Equipartition in multicomponent gravitational systems

Inagaki, Shogo; Saslaw, William C.

doi:10.1086/163164

Cited by 60 publications

(68 citation statements)

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“…a core of zero size and formally infinite density) is t cc ∼ 15t rh for an initial Plummer sphere of identical masses. Starting with a more concentrated King (1966) distribution shortens the time of core collapse considerably (Quinlan 1996), as does a broad spectrum of masses (Inagaki & Saslaw 1985). In systems with a mass spectrum, two-body interactions accelerate the dynamical evolution by driving the system toward energy equipartition, in which the velocity dispersions of stars of different masses would have mv 2 ∼ constant.…”

Section: Core Collapsementioning

confidence: 99%

Young Massive Star Clusters

Zwart

McMillan

Gieles

2010

Annu. Rev. Astron. Astrophys.

920

243

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Young massive clusters are dense aggregates of young stars that form the fundamental building blocks of galaxies. Several examples exist in the Milky Way Galaxy and the Local Group, but they are particularly abundant in starburst and interacting galaxies. The few young massive clusters that are close enough to resolve are of prime interest for studying the stellar mass function and the ecological interplay between stellar evolution and stellar dynamics. The distant unresolved clusters may be effectively used to study the star-cluster mass function, and they provide excellent constraints on the formation mechanisms of young cluster populations. Young massive clusters are expected to be the nurseries for many unusual objects, including a wide range of exotic stars and binaries. So far only a few such objects have been found in young massive clusters, although their older cousins, the globular clusters, are unusually rich in stellar exotica.In this review we focus on star clusters younger than ∼ 100 Myr, more than a few current crossing times old, and more massive than ∼ 10 4 M ⊙ , irrespective of cluster size or environment. We describe the global properties of the currently known young massive star clusters in the Local Group and beyond, and discuss the state of the art in observations and dynamical modeling of these systems. In order to make this review readable by observers, theorists, and computational astrophysicists, we also review the cross-disciplinary terminology.

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Section: Core Collapsementioning

confidence: 99%

Young Massive Star Clusters

Zwart

McMillan

Gieles

2010

Annu. Rev. Astron. Astrophys.

920

243

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“…The time-scale for the onset of significant dynamical mass segregation is comparable to the cluster's dynamical relaxation time (Spitzer & Shull 1975;Inagaki & Saslaw 1985;Bonnell & Davies 1998;Elson et al 1998). A cluster's characteristic time-scale may be taken to be its half-mass (or median) relaxation time, i.e., the relaxation time at the mean density for the inner half of the cluster mass for cluster stars with stellar velocity dispersions characteristic for the cluster as a whole (Spitzer & Hart 1971;Lightman & Shapiro 1978;Meylan 1987;Malumuth & Heap 1994).…”

Section: Mass Segregationmentioning

confidence: 99%

The Long-term Survival Chances of Young Massive Star Clusters

Grijs

Parmentier

2007

Chin. J. Astron. Astrophys.

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We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered protoglobular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.

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“…Direct searches by Lindegren et al (2000) and Madsen et al (2001) for a relation between the observed velocity dispersion and mass (or absolute magnitude), did however prove inconclusive. Evidence of any equipartition of kinetic energy is best sought among the stars in the core of the cluster (Inagaki & Saslaw 1985). For the present study, a limiting radius of 3 pc is therefore used.…”

Section: Dispersion Versus Stellar Massmentioning

confidence: 99%

Hyades dynamics fromN-body simulations: Accuracy of astrometric radial velocities from Hipparcos

Madsen

2003

A&A

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Abstract. The internal velocity structure in the Hyades cluster as seen by Hipparcos is compared with realistic N-body simulations using the NBODY6 code, which includes binary interaction, stellar evolution and the Galactic tidal field. The model allows to estimate reliably the accuracy of astrometric radial velocities in the Hyades as derived by Lindegren et al. (2000) and Madsen et al. (2002) from Hipparcos data, by applying the same estimation procedure on the simulated data. The simulations indicate that the current cluster velocity dispersion decreases from 0.35 km s −1 at the cluster centre to a minimum of 0.20 km s −1 at 8 pc radius (2-3 core radii), from where it slightly increases outwards. A clear negative correlation between dispersion and stellar mass is seen in the central part of the cluster but is almost absent beyond a radius of 3 pc. It follows that the (internal) standard error of the astrometric radial velocities relative to the cluster centroid may be as small as 0.2 km s −1 for a suitable selection of stars, while a total (external) standard error of 0.6 km s −1 is found when the uncertainty of the bulk motion of the cluster is included. Attempts to see structure in the velocity dispersion using observational data from Hipparcos and Tycho-2 are inconclusive.

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Equipartition in multicomponent gravitational systems

Cited by 60 publications

References 0 publications

Young Massive Star Clusters

Young Massive Star Clusters

The Long-term Survival Chances of Young Massive Star Clusters

Hyades dynamics fromN-body simulations: Accuracy of astrometric radial velocities from Hipparcos

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