NGC-7027 AT MILLIMETER WAVELENGTHS - RADIAL GRADIENT OF THE IONIZED SHELL DENSITY

Spectroscopic observations of the planetary nebula NGC 7027 in the H30 alpha recombination line (1.3 mm wavelength) were made with the James Clerk Maxwell Telescope in Hawaii. The new JCMT data, along with the f ew other published recombination line data at millimeter wavelengths, are interpreted with a model of the ionised shell density n as a funct ion of the radius r, of the form n approximately r(k). Values of k in the range 0 to -4 were attempted: for the millimeter radio wavelength range the best results were found for k = -2; for the combined millime ter and centimeter wavelength range the best results were found for k = -1.8 +/- 0.6 (s.d. of mean).