Monte Carlo simulations of star clusters - V. The globular cluster M4

Abstract

We describe Monte Carlo models for the dynamical evolution of the nearby globular cluster M4. The code includes treatments of two-body relaxation, three- and four-body interactions involving primordial binaries and those formed dynamically, the Galactic tide and the internal evolution of both single and binary stars. We arrive at a set of initial parameters for the cluster which, after 12 Gyr of evolution, gives a model with a satisfactory match to the surface-brightness profile, the velocity-dispersion profile and the luminosity function in two fields. We describe in particular the evolution of the core: according to our model, M4 (which has a classic King profile) is actually a post-collapse cluster, its core radius being sustained by binary burning. We also consider the distribution of its binaries, including those which would be observed as photometric binaries. Finally, we consider the populations of white dwarfs, neutron stars, black holes and blue stragglers, though not all channels for blue straggler formation are represented yet in our simulations.