Evolutionary history of four binary blue stragglers from the globular clusters ω Cen, M 55, 47 Tuc, and NGC 6752

¹ Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
e-mail: kst@astrouw.edu.pl
² Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland
e-mail: alosza@camk.edu.pl; mnr@camk.edu.pl

Received: 10 August 2016
Accepted: 30 September 2016

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 that we developed, 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 as a result of mass transfer from its more massive companion overflowing the inner critical Roche surface. The parameters of V209 from ω Cen indicate that the binary is substantially enriched in helium. This is an independent and strong evidence of the existence of the helium rich subpopulation in this cluster.