Ultraviolet spectra of planetary nebulae. VIII. The C/O abundance ratio in the ring nebula.

Abstract

The Ring nebula (NGC 6720) has been observed with the International Ultraviolet Explorer satellite. Measurements of line intensities at a position on the ring, offset from the central star, lead to a value of the abundance ratio C/O approximately 1.2, a result which is insensitive to the adopted value of the electron temperature in the nebula.