Binary formation within globular clusters: X-ray clues

CESR, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 4, France e-mail: gendre@rm.iasf.cnr.it

Received: 7 September 2004
Accepted: 22 November 2004

Abstract

We have investigated the effect of the number of primordial binaries on the relationship between the total number of detected binaries within globular cluster and its collision rate. We have used simulated populations of binary stars in globular clusters: primordial binaries and binaries formed through gravitational interactions. We show that the initial number of primordial binaries influences the relationship between the number of detected sources and the collision rate, which we find to be a power law. We also show that observing an incomplete sample provides the same results as those obtained with a complete sample. We use observations made by XMM-Newton and Chandra to constrain the formation mechanism of sources with X-ray luminosities larger than 10³¹ erg s^-1, and show that some of the cataclysmic variables within globular clusters should be primordial objects. We point out a possibly hidden population of neutron stars within high mass globular clusters with a low collision rate.