scholarly journals Dynamics of Star Clusters: Comparison of Theory with Observations and Simulations

1975 ◽  
Vol 69 ◽  
pp. 119-131 ◽  
Author(s):  
R. Wielen
Keyword(s):  
Monte Carlo ◽  
Density Distribution ◽  
Age Distribution ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Average Mass ◽  
Low Mass ◽  
Good Agreement

Stellar dynamical theories for collisional systems are tested by numerical N-body simulations of isolated star clusters with N up to 500. For the dynamical evolution of the density distribution in star clusters, good agreement is found between Monte Carlo results and N-body models. There remains a discrepancy between theory and simulations in the rate of stellar escape from clusters and/or in the mechanism by which escapers are produced. Simulations of non-isolated star clusters are compared with observations of open clusters. The observed age distribution of open clusters can be explained by the dynamical dissolution of clusters. Stars of low mass do not escape relatively more frequently than stars of average mass.

scholarly journals Dynamical explorations of nuclear structures in barred galaxies

2000 ◽  
Vol 174 ◽  
pp. 261-272
Author(s):  
J. Anosova ◽  
G. F. Benedict
Keyword(s):  
Black Hole ◽  
Velocity Field ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Galactic Nuclei ◽  
Barred Galaxies ◽  
One Stage ◽  
Low Mass ◽  
Nuclear Structures ◽  
Good Agreement

AbstractWe construct models of a galaxy in order to provide a possible identification of the dynamical processes that lead to the formation of structure observed in galactic nuclei. We assume that the center of our model contains a very massive double black hole, surrounded by relatively low-mass particles - star clusters, gas, and dust complexes. Our previous work (Anosova et al. 1994, 1995) snowed that the dynamical evolution of such a model produces many structures similar to those observed in the nuclei of galaxies, including rings and various types of flows and jets. In such models the ’gravitational slingshot’ effect frequently occurs.We consider a number of such models with different initial parameters. Comparison of our models with the observed structure of NGC 4314 shows good agreement at one stage of the evolution for certain combinations of initial parameters. The model predicts the velocity field observed in NGC 4314.

scholarly journals Dynamics of Open Star Clusters

1985 ◽  
Vol 113 ◽  
pp. 449-462 ◽  
Author(s):  
Roland Wielen
Keyword(s):  
Black Holes ◽  
Molecular Clouds ◽  
Age Distribution ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Giant Molecular Clouds ◽  
Open Star Clusters ◽  
Massive Black Holes ◽  
Open Star

The dynamical evolution of open star clusters has been studied successfully by numerical N-body simulations. We compare in detail the theoretically predicted lifetimes with those derived from the observed age distribution of open clusters. Rare but efficient encounters between clusters and giant molecular clouds are probably responsible for the sudden disruption of many open clusters. Massive black holes from the galactic corona would, on the average, affect only old open clusters.

scholarly journals Ages of Galactic and Extragalactic Star Clusters of Various Abundances

1983 ◽  
Vol 6 ◽  
pp. 109-117 ◽  
Author(s):  
R.D. Cannon
Keyword(s):  
Star Clusters ◽  
Magellanic Clouds ◽  
Open Clusters ◽  
Simultaneous Solution ◽  
Low Mass Stars ◽  
Cluster Systems ◽  
Distant Cluster ◽  
Low Mass

In this review I shall concentrate mainly on globular star clusters in our Galaxy since these are the objects for which most work has been done recently, both observationally and theoretically. However, I shall also discuss briefly the oldest open clusters and clusters in the Magellanic Clouds. Little can be said about more distant cluster systems, since the only observations available are of integrated colours or spectra and these seem to be rather unreliable indicators of age. It is perhaps worth pointing out that the title may be slightly misleading; the problem is not so much to determine the ages of clusters of known abundances, as to obtain the best simultaneous solution for both age and composition, since some of the most important abundances (notably helium and oxygen) are virtually unobservable in little-evolved low mass stars.

scholarly journals X-ray sources in Galactic globular clusters and old open clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 367-376
Author(s):  
Maureen van den Berg
Keyword(s):  
Globular Clusters ◽  
Cataclysmic Variables ◽  
Star Clusters ◽  
Open Clusters ◽  
Encounter Rate ◽  
X Ray ◽  
Low Mass ◽  
New Perspective ◽  
X Ray Binaries ◽  
Cluster Age

