Journal Article

An analytic model for blue straggler formation in globular clusters

Nathan Leigh, Alison Sills and Christian Knigge

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 2, pages 1410-1418
Published in print September 2011 | ISSN: 0035-8711
Published online September 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19136.x
An analytic model for blue straggler formation in globular clusters

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We present an analytic model for blue straggler formation in globular clusters. We assume that blue stragglers are formed only through stellar collisions and binary star evolution, and compare our predictions to observed blue straggler numbers. We can summarize our key results as follows. (1) Binary star evolution consistently dominates blue straggler production in all our best-fitting models. (2) In order to account for the observed sublinear dependence of blue straggler numbers on the core masses, the core binary fraction must be inversely proportional to the total cluster luminosity and should always exceed at least a few per cent. (3) In at least some clusters, blue straggler formation must be enhanced by dynamical encounters (either via direct collisions or by stimulating mass transfer to occur by altering the distribution of binary orbital parameters) relative to what is expected by assuming a simple population of binaries evolving in isolation. (4) The agreement between the predictions of our model and the observations can be improved by including blue stragglers that form outside the core but later migrate in due to dynamical friction. (5) Longer blue straggler lifetimes are preferred in models that include blue stragglers formed outside the core since this increases the fraction that will have sufficient time to migrate in via dynamical friction.

Keywords: blue stragglers; stars: statistics; globular clusters: general; stars: kinematics and dynamics

Journal Article.  8668 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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