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.45in for Advanced Study, Princeton, NJ 08540, U.S.A.


Blue stragglers are natural phenomena in star clusters. They originate through mass transfer in isolated binaries, as well as through encounters between two or more stars, in a complex interplay between stellar dynamics and stellar evolution. While this interplay cannot be modeled quantitatively at present, we will be able to do so in one or two years time. With this prospect, the present paper is written largely as a preview.

Star clusters with a high central density contain an ecological network of evolving binaries, affected by interactions with passing stars, while in turn affecting the energy budget of the cluster as a whole by giving off binding energy. The energy liberated can balance the losses from the central regions by escaping stars as well as the energy lost by a heat flow toward the relatively colder cluster halo.

The `gravitational fusion' of single stars into binaries, triples, and collisional merger products proceeds via a complex reaction network. Although we are beginning to chart the activity in some of the major channels, there are still major uncertainties, and consequently our present knowledge of blue straggler formation and evolution is largely qualitative.

Quantitative progress is contingent on advances in the following four areas: 1) observations of fundamental cluster parameters, such as the mass spectrum and the abundance of blue stragglers in the central regions; 2) availability of faster computers to model clusters on a star-by-star basis, with a Teraflops speed being desirable; 3) further improvement in N-body codes to make full use of such speeds; and 4) the development of consistent `evolutionary recipes' to treat the interplay between stellar evolution and stellar dynamics. These requirements can be met in the next couple years.

Thu Feb 24 00:52:57 EST 1994