Keegan Thomson-Paressant

Astronomy PhD Student

Welcome to my page! My name is Keegan, and I'm a recently graduated Masters student from Leiden University. I have dual French-Australian citizenship, and am fluent in both languages. I completed my undergraduate diploma at the Australian National University (Australia), specialising in Astronomy and Astrophysics, before moving on to complete a Masters degree in Astronomy research at Leiden University (Netherlands).

I specialise in exoplanetary astronomy, particularly in the analysis of transit spectroscopy. To this end, I have completed two separate research projects in this area, one working with Kepler K2 data proving its continued viability as an exoplanet-detecting instrument, and another comparing TESS lightcurves with those retrieved from MASCARA, a set of ground-based observatories, to determine the latter's abilities as a follow-up tool for current and future observations.

I am currently studying a PhD at the Paris Observatory working with Dr. Coralie Neiner, studying the magnetic fields around Delta Scuti stars. We are using spectropolarimetric data from NeoNarval and ESPaDOnS to characterise and model the field, as well as its structure at the surface, and speculate as to its origin.
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Programming Skills

Comfortable working with Python, with intermediate knowledge in CASA, Miriad and Java. Currently learning C++ in my free time.

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Spoken Languages

Fluent in English and French, with conversational skills in both Italian and Spanish.

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Others

Experienced in working with LaTeX for article preparation, as well as Matlab and Mathematica input for computation and graphing purposes. I also have some experience with SQL and Github.

 

Bachelor of Science, ANU

Graduated from the Australian National University, Australia, with a Bachelor of Science, Major in Physics, Specialising in Astronomy and Astrophysics.

Learn More01/06/2017
 

Masters in Astronomy Research, Leiden University

Graduated from Leiden University, Netherlands, with a Masters degree in Astronomy Research.

Learn More24/09/2019
 

Internship, Paris Observatory.

Observation of magnetic fields in O, B and A-type stars.

Learn More05/10/2019
 

PhD, Paris Observatory

Spectropolarimetric analysis of magnetic Delta Scuti stars, aiming at characterising their magnetic fields, modelling their surface structure, and hypothesising their origin.

Learn More01/09/2020
 

1-year Studentship, European Southern Observatory - Garching

High resolution differential astronomy of Alpha Centauri system to search for exoplanets, using interferometric data taken using VLTI/GRAVITY.

Learn More01/09/2021

Searching for Hot Jupiters with Kepler K2 - Fall 2015

Supervisor: Prof. Michael Ireland, Australian National University

During this short, 6 month research project, a colleague and I worked with M. Ireland to determine the continued viability of the Kepler satellite for detecting exoplanets after having broken two of its reaction wheels. Labelled the Kepler K2 mission, we used a number of programming and transit spectroscopy skills to generate a new data reduction pipeline for the K2 data. The easiest targets to detect were Hot Jupiters, large planets orbiting in very close proximity to their parent star, due to their significant transit depths and short orbital period. The team proposed a number of candidates requiring follow-up radial velocity observations.


Hydrogen and Carbon Radio Recombination Lines in the W3 Starforming Region - 2017/2018

Supervisors: Prof. Alexander Tielens, Leiden University, Dr. Raymond Oonk, Leiden University

Under the tutelage of my supervisors, we observed the W3 starforming region at 1.4 GHz using the APERTIF upgrade on the Westerbork Synthesis Radio Telescope. The goal was to analyse the hydrogen and carbon emission coming from the W3 complex on both large and small scales. To this end, a full data reduction suite was performed on the APERTIF radio data to uncover the recombination lines hidden within. Once completed the results could be compared with past work, such as that of the Effelsberg-Bonn HI Survey (EBHIS), to determine the distribution of the emission. It was determined that there is quite a significant disparity in what was observed by APERTIF on small scales, revealing the existence of quite a complex region, versus what EBHIS saw in the broader picture. 


Detecting Exoplanets with TESS and MASCARA - 2018/2019

Supervisors: Prof. Ignas Snellen, Leiden University, Dr. Aurélien Wyttenbach, Leiden University

With the Transiting Exoplanet Survey Satellite (TESS) having recently come out of beta testing, there were already quite a number of potential transiting exoplanet candidates requiring follow-up observations. It was this hole that the Multi-site All-Sky CAmeRA (MASCARA) hoped to fill. The project was split into two sections, with my colleague R. Wang performing follow-ups of candidates brighter than apparent magnitude of 8.4 (the theoretical limit of MASCARA), and myself following up targets between 8.4 and about 10 apparent magnitude. Using the accurate TESS information as a guide, data reduction processes were performed on the MASCARA data to recover the transit signal seen by TESS. Simulations of 10,000 transits were also performed, in order to calculate theoretical limits of the MASCARA instrument within our magnitude range and determine a family of "ideal" candidates for future follow-up observations.


Magneto-asteroseismology in Delta Scuti Variable Stars - 2020/present

Supervisor: Dr. Coralie Neiner, Paris Observatory

Delta Scuti stars (δ Sct) are intermediate mass stars that present pulsations and brightness variations lasting anywhere from a few minutes to several hours. To date, only a handful of these stars have been shown to host magnetic fields, and amongst them their characteristics vary greatly. While it isn't entirely clear how the magnetic fields interact with the pulsations, what is certain is that there appears to be an underrepresentation of magnetic candidates within this family of stars. While about 10% of typical intermediate mass stars present some kind of magnetic field, the percentage for δ Sct stars appears to be well below that, which begs the question of why that might be. 

We perform spectropolarimetric analysis on a sample of these stars, using data from the NeoNarval (TBL) and ESPaDOnS (CFHT) instruments, in an attempt to identify additional magnetic candidates, characterise their magnetic fields, model their field structure at the surface, and finally theorise as to their origin. Once a reasonably-sized sample is achieved, we will be better equipped to infer potential hypotheses as to the representation of magnetic fields within this family of stars.


Searching for Exoplanets in Alpha Centauri using GRAVITY - 2021/2022

Supervisor: Dr. Antoine Mérand, ESO Garching

The Alpha Centauri (α Cen) system is composed of three stars: 2 Sun-like stars (α Cen A and B) in a binary pair and an M-dwarf (Proxima Cen) that orbits the pair at some distance. At the time of the project, 3 exoplanets had been confirmed around Proxima, though none yet had been detected around the A or B components. Studies suggest that stable orbits exist around either star, including their theoretical habitable zones. Combining this with the fact that they are the closest stars to Earth, as well as potential analogs to our own Solar System, make them appealing targets for exoplanetary investigation. 

With this in mind we performed high resolution differential astrometry on the pair, using the GRAVITY instrument operating on the Very Large Telescope Interferometer (VLTI) in Chile, and measuring the minute deviations from their expected orbits that would result from hidden mass within the system, such as a planet orbiting one of the stars. Between the proximity of the α Cen system to our own, combined with the fact that GRAVITY wasn't originally designed to observe this type of object, resulted in us being required to resolve a number of unique challenges in order to properly exploit the data and achieve the precision required to detect exoplanets.

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