclination angle i (angle between the object axis and the line of sight) must be specified. Literature values based on optical spectra were available for NGC 2346 (Walsh 1983) and NGC 7009 (Preston and Willson 1990), for NGC 6563 and NGC 6826 lower limits were derived from deprojections.
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