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Completed Project

Time Series Photometry of Contact Binaries

Claire Freehafer, Colgate University ’15, Caitlin Rose, Vassar College ’17 and Prof. Fred Chromey

Binary star systems are instances in which two stars orbit a shared center of mass. In a surprisingly large number of cases, the two stars are close enough to touch and exchange mass.  These systems are known as contact binaries. The two stars in the system will eclipse each other, causing their observed brightness to vary over time. Tracking the brightness of these systems will produce the stars’ light curves, which are brightness vs. time graphs. Using Vassar College’s 0.8-meter telescope and CCD camera, we observed and analyzed light curves for 82 different contact binaries. We calibrated and performed photometry on thousands of images collected between February 6, 2014 and July 5, 2014, producing a total of 87 times of minima for these contact binaries. The difference between the predicted times and our observed times, called O-C values, may indicate changes in the period over time. These changes could have any number of causes, including mass transfer, mass loss, magnetic braking, or the presence of unseen companions. We chose to observe a few systems with well-established O-C trends as well as many that have not been observed so much in the past. Our results for the former help confirm and modify established trends, while for the latter our data will help establish trends for these lesser-studied systems. We also studied one system, V344 Lac, in greater detail and modeled its basic parameters, i.e. the size, mass, and temperature of each component.