At an age of 4 Gyr , typical solar-type stars in M67 have rotation rates of 20-30 days .
Using K2 Campaign 5 and 16 light curves and the spectral archive of the WIYN Open Cluster Study , we identify eleven three-dimensional kinematic members of M67 with anomalously fast rotation periods of 2-8 days , implying ages of less than 1 Gyr .
We hypothesize that these anomalously fast rotators have been spun up by mass transfer , mergers , or stellar collisions during dynamical encounters within the last Gyr , and thus represent lower-luminosity counterparts to the blue straggler stars .
These 11 candidate post-interaction stellar systems have much in common with the blue stragglers including a high binary fraction ( 73 % ) , a number of long-period , low-eccentricity binary systems , and in at least one case a UV excess consistent with the presence of a hot white dwarf companion .
The identification of these 11 systems provides the first picture of the low-luminosity end of the blue straggler distribution , providing new constraints for detailed binary evolution models and cluster population studies .
This result also clearly demonstrates the need to properly account for the impact of binaries on stellar evolution , as significant numbers of post-interaction binaries likely exist on cluster main sequences and in the field .
These stars are not always easy to identify , but make up \sim 10 % or more of the spectroscopic binary population among the solar-type stars in M67 .