scholarly journals Masses and Relaxation Times of Star Clusters in the SMC

1984 ◽  
Vol 108 ◽  
pp. 25-26
Author(s):  
M. Kontizas ◽  
E. Kontizas
Keyword(s):  
Globular Clusters ◽  
Relaxation Times ◽  
Star Clusters ◽  
Open Clusters ◽  
Schmidt Telescope ◽  
Density Profiles ◽  
Show Evidence

Plates taken with the 1.2m U.K. Schmidt Telescope and the 3.8 AAT Telescope have been used in order to derive the dynamical parameteres of 43 various clusters of the SMC by means of star counts. The clusters are divided into two main categories: (i) the disk, “blue” and “intermediate” in colour, young, mainly globulars and (ii) the halo, “red”, old globular clusters. The disk clusters have been found to be more massive and older than the galactic open clusters, whereas the halo clusters are at least 10 times less massive than the galactic globulars. The relaxation times of the disk clusters are larger than their evolutionary age while the observed density profiles always show evidence of well relaxed systems.

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 Star clusters as tracers of galactic subsystems

1993 ◽  
Vol 153 ◽  
pp. 323-324
Author(s):  
B. Barbuy ◽  
E. Bica ◽  
S. Ortolani
Keyword(s):  
Spatial Distribution ◽  
Galaxy Formation ◽  
Formation Process ◽  
Globular Clusters ◽  
Star Clusters ◽  
Open Clusters ◽  
Horizontal Branch ◽  
The Galaxy ◽  
Magnitude Difference

We have obtained CCD BVRI colour-magnitude diagrams for a series of disk globular clusters, improving parameters and detecting a new one: Lyngå 7. Using the magnitude difference between turn-off and horizontal branch Δ(TO-HB) as an age discriminator, and their spatial distribution we compare old disk open clusters, young halo globular clusters, and metal-rich disk globular clusters, obtaining clues to the Galaxy formation process.

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 Star Clusters in Irregular Galaxies in the Local Group

2002 ◽  
Vol 207 ◽  
pp. 94-104
Author(s):  
Eva K. Grebel
Keyword(s):  
Globular Clusters ◽  
Local Group ◽  
Cluster Formation ◽  
Star Clusters ◽  
Open Clusters ◽  
High Angular Resolution ◽  
Star Clusters And Associations ◽  
Star Forming ◽  
Star Forming Regions ◽  
Irregular Galaxies

I summarize our knowledge of star clusters and associations in irregular galaxies other than the Magellanic Clouds in the Local Group. Surveys affording complete area coverage at high angular resolution are still lacking. Confirmed globular clusters are known only in NGC 6822 and WLM. Very few dIrrs contain populous or sparse open clusters. There is a pronounced deficiency of intermediate-age and young clusters. Apart from parent galaxy mass, the lack of interactions may be a key reason for the lack of cluster formation in the dIrrs. All dIrrs have one or several short-lived OB associations in the star-forming regions in their centers.

Commission 37: Star Clusters and Associations (Amas Stellaires Et Associations)

1988 ◽  
Vol 20 (01) ◽  
pp. 509-535
Author(s):  
D.C. Heggie ◽  
G.L.H. Harris ◽  
K.C. Freeman ◽  
J.E. Hesser ◽  
P.E. Nissen ◽  
...  
Keyword(s):  
Observational Data ◽  
Rapid Growth ◽  
Globular Clusters ◽  
Star Clusters ◽  
Dynamical Theory ◽  
Open Clusters ◽  
Star Clusters And Associations ◽  
Cluster Systems ◽  
The Individual ◽  
Astronomy And Astrophysics

The last three years have been very productive for cluster research, especially now that observations with CCDs have become so routine. After a section on recent meetings, and one on data catalogues (by J.-C. Mermilliod), subsequent sections of this report go into details on individual topics: associations (P.E. Nissen), open clusters (G.L.H. Harris), globular clusters and cluster systems (R.E. White) and dynamical theory (D.C. Heggie).The rapid growth in the volume of observational data has meant regrettably that the information has had to be tabulated in an even more compressed form than in earlier Reports. As in previous Reports, three-figure references are to Astronomy and Astrophysics Abstracts, and two-figure references to Physics Abstracts. Most entries cover publications from 1 July 1984 to 30 June 1987, but some exceptions are noted under the individual sections. For abbreviations see §6.

scholarly journals COMMISSION 37: STAR CLUSTERS AND ASSOCIATIONS

2008 ◽  
Vol 4 (T27A) ◽  
pp. 277-279
Author(s):  
Despina Hatzidimitriou ◽  
Charles J. Lada ◽  
Ata Sarajedini ◽  
Russell D. Cannon ◽  
Kyle McC. Cudworth ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Globular Clusters ◽  
Galactic Disk ◽  
Star Clusters ◽  
Open Clusters ◽  
Stellar Rotation ◽  
Star Clusters And Associations ◽  
Stellar Spectroscopy ◽  
Wide Range ◽  
Massive Star Evolution

Star clusters are valuable tools for theoretical and observational astronomy across a wide range of disciplines from cosmology to stellar spectroscopy. For example, properties of globular clusters are used to constrain stellar evolutionary models, nucleosynthesis and chemical evolution, as well as the star formation and assembly histories of galaxies and the distribution of dark matter in present-day galaxies. Open clusters are widely used as stellar laboratories for the study of specific stellar phenomena (e.g., various emission-line stars, pulsating pre-MS stars, magnetic massive stars, binarity, stellar rotation, etc.). They also provide observational constraints on models of massive star evolution and of Galactic disk formation and chemical evolution.

