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Astrophysical Applications of Gravitational Microlensing

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Astrophysical Applications of Gravitational Microlensing Astrophysical Applications of Gravitational Microlensing Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Subo Dong, M.S. Graduate Program in Astronomy The Ohio State University 2009 Dissertation Committee: Professor Andrew Philip Gould, Advisor Professor Bernard Scott Gaudi Professor Krzysztof Zbigniew Stanek Copyright by Subo Dong 2009 ABSTRACT In this thesis, I present several astrophysical applications of Galactic and cosmological microlensing. The first few topics are on searching and characterizing extrasolar planets by means of high-magnification microlensing events. The detection efficiency analysis of the A 3000 event OGLE-2004-BLG-343 is presented. Due to max ∼ human error, intensive monitoring did not begin until 43 minutes after peak, at which point the magnification had fallen to A 1200. It is shown that, had a ∼ similar event been well sampled over the peak, it would have been sensitive to almost all Neptune-mass planets over a factor of 5 in projected separation and even would have had some sensitivity to Earth-mass planets. New algorithms optimized for fast evaluation of binary-lens models with finite-sources effects have been developed. These algorithms have enabled efficient and thorough parameter-space searches in modeling planetary high-magnification events. The detection of the cool, Jovian-mass planet MOA-2007-BLG-400Lb, discovered from an Amax = 628 event with severe finite-source effects, is reported. Detailed analysis yields a fairly precise planet/star mass ratio of q = (2.5+0.5) 10−3, while the planet/star −0.3 × ii projected separation is subject to a strong close/wide degeneracy. Photometric and astrometric measurements from Hubble Space Telescope, as well as constraints from higher order effects extracted from the ground-based light curve (microlens parallax, planetary orbital motion and finite-source effects) are used to constrain the nature of planetary event OGLE-2005-BLG-071Lb. Our primary analysis leads to the conclusion that the host is an M = 0.46 0.04 M M dwarf and that the planet ± ⊙ has mass M = 3.8 0.4 M , which is likely to be the most massive planet yet p ± Jupiter discovered that is hosted by an M dwarf. Next a spaced-based microlens parallax is determined for the first time using Spitzer and ground-based observations for binary-lens event OGLE-2005-SMC-001. The parallax measurement yields a projected velocityv ˜ 230 km s−1, the typical ∼ value expected for halo lenses, but an order of magnitude smaller than would be expected for lenses lying in the Small Magellanic Cloud (SMC) itself. Finally, I propose using quasar microlensing to probe Mg II and other absorption “cloudlets” with sizes 10−4.0 10−2.0pc in the intergalactic medium. ∼ − I show that significant spectral variability on timescales of months to years can be induced by such small-scale absorption “cloudlets” toward a microlensed quasar. With numerical simulations, I demonstrate the feasibility of applying this method to Q2237+0305, and I show that high-resolution spectra of this quasar in the near future would provide a clear test of the existence of such metal-line absorbing “cloudlets”. iii Dedicated to my mother and father iv ACKNOWLEDGMENTS In modern times, most of the necessities of people’s daily lives rely upon others, therefore, no matter how highly the lofty ideal of individual freedom is acclaimed, most people have to choose their jobs according to the needs of the society rather than following their inner voices (i.e., what they are interested in the most). I consider myself very lucky to have five years’ opportunity to pursue my childhood dream in becoming an astronomer with no financial burden. I am thankful to everyone who has made this possible. I thank Andy Gould for being an unparalleled advisor. He has taken immense care in guiding me along my path to becoming a scientist. His influence and help have permeated every aspect of my scientific activities as a graduate student. Whenever I need discussions or advice (or whenever he perceives me as needing them), he is always ready to offer them in most timely fashion. His excitement by new findings, creativity in novel ideas, and self-driven “Gung-ho” working spirit exhibit no trace of his age. It is difficult to describe how exhilarating an experience it is to work with him. v I thank Andy for being a truthful person – for being truthful to himself, to others, and to nature. I was initially intimidated by the way he spoke in morning coffee and colloquia. But I have come to realize that, if one is offended by sincere efforts to pursue the truth, or not offended by distortion or fabrication of facts and careless or superficial analyses, he/she