Talk

The Rotational Evolution of Blue Straggler Stars

Emily Leiner, Northwestern University

Blue straggler stars, found brighter and bluer than the main-sequence turnoff in many clusters, are thought to form via binary mergers, mass transfer, or stellar collisions during dynamical encounters. All these interactions are expected to spin blue stragglers up to large rotational velocities at formation, resetting their gyro-age clocks. Less is known about the subsequent spin down of these post-interaction stars. I will review our theoretical and observational understanding of blue straggler rotational evolution, including new results demonstrating that post-mass-transfer blue stragglers spin down at the same rate as normal main-sequence stars. As a result, gyrochronology could be a useful new way to age-date blue stragglers and other post-interaction binaries. Furthermore, using the old open cluster M67 as an example, I will demonstrate that rotation can be used to detect a hidden population of post-interaction stars on the cluster main sequence. These detections indicate that up to 10% of the FGK main-sequence stars in older open clusters may have been through an interaction. These results illustrate that mass-transfer and mergers are common outcomes of stellar evolution in binary systems, and that understanding post-interaction rotational evolution has important implications for binary evolution physics, for identifying post-interaction binary populations, and for calibrating precise gyrochronology relationships in clusters.