Chemical Abundances and Kinematics of the Ring Nebula and Its Halos

Guerrero, M. A.; Manchado, A.; Chu, Y.-H.
Bibliographical reference

Astrophysical Journal v.487, p.328

Advertised on:
9
1997
Number of authors
3
IAC number of authors
1
Citations
38
Refereed citations
36
Description
We have obtained new narrowband CCD images, spatially resolved intermediate- and high-dispersion spectroscopic observations of the Ring Nebula (NGC 6720). These data reveal that the bright main nebula is not a real ring, but a closed shell. A prolate ellipsoidal geometry for this shell is inferred from the observed tilts in the [N II] velocity ellipses at different position angles. The shell has enhanced densities near the equator; the shell surface is fragmented with protruding bubbles and outflows. The high-resolution spatially resolved echellograms allow us to identify the kinematic components associated with small-scale morphological features. The morphologically identified inner and outer halos show neither distinct kinematic discontinuity at the transition nor different chemical abundances, indicating that they have a common origin, the red giant wind. The kinematic and chemical properties of the Ring Nebula do not support the hypothesis that the Ring is a nearly pole-on bipolar nebula. We propose that the Ring Nebula contains a bubbling prolate ellipsoidal shell and a halo of remnant red giant wind, and that the combination of a nonisotropic excitation and the interaction of the main shell's bubbles and outflows with the surrounding red giant wind produces the petal-like morphology in the inner halo.