Despite the fact that nearly half of all stars are in close binaries (double star systems), our understanding of their evolution is far less advanced than it is for single stars, primarily because an appreciable fraction of mass can be transferred from one star to the other, and sometimes back again, or even lost to the system altogether. The beta Lyrae class is an important system among high-mass, eclipsing stellar binary systems in which mass transfer from the initially more massive star has progressed to the stage where the ratio of masses has been reversed. Despite a large number of beta Lyrae systems now known, our understanding of these systems has been stymied by the absence of any systems that have just begun this mass transfer as the massive star first evolves and enlarges. The PI argues that the binary star named SV Cen is just such a system. He also suggests that results from earlier attempts to model the light variations of this system as the stars eclipse one another can be best explained by a binary early in its mass-transfer evolution. In his picture mass is lost from the more massive star to an accretion disk around the less massive star. The PI plans to simulate the light variations and ultraviolet spectra with a computer model of this picture. The results are expected not only to clarify the role SV Cen itself plays in binary evolution but to test the correctness of many past models of light curves of similar eclipsing binary systems by many authors. Finally, the results of this study are expected to force a greater interaction between researchers investigating binary star evolution and the phenomenon of accretion disks.
