Events at Physics |
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Open clusters occupy a compelling regime for blue straggler formation. Their moderate stellar densities permit blue straggler formation through all of the known mechanisms, namely collisions, mergers and mass transfer. Furthermore, the accessibility of open clusters to both detailed observations and sophisticated N-body simulations provides unique opportunities to investigate the origins of blue stragglers in great detail. Perhaps the most well-studied blue straggler population in an open cluster is that of NGC 188. This ~7 Gyr open cluster hosts 21 blue stragglers, 16 of which are known to have binary companions, as revealed by our multi-epoch WIYN/Hydra radial-velocity survey. The majority of these blue stragglers have ~0.5 Msun companions that orbit with periods of order 1000 days and have modest eccentricities. Comparisons with predictions from N-body simulations of NGC 188 show that collisions and mergers cannot create such blue stragglers. (Although these mechanisms may account for some or all of the other blue stragglers in the cluster.) Instead the dominant formation mechanism for the blue stragglers in NGC 188 is most likely mass transfer processes.<br>