Where the Blue Stragglers Roam: Searching for a Link between Formation and Environment

The formation of blue stragglers is still not completely understood,particularly the relationship between formation environment and mechanism. Weuse a large, homogeneous sample of blue stragglers in the cores of 57 globularclusters to investigate the relationships between blue straggler populationsand their environments. We use a consistent definition of "blue straggler"based on position in the color-magnitude diagram, and normalize the populationrelative to the number of red giant branch stars in the core. We find that thepreviously determined anti-correlation between blue straggler frequency andtotal cluster mass is present in the purely core population. We find some weakcorrelations with central velocity dispersion and with half-mass relaxationtime. The blue straggler frequency does not show any trend with any othercluster parameter. Even though collisions may be expected to be a dominant bluestraggler formation process in globular cluster cores, we find no correlationbetween the frequency of blue stragglers and the collision rate in the core. Wealso investigated the blue straggler luminosity function shape, and found norelationship between any cluster parameter and the distribution of bluestragglers in the color-magnitude diagram. Our results are inconsistent withsome recent models of blue straggler formation that include collisionalformation mechanisms, and may suggest that almost all observed blue stragglersare formed in binary systems.Comment: Important changes to tables and figures have been made in the included erratum. Our results remain unchange