Close Young Binary Stars, Early Stellar Evolution, and Planet Formation*

Most stars in our Galaxy are located in close binary and multiple systems but their formation is complex and satisfactory models that account for the diverse characteristics of these systems have proved elusive. Accurate theoretical calculations of binary formation and young star evolution are essential not only to hone our understanding of the associated planet formation process, but also to determine the viability of planet formation in dynamically diverse environments. The closest young binaries, with orbital periods of less than a few years and ages less than 5 Myr, provide a pathway for the determination of precise young star masses, a notoriously challenging parameter to measure. Furthermore, those systems that host circumbinary disks composed of primordial gas and dust, the sites of planet formation, provide the opportunity to study disk structure and evolution and the process of disk to star mass transfer, yielding clues to the dynamics of accretion onto massive planets and to disk dissipation. I will present an overview of these closest binaries and the unique and critical information that may be extracted from their observation.