c 2012 by Jana Bilikova. All rights reserved. DUST DISKS AROUND HOT WHITE DWARFS AND CENTRAL STARS OF PLANETARY NEBULAE BY JANA BILIKOVA DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Astronomy in the Graduate College of the University of Illinois at Urbana-Champaign, 2012 Urbana, Illinois Doctoral Committee: Professor You-Hua Chu, Chair, Director of Research Professor Charles F. Gammie Dr. Kate Y.-L. Su, University of Arizona Professor Laird A. Thompson Associate Professor Leslie W. Looney Professor Emeritus Ronald F. Webbink Abstract Two types of dust disks have been discovered around white dwarfs (WDs): small dust disks within the Roche limits of their WDs, and a large dust disk around the hot central WD of the Helix planetary nebula (PN), possibly produced by collisions among Kuiper Belt-like objects.To search for more dust disks of the latter type, we have carried out a Spitzer MIPS 24 µm survey of 71 hot WDs or pre-WDs, and found nine WDs with excess 24 µm emission, seven of which are still central stars of planetary nebulae (CSPNs). We have therefore used archival Spitzer IRAC and MIPS observations of PNe to search for CSPNs with excess IR emission, and found five additional IR excesses likely originating from dust disks. For some of these CSPNs, we have acquired follow-up Spitzer MIPS images and IRS spectra, and Gemini NIRI and Michelle spectroscopic observations. The spectral energy distributions show great diversity in the emission characteristics of the IR excesses, which may imply different mechanisms responsible for the excess emission. The two most likely dust production mechanisms are: (1) breakup of bodies in planetesimal belts through collisions, (2) formation of circumstellar dust disks through binary interactions. In addition, we have derived basic dust disk parameters using simple blackbody approxima- tions, or optically thin dust disk models with realistic grain and disk properties. The dust disk physical parameters for CSPNs without near-IR excesses appear consistent with the origin as collisionally disrupted planetesimals. The dust disks around CSPNs with near-IR excesses are likely optically thick, and possibly descended from binary post-AGB stars. The Helix Nebula’s CSPN is also associated with a hard X-ray point source, whose origin is not known. We have correlated the Galactic WD catalog with the XMM-Newton and ROSAT ii point source catalogs to search for more single WDs with hard X-ray emission. Apart from the central WD of the Helix Nebula, none of the single WDs with hard X-ray emission are known to have excess IR emission. A better understanding of post-AGB binary evolution as well as debris disk evolution along with its parent star is needed to distinguish between these different origins.Future observations to better establish the physical parameters of the dust disks and the presence of companions are needed for models to discern between the possible dust production mech- anisms. iii In memory of my grandparents. iv Acknowledgments Graduate school has not been a smooth ride for me, and it took a team of experts to get me to the finish line without losing my sanity. I am glad to have the opportunity to acknowledge the people that have helped me along the way to my PhD. First of all, I would like to thank my thesis commitee, You-Hua Chu, Kate Su, Leslie Looney, Laird Thompson, Ron Webbink and Charles Gammie for their helpful comments and the feedback during my preliminary and PhD examination. I want to thank my advisor You-Hua Chu for all the opportunities and guidance that she has given me throughout the years. The education I got from her was broad; the astronomical observations were intermingled with observations of viral videos, and my scientific writing was balanced out by increasing knowledge of the urban dictionary. I don’t think that any student got to laugh more with their advisor than I did, as we photographed the double rainbows of Slovakia, observed more than just Mozart’s statue in Vienna, or walked the Ulmenweg and Ahornweg in Germany. You-Hua is one of the most generous people that I know, with all the delicious food that she brings in daily, or the upgrades and airplane tickets that she gives away. We have broken the barrier between the professional and personal life, and I am glad to be graduating not only with a great advisor, but also a good friend. I might never have graduated if it wasn’t for Robert Gruendl. Almost everything that I have learned about data, I have learned from him. I appreciate his patience in answering my ”quick questions”, his help with data reduction, observation preparation