Diagnostics of the thermodynamic properties of solar prominences

Peat, Aaron William (2023) Diagnostics of the thermodynamic properties of solar prominences. PhD thesis, University of Glasgow.

Abstract

Solar prominences have been observed for years, with observations dating back to the 12th century. Only in recent history however, have we had the spectroscopic tools required to probe and understand their structure and dynamics. Even then, with ground bases observations we have been unable to observe the hottest parts of solar prominences due to the atmosphere which cruelly hides this ultraviolet radiation from us. Several observational satellites have been launched over the years so that we may observe these high temperatures. With the launch of the Interface Region and Imaging Telescope (IRIS), we were able to observe the Mg II h&k lines. Which gives us a unique view into the atmosphere surrounding solar prominences.

In Chap 1, we give a brief overview of the solar atmosphere and what we know about the life and evolution of solar prominences. We cover their morphology, typical thermodynamic parameters, velocity distributions, and surrounding magnetic field strength. This is followed by a brief aside into radiative transfer where the basic equations are outlined with the LTE solution for radiative transfer through some emitting material. The principle ion in this work, Mg II h&k, is also presented with mention of its key features. The instrumentation used in the study are then introduced; IRIS, the X-Ray Telescope (XRT) onboard Hinode, Atmospheric Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO), and the Sun-Earth Connection Coronal and Heliospheric Imager (SECCHI) onboard the Solar Terrestrial Relations Observatory Ahead (STEREO-A).

In Chap 2, we cover the coordinated observation of a solar prominence on the 19 April 2018 by IRIS, AIA, and XRT.We show the distribution of the following statistical measures of the prominence, the integrated line intensity, Doppler velocity, line widths, and asymmetries using the quantile method. We also present the distribution of line profile types, whether they be singe, double, or complexly peaked. A method for filtering out coronal pixels using the line widths, peak intensities, and pixel connectivity is presented and shown to work to effectively isolate the prominence. We draw conclusions surrounding its observed dynamics and the relationships between its statistical measures.

Chap 3 sees the introduction of a new method used to ascertain the properties of solar prominences observed in Mg II h&k. This is achieved by the point-for-point comparison of 1007 line profiles generated by the 1D non-local thermodynamic equilibrium (NLTE) radiative transfer code, PROM, with that of the observations. PROM treats its resonance lines in PRD and allows us to generate the Mg II h&k line profiles, with the three Mg II triplet lines and the principle Hydrogen lines, which are not used in this method. This matching method is named rRMS. Not only do we find the best fitting profiles in our bank, but we also find some measure of the ‘goodness’ of these fits. Therefore we can set a cut-off for what is considered a good or a bad fit. This is the first time a prominence has been inverted in this way. An updated version of rRMS called xRMS is then presented. It demonstrates a significant computational improvement over rRMS, allowing us to use a larger grid of 23940 line profiles. We present both of these results and compare what is found for the smaller and bigger grids. While both achieve similar levels of successful fits, the parameters which they recover are not exactly the same.

Chap 4 introduces the radiative transfer code RTCY. It is a 2D cylindrical radiative transfer code. With which we are able to simulate an array of geometric configurations and velocity fields. As such, we explore the effect that these velocities have on line formation through the use of plots similar to that of Figs 4 through 7 of (Carlsson & Stein 1997). The most interesting result is that of the expanding velocity field where the prominence moves radially away from the axis of rotational symmetry of the cylinder. Following this, we explore multithread simulations where we stack these cylinders behind each other. We see how this affects the observed line profiles and how adding random line-of-sight velocities produces interesting asymmetries. In addition to the latter, the spectral and spatial point spread function (PSF) of the IRIS spectrograph is convolved with our final profiles demonstrating what IRIS would see if presented with these profiles. Finally to close the chapter, we perform a manual multithread forward fit.

In Chap 5, we explore the formation of a coronal bright point (CBP) due to flux emergence and the associated filament channel of this emergence. Using Fourier Local Correlation tracking on HMI intensity images, we are able to recover the overall global velocity vectors of magnetic patches predict their global movement. The flows of these patches are seen to influence the stability of a minifilaments which form in the filament channel. These minifilaments are both seen to erupt when certain magnetic phenomena, such as flux cancellation occur.

Chap 6 offers our conclusions where we outline the main results found and present our plans for future work.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QB Astronomy
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Labrosse, Dr. Nicolas
• Date of Award: 2023
• Depositing User: Theses Team
• Unique ID: glathesis:2023-83360
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 13 Jan 2023 14:15
• Last Modified: 13 Jan 2023 14:58
• Thesis DOI: 10.5525/gla.thesis.83360
• URI: https://theses.gla.ac.uk/id/eprint/83360