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Paper: Cluster IMF's and mass segregation: dynamical effects
Volume: 198, Stellar Clusters and Associations: Convection, Rotation, and Dynamos
Page: 151
Authors: de la Fuente Marcos, R.
Abstract: In this paper we review the role of the initial mass function (IMF) on the evolution of open star clusters and summarize several results from simulations. These results suggest that the dynamical evolution of small clusters is very dependent of the IMF but its importance decreases when considering richer clusters. The IMF induces a differential behavior as regards cluster life-time: small clusters disrupt earlier and the longevity of rich (N > 500) clusters is increased. Preferential escape of low-mass stars may contribute by a non-negligible factor to underestimate the slope of the IMF for light stars. The importance od this effect increases with the age of the cluster and it is expected that it will be the dominant source of error for old clusters providing a so-called age bias in the determination of the IMF. This preferential escape is connected with dynamically induced mass segregation in clusters as a result of energy equipartition. On the other hand, observations suggest that there is a different IMF for binaries. Primordial binaries dominate completely the evolution of poor clusters and control it until they are ejected or disrupted. Binaries have a greater mass that single stars and due to energy equipartition, they spiral towards the cluster core. Binaries reach the core before massive singles, so the binary density in the central regions of the cluster is increased during the first stages of the evolution of the cluster, producing high velocity escapers as a result of close encounters with single stars and/or other binaries. In this way, energy equipartition is also producing binary segregation, i.e. an increase in the percentage of binaries towards the center of the cluster.
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