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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

Basu, SandipanGENERAL RELATIVITY EFFECTS FOR EXTRASOLAR SYSTEMS WITH CLOSE IN GAS GIANTS
Master of Science, Miami University, 2008, Physics
To date, almost all of the extrasolar planets discovered are giant massive planets in orbits very close to their parent star. So, general relativistic effects of the parent star on these planets could be greatly important when their orbital stability is investigated. This research project deals with general relativistic effects on three major extrasolar planetary systems - Upsilon Andromedae, 55Cancri, and HD 74156. It shows that relativistic effects are quite important for the planets which are closest to the parent star. It also shows that general relativity suppresses eccentricity excitations, especiallyin the Upsilon Andromedae system. It also investigates the orbital stability of HD74156 d the middle planet in HD714156 system. Simulation results show that the zone where HD714156 d is supposed to exist is a highly unstable place to have any planet. Results are presented primarily to show that general relativity could be highly important when orbital stability of planets are concerned.

Committee:

Stephen Alexander (Advisor); Perry Rice (Committee Member); James Clemens (Committee Member)

Subjects:

Astronomy; Astrophysics; Physics

Keywords:

Extrasolar Planets; Upsilon andromedae; 55 Cancri; HD74156; general relativity effects

Mogren, Karen NicoleAnalytic Expressions for the Detectability of Exoplanets in Radial Velocity, Astrometric, and Transit Surveys
Master of Science, The Ohio State University, 2012, Astronomy
We derive analytic expressions for the detectability of exoplanets in radial velocity (RV), astrometric (AST), and transit (TR) data. We quantify detectability based on the total signal-to-noise ratio, S/N, but we do not attempt to determine the appropriate S/N value required for a robust detection. We first find analytic expressions for S/N in the limit of small, uniform errors, continuous sampling, and monitoring campaigns much longer than the orbital period. In this limit, we find exact expressions for S/N for RV and AST measurements considering arbitrary eccentricity and orbit viewing geometry. Eccentricity affects RV data in two ways. First, the semi-amplitude of the signal increases, which also increases S/N. However, the RV curve becomes skewed such that the deviation from the average velocity is smaller over most of the orbit and greater only near periastron, which decreases S/N. These two effects approximately cancel for e ≲ 0.6, thus making S/N only weakly dependent on eccentricity and differing by < 30% for e < 0.95. We also consider the effects of finite, uniform sampling, finding that detectability drops precipitously when eccentricity exceeds a certain value, ebreak = [1 – (1/(0.12*Nd))2/3]1/2, where Nd is the number of data points. For random sampling, the detectability is less sensitive to eccentricity. For RV, we further consider the effect on S/N when the duration of observations is less than the orbital period. For AST, S/N declines with increasing eccentricity in a manner that depends on both the inclination and argument of periastron. For TR, we derive approximate analytic expressions for S/N considering finite ingress/egress times and limb-darkening. Finally, we consider the scaling of S/N as a function of host star mass for planets at fixed mass and period, as well as planets in the habitable zones of their parent stars.

Committee:

Scott Gaudi (Advisor); Andrew Gould (Committee Member)

Subjects:

Astronomy; Astrophysics

Keywords:

radial velocity; astrometry; transits; exoplanets; extrasolar planets; detectability

Beatty, Thomas GExtrasolar Planet Detection and Characterization With the KELT-North Transit Survey
Doctor of Philosophy, The Ohio State University, 2014, Astronomy
My dissertation focuses on the detection and characterization of new transiting extrasolar planets from the KELT-North survey, along with a examination of the processes underlying the astrophysical errors in the type of radial velocity measurements necessary to measure exoplanetary masses. Since 2006, the KELT-North transit survey has been collecting wide-angle precision photometry for 20% of the sky using a set of target selection, lightcurve processing, and candidate identification protocols I developed over the winter of 2010-2011. Since our initial set of planet candidates were generated in April 2011, KELT-North has discovered seven new transiting planets, two of which are among the five brightest transiting hot Jupiter systems discovered via a ground-based photometric survey. This highlights one of the main goals of the KELT-North survey: to discover new transiting systems orbiting bright, V<10, host stars. These systems offer us the best targets for the precision ground- and space-based follow-up observations necessary to measure exoplanetary atmospheres. In September 2012 I demonstrated the atmospheric science enabled by the new KELT planets by observing the secondary eclipses of the brown dwarf KELT-1b with the Spitzer Space Telescope. For the first time, these eclipse observations demonstrated that hot, transiting, brown dwarfs have atmospheres similar to other, cold, brown dwarfs, and not to hot Jupiters. This opens up the use of the transiting brown dwarfs as objects of comparative study relative to the directly imaged cold brown dwarfs. Additionally, the strong focus on statistical repeatability I brought to the design of the KELT-North candidate selection process means that the results from the survey may be used in the future for a rigorous statistical analysis of the new, and old, transiting planets discovered by KELT-North. This will be only the fourth such analysis done using a transit survey, and, with approximately 80,000 target dwarf stars, will use the largest sample size to date. As a prelude to this project, my dissertation also provides the first a priori, descriptive, formulation of the astrophysical sources of uncertainty in radial velocity measurements. Exoplanetary masses are typically measured using radial velocity, and a thorough understanding of the sources of error in these observations provides crucial insight into the selection biases in searches for extrasolar planets, and allows for the design of more efficient surveys in the future.

Committee:

Scott Gaudi (Advisor); Gould Andrew (Committee Member); Pinsonneault Marc (Committee Member)

Subjects:

Astronomy; Astrophysics

Keywords:

extrasolar planets;photometry;transits;radial velocity;KELT-North;Spitzer;brown dwarfs

Pepper, Joshua AaronKELT: The Kilodegree Extremely Little Telescope
Doctor of Philosophy, The Ohio State University, 2007, Astronomy
The Kilodegree Extremely Little Telescope (KELT) project is an effort to find the best way to discover planetary transits of bright stars and to implement that method by building a telescope and discovering planets. In order to learn how to design a survey for transits of bright stars, we start by constructing a model of an all-sky survey for transits. That model points to an optimal survey configuration that uses a small-aperture, wide-field telescope to search for transits of stars in the range 8 < V < 10 magnitude. We used the parameters suggested by the model to build the KELT telescope, and we have deployed it to Winer Observatory in Arizona and begun a long-term survey for planets in a series of fields around the sky. The survey area covers about 25% of the Northern hemisphere and should allow us to detect the most scientifically valuable transiting planets. We examine the performance of the telescope with a number of metrics, and we find that it is performing at the level needed to detect the types of transits we are seeking. We have completed the analysis of the first data set from KELT - a commissioning run from early 2005 that observed the Praesepe open cluster over 74 nights. We obtained lightcurves of 69,337 stars, and detected 58 long period variables and 153 periodic variables. Sixteen of these are previously known variables, yielding 195 newly discovered variables for which we provide properties and lightcurves. We also searched for planetary-like transits, finding four transit candidates. Follow-up observations indicate that three of the candidates are astrophysical false positives, with one candidate inconclusively characterized.

Committee:

Richard Pogge (Advisor)

Subjects:

Physics, Astronomy and Astrophysics

Keywords:

extrasolar planets; planetary transits; astronomical surveys; small telescopes