3D stereoscopic analysis of a Coronal Mass Ejection and comparison with UV spectroscopic data

TL;DR

This study combines 3D reconstructions of a CME from STEREO images with UV spectroscopic data to analyze its structure, dynamics, and plasma heating, revealing that line broadening indicates additional heating mechanisms beyond expansion.

Contribution

First integration of 3D CME geometry with UV spectroscopic measurements to analyze plasma heating and dynamics in a partial-halo CME.

Findings

Reproduced observed line widths in peripheral CME regions

Identified plasma heating mechanisms beyond bulk expansion

Confirmed CME core as expelled prominence plasma

Abstract

A three-dimensional (3D) reconstruction of the 2007, May 20 partial-halo Coronal Mass Ejection (CME) has been made using STEREO/EUVI and STEREO/COR1 coronagraphic images. The trajectory and kinematics of the erupting filament have been derived from EUVI image pairs with the "tie-pointing" triangulation technique, while the polarization ratio technique has been applied to COR1 data to determine the average position and depth of the CME front along the line of sight. These 3D geometrical information have been combined for the first time with spectroscopic measurements of the OVI $\lambda\lambda$1031.91, 1037.61 \AA\ line profiles made with the Ultraviolet Coronagraph Spectrometer (UVCS) on board SOHO. Comparison between the prominence trajectory extrapolated at the altitude of UVCS observations and the core transit time measured from UVCS data made possible a firm identification of the CME core observed in white light and UV with the prominence plasma expelled during the CME. Results on the 3D structure of the CME front have been used to calculate synthetic spectral profiles of the OVI $\lambda\lambda1031.91$ \AA\ line expected along the UVCS slit, in an attempt to reproduce the measured line widths. Observed line widths can be reproduced within the uncertainties only in the peripheral part of the CME front; at the front center, where the distance of the emitting plasma from the plane of the sky is greater, synthetic widths turn out to be $\sim 25$% lower than the measured ones. This provides strong evidence of line broadening due to plasma heating mechanisms in addition to bulk expansion of the emitting volume.