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Stellar Death in the Nearby Universe

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Stellar Death in the Nearby Universe Stellar Death in the Nearby Universe DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Thomas Warren-Son Holoien Graduate Program in Astronomy The Ohio State University 2017 Dissertation Committee: Professor Krzysztof Z. Stanek, Advisor Professor Christopher S. Kochanek, Co-Advisor Professor Todd A. Thompson Copyright by Thomas Warren-Son Holoien 2017 Abstract The night sky is replete with transient and variable events that help shape our universe. The violent, explosive deaths of stars represent some of the most energetic of these events, as a single star is able to outshine billions during its final moments. Aside from imparting significant energy into their host environments, stellar deaths are also responsible for seeding heavy elements into the universe, regulating star formation in their host galaxies, and affecting the evolution of supermassive black holes at the centers of their host galaxies. The large amount of energy output during these events allows them to be seen from billions of lightyears away, making them useful observational probes of physical processes important to many fields of astronomy. In this dissertation I present a series of observational studies of two classes of transients associated with the deaths of stars in the nearby universe: tidal disruption events (TDEs) and supernovae (SNe). Discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN), the objects I discuss were all bright and nearby, and were subject to extensive follow-up observational campaigns. In the first three studies, I present observational data and theoretical models of ASASSN-14ae, ASASSN-14li, and ASASSN-15oi, three TDEs discovered by ASAS-SN and three ii of the most well-studied TDEs ever discovered. Next I present the discovery of ASASSN-13co, an SN that does not conform to the traditional model of Type II SNe. Finally, I discuss the full sample of bright SNe discovered from 2014 May 1 through 2016 December 31, which is significantly less biased than previous nearby SN samples due to the ASAS-SN survey approach, and perform statistical analyses on this population that will be used for future studies of nearby SNe and their hosts. iii Dedication To my grandfather, Warren Dean Chinn, who would have loved to read this. iv Acknowledgments My unorthodox path to writing this dissertation would not have been possible without the support, kindness, friendship, and guidance of many individuals. While I am only able to name a few of them here, I am grateful to all the others who have been instrumental to my success throughout my life. I would first like to thank my Ph.D. advisor, Kris Stanek, for his lessons about life and science during the course of my graduate studies. Kris taught me that when it comes to science, “keep it simple, stupid,” and “perfect is the enemy of the good” are invaluable words to live by, and I would not have achieved nearly the same level of success without his guidance and encouragement. Kris was always available but never overbearing, was extremely accommodating to my living situation, and always had a joke ready to lighten the mood when I was bogged down by research. It has been a privilege to work with Kris, and I am proud to be one of his students. I am thankful to Chris Kochanek for being available and able to answer any questions I had about science, ASAS-SN, or pretty much anything else during my four years at Ohio State. Chris never failed to provide feedback on paper drafts within 24 hours of receiving them, and he has helped me improve my academic v writing more than anyone. If I can emulate even a fraction of his dedication and discipline in my own career, I know I will be successful. I am grateful to Todd Thompson for showing me how to approach learning new material in a way that allows me to more efficiently remember the most important facts. Todd’s ability to discuss any field of astronomy at an order-of-magnitude level is truly impressive, and his example has inspired me to improve the breadth of my knowledge. Todd was also an extremely effective spokesperson for the department in the year I applied to Ohio State, and I would not be here without his influence. I thank my undergraduate advisor, Saurabh Jha, for giving me my first research experience and for encouraging me to apply to OSU for graduate school. I also thank Risa Weschler and Phil Marshall for advising me during my summer at SLAC. Ben Shappee has been both a good friend and a mentor to me since I came to Ohio State, and I appreciate his quick acceptance of my joining the ASAS-SN team. I hope I can continue to (literally) follow in his career footsteps in the future. Jose Prieto has also been an important mentor