Dissertation

The Search for Circumbinary Exoplanets with the Bebop Radial Velocity Survey

Standing, Matthew R

2022

Overview

This thesis is about the field of exoplanets, with a particular focus on the search for circumbinary exoplanets with Radial Velocity (RV) observations. Chapter 1 introduces the field of exoplanet science, provides an overview of relevant techniques for exoplanet detection, discusses what we have learnt about exoplanets through their demographics, and provides background information on circumbinary exoplanets. Chapter 2 covers the data analysis techniques that were utilised in this work. It introduces Bayesian statistics and nested sampling, explains the Kima package used to fit Keplerian signals to RV data in this work, best practises in its use, and how planetary parameters are obtained through this analysis. Chapter 3 describes my contribution to the analysis of the RV data for the star HD-16417 (λ²) Fornacis) and includes the full paper. In this work we constrain the parameters of a known planet host star, and in turn update the planet's parameters. Chapter 4 provides a detailed description of the Binaries Escorted By Orbiting Planets (BEBOP) survey, the main topic of work in this thesis. Previous attempts to discover circumbinary planets with RV observations are discussed, before describing how the BEBOP survey is carried out. In Section 4.3, I present my work on the calculation of detection limits for the BEBOP survey, along with the calculation of circumbinary planet occurrence rates, and present some preliminary candidate circumbinary signals. I find the BEBOP survey is sensitive to planets with masses down to that of Saturn and Neptune, and that our circumbinary planet occurrence rates agree with those from other works, including those of gas giants around single stars. Chapter 5 details the detection of the first circumbinary planet with ground-based RV observations, along with my contributions to this work. We are able to independently detect the circumbinary planet Kepler-16b, confirm its orbital parameters, and place constraints on the presence of additional planets in the system. In Chapter 6, I describe the first discovery of a circumbinary planet with RV observations alone, BEBOP-1c. This second planet in the system has a mass of 0.2 M_J and an orbital period of 215 days. We are also able to place an upper limit on the smaller inner transiting planet's mass at 23.6 M_⊕ with 99% confidence. In this chapter I also describe an attempt to view the signal of the secondary star in the binary star system. Finally, in Chapter 7, I describe additional contributions I have made to other bodies of work during my PhD, and conclude the thesis while discussing future avenues of work to increase our sensitivity to circumbinary planets with RV observations.

• Publisher: ProQuest Dissertations & Theses