RADIO RECOMBINATION LINE OBSERVATIONS OF THE PLANETARY-NEBULA NGC-7027

The planetary nebula NGC 7027 has been observed in the 76-alpha and 110-alpha radio recombination lines. An electron temperature of 14 500 +/- 1000 K is found in most of the nebula. The observed H110-alpha and H76-alpha line to continuum ratios are in good agreement with a true electron density of n(e, true) = 6 10(4) cm-3. The velocity structure of the line emission implies that the ionized gas in NGC 7027 is expanding anisotropically. A radially expanding prolate spheroidal shell model for the ionized gas distribution is found to be consistent both with the observed recombination line velocities and with the observed continuum brightness distribution. The relation between the outflowing ionized gas and the molecular cloud surrounding NGC 7027 is discussed.