to me, and I am grateful for his help with data analysis and his guidance on navigating my graduate career. Jon Brown has been both a great friend at Ohio State and my office mate for three years, and I thank him for providing insightful conversation, lightening the mood, and helping to handle the day-to-day work of ASAS-SN. I am also grateful to the many others who work on ASAS-SN, without whom the survey would not be nearly as successful. vi I thank the entire OSU Department of Astronomy for fostering an environment where science is held in high regard, collaboration is encouraged, and graduate students are valued both for their opinions and as people. I am thankful to the OSU Graduate School, the Center for Cosmology and AstroParticle Physics, and the US Department of Energy for financial support over the past four years. I would like to close by thanking those whose support and love have impacted my life the most: my family. Mom, thank you for being there for me no matter what, and for always pushing me to do my best. Dad, you showed me how amazing this Universe is when we looked at the skies together. Thank you for inspiring me and showing me how to enjoy life. Peter, thank you for providing me with laughter, friendship, and countless nicknames over the last 26 years. Melani, thank you for being the big sister I never had. Nana and Grandad, you provided me with the financial freedom to pursue a career in astronomy and you have been my most vocal cheerleaders throughout my life. I cannot thank you enough. Son family, thank you for accepting me into your family and supporting me like one of your own. To my extended family: I love you all and could not have asked for better relatives. Most importantly, Deborah: you are the most loving, supportive, and kind person I know, and I never would have reached this point without you. You have made me a better scientist and a better person, and I will always be striving to be worthy of you. Finally, I thank God, without whom the wonders of this Universe would not exist, for guiding me down the long and winding path that led me here. vii Vita June 2, 1986 ................... Born – Stanford, CA, USA B.A., East Asian Studies, Stanford University, 2008............................ Stanford, CA, USA SAS Excellence Award, Class of 1925 Scholarship, 2013 ........................... Rutgers University, New Brunswick, NJ, USA B.S., Astrophysics, Rutgers University, 2013 ........................... New Brunswick, NJ, USA Center for Cosmology and AstroParticle Physics 2013 ........................... Early Start Award, Columbus, OH, USA University Fellow for Graduate Studies, 2013 ........................... The Ohio State University, Columbus, OH, USA US Department of Energy 2014 – 2017 .................... Computational Science Graduate Fellow M.S., Astronomy, The Ohio State University, 2016 ........................... Columbus, OH, USA Allan Markowitz Award in Observational Astronomy, 2017 ........................... The Ohio State University, Columbus, OH, USA viii Publications Research Publications 1. T. W.-S. Holoien, et al., “The ASAS-SN Bright Supernova Catalog – III. 2016”, arXiv:1704.02320, (2017). 2. T. W.-S. Holoien, P. J. Marshall, and R. H. Wechsler, “EmpiriciSN: Re- Sampling Observed Supernova/Host Galaxy Populations Using an XD Gaussian Mixture Model”, AJ, 153, 249, (2017). 3. T. W.-S. Holoien, et al., “The ASAS-SN Bright Supernova Catalog – II. 2015”, MNRAS, 467, 1098, (2017). 4. T. W.-S. Holoien, et al., “The ASAS-SN Bright Supernova Catalog – I. 2013 − 2014”, MNRAS, 464, 2672, (2017). 5. T. W.-S. Holoien, et al., “ASASSN-15oi: A Rapidly Evolving, Luminous Tidal Disruption Event at 216 Mpc”, MNRAS, 463, 3813, (2016). 6. T. W.-S. Holoien, et al., “Discovery and Observations of the Unusually Luminous Type-Defying Type II-P/II-L Supernova ASASSN-13co”, Acta Astronom- ica, 66, 219, (2016). 7. T. W.-S. Holoien, et al., “Six Months of Multi-Wavelength Follow-up of the Tidal Disruption Candidate ASASSN-14li and Implied TDE Rates from ASAS-SN”, MNRAS, 455, 2918, (2016). 8. T. W.-S. Holoien, et al., “ASASSN-14ae: A Tidal Disruption Event at 200 Mpc”, MNRAS, 445, 3263, (2014). 9. T. W.-S. Holoien, et al., “Discovery and Observations of ASASSN-13db, an EX Lupi-Type Accretion Event on a Low-Mass T Tauri Star”, ApJL, 785L, 35, (2014). 10. S. Mathur, et al., “Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the UV anomaly in NGC 5548 with X-Ray Spec- troscopy”, arXiv:1704.06345, (2017). 11. J. S. Brown, T. W.-S. Holoien, et al., “The Ultraviolet Spectroscopic Evolution of the Low-Luminosity Tidal Disruption Event iPTF16fnl”, arXiv:1704.02321, (2017). ix 12. M. G. Aartsen, et al. (incl. T. W.-S. Holoien), “Multiwavelength Follow-up of a Rare IceCube Neutrino Multiplet”, arXiv:1702.06131, (2017).
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