Exploring the Extremes of Exoplanet Detection and Characterization in High-Magnification Microlensing Events Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Jennifer C. Yee Graduate Program in Astronomy The Ohio State University 2013 Dissertation Committee: Professor Andrew P. Gould, Advisor Professor B. Scott Gaudi Professor Richard W. Pogge Copyright by Jennifer C. Yee 2013 ABSTRACT The field of microlensing planet searches is about to enter a new phase in which wide-field surveys will be the dominant mode of planet detection. In addition, there are now plans to execute microlensing surveys from space allowing the technique to reach smaller planets and resolve some of difficulties of ground-based microlensing where the resolution is poor. This new phase of observations also requires a new mode of analysis in which events are analyzed en masse rather than as individuals. Until now, there has not been any investigation into the detection threshold for planets in real data. Some people have suggested that the threshold for detecting planets may be as small as ∆χ2 of 160, and that is frequently used in microlensing simulations of planet yields. However, no planets have been published with signals that small. I have done the first empirical investigation of the detection threshold for planets in high-magnification microlensing events. I found that MOA-2008-BLG-310 (∆χ2 = 880), MOA-2011-BLG-293 (∆χ2 = 500 without followup data), and MOA-2010-BLG-311 (∆χ2 = 80) form a sequence that spans from detected with high confidence (mb310) to marginally detected (mb293) to something too small ii to claim with confidence (mb311). This suggests that the detection threshold for planets in high-magnification events is 500 ∆χ2 < 880. ≤ I have also analyzed OGLE-2008-BLG-279 to determine the range of planets that are detectable for this event given the excellent data quality and the high- magnification. This event illustrates that high-magnification events will still be important in the era of surveys because each event is much more sensitive to planets than any individual low-magnification event. Because they probe the central caustics, high-magnification events are sensitive to planets at any angle, meaning that they place more stringent limits on the presence of planets. For this event, Jupiter-mass companions can be ruled out from 0.5-20 AU. As the field extends to new modes of observations, it is worth considering how we can maximize the information we can obtain for each microlensing event, particularly given the limitation that microlensing is primarily sensitive to mass ratio rather than planet mass. I propose a means to take advantage of the excellent light curves that will be available from space and combine them with ground-based observations to measure microlens parallax for a large fraction of the microlensing events that will be seen by a space-based microlensing survey. This measurement will enable the measurement of the planet masses for these events. iii Dedicated to my parents and the memory of my grandfather Thomas P. Vogl iv ACKNOWLEDGMENTS First and foremost, I would like to thank my advisor Andy Gould, who has carefully steered all of the projects presented in this dissertation. He has helped me develop from a very uncertain student to a scientist confidently pursuing a research career. He has challenged me to think and operate at a much higher level. His passion for science has inspired me to work harder and push my limits. I would also like to thank the other members of my committee: Scott Gaudi and Rick Pogge. Scott Gaudi got me started as my first research advisor at Ohio State. He also carefully read and commented on my papers and was an excellent Graduate Studies Chair. Rick Pogge kept MicroFUN running smoothly for many years and always made time to help me with the latest crisis. I would like to thank my microlensing collaborators. The OGLE, MOA, PLANET, RoboNET, and MiNDSTEp have all provided data used in this dissertation as well as feedback on the analysis. I would also like to thank the SMARTS team at Yale and CTIO who make our observations from the CTIO SMARTS 1.3m possible. A special thanks to the members of MicroFUN, especially the amateur astronomers whose dedication to the project continues to inspire me. v Thank you to the Department of Astronomy and its members past and present for maintaining a scientifically lively atmosphere dedicated to the success of its graduate students. Thank you to my friends who have helped me maintain perspective and provided support and commiseration. I would like to thank my parents for giving me the confidence to know I can succeed at anything: my mother for her strength and my father for sharing his enthusiasm for astronomy and science fiction. Thanks