Studies of the initial phases of CME heating and of the formation of the current sheet (CS) after the ejection are of crucial importance for understanding the physics behind CME ejections. In recent studies, Landi et al (2010, 2011) observed a CME event with a suite of instruments including EIS and XRT and were able to study the thermal structure of the ejecta and monitor the evolution of the CS that formed afterwards. They found that:
1 - The CME core were formed by three distinct plasmas, with different density and temperature, which ranged from Log T=5.1 to Log t=5.7
2 - The CME core was enveloped in a much hotter plasma with temperature in excess of 3MK.
3 - The current sheet observed afterwards had lower temperature than the surrounding corona, and temperatures of ~2-3MK; very hot plasma was not observed.
These results are very important for quantitative, predicting models of CME initiation and energetics, but they need to be improved. In fact, the identification of the hot plasma was made through the only XRT filter available in the observations (Al-poly) and no detailed plasma diagnostics could be carried out to determine its physical properties. The measured temperature and densities of the current sheet contradict all current models, but they were carried out at low altitudes where significant contamination from a post-CME arcade decreased the accuracy of the measurements.
Here we propose to carry out a series of "CME-watch" simultaneous observations with EIS and XRT on limb active regions that have a potential for CME ejections; these observations are designed to maximize the diagnostic capabilities of the data, and minimize contamination from background sources. |
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