The photometric evolution of star clusters and the preferential loss of low-mass bodies – with an application to globular clusters

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.

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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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The nature and nurture of star clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309990809 ◽

2009 ◽

Vol 5 (S266) ◽

pp. 3-13 ◽

Cited By ~ 2

Author(s):

Bruce G. Elmegreen

Keyword(s):

Globular Clusters ◽

Dwarf Galaxy ◽

Cluster Formation ◽

Star Clusters ◽

Mass Function ◽

Radial Gradient ◽

Cluster Mass ◽

Low Mass ◽

Nature And Nurture ◽

Gas Loss

AbstractStar clusters have hierarchical patterns in space and time, suggesting formation processes in the densest regions of a turbulent interstellar medium. Clusters also have hierarchical substructure when they are young, which makes them all look like the inner mixed parts of a pervasive stellar hierarchy. Young field stars share this distribution, presumably because some of them came from dissolved clusters and others formed in a dispersed fashion in the same gas. The fraction of star formation that ends up in clusters is apparently not constant, but may increase with interstellar pressure. Hierarchical structure explains why stars form in clusters and why many of these clusters are self-bound. It also explains the cluster mass function. Halo globular clusters share many properties of disk clusters, including what appears to be an upper cluster cutoff mass. However, halo globulars are self-enriched and often connected with dwarf galaxy streams. The mass function of halo globulars could have initially been like the power-law mass function of disk clusters, but the halo globulars have lost their low-mass members. The reasons for this loss are not understood. It could have happened slowly over time as a result of cluster evaporation, or it could have happened early after cluster formation as a result of gas loss. The latter model explains best the observation that the globular cluster mass function has no radial gradient in galaxies.

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Metal-poor nuclear star clusters in two dwarf galaxies near Centaurus A suggesting formation from the in-spiraling of globular clusters

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937120 ◽

2020 ◽

Vol 634 ◽

pp. A53 ◽

Cited By ~ 2

Author(s):

Katja Fahrion ◽

Oliver Müller ◽

Marina Rejkuba ◽

Michael Hilker ◽

Mariya Lyubenova ◽

...

Keyword(s):

Globular Clusters ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Star Clusters ◽

High Resolution Spectroscopy ◽

High Signal ◽

Main Body ◽

Host Galaxies ◽

Low Mass ◽

The Masses

Studies of nucleated dwarf galaxies can constrain the scenarios for the formation and evolution of nuclear star clusters (NSC) in low-mass galaxies and give us insights on the origin of ultra compact dwarf galaxies (UCDs). We report the discovery of a NSC in the dwarf galaxy KKs58 and investigate its properties together with those of another NSC in KK197. Both NSCs are hosted by dwarf elliptical galaxies of the Centaurus group. Combining ESO VLT MUSE data with photometry from VLT FORS2, CTIO Blanco DECam, and HST ACS, as well as high-resolution spectroscopy from VLT UVES, we analyse the photometric, kinematic and stellar population properties of the NSCs and their host galaxies. We confirm membership of the NSCs based on their radial velocities and location close to the galaxy centres. We also confirm the membership of two globular clusters (GCs) and detect oblate rotation in the main body of KK197. Based on high signal-to-noise spectra taken with MUSE of the NSCs of both KKs58 and KK197 we measure low metallicities, [Fe/H] = −1.75 ± 0.06 dex and [Fe/H] = −1.84 ± 0.05 dex, and stellar masses of 7.3 × 105 M⊙ and 1.0 × 106 M⊙, respectively. Both NSCs are more metal-poor than their hosts that have metallicities of −1.35 ± 0.23 dex (KKs58) and −0.84 ± 0.12 dex (KK197). This can be interpreted as NSC formation via the in-spiral of GCs. The masses, sizes and metallicities of the two NSCs place them among other NSCs, but also among the known UCDs of the Centaurus group. This indicates that NSCs might constitute the progenitors of a part of the low-mass UCDs, although their properties are almost indistinguishable from typical GCs.