to my sister for sharing my morbid sense of humor and always providing moral support. Finally, I would especially like to thank my husband Eric for his unwavering love and support and for sticking with me even when I was crabby and miserable. This work was supported in part by an allocation of computing time from the Ohio Supercomputing Center. vi VITA April 3, 1985 ................... Born – Poughkeepsie, NY 2007 . B.A. Astrophysics, Swarthmore College 2007 – 2008 . Distinguished University Fellow, The Ohio State University 2008 – 2006 .................... Graduate Teaching and Research Associate, The Ohio State University 2009 – 2012 . National Science Foundation Graduate Research Fellow, The Ohio State University 2010 ........................... M.S. Astronomy, The Ohio State University 2012 – 2013 . Distinguished University Fellow, The Ohio State University PUBLICATIONS Research Publications 1. C.J. Grier, et al. (16 coauthors including J.C. Yee), “The Mass of the Black Hole in the Quasar PG 2130+099”, ApJ, 688, 837 (2008). 2. J.C. Yee and B. S. Gaudi, “Characterizing Long-Period Transiting Plan- ets Observed by Kepler”, ApJ, 688, 616 (2008). 3. J.A. Carter, J.C. Yee, J.D. Eastman, B.S. Gaudi, and J.N. Winn, “Ana- lytic Approximations for Transit Light-Curve Observables, Uncertainties, and Covariances”, ApJ, 689, 499 (2008). 4. M.J. Valtonen, et al. (40 coauthors including Yee, J.C.), “Tidally In- duced Outbursts in OJ 287 during 2005-2008”, ApJ, 698, 781 (2009). vii 5. J.C. Yee, et al. (84 coauthors), “Extreme Magnification Microlensing Event OGLE-2008-BLG-279: Strong Limits on Planetary Companions to the Lens Star”, ApJ, 703, 2082 (2009). 6. C. Villforth, et al. (47 coauthors including J.C. Yee), “Variability and stability in blazar jets on time scales of years: Optical polarization monitoring of OJ287 in 2005-2009”, MNRAS, 402, 2087 (2010). 7. J.C. Yee and E.L.N. Jensen, “A Test of Pre-Main-Sequence Lithium De- pletion Models”, ApJ, 711, 303 (2010). 8. P. Fouque, et al. (112 coauthors including J.C. Yee), “OGLE 2008-BLG- 290: an accurate measurement of the limb darkening of a galactic bulge K Giant spatially resolved by microlensing”, A&A, 518, 51 (2010). 9. A. Gould, et al. (126 coauthors including J.C. Yee), “Frequency of Solar-like Systems and of Ice and Gas Giants Beyond the Snow Line from High-magnification Microlensing Events in 2005-2008”, ApJ, 720, 1073 (2010). 10. Y.-H. Ryu, et al. (107 coauthors including J.C. Yee), “OGLE-2009- BLG-092/MOA-2009-BLG-137: A Dramatic Repeating Event with the Second Perturbation Predicted by Real-time Analysis”, ApJ, 723, 81 (2010). 11. N. Miyake, T. Sumi, S. Dong, R. Street, L. Mancini, A. Gould, D.P. Bennett, Y. Tsapras, J.C. Yee, et al. (109 additional coauthors), “A Sub-Saturn Mass Planet, MOA-2009-BLG-319Lb”, ApJ, 728, 120 (2011). 12. V. Batista, et al. (125 coauthors including Yee, J. C.), “MOA-2009- BLG-387Lb: a massive planet orbiting an M dwarf”, A&A, 529, 102 (2011). 13. “Binary microlensing event OGLE-2009-BLG-020 gives a verifiable mass, distance and orbit predictions” Skowron, J., et al. (101 coauthors including Yee, J. C.) ApJ, 738, 87 (2011). 14. Y. Muraki, et al. (128 coauthors including Yee, J. C.), “Discovery and Mass Measurements of a Cold, 10 Earth Mass Planet and Its Host Star”, ApJ, 741, 22 (2011). 15. T. Bensby, et al. (23 coauthors including J.C. Yee), “Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. IV. Two bulge populations”, A&A, 533, 134 (2011). viii 16. I.-G. Shin, et al. (151 coauthors including J.C. Yee) “Microlensing Bina- ries Discovered through High-magnification Channel”, ApJ, 746, 127 (2012). 17. J.-Y. Choi, et al. (150 coauthors including J.C. Yee), “Characterizing Lenses and Lensed Stars of High-magnification Single-lens Gravitational Microlens- ing Events with Lenses Passing over Source Stars”, ApJ, 751, 41 (2012). 18. E. Bachelet, et al. (140 coauthors including J.C. Yee), “MOA 2010- BLG-477Lb: Constraining the Mass of a Microlensing Planet from Microlensing Parallax, Orbital Motion, and Detection of Blended Light”, ApJ, 754, 73 (2012). 19. A. Gould and J.C. Yee “Cheap Space-Based Microlens Parallaxes for High-Magnification Events”, ApJL, 755, 73 (2012). 20. I-G. Shin, et al. (120 coauthors including J.C. Yee), “Characterizing Low-mass Binaries from Observation of Long-timescale Caustic-crossing Gravita- tional Microlensing Events”, ApJ, 755, 91 (2012). 21. J.C. Yee, et al. (77 coauthors), “MOA-2011-BLG-293Lb: A test of pure survey microlensing planet detections”, ApJ, 755, 102 (2012). 22. J.-Y. Choi, et al. (120 coauthors including J.C. Yee), “A New Type of Ambiguity in the Planet and Binary Interpretations of Central Perturbations of High-Magnification Gravitational Microlensing Events”, ApJ, 756, 48 (2012).