Observations of the gum nebula with a Fabry-Perot spectrometer

Scans have been made of Hα, N ii lambda6584, O iii lambda5007, and He i lambda5876 in selected directions in the Gum Nebula. Analyses of the line profiles and line intensities indicate that much of the emitting gas in the Gum Nebula is confined to an expanding shell which has a radius of about 125 pc, an expansion velocity of approximately 20 km s-1, an emission measure which ranges from about 15 cm-6 pc to about 500 cm-6 pc, and a temperature near 11,000 K. The ultraviolet (hν>13.6 eV) flux from xi Pup and γ2 Vel appears to be capable of producing most of the observed ionization, although the origin of the shell structure and high expansion velocity is not certain