Bibcode
DOI
Guerrero, M. A.; Manchado, A.; Chu, Y.-H.
Referencia bibliográfica
Astrophysical Journal v.487, p.328
Fecha de publicación:
9
1997
Número de citas
38
Número de citas referidas
36
Descripción
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.