Monte Carlo Simulations of Star Clusters - VI. The globular cluster NGC 6397

TL;DR

This paper presents Monte Carlo models simulating the dynamical evolution of the globular cluster NGC 6397, matching observed profiles after 12 billion years and exploring differences with similar clusters.

Contribution

It introduces detailed Monte Carlo simulations incorporating complex stellar interactions and Galactic effects to model NGC 6397's evolution over 12 Gyr.

Findings

Model matches observed surface brightness and velocity dispersion profiles.

Differences with M4 explained by core fluctuation phenomena.

Clusters are post-collapse objects with variable core resolvability.

Abstract

We describe Monte Carlo models for the dynamical evolution of the nearby globular cluster NGC 6397. The code includes treatments of two-body relaxation, most kinds of 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 12Gyr of evolution, gives a model with a fairly satisfactory match to the surface brightness profile, the velocity dispersion profile, and the luminosity function in two fields. We describe in particular those aspects of the evolution which distinguish this cluster from M4, which has a roughly similar mass and Galactocentric distance, but a qualitatively different surface brightness profile. Within the limitations of our modelling, we conclude that the most plausible explanation for the difference is fluctuations: both clusters are post-collapse objects, but sometimes have resolvable cores and sometimes not.