A prescription and fast code for the long-term evolution of star
  clusters
  We introduce the star cluster evolution code Evolve Me A Cluster of StarS
(EMACSS), a simple yet physically motivated computational model that describes
the evolution of some fundamental properties of star clusters in static tidal
fields. We base our prescription upon the flow of energy within the cluster,
which is a constant fraction of the total energy per half-mass relaxation time.
According to Henon's predictions, this flow is independent of the precise
mechanisms for energy production within the core, and therefore does not
require a complete description of the many-body interactions therein. For a
cluster of equal-mass stars, we thence use dynamical theory and analytic
descriptions of escape mechanisms to construct a series of coupled differential
equations expressing the time evolution of cluster mass and radius. These
equations are numerically solved using a fourth-order Runge-Kutta integration
kernel, and the results benchmarked against a data base of direct N-body
simulations. We use simulations containing a modest initial number of stars
(1024 <= N <= 65 536) and point-mass tidal fields of various strengths. Our
prescription is publicly available and reproduces the N-body results to within
~10 per cent accuracy for the entire post-collapse evolution of star clusters.
