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LIAM EDWARDS

Solar Physics Postgraduate Researcher


Research


Postgraduate

Primary PhD Supervisor: Dr. Huw Morgan

Secondary PhD Supervisor: Dr. Matt Gunn

Rotation of the Solar Corona

The nature of the rotation of the Sun’s outer atmosphere – the corona – is not very well understood. Some studies state that the corona rotates as a rigid body, whereas others point towards a rotation which varies as a function of both latitude and height above the solar surface. This is partly due to the fact that, unlike the solar surface (photosphere) which has many prominent features that vary dynamically over time, the solar corona lacks features prominent enough to perform a sufficiently accurate tracking method to determine its rotation.

One method of determining this coronal rotation is by tracking coronal features using full-disk images of the Sun taken by satellites such as the Solar Dynamics Observatory (SDO), Yohkoh, and Hinode. My research focuses on using 3D density maps gained by tomography of the solar corona produced by Dr. Huw Morgan - Morgan (2019). These maps range from 4 – 8 solar radii above the Sun and cover around 12 years from 2007 – 2019. They provide a unique window of the coronal structure and its evolution over long time periods. The aim of my research is to track high density features (streamers) in these density maps and determine their rotation rate. Findings will have an impact on solar wind forecasting at Earth (the rotation rate is a fundamental parameter for forecasting) and understanding the magnetic connection between the photosphere and extended corona.

White-light Polarisation Imagery of the 2020 Total Solar Eclipse

Total solar eclipses provide a unique - albeit temporary - window into the lower corona. Normally, researchers use coronagraphs, such as the Large Angle Spectrometric Coronagraph (LASCO), to observe the solar corona. A coronagraph is an observing instrument with an occulting disk which blocks the bright disk of the Sun, allowing the fainter corona to shine out behind it. However, the issue with coronagraphs lies in the fundamental nature of electromagnetic waves and how they scatter off the limb of the occulting disk and are therefore detected by the instrument as stray light. Consequently, the very lower part of the corona is difficult to observe in this way. This is where the perfect cosmic coincidence of a total solar eclipse comes into play. Since the Moon is 400 times smaller than the Sun, and the Sun happens to be 400 times further away from the Earth than the Moon, the lunar and solar disks, therefore, appear the same size in the sky to an observer on Earth – a perfect occulting disk!

One of the important physical parameters to determine when studying the solar corona is the electron density. This can be determined by taking white-light polarisation images of the corona during totality of a total solar eclipse. Various image processing techniques can then be used to bring out as much information in the images as possible, followed by an inversion technique, originally developed in the 1950’s, can be used to determine the electron density from the brightness of these polarised images. I am part of the team which sent an instrument - the Coronal Imaging Polariser (CIP) - to the total solar eclipse which occured on December 14th 2020 in South America. The instrument was named CIP since, in Welsh, to take a "cip" at something is to take a quick look - fitting since totality during a total solar eclipse typically only lasts a few minutes!

CIP
Coronal Imaging Polariser (CIP) - consisting of a DSLR lens (left), Thorlabs Rotation Mount and polariser (middle), and the Atik Horizon II CMOS camera (right)

Undergraduate

Fourth Year (MPhys) Project

Transmission Spectroscopy of Exoplanets

Project Supervisor: Dr. Maire Gorman

The aims of this project were to investigate the effect that various physical parameters, such as planetary mass, radius, and composition had on an exoplanet's transmission spectrum and, secondly, to assess the detectability of phosphine in exoplanetary atmospheres. Three different open-source software were used to carry out this investigation. Firstly, Exo-Transmit was used to produce simulated transmission spectra for hypothetical exoplanets. The second software used was PLATON which is a more accurate and faster alternative to Exo-Transmit. PLATON was also used to produce simulated transmission spectra for specific exoplanets - both hypothetical and observed. The final software used was PandExo which was used to simulate observational data for the upcoming James Webb Space Telescope and to match the simulated output to a transmission spectrum produced using PLATON.

PandExo
Transmission spectrum for the exoplanet HD 189733 b using PLATON and PandExo to simulate the transmission spectrum and a simulation of JWST observational data, respectively.

Third Year Project

A multi-wavelength study of the Sun

Project Supervisor: Dr. Huw Morgan

The aim of this project was two-fold: to gain a sufficient level of proficiency in SolarSoftware (SSW) so as to be able to present SDO/AIA data (taken in different ultraviolet wavelengths) in different ways, and to obtain temperature estimates using differential emission measure (DEM) analysis for an active region. This project made use of SolarSoftware (SSW) in Interactive Data Language (IDL) to plot these ultraviolet images of the Sun in multiple wavelengths and achieve an accurate estimate for the temperature of an active region by the use of DEM analysis. It also used ImageJ (FIJI) in a minor capacity.

DEM
Average emission differential emission measure (DEM) of active region AR 11158 using SDO/AIA observational data in the extreme ultraviolet.