AbstractThe features and make up of the population of X-ray sources in Galactic star clusters reflect the properties of the underlying stellar environment. Cluster age, mass, stellar encounter rate, binary frequency, metallicity, and maybe other properties as well, determine to what extent we can expect a contribution to the cluster X-ray emission from low-mass X-ray binaries, millisecond pulsars, cataclysmic variables, and magnetically active binaries. Sensitive X-ray observations withXMM-Newton and certainlyChandra have yielded new insights into the nature of individual sources and the effects of dynamical encounters. They have also provided a new perspective on the collective X-ray properties of clusters, in which the X-ray emissivities of globular clusters and old open clusters can be compared to each other and to those of other environments. I will review our current understanding of cluster X-ray sources, focusing on star clusters older than about 1 Gyr, illustrated with recent results.

scholarly journals Observations of low mass stars in clusters: Some constraints and puzzles for stellar evolution theory

1984 ◽  
Vol 105 ◽  
pp. 123-138
Author(s):  
R.D. Cannon
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Star Clusters ◽  
Variable Stars ◽  
Open Clusters ◽  
Low Mass Stars ◽  
Theory Of Evolution ◽  
Theoretical Predictions ◽  
Low Mass ◽  
Red Giant

This review will attempt to do two things: (i) discuss some of the data which are available for testing the theory of evolution of low mass stars, and (ii) point out some problem areas where observations and theory do not seem to agree very well. This is of course too vast a field of research to be covered in one brief review, so I shall concentrate on one particular aspect, namely the study of star clusters and especially their colour-magnitude (CM) diagrams. Star clusters provide large samples of stars at the same distance and with the same age, and the CM diagram gives the easiest way of comparing theoretical predictions with observations, although crucial evidence is also provided by spectroscopic abundance analyses and studies of variable stars. Since this is primarily a review of observational data it is natural to divide it into two parts: (i) galactic globular clusters, and (ii) old and intermediate-age open clusters. Some additional evidence comes from Local Group galaxies, especially now that CM diagrams which reach the old main sequence are becoming available. For each class of cluster I shall consider successive stages of evolution from the main sequence, up the hydrogen-burning red giant branch, and through the helium-burning giant phase.

scholarly journals Characterizing dynamical stages of open clusters located in the Sagittarius spiral arm

2019 ◽  
Vol 488 (2) ◽  
pp. 1635-1651 ◽  
Author(s):  
M S Angelo ◽  
A E Piatti ◽  
W S Dias ◽  
F F S Maia
Keyword(s):  
Structural Parameters ◽  
Three Dimensional ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Mass Star ◽  
Proper Motions ◽  
Concentration Parameter ◽  
Low Mass ◽  
Gaia Dr2 ◽  
Spiral Arm

Abstract The study of dynamical properties of Galactic open clusters (OCs) is a fundamental prerequisite for the comprehension of their dissolution processes. In this work, we characterized 12 OCs, namely: Collinder 258, NGC 6756, Czernik 37, NGC 5381, Ruprecht 111, Ruprecht 102, NGC 6249, Basel 5, Ruprecht 97, Trumpler 25, ESO 129−SC32, and BH 150, projected against dense stellar fields. In order to do that, we employed Washington CT1 photometry and Gaia DR2 astrometry, combined with a decontamination algorithm applied to the three-dimensional astrometric space of proper motions and parallaxes. From the derived membership likelihoods, we built decontaminated colour–magnitude diagrams, while structural parameters were obtained from King profiles fitting. Our analysis revealed that they are relatively young OCs (log(t  yr−1) ∼7.3–8.6), placed along the Sagittarius spiral arm, and at different internal dynamical stages. We found that the half-light radius to Jacobi radius ratio, the concentration parameter and the age to relaxation time ratio describe satisfactorily their different stages of dynamical evolution. Those relative more dynamically evolved OCs have apparently experienced more important low-mass star loss.

scholarly journals Young and intermediate-age massive star clusters

2010 ◽  
Vol 368 (1913) ◽  
pp. 867-887 ◽  
Author(s):  
Søren S. Larsen
Keyword(s):  
Star Formation ◽  
Star Clusters ◽  
Mass Function ◽  
Starburst Galaxies ◽  
Open Clusters ◽  
High Mass ◽  
Current Evidence ◽  
Power Law Distribution ◽  
Low Mass ◽  
Massive Clusters

