Two-dimensional photometry of planetary nebulae

In connection with the study of planetary nebulae, problems still exist in understanding such basic properties as three-dimensional structure, optical opacity to the central star's ionizing flux, and electron temperature and electron density variations within the nebular gas. To study these properties, two-dimensional images taken in many spectral lines are required. However, such a study presents a formidable problem in data analysis. In the present investigation, an attempt has been made to overcome the difficulties by using an imaging system which encodes the data digitally. Calibrated intensity maps could be constructed to test models of ionization structure and to produce two-dimensional maps of electron temperature and density. Both the results of a uniform-shell test and the nature of the solutions for the volume emissivity were found to support a nebular model in which the bright ring is part of a closed shell of variable density that resembles the torus proposed by Minkowski and Osterbrock (1960).