Searching the Entirety of Kepler Data New Exoplanets and Occurrence Rate Estimates by Michelle Kunimoto B.Sc., The University of British Columbia, 2016 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in The Faculty of Graduate and Postdoctoral Studies (Astronomy) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April 2020 c Michelle Kunimoto 2020 The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a dissertation entitled: Searching the Entirety of Kepler Data: New Exoplanets and Occurrence Rate Estimates submitted by Michelle Kunimoto in partial fulfillment of the require- ments for the degree of Doctor of Philosophy in Astronomy Examining Committee: Jaymie Matthews, Physics and Astronomy Supervisor Aaron Boley, Physics and Astronomy Supervisory Committee Member Brett Gladman, Physics and Astronomy University Examiner Ronald Clowes, Earth, Ocean and Atmospheric Sciences University Examiner Additional Supervisory Committee Members: Vesna Sossi, Physics and Astronomy Supervisory Committee Member Catherine Johnson, Earth, Ocean and Atmospheric Sciences Supervisory Committee Member ii Abstract First, I present the results of an independent search of all ∼200,000 stars observed over the four-year Kepler mission for multiplanet systems, using a three-transit minimum detection criteria to search orbital periods up to hundreds of days. My search returned 17 planet candidates in addition to thousands of known Kepler Objects of Interest (KOIs), with a 98.8% recovery rate of already confirmed planets. I highlight the discovery of one candidate, KIC-7340288 b, that is both rocky (radius ≤ 1:6RL) and in the habitable zone (insolation between 0:25 and 2:2 times the Earth's insolation). Another candidate is an addition to the already known KOI-4509 system. I also present adaptive optics imaging follow-up for six of my new candidates, two of which reveal a line-of-sight stellar companion within 400. Using my planet catalogue, I then present exoplanet occurrence rates estimated with approximate Bayesian computation for planets with radii between 0:5 and 16 RL and orbital periods between 0:78 and 400 days, or- biting FGK dwarf stars. I characterize the efficiency of planet recovery by both my search and vetting pipelines using injection/recovery tests, and ac- count for both planet radius uncertainty and the estimated false positive rate due to transit-like noise signals in the data, unlike the majority of previous works. By analyzing my FGK occurrence rates as well as those computed after separating F-, G-, and K-type stars, I explore dependencies on stel- lar effective temperature, planet radius, and orbital period. I reveal new characteristics of the photoevaporation-driven \radius gap" between ∼1.5 and 2 RL, indicating that the significant bimodal distribution previously revealed for P < 100 days only exists over a much narrower range of orbital periods, above which sub-Neptunes dominate and below which super-Earths dominate. Finally, I provide several estimates of the \eta-Earth" value | iii the frequency of potentially habitable, rocky planets orbiting Sun-like stars. For planets with sizes 0:75 − 1:5 RL orbiting in a conservatively defined habitable zone (0.99 - 1.70 AU) around G-type stars, my calculations place an upper limit (84.1th percentile) of < 0:18 planets per star. iv Lay Summary The discovery of thousands of planets outside of the Solar System over the past decade has revolutionized our understanding of planet diversity. By analyzing results from missions dedicated to finding new planets, invaluable information about planet formation and evolution can be uncovered. This dissertation makes contributions on both fronts. First, I present the results of my own planet search. I found 17 new planet candidates, including a rare small planet in the habitable zone | where liquid water could potentially exist on a rocky planet's surface. Then, I analyze the search results to estimate the commonality of different kinds of planets, and explore what this can tell us about current theories. I estimate that there is likely less than one potentially habitable planet for every five Sun-like stars. Determining this is one of the major goals of astronomy, with implications for the search for life elsewhere in the Universe. v Preface Chapter 3, which details my full independent search of Kepler data and its results, was adapted from a first-author paper published in The Astro- nomical Journal: Kunimoto, M., Matthews, J., & Ngo, H. 2020, Searching the Entirety of Kepler Data. I. 17 New Planet Candidates Including 1 Habitable Zone World, AJ, 159, 124. I wrote the paper, with co-authors providing valuable feedback on the manuscript. The development of the full pipeline from start to finish, the downloading, reduction, and search of the light curves for planets, the vetting of surviving candidates, the follow-up analysis, and the interpretation of the results, was done by me. Henry Ngo was the PI for the adaptive optics (AO) observations. He also wrote the technical justification for our telescope proposal, while I