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Cataclysmic Variables and Double-Detonation Supernovae

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Cataclysmic Variables and Double-Detonation Supernovae A STUDY OF WHITE DWARFS: CATACLYSMIC VARIABLES AND DOUBLE-DETONATION SUPERNOVAE by SPENCER CALDWELL DEAN M. TOWNSLEY, COMMITTEE CHAIR JEREMY BAILIN JULIA CARTWRIGHT A THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Physics in the Graduate School of The University of Alabama TUSCALOOSA, ALABAMA 2019 Copyright Spencer Caldwell 2019 ALL RIGHTS RESERVED ABSTRACT Novae, be it classical, dwarf, or supernovae, are some of the most powerful and luminous events observed in the Universe. Although they share the same root, they are produced by di↵erent physical processes. We research systems capable of experiencing novae with the intention of furthering our understanding of these astrophysical phenomena. A cataclysmic variable is a binary star system that contains a white dwarf with the potential of undergoing classical or dwarf novae. A recent observation of a white dwarf within one of these systems was found to have an unusually high surface temperature for its orbital period. The discovery contradicts current evolutionary models, motivating research to determine a theoretical justification for this outlier. We simulated novae for a progenitor designed to represent a white dwarf in an interacting binary. We developed post-novae cooling timescales to constrain the temperature value. We found the rate at which classical 1 novae cool post-outburst (< 1Kyr− )isingeneralagreementwiththefour year − follow-up observation ( 2K).Theevolutionofwhitedwarfsduringdouble-detonation ⇠ type Ia supernovae was also studied. The progenitors capable of producing these events are not fully established, requiring a consistent model to be developed for parametric analysis. Three improvements were made to the simulation model used in (Townsley et al., 2019): the inclusion of a de-refinement condition, a new particle distribution, and a burning limiter. The focus here was to enhance the computational efficiency, o↵er better representation of particles in the supernova ejecta, and control the nuclear energy release. These developments were employed to test double-detonation scenarios capable of producing spectra analogous to type Ia supernovae, which will o↵er insight into their prevalence and strengthen their use in measuring cosmological distance. ii ACKNOWLEDGMENTS Foremost, I would like to express my profound gratitude to my advisor Dr. Dean Townsley. He has been integral to both my success and enjoyment as a graduate student at the University of Alabama. His support and guidance throughout all my research is and always will be appreciated. Thanks to Dr. Boris G¨ansicke and Dr. Anna Pala at the University of Warwick for providing the observational foundation for my work on cataclysmic variables. My special thanks to Dr. Broxton Miles for setting a lot of the groundwork for the double-detonation simulations performed and for composing the particle distribution implemented in this study. Thank you to my committee members Dr. Jeremy Bailin and Dr. Julia Cartwright for agreeing to participate and help me through the process. I also would like to thank Dr. Ken Shen at the University of California, Berkley who provided generous support with the double-detonation supernovae. iii CONTENTS ABSTRACT........................................ ii ACKNOWLEDGMENTS................................. iii LISTOFTABLES..................................... vi LISTOFFIGURES.................................... vii 1 CATACLYSMICVARIABLES ............................ 1 1.1 INTRODUCTION ................................ 1 1.2 METHODOLOGY ................................ 5 1.3 RESULTS..................................... 7 1.3.1 OBSERVATIONAL INFLUENCE . 7 1.3.2 CLASSICAL NOVAE . 9 1.3.3 DWARFNOVAE............................. 13 1.4 DISCUSSION................................... 16 1.4.1 VARIABILITY OF IGNITION IN NOVAE EVOLUTION . 16 1.5 CONCLUSION .................................. 21 2 SUPERNOVAE .................................... 22 2.1 INTRODUCTION ................................ 22 2.2 SIMULATIONSETUP.............................. 24 2.2.1 REFINEMENT.............................. 29 2.2.2 PARTICLEDISTRIBUTION . 31 2.2.3 BURNINGLIMITER .......................... 34 iv 2.3 RESULTS..................................... 37 2.3.1 DE-REFINEMENTSTUDY....................... 37 2.3.2 BURNING LIMITER STUDY . 38 2.3.3 RESOLUTIONSTUDIESONIGNITION . 41 2.4 DISCUSSION................................... 46 2.5 CONCLUSION .................................. 53 REFERENCES ...................................... 55 v LIST OF TABLES 2.1 ParametersforWhiteDwarfProgenitors . 27 2.2 NuclearReactionNetwork ............................ 