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Prominences and their eruptions as observed with the IRIS mission and ancillary instruments

Abstract : Solar prominences are fascinating, large-scale magnetic structures in the solar atmosphere. They have been investigated for many decades, but the issues of their formation, stability, and eruption are still not well understood. Much progress has been made in our knowledge of prominences and their eruptions with both synoptic measurements from space (with SoHO/EIT, STEREO/SECCHI/EUVI, and SDO/AIA) and multiwavelength spectro-imaging. Since the launch of IRIS in 2013, a lot of results have been obtained in both observational and modeling domains with IRIS high spectral and spatial resolution imaging and spectroscopy. In this thesis, we focus on the observational signatures of the processes which have been put forward for explaining eruptive prominences. We also try to figure out the variations of physical conditions of the eruptive prominence and estimate the masses leaving the Sun vs. the masses returning to the Sun during the eruption. As far as velocities are concerned, we derive a full velocity vector for each pixel of the observed prominence by combining an optical flow method on the AIA 304Å and IRIS Mg II h&k images in order to derive the plane-of-sky velocities and a Doppler technique on the IRIS Mg II h&k profiles to compute the line-of-sight velocities. As far as densities and temperatures are concerned, we compare the absolute observed intensities with values derived from Non-Local Thermodynamic Equilibrium (NLTE) radiative transfer computations to build maps of these quantities. The derived electron densities range from 1.3E9 to 7.0E10 cm⁻³ and the derived total Hydrogen densities range from 1.5E9 to 3.6E11 cm⁻³ in different regions of the prominence. The mean temperature is around 1.1E4 K which is higher than in quiescent prominences. The ionization degree is in the range of 0.1 to 10. The mass flows in the prominence and their variations with time are consequently computed. The total mass is 1.3E14 to 3.2E14 g. The total mass drainage from the prominence to the solar surface during the observation of IRIS is about one order of magnitude smaller than the total mass of prominence. We also explore the correlations between the observable spectral features in h and k lines of Mg II to physical quantities such as the density and the Emission Measure (EM). We choose to compute one-dimensional (1D) isothermal and isobaric models using the PRODOP_Mg NLTE code available at MEDOC (IAS) with the exact computation of the incident radiation. Then we derive correlations between the k and h emergent intensities on one hand and the densities and EM on the other hand. With some assumptions on the temperature, we obtain a unique relation between the k (and h) intensities and the EM that should be useful for deriving either the hydrogen and electron densities or the effective thickness of an observed prominence. Thus, the evolution of the morphology and thermodynamic properties of an erupting prominence have been studied in the thesis. These investigations lead to our understanding in some aspects of prominences, e.g., the distribution and evolution of densities, temperatures, velocities and ionization degree. These could be useful constraints for theoretical prominence models. In the conclusion, we summarize our results and provide some suggestions for future analysis, observations and ideal observing capabilities.
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  • HAL Id : tel-02094359, version 1

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Ping Zhang. Prominences and their eruptions as observed with the IRIS mission and ancillary instruments. Solar and Stellar Astrophysics [astro-ph.SR]. Université Paris Saclay (COmUE), 2019. English. ⟨NNT : 2019SACLS064⟩. ⟨tel-02094359⟩

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