co-wrote the scien- tific justification. The observations themselves were obtained by staff at the Gemini North telescope in Hawaii. Dr. Ngo also helped me write my own AO data reduction scripts. In terms of resources used to perform the research described in this chap- ter, all Kepler data was downloaded from the Mikulski Archive for Space Telescopes (http://archive.stsci.edu/). Some of the codes I used for the data reduction and transit search were written by Jason Rowe. These are all publicly available as part of the Kepler Transit Model Codebase (https://github.com/jasonfrowe/Kepler). Specifically, I used kfitsread to convert the data into a readable file format and combine each star's light curve into a single file, detrend5 to detrend the light curves, and transitfind2 to search through the data for transit signals. For the vet- ting pipeline, the code for my first uniqueness test was written by Kelsey Hoffman (private communication), while I used Jeffrey Coughlin's Model Shift package (https://github.com/JeffLCoughlin/Model-Shift) for the vi second uniqueness test, the shape metric, significant secondary test, and second odd-even depth test. For the follow-up analysis of planet candi- dates, I used emcee (https://github.com/dfm/emcee) to perform Markov Chain Monte Carlo fitting of transit models to the data. The transit models themselves were adapted from code available from Ian's Astro-Python Codes (http://www.lpl.arizona.edu/∼ianc/python/). I used isochrones (https://github.com/timothydmorton/isochrones) to produce posteri- ors for stellar parameters. I also analyzed each transit with vespa (https://github.com/timothydmorton), which is a probabilistic valida- tion tool for transiting exoplanets. All other code was written by me (e.g. code for other candidacy tests not mentioned here, scripts for automating the search and vetting pipeline to run on thousands of light curves, etc.). Lastly, due to the computational time required to search each star suffi- ciently, I performed the majority of my work on the Orcinus and Cedar computing clusters, provided by WestGrid (www.westgrid.ca) and Com- pute Canada (www.computecanada.ca). Chapter 4, which details the use of my independent search results for exoplanet occurrence rate estimates, was adapted from a first-author paper accepted for publication in The Astronomical Journal: Kunimoto, M. & Matthews, J. 2020, Searching the Entirety of Kepler Data. II. Occurrence Rate Estimates for FGK Stars. I wrote the paper, and performed the full occurrence rate estimates, analysis, and interpretation of the results. My co-author provided feedback on the manuscript. In terms of resources, I used cosmoabc (https:/github.com/ COINtoolbox/CosmoABC) to implement approximate Bayesian computation (ABC) in my occurrence rate estimates, and emcee to perform Markov Chain Monte Carlo fitting of power law-based functions to my occurrence rates as a function of orbital period. All other code was written by me (e.g. the exoplanet population simulator/forward model, scripts for automating the calculation of occurrence rates with different inputs, etc.). Lastly, due to the computational time required to compute ABC occurrence rates, I used the Graham Compute Canada cluster. Chapter 2 describes the motivation behind my research, and Chapter 5 vii concludes my results and summarizes their significance. These were each partially adapted from the Introduction and Conclusion sections of the two papers discussed previously. viii Table of Contents Abstract ................................. iii Lay Summary ..............................v Preface .................................. vi Table of Contents ............................ ix List of Tables .............................. xiii List of Figures .............................. xvi List of Symbols ............................. xxii List of Abbreviations .........................xxiii Acknowledgements ........................... xxiv 1 Introduction .............................1 1.1 Exoplanet Detection Techniques . .3 1.1.1 Pulsar Timing Variations . .3 1.1.2 Radial Velocity . .4 1.1.3 The Transit Method . .6 1.1.4 Microlensing . 10 1.1.5 Direct Imaging . 11 1.2 Confirmation of Transiting Exoplanets . 12 1.2.1 False Positives . 12 1.2.2 Follow-Up Observations and Validation . 16 ix 1.3 Exploring Exoplanet Populations . 19 1.3.1 Survey Selection Effects . 21 1.3.2 Occurrence Rate Methodologies . 22 1.4 The Habitable Zone . 28 2 Motivations for this Thesis .................... 31 2.1 An Independent Search of Kepler Data . 31 2.2 Occurrence Rate Estimates . 32 3 An Independent Search of Kepler Data ............ 36 3.1 Chapter Outline . 36 3.2 Planet Detection Pipeline . 36 3.2.1 Preparing the Light Curves . 36 3.2.2 Searching for Transiting Planets . 38 3.2.3 Initial Vetting and Identification of Transit Candi- dates . 39 3.3 Vetting Pipeline . 42 3.3.1 Choice of Candidacy Test Thresholds . 42 3.3.2 Transit Model Fitting . 43 3.3.3 Candidacy Tests Against Noise False Positives . 44 3.3.4 Candidacy Tests Against Eclipsing Binary False Pos- itives .