On the lifetimes of galactic clusters

Wielen, Roland

doi:10.1007/bf00649160

Cited by 103 publications

(149 citation statements)

References 5 publications

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“…It is encouraging that the mean relaxation time for centrally concentrated systems is in substantial agreement with the corresponding numerical values for cases with ^= 1 0 0 (Aarseth, 1966;Wielen, 1967). A systematic dynamical comparison with the predicted dependence on particle number has not yet been attempted because of the uncertainty in defining a satisfactory numerical procedure.…”

Section: Comparison With Theorymentioning

confidence: 57%

“…The escape rate is increased further by the disruptive effect of passing interstellar clouds (Bouvier and Janin, 1971). Mass loss effects in heavy stars during advanced stages of physical evolution have also been considered (Wielen, 1968); more recent results of realistic cluster simulations are given elsewhere in this volume (Wielen, 1971).…”

Section: General Discussion Of Resultsmentioning

confidence: 99%

“…Experimental determinations of the relative escape rate have been made for several cases with ^= 1 0 0 giving L m~( 0.7 + 0.1) x 10~2 for three mass groups (Wielen, 1967). The conclusion of nearly constant relative escape over a wide mass range is supported by one case with iV = 250 integrated over 28 mean crossing times (Aarseth, 1968); viz.…”

Section: An Mtcrmentioning

confidence: 92%

“…The coefficients A k are given by divided backwards differences weighted by constant coefficients (Wielen, 1967) and the expansion is valid over an interval At -t -1 0 which may be determined from the convergence property of Equation (2) itself. Integrating the polynomial twice we obtain the corresponding expression for the predicted position " + 2…”

Section: F(0= T A(t-t O Ymentioning

confidence: 99%

“…Alternatively, more specific cases may be considered with starting conditions based on theoretical or astrophysical models. In particular it is of interest to study centrally concentrated stationary systems based on theoretical solutions of the Liouville equation (Wielen, 1967). Of the many possible mass distributions, the function f(m)ozm~2 is representative of the mass spectrum in young galactic clusters and is also sufficiently steep to be of general dynamical interest.…”

Section: <--Y • (I6)mentioning

confidence: 99%

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Numerical Experiments on the N-Body Problem

Aarseth¹

1971

International Astronomical Union Colloquium

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Abstract. This review first discusses the different types of numerical methods available for integrating the equations of motion of N-body systems. It is desirable to supplement ordinary integration schemes with special treatments of close encounters using a two-body perturbation description or introducing regularizing transformations of the co-ordinates and time. Direct methods are at present limited to the study of a few hundred particles but larger systems may be investigated using Monte Carlo techniques or the Boltzmann moment equations.N-body computations have been performed for a whole range of initial conditions and the general results are summarized. Numerical investigations have already clarified a number of important aspects of cluster evolution and the qualitative behaviour of small stellar systems is now quite well understood. Recent theoretical modifications have reduced the disagreement with experiments but further improvements are still needed.

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Section: Comparison With Theorymentioning

confidence: 57%

Section: General Discussion Of Resultsmentioning

confidence: 99%

Section: An Mtcrmentioning

confidence: 92%

Section: F(0= T A(t-t O Ymentioning

confidence: 99%

Section: <--Y • (I6)mentioning

confidence: 99%

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Numerical Experiments on the N-Body Problem

Aarseth¹

1971

International Astronomical Union Colloquium

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Open Clusters and the Galactic Disk

Röser¹,

Kharchenko²,

Пискунов³

et al. 2010

Reviews in Modern Astronomy

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It is textbook knowledge that open clusters are conspicuous members of the thin disk of our Galaxy, but their role as contributors to the stellar population of the disk was regarded as minor. Starting from a homogenous stellar sky survey, the ASCC-2.5 , we revisited the population of open clusters in the solar neighbourhood from scratch. In the course of this enterprise we detected 130 formerly unknown open clusters, constructed volume-and magnitude-limited samples of clusters, re-determined distances, motions, sizes, ages, luminosities and masses of 650 open clusters. We derived the present-day luminosity and mass functions of open clusters (not the stellar mass function in open clusters), the cluster initial mass function CIMF and the formation rate of open clusters. We find that open clusters contributed around 40 percent to the stellar content of the disk during the history of our Galaxy. Hence, open clusters are important building blocks of the Galactic disk.

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Nearby stars of the Galactic disk and halo. III.

2003

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Abstract. High-resolution spectroscopic observations of about 150 nearby stars or star systems are presented and discussed. The study of these and another 100 objects of the previous papers of this series implies that the Galaxy became reality 13 or 14 Gyr ago with the implementation of a massive, rotationally-supported population of thick-disk stars. The very high star formation rate in that phase gave rise to a rapid metal enrichment and an expulsion of gas in supernovae-driven Galactic winds, but was followed by a star formation gap for no less than three billion years at the Sun's galactocentric distance. In a second phase, then, the thin disk -our "familiar Milky Way" -came on stage. Nowadays it traces the bright side of the Galaxy, but it is also embedded in a huge coffin of dead thick-disk stars that account for a large amount of baryonic dark matter. As opposed to this, cold-dark-matter-dominated cosmologies that suggest a more gradual hierarchical buildup through mergers of minor structures, though popular, are a poor description for the Milky Way Galaxy -and by inference many other spirals as well -if, as the sample implies, the fossil records of its long-lived stars do not stick to this paradigm. Apart from this general picture that emerges with reference to the entire sample stars, a good deal of the present work is however also concerned with detailed discussions of many individual objects. Among the most interesting we mention the blue straggler or merger candidates HD 165401 and HD 137763/HD 137778, the likely accretion of a giant planet or brown dwarf on 59 Vir in its recent history, and HD 63433 that proves to be a young solar analog at τ ∼ 200 Myr. Likewise, the secondary to HR 4867, formerly suspected non-single from the Hipparcos astrometry, is directly detectable in the highresolution spectroscopic tracings, whereas the visual binary χ Cet is instead at least triple, and presumably even quadruple. With respect to the nearby young stars a complete account of the Ursa Major Association is presented, and we provide as well plain evidence for another, the "Hercules-Lyra Association", the likely existence of which was only realized in recent years. On account of its rotation, chemistry, and age we do confirm that the Sun is very typical among its G-type neighbors; as to its kinematics, it appears however not unlikely that the Sun's known low peculiar space velocity could indeed be the cause for the weak paleontological record of mass extinctions and major impact events on our parent planet during the most recent Galactic plane passage of the solar system. Although the significance of this correlation certainly remains a matter of debate for years to come, we point in this context to the principal importance of the thick disk for a complete census with respect to the local surface and volume densities. Other important effects that can be ascribed to this dark stellar population comprise (i) the observed plateau in the shape of the luminosity function of the local FGK stars, (ii) a small though syst...

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On the lifetimes of galactic clusters

Cited by 103 publications

References 5 publications

Numerical Experiments on the N-Body Problem

Numerical Experiments on the N-Body Problem

Open Clusters and the Galactic Disk

Nearby stars of the Galactic disk and halo. III.

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