We have performed a detailed analysis of the electron temperature and density in the Ring Nebula using the calibrated Hubble Space Telescope WFC3 images described in the preceding paper. The electron temperature (Te) determined from [NII] and [O III] rises slightly and monotonically toward the central star. The observed equivalent width (EW) in the central region indicates that Te rises as high as 13,000 K. In contrast, the low EWs in the outer regions are largely due to scattered diffuse Galactic radiation by dust. The images allowed determination of unprecedented small-scale variations in Te. These variations indicate that the mean square area temperature fluctuations are significantly higher than expected from simple photoionization. The power producing these fluctuations occurs at scales of less than 3.5 × 1015 cm. This scale length provides a strong restriction on the mechanism causing the large t2 values observed.
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. CRO'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. II. Physical Conditions" (2013). Physics and Astronomy Faculty Publications. 63.