Library Declaration and Deposit Agreement 1. STUDENT DETAILS David John Wilson 1357803 2. THESIS DEPOSIT 2.1 I understand that under my registration at the University, I am required to deposit my thesis with the University in BOTH hard copy and in digital format. The digital version should normally be saved as a single pdf file. 2.2 The hard copy will be housed in the University Library. The digital ver- sion will be deposited in the Universitys Institutional Repository (WRAP). Unless otherwise indicated (see 2.3 below) this will be made openly ac- cessible on the Internet and will be supplied to the British Library to be made available online via its Electronic Theses Online Service (EThOS) service. [At present, theses submitted for a Masters degree by Research (MA, MSc, LLM, MS or MMedSci) are not being deposited in WRAP and not being made available via EthOS. 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Please sign this agreement and return it to the Graduate School Office when you submit your thesis. Student's signature: ..................................Date: ................. Observations of Remnant Planetary Systems at White Dwarfs by David John Wilson Thesis Submitted to the University of Warwick for the degree of Doctor of Philosophy Department of Physics September 2017 Some say the world will end in fire, Some say in ice. From what I’ve tasted of desire I hold with those who favour fire. But if it had to perish twice, I think I know enough of hate To say that for destruction ice Is also great And would suffice. Robert Frost i Contents Acknowledgments v 0.1 Personal acknowledgements . v 0.2 Institutional acknowledgements . vi Declarations vii Abstract viii Abbreviations ix Chapter 1 Introduction 1 1.1 The post-main sequence evolution of the Solar system . 2 1.2 Physical properties of white dwarfs . 5 1.2.1 Classification . 5 1.2.2 Cooling timescales . 6 1.2.3 Mass distribution . 7 1.2.4 Metal diffusion timescales . 9 1.3 Remnants of planetary systems . 11 1.3.1 Historical Background . 11 1.3.2 State of the art . 14 1.4 Thesis Outline . 19 Chapter 2 Methods 20 2.1 Spectroscopy . 21 2.1.1 Reduction . 23 2.1.2 Space telescopes . 25 2.2 Measuring metal accretion onto white dwarfs . 27 2.2.1 White dwarf model atmospheres . 27 2.2.2 The accretion-diffusion scenario . 28 ii 2.3 Gaseous emission from debris discs . 30 2.4 Conclusion . 32 Chapter 3 Variable emission from gas in a debris disc around a metal-polluted white dwarf 33 3.1 Discovery . 34 3.2 Follow-up observations . 36 3.3 White Dwarf Parameters . 38 3.4 Variability of the Calcium II Triplet . 38 3.5 Accretion of Planetary Material . 41 3.6 Discussion . 42 3.7 Conclusion . 45 Chapter 4 The chemical composition of a disrupted extrasolar planetesimal 46 4.1 Observations . 50 4.2 White dwarf parameters . 51 4.3 Accretion of planetary material . 55 4.3.1 Total accretion rate and mass of the parent body . 58 4.3.2 Carbon . 59 4.3.3 Oxygen . 61 4.3.4 Refractory lithophiles . 63 4.3.5 Iron and nickel . 64 4.4 Variability of the Ca ii triplet . 67 4.5 Short term variability . 68 4.6 Conclusion . 70 Chapter 5 Carbon to oxygen ratios in extrasolar planetesimals 71 5.1 Carbon and oxygen debris abundances at white dwarfs . 73 5.2 Discussion . 78 Chapter 6 Multi-wavelength observations of the EUV variable metal-rich white dwarf GD 394 82 6.1 Observations . 84 6.1.1 Spectroscopy . 87 6.1.2 Archival data . 92 6.1.3 Photometric observations . 92 6.2 Non-detection of variability . 96 6.2.1 Short-term . 96 iii 6.2.2 Long-term . 98 6.3 Atmospheric parameters and metal abundances . 100 6.3.1 STIS . 100 6.3.2 FUSE . 103 6.3.3 WHT . 103 6.3.4 HIRES . 103 6.3.5 Diffusion, radiative levitation and the origin of the metal lines . 104 6.3.6 High-excitation lines . 104 6.4 Modelling the EUV variability . 107 6.5 Non-detection of gaseous emission . 107 6.6 Discussion . 108 6.7 Conclusion . 110 Chapter 7 Conclusion 111 7.1 Discussion . 112 7.1.1 Thesis summary . 112 7.1.2 Future work . 113 7.2 Conclusion . 116 Appendix A Absorption line lists for GD 394 117 iv Acknowledgments 0.1 Personal acknowledgements This PhD would not be possible without many people, most of whom I will probably forget to mention. Sorry. Foremost in those I have remembered is my supervisor, Professor Boris Gansicke,¨ who, since convincing me that white dwarfs were interesting over a free lunch, has never been anything but supportive and encouraging, except when I made terrible plots, which was probably a good thing, and when I wrote overly long sentences, which I still think have their merits. Thanks also to my various collaborators, especially to Detlev Koester for being patient when my physics was incorrect and to Jay Farihi for being impatient when my spelling was incorrect. Thank you also to all of my fellow PhD students at Warwick for their friendship, support and advice, along with a steady supply of boardgames and other distractions. Par- ticular thanks to Mark for helping me pretend I know how to code. Thank you to the Astrobites Collaboration for letting me write about space (and/or microwaves) on the internet and to astronomy Twitter for connecting me to a wider world. Finally, thank you to my family and above all my parents, for feeding and clothing me for most of my life, supplying me with a steady stream of books with pictures of space rockets, and for taking me outside one night in 1997 to look at Comet Hale-Bopp. I promise to continue to do my best to never get a real job. v 0.2 Institutional acknowledgements The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 320964 (WDTracer). This thesis has made use of observations from the following observatories and in- stitutions: The NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.