Evolutionary history of four binary blue stragglers from the globular clusters \omega Cen, M55, 47 Tuc and NGC 6752

TL;DR

This study models the evolutionary history of four binary blue stragglers in globular clusters, revealing their progenitors as close binaries that become blue stragglers through mass transfer and highlighting helium enrichment in one case.

Contribution

It provides detailed evolutionary models for four binary blue stragglers, demonstrating their progenitors and the role of mass transfer and helium enrichment, which advances understanding of blue straggler formation.

Findings

Progenitors are close binaries with periods of a few days.

Blue stragglers form via mass transfer and rejuvenation.

Helium enrichment observed in V209 supports helium-rich subpopulations.

Abstract

Context. Origin and evolution of blue stragglers in globular clusters is still a matter of debate. Aims. The aim of the present investigation is to reproduce the evolutionary history of four binary blue stragglers in four different clusters, for which precise values of global parameters are known. Methods. Using the model for cool close binary evolution, developed by one of us (KS), progenitors of all investigated binaries were found and their parameters evolved into the presently observed values. Results. The results show that the progenitors of the binary blue stragglers are cool close binaries with period of a few days, which transform into stragglers by rejuvenation of the initially less massive component by mass transfer from its more massive companion overflowing the inner critical Roche surface. The parameters of V209 from \omega Cen indicate that the binary is substantially enriched in helium. This is an independent and strong evidence for the existence of the helium rich subpopulation in this cluster.