Spatial Structure of Star Clusters by the 2MASS Database

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900030709 ◽

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.

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HII regions and young star clusters in the Magellanic Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900200387 ◽

1991 ◽

Vol 148 ◽

pp. 207-208

Author(s):

Myung Gyoon Lee

Keyword(s):

Main Sequence ◽

Star Clusters ◽

Hii Regions ◽

Young Star ◽

Magellanic Clouds ◽

Stellar Content ◽

Ccd Photometry ◽

Luminosity Functions ◽

Young Star Clusters ◽

Mass Functions

Using U BV CCD photometry, the stellar content of HII regions and young star clusters in the Magellanic Clouds has been studied: (1) the reddenings have been determined, and ages of OB associations and young star clusters have been measured; (2) the stellar initial mass functions have been determined by using the main-sequence luminosity functions; and (3) U BV CCD surface photometry of nine young star clusters has been obtained and their structural properties investigated.

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A Dynamical Origin for Early Mass Segregation in Young Star Clusters

Proceedings of the International Astronomical Union ◽

10.1017/s174392130801524x ◽

2007 ◽

Vol 3 (S246) ◽

pp. 41-45

Author(s):

Steve McMillan ◽

Enrico Vesperini ◽

Simon Portegies Zwart

Keyword(s):

Cluster Formation ◽

Star Clusters ◽

Young Star ◽

Mass Segregation ◽

Young Star Clusters ◽

Dynamical Origin ◽

Significant Mass

AbstractSome young star clusters show a degree of mass segregation that is inconsistent with the effects of standard two-body relaxation from an initially unsegregated system without substructure, in virial equilibrium, and it is unclear whether current cluster formation models can account for this degree of initial segregation in clusters of significant mass. We show that mergers of small clumps that are either initially mass segregated, or in which mass segregation can be produced by two-body relaxation before they merge, generically lead to larger systems which inherit the progenitor clumps' segregation. We conclude that clusters formed in this way are naturally mass segregated, accounting for the anomalous observations and suggesting that this process of prompt mass segregation due to initial clumping should be taken into account in models of cluster formation and dynamics.

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The Mass Function of Young Star Clusters in our Galaxy and Nearby Galaxies: Is It Universal?

Symposium - International Astronomical Union ◽

10.1017/s0074180900224327 ◽

2002 ◽

Vol 207 ◽

pp. 515-524

Author(s):

Ram Sagar

Keyword(s):

Star Clusters ◽

Dynamical Evolution ◽

Mass Function ◽

Young Star ◽

Initial Mass Function ◽

Galactocentric Distance ◽

Photometric Observations ◽

Nearby Galaxies ◽

Mass Segregation ◽

Young Star Clusters

Mass functions (MFs) derived from photometric observations of young star clusters of our Galaxy, the Magellanic Clouds (MCs), M31 and M33 have been used to investigate the question of universality of the initial mass function and presence of mass segregation in these systems. Observational determination of the MF slope of young star clusters have an inherent uncertainty of at least ∼ 1.0 dex in the Milky Way and of ∼ 0.4 dex in the MCs. There is no obvious dependence of the MF slope on either galactocentric distance or age of the young star clusters or on the spatial concentration of the stars formed or on the galactic characteristics including metallicity. Effects of mass segregation have been observed in a good number of young stellar groups of our Galaxy and MCs. As their ages are much smaller than their dynamical evolution times, star formation processes seem to be responsible for the observed mass segregation in them.

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Comparisons between observational color-magnitude diagrams and synthetic cluster diagrams for young star clusters in the Magellanic Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900030588 ◽

1984 ◽

Vol 105 ◽

pp. 83-87

Author(s):

Stephen A. Becker ◽

Grant J. Mathews ◽

Wendee M. Brunish

Keyword(s):

Stellar Evolution ◽

Main Sequence ◽

Star Clusters ◽

Theoretical Models ◽

Young Star ◽

Asymptotic Giant Branch ◽

Current Status ◽

Large Numbers ◽

Young Star Clusters ◽

Convective Overshoot

Young star clusters (<3 × 108 yr) in the Maqellanic Clouds (MC) can be used to test the current status of the theory of stellar evolution as applied to intermediate and massive stars. The color-magnitude diagram of many young clusters in the MC shows, unlike the case of clusters in our Galaxy, large numbers of stars in both the main sequence and post main sequence evolutionary phases. Usina a arid of stellar evolution models, synthetic cluster H-R diagrams are constructed and compared to observed color-magnitude diagrams to determine the age, age spread, and composition for any given cluster. In addition, for those cases where the data is of high quality, detailed comparisons between theory and observation can provide a diagnostic of the accuracy of the stellar evolution models. Initial indications of these comparisons suggest that the theoretical models should be altered to include: a larger value for the mixing length parameter (α), a larger rate of mass loss during the asymptotic giant branch (AGB) phase, and possibly convective overshoot during the core burning phases.

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Rapid mass segregation in young star clusters without substructure?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311017935 ◽

2010 ◽

Vol 6 (S271) ◽

pp. 389-390

Author(s):

C. Olczak ◽

R. Spurzem ◽

Th. Henning

Keyword(s):

Initial Conditions ◽

Star Clusters ◽

Building Blocks ◽

Young Star ◽

Subsequent Formation ◽

Multiple Systems ◽

Mass Segregation ◽

New Generation ◽

The Impact ◽

Young Star Clusters

AbstractThe young star clusters we observe today are the building blocks of a new generation of stars and planets in our Galaxy and beyond. Despite their fundamental role we still lack knowledge about the initial conditions under which star clusters form and the impact of these often harsh environments on the formation and evolution of their stellar and substellar members.We present recent results showing that mass segregation in realistic models of young star clusters occurs very quickly for subvirial spherical systems without substructure. This finding is a critical step to resolve the controversial debate on mass segregation in young star clusters and provides strong constraints on their initial conditions. The rapid concentration of massive stars is usually associated with strong gravitational interactions early on during cluster evolution and the subsequent formation of multiple systems and ejection of stars.

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Young Star Clusters in the LMC

Australian Journal of Physics ◽

10.1071/ph920407 ◽

1992 ◽

Vol 45 (4) ◽

pp. 407

Author(s):

KC Freeman

Keyword(s):

Mass Loss ◽

Globular Clusters ◽

Star Clusters ◽

Dynamical Evolution ◽

Mass Function ◽

Young Star ◽

Stellar Mass ◽

Initial Mass Function ◽

Initial Mass ◽

Young Star Clusters

The young globular star clusters in the LMC offer us insights into the formation and early dynamical evolution of globular clusters which are unobtainable from the old globular clusters in our Galaxy. Because these young clusters are so young and populous, they provide an opportunity to measure the upper end of the initial mass function by direct means and also through the dynamical effects of stellar mass loss on the structure of the clusters.

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