Electron Densities in the Solar Corona Measured Simultaneously in the Extreme-Ultraviolet and Infra-Red

TL;DR

This study demonstrates that electron densities in the solar corona can be accurately measured using both EUV and NIR lines, showing excellent agreement and validating ground-based NIR diagnostics as a reliable method.

Contribution

The paper compares electron density measurements from EUV and NIR lines, establishing the viability of ground-based NIR diagnostics for solar corona studies.

Findings

EUV and NIR measurements agree within 10%

Electron densities range from log(Ne) = 8.2 to 8.6

NIR line center intensities are unaffected by stray light

Abstract

Accurate measurements of electron density are critical for determination of the plasma properties in the solar corona. We compare the electron densities diagnosed from Fe XIII lines observed by the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode mission with the near infra-red (NIR) measurements provided by the ground-based Coronal Multichannel Polarimeter (COMP). To do that, the emissivity-ratio method based on all available observed lines of Fe XIII is used for both EIS and CoMP. The EIS diagnostics is further supplemented by the results from Fe XII lines. We find excellent agreement, within 10%, between the electron densities measured from both EUV and NIR lines. In the five regions selected for detailed analysis, we obtain electron densities of log(Ne [cm-3]) = 8.2-8.6. Where available, the background subtraction has a significant impact on the diagnostics, especially on the NIR lines, where the loop contributes less than a quarter of the intensity measured along the line of sight. For the NIR lines, we find that the line center intensities are not affected by stray light within the instrument, and recommend using these for density diagnostics. The measurements of the Fe XIII NIR lines represent a viable method for density diagnostics using ground-based instrumentation.