Inferring atomic line parameters from solar spectra
by Dušan Vukadinović
Date of Examination:2024-01-23
Date of issue:2024-09-19
Advisor:Prof. Dr. Sami Solanki
Referee:Prof. Dr. Sami Solanki
Referee:Prof. Dr. Stefan Dreizler
Persistent Address:
http://dx.doi.org/10.53846/goediss-10672
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Abstract
English
The proximity of the Earth to the Sun offers a unique opportunity to study different plasma phenomena that occur in its atmosphere, which are unattainable in plasma laboratories. Advances in the instruments used for solar observations brought a wealth of high-quality, low-noise data that give insight into the dynamics of small scales (~70 km) in the solar atmosphere and its magnetic properties. Along with the developments in instrumentation, methods used to analyse these observations have also improved, allowing for more feasible inference of different physical parameters of the solar atmosphere, such as temperature, velocity and magnetic field. Concurrently, the solar atmosphere can also be used as an atomic physics laboratory to infer atomic parameters. Over many decades, the spatially averaged disc-centre quiet-sun spectrum has been used to infer the transition probability (also known as log(gf)) of many spectral lines, predominantly in the visible and infrared wavelengths. The advancement in this field was achieved with the pixel-by-pixel based inference of the log(gf) parameter from spatially resolved spectropolarimetric observations. In this thesis, I developed a new method called the coupled method, which infers spatially coupled atomic line parameters from high spatial and spectral resolution spectropolarimetric observations of the solar atmosphere. The coupling of atomic parameters across the observed field of view is a natural consequence of atomic parameters being independent of the underlying physical structure of the solar atmosphere. The coupled method simultaneously fits all observed spectra from a given field of view and infers the atmospheric and atomic parameters self-consistently. Part of this thesis is also dedicated to developing a new inversion code in which I have integrated the coupled method. The strength of the coupled method is in resolving the contribution of blended spectral lines and retrieving their log(gf) parameter and the central wavelength reliably. This result is achieved by coupling spectra emerging from atmospheres with very diverse thermodynamic and magnetic structures, such as those describing atmospheres of umbra, penumbra, granules and intergranular lanes. This result is essential for analysing near ultraviolet observations of the solar atmosphere, where spectral lines are severely blended. Many of these lines have poorly determined atomic parameters that impact the inference of atmospheric parameters from this spectral region. The coupled method is tested on spectra formed under the assumption of local thermodynamic equilibrium (LTE), where the populations of atomic levels are determined from the Boltzmann-Saha distribution. The method can be extended to infer other atomic parameters of lines formed under the assumption of LTE, such as the lower excitation level, abundance, Lande g-factors, and collisional broadening coefficients. However, it is also flexible enough to be applied to the non-LTE lines, for which the LTE assumption fails. The coupled method is applicable to spectral lines from the near ultraviolet to the infrared.
Keywords: spectropolarimetric inversion; solar physics; atomic parameters
