Abstract
SOLAR-C is a Japanese solar mission scheduled for launch in 2028. It carries an EUV spectrometer and slit jaw system, the EUVST, which will observe the Sun in four wavelength bands in the extreme ultraviolet part of the spectrum, while providing high spatial and temporal resolution, and a seamless temperature coverage of the solar atmosphere from the chromosphere to the corona. In this work, we investigate the EUVST observational capabilities for chromospheric lines within these wavelength bands. We estimate the total number of photons integrated over the lines that the EUVST instrument could observe for lines from neutral carbon, nitrogen, and oxygen, taking into account the estimated effective area of EUVST. We investigate the diagnostic power of the O I 1152 Å spectral line as a potential line that can be used to help understand the properties of the chromosphere. In addition, we study the O I 1039, 1040, and 1041 Å spectral line transitions, and give a comprehensive overview of the background processes that affect the continuum around the lines. The oxygen transitions are located within the planned observational wavelength range for the SOLAR-C (EUVST) mission. The lines are synthesized in non-local thermodynamic equilibrium while taking into account the effects of partial redistribution, and the properties of the lines are examined for a quiet Sun. Using a 1D semi-empirical atmospheric model, we investigate the optical thickness and estimate the height of formation for the lines. The results indicate that the O I 1152 line is optically thick with a formation that covers much of the chromosphere (from around 0.6 Mm to 1.9 Mm). However, the synthesized lines are weaker than what is observed, for which we found that a possible explanation could be a lack of coupling between energy levels in the oxygen atom.
Supervisor: Professor Mats Carlsson, Institute of Theoretical Astrophysics, UiO
Intern. assessor: Professor Boris V. Gudiksen, Institute of Theoretical Astrophysics, UiO
Extern. assessor: Senior Researcher Jaime de la Cruz Rodriguez, Stockholm University