Studies of NGC 6720 with Calibrated HST WFC3 Emission-Line Filter Images--I: Structure and Evolution

Abstract

We have performed a detailed analysis of the Ring Nebula (NGC 6720) using HST WFC3 images and derived a new 3-D model. Existing high spectral resolution spectra played an important supplementary role in our modeling. It is shown that the Main Ring of the nebula is an ionization-bounded irregular non-symmetric disk with a central cavity and perpendicular extended lobes pointed almost towards the observer. The faint outer halos are determined to be fossil radiation, i.e. radiation from gas ionized in an earlier stage of the nebula when it was not ionization bounded. The narrow-band WFC3 filters that isolate some of the emission-lines are affected by broadening on their short wavelength side and all the filters were calibrated using ground-based spectra. The filter calibration results are presented in an appendix.

Accepted for publication by the Astronomical Journal

References in corpus (5)

• Trigonometric Parallaxes of Central Stars of Planetary Nebulae
• Determination of the Physical Conditions of the Knots in the Helix Nebula from Optical and Infrared Observations
• Merged ionization/dissociation fronts in planetary nebulae
• Discovery of Multiple Shells Around the Planetary Nebula IC 418
• Tangential Motions and Spectroscopy within NGC 6720, the Ring Nebula

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