Schedule Jan 17, 2009
Effect of Hardness of Primordial Binaries on Evolution of Star Clusters
Ataru Tanikawa (Nat'l Obs. of Japan)

We investigated the dynamical evolutions of star clusters with primordial binaries by means of GORILLA, an N-body simulation code we develop from scratch. We simulated eleven clusters consisting of N=16384 equal-mass stars. The clusters have primordial binaries whose binding energies are equal in each cluster. Six clusters of these contain 10 percent (in mass) primordial binaries with 1kT, 3kT, 10kT, 30kT, 100kT, and 300kT, three clusters contain 3 percent primordial binaries with 3kT, 30kT, and 300kT, and two clusters contain 30 percent primordial binaries with 3kT and 30kT, where 1.5kT is average stellar kinetic energy. We found that, in both soft (< 3kT) and hard (> 300kT) limits, clusters experiences deep core collapse when the clusters contain 10 percent primordial binaries. On the other hands, in the intermediate hardness (10-100kT), the core collapses halt halfway. The boundary of the depth of core collapse depends on the mass fraction of the primordial binaries. The cluster with 3kT primordial binaries experiences shallow core collapse when the mass fraction is 30 percent. The core radii at the halt can be explained by their energy budget.

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