We have performed a detailed analysis of the Ring Nebula (NGC 6720) using Hubble Space Telescope WFC3 images and derived a new three-dimensional 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 toward 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 narrowband 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.
Digital Object Identifier (DOI)
G.J.F. acknowledges support by NSF (0908877; 1108928; and 1109061), NASA (10-ATP10-0053, 10-ADAP10-0073, and NNX12AH73G), JPL (RSA No 1430426), and STScI (HST-AR-12125.01, GO-12560, and HST-GO-12309). M.P. received partial support from CONACyT grant 129553. W.J.H. acknowledges financial support from DGAPA–UNAM through project PAPIIT IN102012. C.R.O.'s participation was supported in part by HST program GO 12309.
O'Dell, C. R.; Ferland, Gary J.; Henney, W. J.; and Peimbert, M., "Studies of NGC 6720 with Calibrated HST/WFC3 Emission-line Filter Images. I. Structure and Evolution" (2013). Physics and Astronomy Faculty Publications. 64.