An overview of our current understanding of the formation and evolution of star clusters is given, with the main emphasis on high-mass clusters. Clusters form deeply embedded within dense clouds of molecular gas. Left-over gas is cleared within a few million years and, depending on the efficiency of star formation, the clusters may disperse almost immediately or remain gravitationally bound. Current evidence suggests that a small percentage of star formation occurs in clusters that remain bound, although it is not yet clear whether this fraction is truly universal. Internal two-body relaxation and external shocks will lead to further, gradual dissolution on time scales of up to a few hundred million years for low-mass open clusters in the Milky Way, while the most massive clusters (>10 5  M ⊙ ) have lifetimes comparable to or exceeding the age of the Universe. The low-mass end of the initial cluster mass function is well approximated by a power-law distribution, , but there is mounting evidence that quiescent spiral discs form relatively few clusters with masses M >2×10 5  M ⊙ . In starburst galaxies and old globular cluster systems, this limit appears to be higher, at least several ×10 6  M ⊙ . The difference is likely related to the higher gas densities and pressures in starburst galaxies, which allow denser, more massive giant molecular clouds to form. Low-mass clusters may thus trace star formation quite universally, while the more long-lived, massive clusters appear to form preferentially in the context of violent star formation.

scholarly journals Survival rates of planets in open clusters: the Pleiades, Hyades, and Praesepe clusters

2019 ◽  
Vol 624 ◽  
pp. A110 ◽  
Author(s):  
M. S. Fujii ◽  
Y. Hori
Keyword(s):  
Open Cluster ◽  
Survival Rates ◽  
Giant Planet ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Major Axis ◽  
Open Clusters ◽  
Semi Major Axis ◽  
Embedded Clusters ◽  
Host Stars

Context. In clustered environments, stellar encounters can liberate planets from their host stars via close encounters. Although the detection probability of planets suggests that the planet population in open clusters resembles that in the field, only a few dozen planet-hosting stars have been discovered in open clusters. Aims. We explore the survival rates of planets against stellar encounters in open clusters similar to the Pleiades, Hyades, and Praesepe and embedded clusters. Methods. We performed a series of N-body simulations of high-density and low-density open clusters, open clusters that grow via mergers of subclusters, and embedded clusters. We semi-analytically calculated the survival rate of planets in star clusters up to ~1 Gyr using relative velocities, masses, and impact parameters of intruding stars. Results. Less than 1.5% of close-in planets within 1 AU and at most 7% of planets with 1–10 AU are ejected by stellar encounters in clustered environments after the dynamical evolution of star clusters. If a planet population from 0.01–100 AU in an open cluster initially follows the probability distribution function of exoplanets with semi-major axis (ap) between 0.03 and 3 AU in the field discovered by RV surveys (∝ ap−0.6), the PDF of surviving planets beyond ~10 AU in open clusters can be slightly modified to ∝ ap−0.76. The production rate of free-floating planets (FFPs) per star is 0.0096–0.18, where we have assumed that all the stars initially have one giant planet with a mass of 1–13 MJup in a circular orbit. The expected frequency of FFPs is compatible with the upper limit on that of FFPs indicated by recent microlensing surveys. Our survival rates of planets in open clusters suggest that planets within 10 AU around FGKM-type stars are rich in relatively-young (≲10–100 Myr for open clusters and ~1–10 Myr for embedded clusters), less massive open clusters, which are promising targets for planet searches.

scholarly journals Extended halo of NGC 2682 (M 67) from Gaia DR2

2019 ◽  
Vol 627 ◽  
pp. A119 ◽  
Author(s):  
R. Carrera ◽  
M. Pasquato ◽  
A. Vallenari ◽  
L. Balaguer-Núñez ◽  
T. Cantat-Gaudin ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Open Cluster ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Galactic Disc ◽  
The Past ◽  
External Perturbations ◽  
Galactic Potential ◽  
Gaia Dr2

Context. NGC 2682 is a nearby open cluster that is approximately 3.5 Gyr old. Dynamically, most open clusters are expected to dissolve on shorter timescales of ≈1 Gyr. That it has survived until now means that NGC 2682 was likely much more massive in the past and is bound to have an interesting dynamical history. Aims. We investigate the spatial distribution of the stars in NGC 2682 to constrain dynamical evolution of the cluster. We particularly focus on the marginally bound stars in the cluster outskirts. Methods. We used Gaia DR2 data to identify NGC 2682 members up to a distance of ∼150 pc (10°). The two methods Clusterix and UPMASK were applied to this end. We estimated distances to obtain 3D stellar positions using a Bayesian approach to parallax inversion, with an appropriate prior for star clusters. We calculated the orbit of NGC 2682 using the GRAVPOT16 software. Results. The cluster extends up to 200′ (50 pc), which implies that its size is at least twice as large as previously believed. This exceeds the cluster Hill sphere based on the Galactic potential at the distance of NGC 2682. Conclusion. The extra-tidal stars in NGC 2682 may originate from external perturbations such as disc-shocking or dynamical evaporation from two-body relaxation. The former origin is plausible given the orbit of NGC 2682, which crossed the Galactic disc ≈40 Myr ago.

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