Extensive Study of a Coronal Mass Ejection with UV and WL coronagraphs: the need for multi-wavelength observations

TL;DR

This study combines UV and white-light observations to analyze a coronal mass ejection, demonstrating the diagnostic potential of multi-wavelength data for understanding CME plasma properties and informing future coronagraph designs.

Contribution

It introduces the first use of UVCS WL channel data for CME position angle measurement and integrates multi-wavelength diagnostics to estimate plasma temperatures and speeds within a CME.

Findings

CME core temperature drops to 10^5 K during expansion

Significant Lyα dimming observed at CME front

Reconstructed plasma speed distribution constrains future observations

Abstract

Coronal Mass Ejections (CMEs) often show different features in different band-passes. By combining data in white-light (WL) and ultraviolet (UV) bands, we have applied different techniques to derive plasma temperatures, electron density, internal radial speed, etc, within a fast CME. They serve as extensive tests of the diagnostic capabilities, developed for the observations provided by future multi-channel coronagraphs (such as Solar Orbiter/Metis, ASO-S/LST, PROBA-3/ASPIICS). The involved data include WL images acquired by SOHO/LASCO coronagraphs, and intensities measured by SOHO/UVCS at 2.45 R$_{\odot}$ in the UV (H I Ly$\alpha$ and O VI 1032 {AA} lines) and WL channels. Data from the UVCS WL channel have been employed for the first time to measure the CME position angle with polarization-ratio technique. Plasma electron and effective temperatures of the CME core and void are estimated by combining UV and WL data. Due to the CME expansion and the possible existence of prominence segments, the transit of the CME core results in decreases of the electron temperature down to $10^{5}$ K. The front is observed as a significant dimming in the Ly$\alpha$ intensity, associated with a line broadening due to plasma heating and flows along the line-of-sight. The 2D distribution of plasma speeds within the CME body is reconstructed from LASCO images and employed to constrain the Doppler dimming of Ly$\alpha$ line, and simulate future CME observations by Metis and LST.