MOCCA code for star cluster simulations - I. Blue stragglers, first results

We introduce an improved code for simulations of star clusters, called MOCCA. It combines the Monte Carlo method for star cluster evolution and the FEWBODY code to perform scattering experiments. The FEWBODY code was added in order to track more precisely dynamical interactions between objects which can lead to the creation of various exotic objects observed in the star clusters, like blue straggler stars (BSSs). The MOCCA code is currently one of the most advanced codes for simulating real size star clusters. It follows the star cluster evolution closely to N-body codes but is much faster. We show that the MOCCA code is able to follow the evolution of BSSs with details. It is a suitable tool to perform full scale evolution of real star clusters and detailed comparison with observations of exotic star cluster objects like BSSs.

This paper is the first one of a series of papers about properties of BSSs in star clusters. This type of stars are particularly interesting today, because by studying them one can get important constraints on the link between the stellar and dynamical evolution of star clusters. We discuss here first results concerning BSSs for an arbitrary chosen test model. We investigate properties of BSSs which characterize different channels of formation like masses, semi-major axes, eccentricities and orbital periods. We show how BSSs from different channels change their types, and discuss the initial and final positions of BSSs, their bimodal distribution in the star cluster, lifetimes and more.