Studies of NGC 6720 with Calibrated HST WFC3 Emission-Line Filter Images--II:Physical Conditions

TL;DR

This study uses calibrated HST WFC3 images to analyze the electron temperature and density variations in the Ring Nebula, revealing small-scale fluctuations and their implications for nebular physics.

Contribution

It provides the first detailed measurement of small-scale temperature fluctuations in the nebula, constraining the mechanisms behind observed t^2 values.

Findings

Electron temperature rises towards the center, reaching up to 13000 K.

Small-scale temperature fluctuations are larger than simple photoionization models predict.

Fluctuations occur at scales less than 3.5E15 cm.

Abstract

We have performed a detailed analysis of the electron temperature and density in the the Ring Nebula using the calibrated HST WFC3 images described in the preceding paper. The electron temperature (Te) determined from [N II] and [O III] rises slightly and monotonically towards the central star. The observed equivalent width (EW) in the central region indicates that Te rises as high as 13000 K. In contrast, the low EW's 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 3.5E15 cm. This scale length provides a strong restriction on the mechanism causing the large t^2 values observed.