scholarly journals Commission 37: Star Clusters and Associations

1982 ◽  
Vol 18 (1) ◽  
pp. 499-526
Keyword(s):  
Globular Cluster ◽  
Working Group ◽  
Globular Clusters ◽  
Star Clusters ◽  
Open Clusters ◽  
General Assembly ◽  
Active Period ◽  
Star Clusters And Associations ◽  
The Past ◽  
Good Number

The past triennium has been a very active period in most branches of cluster research. Some controversial subjects, notably globular cluster abundances and ages have received much attention. A good number of photometric papers on clusters as well as associations have been published. Observational effects of mass loss have been discussed by several astronomers.This report has been assembled by the president of the commission although several sections have been contributed by other members. The report will first list some highlights in the activities of our commission. Then follow the tables containing current investigations of OB associations, open clusters and globular clusters. These have been assembled by B. Balázs, G. Harris and R. White, respectively. After these tables comes a section by D. Heggie about dynamics of star clusters. A working group under the chairmanship of A. Moffat has made a proposal about the numbering of stars in clusters. The proposal, which is included here will be discussed by our commission at the IAU General Assembly.

Radial Velocity Studies of the Internal Kinematics of Open Clusters

1984 ◽  
Vol 88 ◽  
pp. 249-256
Author(s):  
Robert D. Mathieu
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Globular Clusters ◽  
Cluster Structure ◽  
Relaxation Times ◽  
Stellar Mass ◽  
Open Clusters ◽  
Radial Velocities ◽  
Order Of Magnitude ◽  
Motion Studies

The internal kinematics of open clusters are a particularly challenging subject for study with radial velocities. Our present sitate of knowledge concerning the structure and kinematics of open clusters has recently been reviewed (Mathieu 1985), so I will only summarize here several of the essential concerns. The most basic goal is to measure a central or global velocity dispersion. Comparison of such measured dispersions with dynamical models fit to the cluster structure is a direct test of our understanding of the dynamics of open clusters. Far more difficult but of great importance to our understanding of cluster dynamics is the observation of assorted differential effects in these clusters. Open clusters provide a unique opportunity to study velocity distributions as a function of stellar mass. Radial velocity studies of nearby clusters can in themselves span a factor 2 in stellar mass; when combined with proper-motion studies which include the earlier stars inaccessible to high-precision radial velocities, a mass spectrum of up to an order of magnitude can be studied. Also, as with globular clusters, anisotropie velocity distributions are to be expected in the halos of those open clusters which are more than a few relaxation times old. Proper-motion studies (Jones 1970, 1971; van Leeuwen 1983) have found that anisotropy exists to within 1 pc of the centers of the Pleiades and Praesepe, much nearer the center than has so far been found in globular clusters. Independent confirmation of these findings as well as an increase in the sample of clusters studied would be of real value. And finally, the very youngest open clusters allow us to study the state of clusters at formation and indeed the star-formation process itself.

scholarly journals Observed Dynamical Parameters of Star Clusters in the SMC

1985 ◽  
Vol 113 ◽  
pp. 85-87
Author(s):  
E. Kontizas ◽  
M. Kontizas
Keyword(s):  
Star Clusters ◽  
Theoretical Models ◽  
Relaxation Mechanism ◽  
Open Clusters ◽  
Dynamical Study ◽  
Density Profiles ◽  
Metal Abundance ◽  
Dynamical Parameters ◽  
Young Clusters

The dynamical study of the SMC clusters is very important for many reasons. (a) The disk “blue” clusters are more massive and older than the galactic open clusters whereas the “halo” red clusters are less massive and younger than the galactic globulars (Kontizas, Danezis, Kontizas, 1982; Kontizas and Kontizas, 1983). (b) All clusters show density profiles that fit the available theoretical models (King, 1962) giving evidence of relaxed systems, even for the young clusters with evolutionary ages 106−108yr. The relaxation mechanism has to be reconsidered for the SMC and possibly in connection to the metal abundance. (c) The ellipticities of young and old SMC clusters have shown that there is no obvious age-ellipticity dependance and that the SMC clusters are statistically more elliptical than the clusters of the LMC and our Galaxy (Frenk and Fall, 1982, Kontizas et al, 1984).

scholarly journals Spatial Structure of Star Clusters by the 2MASS Database

2001 ◽  
Vol 183 ◽  
pp. 331-332
Author(s):  
J.W. Chen ◽  
W.P. Chen
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Star Clusters ◽  
Young Star ◽  
Open Clusters ◽  
Main Sequence Stars ◽  
Giant Stars ◽  
Sky Survey ◽  
Mass Segregation ◽  
Young Star Clusters

AbstractWe present some results of a pilot program to study star clusters with the Two-Micron All-Sky Survey (2MASS) observations. While 2MASS cannot resolve the cores or detect much of the main sequence of globular clusters, the homogeneity and large angular coverages make the database suitable to study young star clusters. We show that member stars are centrally concentrated in open clusters, with a density distribution markedly shallower than that for globular clusters. In NGC2506 (age 3 Gyr) giant stars appear to occupy a smaller region than main sequence stars—a natural consequence of mass segregation.

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