Microlensing Theory: Applications to Stellar and Galactic Astrophysics

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AST 0201266GouldMicrolensing observational capabilities are continuing to expand rapidly in several directions: for the first time, microlensing is being used to look for planets and probe the atmospheres of stars. Microlensing surveys toward M31 are returning their first substantial lists of candidate events. Within the next decade, microlensing should give us a detailed picture of the galactic bulge mass function down to 0.01 solar masses. These developments are presenting both new theoretical challenges and new observational opportunities. At the same time, they lay the basis for a strong interplay between microlensing and Galactic-structure studies. Dr. Andrew Gould, at Ohio State University, will build on these developments with two specific projects. 1. Characterization and Resolution of Binary and Planetary Degeneracies. Microlensing by binary and planetary systems often gives rise to dramatic caustic-induced jumps in the light curve, that both signal the presence of the binary or planet, and can be exploited to learn about the atmosphere of the source star being lensed. However, to fully extract this information, an unambiguous reconstruction of the geometry of the lensing system is required. Dr. Gould has demonstrated that even with the spectacular improvements in microlensing photometry, binary light curves can be subject to multiple interpretations. He has already solved the problem of classifying (and so understanding how to break) these degeneracies for the larger subclass of binary-lensing events. He will now do an analogous study of the smaller, but more difficult (and often more valuable) subclass. Similarly, he has already solved the problem of classifying the larger subclass of planetary degeneracies, and will now tackle the smaller, more difficult subclass. 2. Pixel Lensing of M31. Dr. Gould will continue his ongoing program of microlensing observations of M31, and will continue to give the data so acquired to competing groups. Good temporal coverage remains the weakest link in this subfield, so Dr. Gould's access to the MDM 1.3m and 2.4m telescopes can be of critical importance. Of almost equal importance to the scientific results to be obtained, is the training of the graduate students who will do a substantial part of the work. Dr. Gould has developed a very intensive and interactive mode of training students with extremely successful results, and that will continue with this award.***