28 vi LIST OF FIGURES 1.1 Cumulative Distribution between Theoretical and Observed Te↵ ....... 8 1.2 Evolution of Te↵ and Tc ............................. 10 1.3 Classical Nova Cooling Timescale for 0.95 M ................. 12 1.4 Binary Evolution Below the Period Gap . 14 1.5 Dwarf Nova Cooling Timescale for 0.819 M .................. 15 1.6 Initial Tc andClassicalNovaeEvolution . 17 1.7 AccretionRateandClassicalNovaeEvolution . 19 2.1 TimeSequenceofHeliumShellDetonation . 23 2.2 ShockAngleDetermination . 30 2.3 FinalParticlePositions.............................. 33 2.4 De-refinement Test . 38 2.5 Burn Limiter Test . 39 2.6 New Burn Routine . 40 2.7 Ignition Refinement Test . 42 2.8 Carbon Detonation Test . 45 2.9 Evolution of Helium Shell Detonation for 1.0 M ............... 47 2.10 Lead-up to Carbon Detonation . 48 2.11 FinalAbundancesofEjectafromDouble-Detonation . 49 2.12 Evolution of Reduced 16OHeliumShellDetonation . 51 2.13 Final Abundances of Ejecta for Reduced 16OProgenitor. 52 vii 1 CATACLYSMIC VARIABLES 1.1 INTRODUCTION Cataclysmic Variables (CVs) are close-interacting binary star systems that contain an accreting white dwarf accompanied by a low-mass main-sequence (MS) donor ( 0.6M ). At the onset of CV formation, the more massive star in a binary star system matures to the giant phase and its matter encloses the entire binary, forming a common envelope. The less-massive donor falls to closer orbits around the degenerate core of the primary, which transfers energy outward and causes the envelope to be ejected. Once stripped of the common envelope, the binary is left detached, semi-detached, or close enough to merge. If detached, the stars still orbit one another, but evolve separately until angular momentum loss (AML) reduces the orbital separation or the donor expands on its nuclear timescale and overflows its Roche lobe, continuing mass transfer (Goliasch and Nelson, 2015). The Roche lobe is the equipotential surface surrounding each star that is at the same potential as the first Lagrange point, where material is equally bound to each star. At this point, material can shift from being bound to one star to the other by an arbitrarily small change in velocity. If the binary system is semi-detached after the common envelope is ejected, it is likely to continue its evolution as a CV. Semi-detached systems contain a donor star overflowing its Roche lobe that delivers matter to the accreting white dwarf, forming an accretion disk. Further evolution of the system is primarily dictated by AML, nuclear evolution of the donor (which will change its radius), and accretion rate. AML is caused by 1 two main sources, gravitational radiation and magnetic braking. Gravitational radiation is apersistentsourceofangularmomentumloss,drivingthesystemtosmallerorbitalperiods (Porb). Gravitational radiation dominates in CVs when Porb < 3hr,whenthe 11 1 time-averaged accretion rate is M˙ =5 10− M yr− (Patterson, 1984), where M is h i ⇥ solar mass = 1.989 1030 kg. AML for CVs with P > 3hrisdominatedbymagnetic ⇥ orb 9 8 1 braking (Spruit and Ritter, 1983) and have accretion rates 10− 10− M yr− .Magnetic − braking is caused by interaction of the departing stellar wind with the magnetic field of the rotating star, reducing angular momentum of the rotating object. CVs with orbital periods between 2 and 3 hr are scarce, so that there is a dichotomy in the angular momentum loss mechanism for observed systems, separated by what is termed the “period gap.” The start of the period gap (P 3hr)signifieswhenthedonorstarhaslostenough orb ⇡ mass (Mdonor 0.23 M ) to become fully convective (Howell et al., 2001). Magnetic braking is interrupted at this point, e↵ectively halting further accretion. The donor, which has become bloated, is then allowed to thermally adjust and shrink back to the equilibrium radius for a MS star with the relevant mass (Townsley and G¨ansicke, 2009). During this stage, mass transfer ceases until AML caused by gravitational radiation drives the binary back to a semi-detached state (P 2 hr). Mass transfer onto the white dwarf orb ⇡ recommences once through the period gap. The orbital separation continues to shrink while the white dwarf accretes material from the donor, which continues to lose mass. Concurrently, while the mass-loss timescale increases, the Kelvin-Helmholtz timescale, ⌧thermal, increases faster. When ⌧thermal becomes greater than the mass-transfer timescale, the donor can no longer thermally adjust. This typically occurs when P 80 min and orb ⇡ Mdonor 0.06 M (Howell et al., 2001). Continued CV evolution leads to a gradual increase ⇡ in the orbital separation and decrease in accretion rate for the remainder of its lifetime. Observations performed by (Pala et al., 2017) were able to ascertain the surface temperatures for CV white dwarfs in their Hubble Space Telescope (HST) survey. Of
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