Planetary systems unlike the solar system

Dransfield, Georgina ORCID: 0000-0002-3937-630X (2024). Planetary systems unlike the solar system. University of Birmingham. Ph.D.

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Abstract

In the field of Exoplanetology, there is palpable excitement about the new era we have now entered: the era of in-depth atmospheric and orbital characterisation with a new generation of observatories. In space, these include the recently launched JWST, soon to be joined by Ariel, as well as the upcoming Extremely Large Telescopes (ELTs) on the ground. Such is the furor, that it might appear the remaining Big Unanswered Questions in the field could all be addressed simply by learning more about the existing planet sample. In this thesis, I seek to show that this is not the case.

The scene is set in Chapter 1, where I introduce the science of exoplanet detection and discovery. In this work, I focus primarily on detection using the transit method, so this technique is explored in the most detail. Discovering new planets via transit photometry requires access to telescopes blindly surveying the night sky, and I describe the main instruments used in this work (the space telescope TESS, ASTEP in Antarctica, and SPECULOOS in Chile, Spain and Mexico), as well as those with historical significance for the field. Finally, I describe some of the aforementioned Big Unanswered Questions that require ongoing active discovery efforts if they are to be settled.

Chapter 2 contains a detailed description of the methods used throughout this thesis. When going about the business of discovering new planets, there is a process that runs almost chronologically, provided there are no hiccups encountered along the way (which is rarely the case). I lay out the now well-choreographed progression from initial signal detection, through reduction of photometric observations and global Bayesian analysis, to the ways of checking if more can be learned about the new system. In this Chapter I also present the first paper of the thesis, which describes the scheduling systems and new automatic photometric analysis pipeline I produced for ASTEP.

The third chapter contains the first planet discoveries of the thesis. In the game of TESS follow-up, there is a distinction to be made between planet confirmations and validations. Here I introduce the second paper of my thesis, which presents the confirmation of a three-planet system orbiting the Solar-like star, HD~28109. These three transiting planets have radii $R_{\rm b}=2.199_{-0.10}^{+0.098}\rm ~R_{\oplus}$, $R_{\rm c}=4.23\pm0.11~\rm R_{\oplus}$ and $R_{\rm d}=3.25\pm0.11\rm~R_{\oplus}$, and the outer two present large transit timing variations. This system is swiftly followed by my third published paper, a validation of a $R_{\rm b}=1.55\pm 0.06\rm~R_{\oplus}$ planet in the habitable zone of its M-dwarf host, TOI-715. There is a lot to learn still about both systems, leaving large scope for future work. I additionally present a Work in Progress in Chapter 3: the now-validated AMY-1 system, consisting of at least one planet orbiting a mid M-dwarf.

In Chapter 4, I introduce an observation programme I have been leading within SPECULOOS for just over a year: MANGOs. MANGOs is an ambitious project of discovery, seeking out new giant objects (planets, Brown Dwarfs and M-dwarfs) orbiting low-mass stars, and I set out our goals and motivations. The project is still young, but the first paper in the series is already submitted and another is in the early preparatory stages. I present our submitted paper (on which I am second author) containing the confirmation of a short-period giant planet orbiting TOI-4860, followed by the Work in Progress of our second paper (to be led by me), which will include eight newly discovered MANGOs systems.

Chapter 5 is my concluding chapter. I summarise the impact of my thesis, and return to some of the Big Unanswered Questions from Chapter 1 to assess whether we are any closer to resolutions. I also describe some future avenues for continued investigation of some of the systems introduced in this thesis.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):