or IRAF problems. His scripts have saved me days of work on many occasions. All this knowledge is wrapped up in a modest and kind person that I am lucky to have learned from. v I also want to thank Kate Su, for her help with Spitzer data and dust disk modeling, journal articles and many proposals. Her work ethic is something that I aspire to. I am also grateful to her for hosting me in Tuscon, introducing me to her dogs, bringing spicy squid to Kitt Peak and for good beer and good conversations at conferences and observing runs. I cannot go without mentioning Rosa Williams, my academic sister, for her help with my first paper, and for pulling me out of a slump at the beginning of the research portion of my PhD. Her success is an encouragement to me whenever self-doubt creeps in. I would like to thank the Astronomy Department Staff, Jeri Cochran, Sandie Osterbur, Mary Margaret O’Connor and Bryan Dunne for always reminding me to register for classes, send in grant reports, or renew paperwork, and for being so nice and friendly. Their kindness makes it easy to feel at home in the department. I am also thankful to Kevin Pointer for tech support and reminders to copy my data to directories that will not be erased. I also want to thank Leslie Looney, whose classes are no doubt the most entertaining ones, where even innocent passerbys get chalk-attacked into participation. Thanksgivings at the Leslies’ are the best, and both me and my stomach are happy to have been included. I am lucky that my peers in Astronomy were such a great bunch of people who like their integrals with a side of late-night chinese takeout and a hackysack, who work and play hard and who were the best part of the grad school experience. I would especially like to thank my officemates of few years and dear friends Hsin-Fang Chiang and Amy Lien, brilliant, hard-working, kind and generous women that I am lucky to know. It’s been great doing research and schoolwork alongside them. I am thankful for all the fun times - sharing bread pudding, fabric and yarn store expeditions, cheering me on at my races, drawing diamonds in the sky above Einstein, owlies, chats about school and life, and all those wonderful small things that made everyday life in Astro 128 so enjoyable. I also want to thank Jonathan Seale for making living on Elm street the opposite of nightmare with our Oscar parties, grocery store runs, evenings sewing snuggies and MJ costumes, and alleged waltzing at Crane Alley; Hsin-Lun Kuo for all the good talks and vi laughs, for our study times at coffee shops, for hot-pot dinners and all the nights we danced away in our early grad years; Brett Hayes for his great generosity and willingness to always help anyone, for bringing me food and proofreading the last chapters of my thesis at a moment’s notice, for his parties, and for putting my bad sleeping habits in perspective; Nick Indriolo for parties and the great laughs during the movie nights, for stopping by the office to chat on the way home, and for always being fashionably on time to every event; Nick Hakobian for chat breaks, movie nights and gettogethers at his place, for all the great naps I took on his floor during movie nights, and for his attempts to explain interferometry to me; Britt Lundgren for enduring our first year together and for her friendship ever since, for the good times in Fiesta, and for always thinking that I am smarter that I think I am; Jessica Evans for bringing me coffee in my most stressed stages of thesis-writing, and for her delicious cookies that I am sure have put my thesis committee into favorable mood for my defense; and all my grad school astronomy friends that have made life in and out of the office so fun: Alfredo Zenteno, Ashley Ross, Chao-Chin Yang, Dominique Segura-Cox, Gary Foreman, Ian Stephens, Jeeseon Song, Jerry Shiao, Karen Yang, Nachiketa Chakraborthy, Rosie Chen, Rukmani Vijayaraghavan, Scott Bain, Tijana Prodanovic, and everyone else. I also want to thank Lesa Scharnett for the 5:30 “happy hours” at the gym, which have kept me fit and sane in the past two years. Of all the classes I took in grad school, hers were by far my favorite. I thank Sara Knaack, for being my first and longest friend here in Urbana, for our movie nights, Ribollita dinners and carrot cake, and all the fun, friendship and gourmet food we shared in the past few years. I also want to thank my friend Suzanne Levine Donnelly, for all the laughs, deep conversations and extremely ridiculous inside jokes, for lessons in slang, but above all, for being someone I can always lean on, no matter how far apart we live.