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Fundamental Properties of White Dwarfs Alone and in Binaries

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Fundamental Properties of White Dwarfs Alone and in Binaries FUNDAMENTAL PROPERTIES OF WHITE DWARFS ALONE AND IN BINARIES Joshua Thomas Fuchs A dissertation submitted to the faculty at the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics and Astronomy. Chapel Hill 2017 Approved by: J. Christopher Clemens Dean M. Townsley Daniel E. Reichart Arthur E. Champagne Nicholas M. Law ○c 2017 Joshua Thomas Fuchs ALL RIGHTS RESERVED ii ABSTRACT Joshua Thomas Fuchs: FUNDAMENTAL PROPERTIES OF WHITE DWARFS ALONE AND IN BINARIES. (Under the direction of J. Christopher Clemens.) White dwarfs are physically simple and numerous. Their properties provide insight into stellar evolution and have applications to many astrophysical questions. In this dissertation, we present new measurements of white dwarf properties in two environments that help further our knowledge of the structure and evolution of white dwarfs. We have undertaken a series of observations that enable the measurement of fundamental parameters of the white dwarf in two magnetic cataclysmic variables. We have chosen these particular systems because the lack of accretion disk and fortunate geometry leading to eclipses makes it possible to observe and characterize the white dwarf. In one system, we confirm that LSQ1725-64 is a magnetic cataclysmic variable by esti- mating the magnetic field strength of the white dwarf from Zeeman splitting. We measure the effective temperature of the white dwarf and the spectral type of the secondary star from spectroscopy during a state of low accretion. Our precise eclipse measurements allow us to estimate the white dwarf mass and other binary parameters of LSQ1725-64. The spectral type and color of the secondary, as well as the eclipse length, are consistent with other sec- ondaries that have not yet evolved through the period minimum expected for cataclysmic variables. In CTCV1928-50, we detect H α emission from the heated face of the secondary that we use to measure the radial velocity amplitude of the secondary star. We combine this with previous measurements to estimate a white dwarf mass and other binary parameters. Our measurements in these two systems add to a limited number of measured white dwarf parameters in magnetic cataclysmic variables. iii We have also completed a spectroscopic survey of pulsating, hydrogen-dominated atmo- sphere white dwarfs. These pulsations have long offered the promise to conduct seismology of white dwarfs to understand their internal structure and composition. We have spectroscopically observed 122 DA white dwarfs that are either pulsating or close to the DA instability strip. We estimate Teff and log g for each white dwarf from the shape of the Balmer line profiles. These parameters provide important initial constraints for both absolute and relative seismology. We have completed a careful study of ten systematics involved in the determination of Teff and log g. Understanding and limiting these systematics has permitted us to obtain the most systematically consistent set of atmospheric parameters ever determined. This work will feed efforts to study and understand pulsating white dwarfs as a whole class instead of individually. iv ACKNOWLEDGMENTS The past six years have been a journey. Like any journey, there have been moments of triumph and joy, as well as moments of discouragement and uncertainty. Perseverance has been required, and there have been numerous people and groups that have supported and encouraged me along the way. They have helped celebrate the triumphs and provided encouragement through the moments of uncertainty. I am thankful for the guidance and support of my advisor, Chris Clemens. In addition to the technical aspects I have learned from him, he has modeled a wonderful approach to being a scientist. His persistence in avoiding dogmatic views and his quest for deeper understanding are two of the qualities I most admire, and I hope I have acquired. Darragh O'Donoghue is responsible for originally piquing my interest in magnetic cata- clysmic variables. I am grateful for his introduction to the field and his thoughts and advice as we sought to understand LSQ 1725-64. Most of all, I am grateful to have learned from his philosophy and approach to science and life. His sudden passing in the course of this work was tragic, and his guidance and presence have been missed. I am also thankful for the work and assistance of my colleagues in the Clemens group at UNC: Bart Dunlap, Erik Dennihy, JJ Hermes, Jesus Meza, and Patrick O'Brien. They have provided support, feedback, and assistance for the work described here. They have also been excellent company on many observing nights and coffee trips. I am thankful to my committee of Chris, Dan Reichart, Dean Townsley, Nick Law, and Art Champagne for their advice, willingness to