Strong /N II/ emission and abundances in the Ring Nebula

Abstract

Measurements of line intensities at six positions in the Ring Nebula showing variations in the degree of ionization are presented. Analysis of forbidden-line intensities indicates that the temperature decreases outward from the central star, while the electron density correlates well with the flux in H . Ionic abundances of He ii, He 111,011,0111, Ne ill, N ii, and Sii relative to H II are derived for each position; total abundances of Ne, N, and S are estimated, using the oxygen ionization distribution to provide corrections for unobserved states of ionization. It is found that the derived total abundances of N and S agree very well over the six positions, even though the corrections for unobserved states vary by nearly a factor of 30. The correction formula for Ne is less successful in providing consistent abundances. It is concluded that the enhanced [N ii] lines observed near the edge of the nebula result entirely from N being nearly all N ii in these regions. The N abundances derived agree well with those found in other planetary nebulae. Subject headings: nebulae: abundances - nebulae: planetary