Zambrana Prado, Natalia; (2020) Spectroscopic diagnostics of the elemental composition of the solar corona. Doctoral thesis (Ph.D), Université Paris-Saclay.

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Abstract

Linking solar activity on the surface and in the corona to the inner heliosphere is one of the main goals of Solar Orbiter. Its unique combination of in-situ and remote sensing instruments can be used to shed light on this difficult task by, e.g., determining the source region of the solar wind measured in-situ at the spacecraft position. A key element in this are data on the elemental composition. Indeed, different structures on the Sun have different abundances as a consequence of the FIP (First Ionization Potential) effect. Comparing in-situ and remote sensing composition data, coupled with modeling, will allow us to trace back the source of heliospheric plasma. During my thesis, I developed a new method for measuring relative abundances of the solar corona using UV spectroscopy, the Linear Combination Ratio (LCR) method. This method can be telemetry efficient while remaining reliable; it is based on optimized linear combinations of spectral lines. This method has been tested on synthetic spectra and on spectroscopic observation data. Using a Bayesian approach, I then developed a way to determine the uncertainties related to the measurements obtained with the LCR method. One of the applications of the method was to provide reliable measurements of elemental composition in the framework of a collaboration whose goal is to find the characteristics of the plasma and the source region of a jet, a jet whose propagation in the corona and in the heliospheric medium will then be modeled to determine its composition in situ and whether it has reached 1 AU. All the methods and tools necessary for the thesis work have been developed with the Solar Orbiter mission (launched in February 2020) in mind. I have modeled the noise that we will obtain in the SPICE observations and I have provided three sets of spectral lines that could in principle be used to make composition measurements and that will be used to design optimal SPICE studies for abundance maps.

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