serve, and having at least read this far. I am thankful to the many individuals who have been part of my physics education before my time at UNC. Dee Willars at Anderson High School first taught me physics. Brent Hoffmeister, Ann Viano, Deseree Meyer, David Rupke, Shubho Banerjee, and Glen v Davis played formative roles in my physics education at Rhodes College. They generated in me an interest and curiosity of physics, and encouraged me to continue my studies. All of the data presented in this dissertation comes from the SOAR Telescope, the Southern African Large Telescope, and PROMPT. I am particularly thankful to the telescope operators, day crew, and staff at SOAR for their work and assistance through many nights of observing. The Goodman Spectrograph has been the ideal instrument for this work. SALTICAM and PROMPT have enabled discoveries that would not have otherwise been possible. Financial support has been provided by two main sources. The National Science Foun- dation, through grant AST-1413001, has allowed me to focus on research the past three years. My first three years I was supported as a Teaching Assistant. I am thankful to the taxpayers of the state of North Carolina for their support in that work. Along that line, I am also thankful to Jennifer Weinberg-Wolf, Alice Churukian, and Duane Deardorff for teaching me how to teach effectively. Computational support has been provided by the Renaissance Computing Institute and Steve Cox. I am thankful to them for helping to significantly speed up the white dwarf fitting discussed in chapter 4. The white dwarf models were provided by Detlev Koester. I am thankful to him for his many years of work on the models and making it possible for us to undertake this project. This work was mostly completed in Phillips Hall and Chapman Hall on the UNC cam- pus. But a number of other locations have also provided a place to sit, think, converse, program, write, and drink caffeine. These include Johnny's Gone Fishing, View=360, the North Carolina Study Center, my car on the drive back from the 19th European White Dwarf Workshop in Montreal, and Chris' cabin in the Uwharrie Mountains. The graduate chapter of InterVarsity at UNC (Focus) has been a source of friendship, community, and relaxation over these past few years. I am thankful to Hank Tarlton for his leadership, friendship, and assistance in understanding the role of graduate education. I am vi also thankful to Fred and Nancy Brooks for their hospitality and involvement with Focus over many years. Many Focus events and trips have provided necessary breaks from work. Grace Community Church has been a wonderful church home the past six years. I am grateful to the many people who have been involved in making it a nurturing community. I appreciate the value placed on deep thinking, serious conversations, hospitality, and good food. Friends near and far have also been a source of assistance and encouragement. I appre- ciate the meals, coffee, games, movies, trips, adventures, and conversations they have been a part of. Tyler Farnsworth, Josh Welch, Alan Tubbs, Andy Garrison, and Alan Moon, in particular, have provided distractions when I needed them and focus when I needed that. My family has been very supportive on this journey. I appreciate their willingness to learn what I do, come visit North Carolina, and support me from afar. I am thankful to my parents for raising me to be curious and encouraging me to follow my passion. I am thankful to my brothers for their support on many of my journeys. I am grateful for the sisters-in-law, brothers-in-law, nieces, nephews, and parents-in-law who have become part of the family and have greatly enriched family gatherings and provided additional sources of support. To my dear wife Rachael, I am grateful that our journey together has been a part of this journey. You have provided words, encouragement, and support that have helped me to continue and persevere. You have expanded my comfort zone and given me room to grow. Your love has helped this work come to fruition. Finally, thank you to the almighty Father. You have created a Universe of beauty and given me a desire to understand it. vii TABLE OF CONTENTS LIST OF FIGURES ................................... xiv LIST OF TABLES .................................... xv LIST OF ABBREVIATIONS AND SYMBOLS ................. xvi 1 INTRODUCTION .................................. 1 1.1 Single Star Evolution . 2 1.1.1 Pulsating White Dwarfs . 4 1.2 Problems in the Measurement of Fundamental Properties of Single White Dwarfs . 5 1.2.1 Asteroseismology . 5 1.2.2 Effective Temperatures . 6 1.2.3 Masses . 7 1.3 The Physics of the Spectroscopic Determination of Teff and log g . 12 1.4 Plan for Measuring Properties of Single White Dwarfs . 15 1.5 Binary Star Evolution . 15 1.5.1 Magnetic Cataclysmic Variables . 16 1.6 Problems in the Measurement of Fundamental Properties of White Dwarfs in Binaries .
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