Program: GS-2019A-Q-230

Models of angular momentum evolution still lack important components, including the influence of a companion star. Interactions between a star's disk and its companion during the first 1-10 Myr may disrupt the disk, allowing stars in binaries to spin up while their single counterparts are still locked to their disks. Disk disruption is maximized when the companion is within 30-40 AU. Thus, binaries likely play an important role in setting the initial rotation distribution in an open cluster. In 2019, we will analyze TESS data for stars in six open clusters in order to constrain stellar rotational evolution around the zero-age main sequence (ZAMS) for the first time. We now propose a 3.5 night speckle-imaging campaign on Gemini-South to search for companions around 160 FGK stars in these clusters. We will measure the binary fractions of fast and slow rotators, and search for any correlations between the orbital separation and the rotation period of the binary components. The results of this work will inform models of stellar rotational evolution, which currently assume that all stars form and evolve in isolation. Finally, since magnetic activity and fast rotation hinder exoplanet detection, correlations between multiplicity and rotation will inform planet occurrence rates.