Presentation #141.01 in the session “Stellar Rotation, Variability, and Flares”.
Binary companions likely affect stellar rotational evolution via tides (for close binaries) and disruption of the protoplanetary disk (for binary semimajor axes out to at least 5 to 80 AU). However, models of angular momentum evolution assume that all stars are single, and tidal models for solar-type stars cannot explain the handful of existing observations. Binary surveys in open clusters are woefully incomplete - we still lack observations for many cluster members with measured rotation periods. We present preliminary results from two complementary surveys that attempt to fill in gaps in our understanding of binary evolution. We have surveyed 51 M0-M1 rotators in the Praesepe open cluster using adaptive optics and non-redundant aperture masking at Keck II. We detect 19 companions and 5 probable chance alignments from our core sample, and combine these with other surveys to examine the impact of companions on the rotation distribution in Praesepe. We have also surveyed 35 FGK rotators in zero-age main sequence (ZAMS) clusters using speckle imaging at Gemini-South. We detect 5 candidate companions in these young clusters. Finally, we combine new and archival imaging data with Gaia DR2 to place constraints on any undetected companions. We present preliminary results showing that rapid rotators tend to have companions within 80 AU, in agreement with other recent surveys.