Chemical compositions of planetary and diffuse nebulae.

The approach taken to determining the chemical compositions of planetary and diffuse nebulae was to calculate a network of models to represent objects with a wide range of excitation, density, and optical thickness. The approach was directed toward supplying a framework within which interpolation could assist in the interpretation of individual objects. The method was applied to the planetary nebula NGC 4361 and to abundance ratios in the Magellanic Clouds.