Mass segregation

About: Mass segregation is a research topic. Over the lifetime, 1024 publications have been published within this topic receiving 57729 citations.

The initial mass function in clusters

Abstract: The stellar initial mass function (IMF) in star clusters is reviewed. Uncertainties in the observations are emphasized. We suggest there is a distinct possibility that cluster IMFs vary systematically with density or pressure. Dense clusters could have additional formation processes for massive stars that are not present in low density regions, making the slope of the upper mass IMF somewhat shallower in clusters. Observations of shallow IMFs in some super star clusters and in elliptical galaxies are reviewed. We also review mass segregation and the likelihood that peculiar IMFs, as in the Arches cluster, result from segregation and stripping, rather than an intrinsically different IMF. The theory of the IMF is reviewed in some detail. Several problems introduced by the lack of a magnetic field in SPH simulations are discussed. The universality of the IMF in simulations suggests that something more fundamental than the physical details of a particular model is at work. Hierarchical fragmentation by any of a variety of processes may be the dominant cause of the power law slope. Physical differences from region to region may make a slight difference in the slope and also appear in the low-mass turnover point.

Dynamical Interactions in Dense Stellar Clusters

Abstract: This chapter reviews the dynamical processes in young stellar clusters. The accretion of gas by individual stars affects the dynamics of the cluster, and the masses of the stars. Dynamical mass segregation cannot explain the degree of mass segregation observed in clusters such as the Trapezium Cluster in Orion, implying that the location of the massive stars is an indication of where they formed. This can, however, be explained by the competitive accretion model. If most, if not all, stars form in binary systems, then the high proportion of pre-main sequence binary systems can evolve in clusters to the smaller proportion of Galactic field stars through binary-binary and binary-single interactions. These models make definite predictions for the distribution of binary properties. The early evolution of a cluster sensitively depends on the primordial binary star proportion. Close encounters between stars with circum-stellar discs have drastic effects on the discs and on the stellar orbits. The discs are truncated at radii comparable to the encounter peri-astron, limiting their lifetimes and affecting their potential for planet formation. If the gas represents a significant fraction of the total cluster mass, its removal on dynamical time-scales can unbind the cluster allowing the stars to escape and populate the field. (shortened)

The stellar distribution of the globular cluster M 55

Abstract: We have used extensive V , I photometry (down to V =2 0 :9) of 33615 stars in the direction of the globular cluster M 55 to study the dynamical interaction of this cluster with the tidal elds of the Galaxy. An entire quadrant of the cluster has been covered, out to ' 1:5 times the tidal radius. A CMD down to about 4 magnitudes below the turn-off is presented and analysed. A large population of BS has been identied. The BS are signicantly more concentrated than the other cluster stars in the inner 300 arcsec, while they become less concentrated in the cluster envelope. We have obtained luminosity functions at various radial in- tervals from the center and their corresponding mass functions. Both clearly show the presence of mass segregation inside the cluster. A dynamical analysis shows that the observed mass segregation is compatible with what is predicted by multi-mass King-Michie models. The global mass function is very flat with a power-law slope of x = 1:0 0:4. This suggest that M 55 might have suffered selective losses of stars, caused by tidal interactions with the Galactic disk and bulge. The radial density prole of M 55 out to 2 rt suggests thepresenceofextra-tidalstarswhosenaturecouldbeconnected with the cluster.