is not a real scientist. I thank Andy for teaching me to be honest to data, to listen to what nature has to say rather than projecting one’s prejudices onto nature. I came to the United States certainly at an interesting time, when “the best and brightest” in the White House and on the Wall Street have drastically transformed the world’s social and economic orders. As a “Stranger in a Strange Land”, I appreciate Andy for many illuminating discussions that shed light on the perplexing and intriguing events in the U.S. and on the world stage. He observes the society at a vantage point beyond his ethnical, national, and cultural background. I never have to worry about offending him by expressing my honest views. I thank Andy for rallying a group of people (mostly astronomers) to have discussions on real-world events in a similar fashion as we discuss science. We attempt to distinguish between real and bogus information from various sources and analyze the events by confronting ideas against distilled evidence and data. Although I do not always agree with Andy, it has always been such a great time talking to him on almost anything. Next I thank my thesis committee members, Scott Gaudi and Kris Stanek. vi I first met Scott back when he was a postdoc at CfA. He has been providing unreserved encouragement and support to me since then. I have benefited greatly from his advice on science and professional development. I thank him for having led me to see the bright side when I was in depression or frustration. I admire his comprehensive knowledge in almost all branches of astronomy and his often amazingly deep physical intuition. I thank Kris for being friendly and humorous and willing to talk to me on any topic. I thank him for inspiring discussions that led to my first original workable science idea. I appreciate his insistence that scientific pictures should fundamentally be simple. He always has great insights into complexity and sees through irrelevant artificial obscuration. I hope I will be able to acquire even a fraction of his ability in seizing the moments by recognizing fleeting opportunities in astronomy. I am grateful to Rick Pogge, Chris Kochanek and many others in the department for providing a lot of great technical help and having interesting science discussions together. And I greatly appreciate many faculty in the department for creating an intellectually stimulating environment which is also very student-friendly. Daily coffee has become an indispensable part of my life. The department staff are always helpful, and I especially thank David Will for solving many of my computer problems. vii I have spent a great time with many graduate students and several postdocs at OSU. I first thank Zheng for having provided me many great advice when I first got to OSU, and for him being a role-model student and astronomer. He shows me how high someone with a similar background as me can possibly achieve in astronomy. I thank Jose, Vimal, Dale, Himel and others for having a lot of interesting discussions and experience together. And I appreciate having many great office mates, Frank, Molly, Ondrej, Kelly, Rob, Deokkeun, etc., during the last five years. Szymon and Xinyu have been great friends and colleagues. I could not possibly have finished my PhD work without many colleagues outside Ohio State. In particular, I thank Andrzej Udalski for being an exemplary astronomer. I never fail to be thrilled by the first-rate data he and the OGLE team have produced. A lot of crucial data I have analyzed come from many “amateur” astronomers: Jennie McCormick, Grant Christie and Berto Monard, to name a few. They are amateurs only in the sense that they are not paid for their observations, otherwise what they do are extraordinarily professional. Their fascination in the sky, enthusiasm and dedication have been a constant source of inspiration to me. I thank all my observer colleagues for offering me the privilege in being the first to see many beautiful light curves and realize the exotic extrasolar worlds that they reveal. The precious moments of discovery transcend anything else. viii I wish to express my deep gratitude to Profs. Dawei Yang, Tianyi Huang, Qiusheng Gu and Dr. Jin Zhu for their selfless help and great guidance at various important stages before I entered the graduate school. At last, I thank my mother and father, who put my education, both in acquiring knowledge and in being a decent member of the society, as the first priority in their life. Without their unequivocal support and sacrifice, I would have never been anywhere near the position I am at today to write this dissertation. ix VITA March 18, 1982 . Born – Chengde, Hebei, China 2004 ........................... B.S. Astronomy, Nanjing University, China 2004 – 2005 . University Fellow, The Ohio State University 2005 – 2006 .
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