eprintid: 10204482
rev_number: 15
eprint_status: archive
userid: 699
dir: disk0/10/20/44/82
datestamp: 2025-03-07 07:47:38
lastmod: 2025-03-07 07:47:38
status_changed: 2025-03-07 07:47:38
type: thesis
metadata_visibility: show
sword_depositor: 699
creators_name: Ho, Sze Kay Cynthia
title: Understanding Demographics of Small Close-in Exoplanets
ispublished: unpub
divisions: B04
divisions: C06
divisions: F60
divisions: F63
divisions: UCL
note: Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
abstract: Exoplanets (planets beyond our own Solar System) offer profound insights into Earth’s origin and dynamics. Over the past years, NASA has launched dedicated missions to search for and characterise exoplanets of various sizes around different types of stars using the transit detection method.

In this thesis, I perform a large-scale study of transiting small exoplanets that are close to their host stars, to better understand the formation and evolution mechanisms of planets. Using the vast amount of data collected by NASA space-based satellites such as \textit{Kepler} and \textit{TESS}, I fit planetary transits to understand the demographics of planetary sizes.

I analyse the 1-minute \textit{Kepler} light curves of over 500 small (planetary radii between 1 and 4 Earth radii), close-in (orbital period between 1 and 100 days) planets, the majority of which have not been previously homogeneously analysed in this way. I update the planetary parameters, revealing a deeper radius valley for FGK host stars compared to several other investigations, suggesting that planets are likely to have more homogeneous internal compositions at formation than was previously realised.

I also investigate the dependence of the radius valley with stellar mass. I observe that the radius valley becomes shallower towards lower mass stars. Upon rigorous statistical comparison, I find that theoretical planetary atmospheric mass-loss models underpredict the number of planets observed inside the radius valley for low-mass stars. I propose that this provides evidence for the presence of icy planets or collision events around low-mass stars.

Finally, I present some initial results on an occurrence rate study of small, close-in planets around different stellar types. I perform systematic planet searches on \textit{TESS} light curves using the box-fitting least-squares (BLS) method, and undergo vetting processes to identify true planetary candidates. This study will shed light on the underlying mechanisms of planetary formation and evolution.
date: 2025-02-28
date_type: published
oa_status: green
full_text_type: other
thesis_class: doctoral_open
thesis_award: Ph.D
language: eng
primo: open
primo_central: open_green
verified: verified_manual
elements_id: 2358863
lyricists_name: Ho, Sze Kay Cynthia
lyricists_id: SKCHO12
actors_name: Ho, Sze Kay Cynthia
actors_id: SKCHO12
actors_role: owner
full_text_status: public
pages: 258
institution: UCL (University College London)
department: Space and Climate Physics
thesis_type: Doctoral
citation:        Ho, Sze Kay Cynthia;      (2025)    Understanding Demographics of Small Close-in Exoplanets.                   Doctoral thesis  (Ph.D), UCL (University College London).     Green open access   
 
document_url: https://discovery.ucl.ac.uk/id/eprint/10204482/2/SKCH_PhD_Thesis_Final.pdf