This project is concerned with interpreting the signals of gravitational microlensing events in searches for Massive Compact Halo Objects (MACHOs) in the halo of the Milky Way. If a significant fraction of halo dark matter consists of MACHOs, monitoring programs should discover more microlensing events than can be generated by known stellar populations. More than 2500 microlensing events have been discovered during the past 15 years. The present rate of discovery is roughly 600 per year, and will soon increase as new monitoring programs begin. Most light curves are of the standard point-source, point-lens type. These "vanilla" light curves are highly degenerate: in the absence of clear parallax effects, only a combination of the lens mass, speed, and position can be estimated. To determine the contribution associated with MACHOs, one must therefore rely on statistical studies. Although results from the first generation of monitoring programs place limits on the MACHO fraction, the results are still highly uncertain.
Binary lens light curves, on the other hand, contain more information. Under ideal circumstances the position, speed, and mass of the lens can be measured, and limits can be placed on the binary's orbital separation and mass ratio. Binary lenses can therefore provide powerful diagnostics. Those located in the source galaxy can potentially be identified and appropriately subtracted from the signature of dark masses in the Halo. Binary MACHOs(if they exist) can be identified, and the wealth of information coded in binary-lens light curves presents the exciting prospect of measuring the properties of individual MACHOs.
The power gained through studying individual events is magnified for an ensemble of binary-lens light curves. This is because the variety of light curve shapes and their connection to the physical parameters of the lens provide multiple opportunities for consistency checks, while also probing the distribution of binary properties among the lens population.
Here, Dr. Di Stefano and collaborators will develop the necessary tools to systematically find and interpret binary lens events in the data collected by monitoring programs of the past, present, and future. By applying this work to data collected by several groups, the number of known binary-lens events will likely be doubled. Most important, these methods will be adaptable to data from all other monitoring programs, including the wide-field surveys, the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS), and the Large Synoptic Survey Telescope (LSST).
This work will also address the automated detection and classification of variability in images, which has broad application, to, e.g., biology. Graduate and undergraduate students will play important roles at every stage of the work. Dr. Di Stefano is also involved in an outreach program with the Cambridge public schools which will include discussions of this work with students in grades K-8.
