Speaker
Description
As Coronal Mass Ejections (CMEs) propagate through the corona, they should cool adiabatically as an almost isolated plasma bubble, yet observations indicate that heating processes can offset this cooling and keep temperatures nearly constant (Sheoran 2023) or increasing (Bemporad et al. 2007; Bemporad 2022). Although several heating mechanisms have been proposed for individual events (e.g. Akmal et al. 2001; Ciaravella et al. 2003; Lee et al. 2009; Landi et al. 2010; Murphy et al. 2011), it remains an open question which mechanisms dominate in general and how much total heating CMEs experience. To study the evolution of plasma temperatures in the expansion phases of a CME, classical coronagraphic images of broadband visible light (VL) from Thomson scattering are not sufficient, and narrowband observations of radiation emitted at specific wavelengths are also needed.
On November 10, 2021, the Metis multichannel coronagraph onboard Solar Orbiter observed the expansion of a fluxrope associated with a slow limb CME (deprojected speed 155 km/s). The observations were acquired with both the VL and UV Lyman-alpha channels, with the field-of-view covering the heliocentric distances between 5.3 and 9.6 solar radii. The eruption manifested as a faint, bubble-like structure, slightly brighter than the surrounding ambient corona. Image analysis exploited the direct UV/VL ratio Doppler-dimming technique (Bemporad et al. 2021), which was used to test a new analysis technique that allowed us to iteratively determine the best fluxrope temperature in each of the image pairs. First results will be presented and discussed here in comparison with the expected adiabatic cooling curve, and typical temperature profiles for the ambient corona.
