Studies of NGC 6720 with calibrated HST/WFC3 emission-line filter images. II. Physical conditions

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 (T _e) determined from [N II] and [O III] rises slightly and monotonically toward the central star. The observed equivalent width (EW) in the central region indicates that T _e 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 T _e. 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 t ² values observed.