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Session 72 - Open Clusters.
Display session, Wednesday, January 15
Metropolitan Ballroom,

[72.07] Evolution of Blue Stragglers

A. Sills (Yale U.), J. Lombardi (Cornell U.), C. Bailyn, P. Demarque (Yale U.), F. Rasio (MIT), S. Shapiro (U. of Illinois at Urbana-Champaign)

Blue stragglers, stars in clusters which are bluer and brighter than the main sequence turnoff, were discovered over forty years ago. However, a definitive theory to explain their formation and subsequent evolution still does not exist. One currently favoured idea is that some blue stragglers are the products of stellar collisions. We have been investigating this hypothesis by combining the results of Smoothed Particle Hydrodynamics (SPH) simulations of the stellar collision (Lombardi, Rasio and Shapiro 1996) with stellar evolution calculations. We convert the results of the SPH simulations into a starting model for our evolution calculations, and then evolve the resulting star through the initial thermal relaxation phase to the main sequence, up the giant branch, and onto the horizontal branch. In this way we can determine lifetimes and distributions of blue stragglers in globular clusters without resorting to previously-employed ad hoc assumptions (eg. Bailyn and Pinsonneault 1995, Ouellette and Prichet 1996, Sandquist, Bolte and Hernquist 1996). The difficulties of converting the results of a hydrodynamic calculation into a starting model for a stellar evolution code which assumes hydrostatic equilibrium will be discussed, and preliminary results will be presented. Bailyn, C. D. and Pinsonneault, M. H. 1995, ApJ, 439, 705. Lombardi, J. C., Rasio, F. A. and Shapiro, S.L. 1996 ApJ, 468, 797. Ouellette, J. and Prichet, C. 1996, in The Origins, Evolution and Destinies of Binary Stars in Globular Clusters, ed. E. F. Milone, p 356. Sandquist, Bolte and Hernquist, 1996, ApJ in press.

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