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Yee, Jennifer Chun MingExploring the Extremes of Exoplanet Detection and Characterization in High-Magnification Microlensing Events
Doctor of Philosophy, The Ohio State University, Astronomy
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 Delta chi^2 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 (Delta chi^2=880), MOA-2011-BLG-293 (Delta chi^2=500 without followup data), and MOA-2010-BLG-311 (Delta chi^2=80) form a sequence that spans from detected with high confidence (mb310) to marginally detected (mb293) to something too small to claim with confidence (mb311). This suggests that the detection threshold for planets in high-magnification events is 500 <= Delta chi^2<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.

Committee:

Andrew Gould (Advisor); B. Scott Gaudi (Committee Member); Richard Pogge (Committee Member)

Subjects:

Astronomy; Astrophysics

Keywords:

gravitational lensing - micro; planets and satellites - detection; microlensing; planets