Mirek Giersz, Douglas C. Heggie, Jarrod Hurley, Arkadiusz Hypki
We describe a major upgrade of a Monte Carlo code which has previously been
used for many studies of dense star clusters. We outline the steps needed in
order to calibrate the results of the new Monte Carlo code against N-body
simulations for large $N$ systems, up to N=200000. The new version of the Monte
Carlo code (called MOCCA), in addition to the old version, incorporates direct
FewBody integrator for three- and four-body interactions, and new treatment of
the escape process based on Fokushige and Heggie (2000). Now stars which fulfil
the escape criterion are not removed immediately, but can stay in the system
for a certain time which depends on the excess of the energy of a star above
the critical energy. They are called potential escapers. FewBody integrator
allows to follow all interaction channels, which are important for the rate of
creation of various types of objects observed in star clusters, and assures
that the energy generation by binaries is treated in a meaner similar to the
N-body model.
There are at most three parameters which have to be adjusted against N-body
simulations for large N. Two (or one, depends on the chosen approach) connected
with the escape process and one responsible for determination of the
interaction probabilities. The adopted free parameters are independent on N.
They allow MOCCA code to reproduce N-body results, in a reasonably precision,
not only for the rate of cluster evolution and the cluster mass distribution,
but also for the detailed distributions of mass and binding energy of binaries.
The MOCCA code is at present the most advanced code for simulations of real
star clusters. It can follow the cluster evolution in details comparable to
N-body code, but orders of magnitude faster.
View original:
http://arxiv.org/abs/1112.6246
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