Wednesday, March 13, 2013

1303.2667 (Alison Sills et al.)

Mock Observations of Blue Stragglers in Globular Cluster Models    [PDF]

Alison Sills, Evert Glebbeek, Sourav Chatterjee, Frederic A. Rasio
We created artificial color-magnitude diagrams of Monte Carlo dynamical models of globular clusters, and then used observational methods to determine the number of blue stragglers in those clusters. We compared these blue stragglers to various cluster properties, mimicking work that has been done for blue stragglers in Milky Way globular clusters to determine the dominant formation mechanism(s) of this unusual stellar population. We find that a mass-based prescription for selecting blue stragglers will choose approximately twice as many blue stragglers than a selection criterion that was developed for observations of real clusters. However, the two numbers of blue stragglers are well-correlated, so either selection criterion can be used to characterize the blue straggler population of a cluster. We confirm previous results that the simplified prescription for the evolution of a collision or merger product in the BSE code overestimates the lifetime of collision products. Because our observationally-motivated selection criterion does not include the brightest collision products, we show that our model blue stragglers follow the same trends with cluster properties (core mass, binary fraction, total mass, collision rate) as the true Milky Way blue stragglers. The total number of blue stragglers in globular clusters is determined mainly by the properties and numbers of binary stars, and not the collision rate, even though the blue stragglers are formed through binary-mediated collisions.
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