Observations and Analysis of Exotic Gravitational Microlensing Events

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AST 0206189BennettThis award supports the investigations of Dr. David Bennett and Dr. Sun Hong Rhie, at Notre Dame University, into "exotic" gravitational microlensing events. Exotic events deviate from the standard gravitational microlensing light curve which assumes a point source, and single point lens, and constant velocities for the source, lens, and observer. These exotic events are particularly useful because they yield much more information about the distance and mass of the lens object than standard microlensing light curves. The study of these exotic microlensing events will address such issues as the possibility that a substantial fraction of the Milky Way's dark matter is composed of very old and cool white dwarfs, the abundance of isolated stellar mass black holes in the Milky Way disk, mass measurements of single stars at distances of kiloparsecs from Earth, and the abundance of low-mass giant planets in Jupiter-like orbits about stars in the Galactic disk and bulge. The work will have a significant impact on our understanding of the structure and composition of our Galaxy, the fundamental properties of stars and stellar remnants, and the basic mechanism of planet formation. This project will involve observations, data analysis, and some theoretical work. The observational effort will focus primarily on microlensing follow-up observations that will take advantage of the tremendous increase in real-time microlensing event discoveries expected from the OGLE-III and Super-MACHO projects which have just begun taking data. The observations will be done with the Boyden Observatory 1.5m telescope in South Africa, which has recently been refurbished for this observing program, as well as with the Mt. Stromlo 1.9m telescope, in Australia that has been used previously. The follow-up program will be done in cooperation with an Ohio State University group which will make a substantial contribution to the Mt. Stromlo 1.9m observations, and has near dedicated access to the CTIO 1.5m telescope in Chile. The combined resources of the Notre Dame and Ohio State groups will yield 24-hour coverage of microlensing events. This is necessary in order to mount a microlensing planet search program that will be sensitive to planets down to the mass of Neptune in Jupiter-like orbits. The observations will enable a stringent test of the "core accretion" model for planet formation. This microlensing follow-up program will also focus on the study of microlensing parallax events which can reveal isolated black holes. Follow-up observations of Large Magellanic Cloud (LMC) microlensing events discovered primarily by the Super-MACHO Project will yield "exotic" microlensing event features which will allow the determination of the lens distances for a statistically significant subset of events. This will determine if most of the LMC microlensing events are due to a part of the Milky Way's dark matter, or whether they are due to lensing by ordinary stars in the LMC. This award will also support a theoretical effort to evaluate potential future microlensing programs which might study dark matter in distance galaxies or terrestrial planets in our own Galaxy. ***