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Super star clusters and their multiple stellar populations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007920 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 350-353

Author(s):

Hans Zinnecker

Keyword(s):

Star Formation ◽

Globular Clusters ◽

Massive Stars ◽

Characteristic Temperature ◽

Star Clusters ◽

Potential Wells ◽

Low Mass ◽

New Feature ◽

Chemical Anomalies ◽

Super Star Clusters

AbstractWe present a scenario for the formation of super star clusters (with masses larger than 105 M⊙) in which multiple generations of star formation will occur. We stress that the gas left over (∼50%) from first generation (1G) star formation should be retained in such massive clusters (thanks to their deep potential wells, with escape speeds larger than 10 km/s) and be available for a second or even third generation of stars, with the basic HeCNONaMgAl chemical anomalies observed in globular clusters, the latter assumed to be the descendents of these super star clusters. One new feature of this model is the role of C+ cooling of the dense warm trapped neutral or ionized gas which defines a characteristic temperature of ∼100 K, leading to a second generation (2G) of stars with a top-heavy IMF (M > 5 M⊙). The ashes of the 2G very massive stars (VMS, M > 100 M⊙) sampled in this IMF quickly pollute and dilute the left-over pristine gas with their slow winds (that cannot escape the cluster), while the majority of massive stars develop fast winds (that actually can escape from the cluster). Meanwhile, much of the remaining dense T = 100 K gas contracts gravitationally in the massive cluster and may reach densities of the order of 109 cm−3, in which case the Jeans mass drops to about 0.2 M⊙ and leads to a substantial low-mass pre-MS 3G population (most likely on a very short timescale). In this way, we may solve both the mass budget and the excess Helium problem in proto-globular clusters, while also explaining the Na-O and Mg-Al anti-correlations resulting from hot H-burning of very massive stars at 45MK and 75MK, respectively.

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Did globular clusters contribute to the stellar population of the Galactic halo?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315010649 ◽

2015 ◽

Vol 11 (S317) ◽

pp. 104-109

Author(s):

Corinne Charbonnel ◽

Martin Krause

Keyword(s):

Globular Clusters ◽

Massive Star ◽

Stellar Population ◽

Local Group ◽

Galactic Halo ◽

Chemical Properties ◽

Star Clusters ◽

Alternative Interpretation ◽

Low Mass Stars ◽

Low Mass

AbstractThe origin of Galactic halo stars and the contribution of globular clusters (GC) to this stellar population have long been (and still are) debated. The discovery of multiple stellar populations with peculiar chemical properties in GCs both in the Milky Way and in Local Group galaxies recently brought a renewal on these questions. Indeed most of the scenarios that compete to reproduce the present-day GC characteristics call for fast expulsion of both gas and low-mass stars from these clusters in their early infancy. In this framework, the initial masses of GCs could have been 8 to 25 times higher than their present-day stellar mass, and they could have contributed to 5 to 20 % of the low-mass stars in the Galactic halo. Here we revisit these conclusions, which are in tension with observations of dwarf galaxies and of young massive star clusters in the Local Group. We come back in particular on the paradigm of gas expulsion from massive star clusters, and propose an alternative interpretation of the GC abundance properties. We conclude by proposing a major revision of the current concepts regarding the role massive star clusters play in the assembly of galactic haloes.

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Dark Matter in Globular Clusters

Symposium - International Astronomical Union ◽

10.1017/s0074180900001649 ◽

1996 ◽

Vol 174 ◽

pp. 303-312 ◽

Cited By ~ 8

Author(s):

Douglas C. Heggie ◽

Piet Hut

Keyword(s):

Dark Matter ◽

Globular Clusters ◽

White Dwarfs ◽

Star Clusters ◽

Low Mass Stars ◽

Interesting Issue ◽

Low Mass ◽

Model Independent

We first review reasons why dark matter is an interesting issue in connection with star clusters. Next we consider to what extent the presence of dark matter is consistent with their dynamics and structure. We review various model-dependent and model-independent methods which have been applied to two well studied clusters, NGC 6397 and 47 Tuc. We suggest that about half of the mass in each object is still unobserved, possibly in the form of a mixture of low-mass stars and white dwarfs.

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Tidal Capture in Star Clusters

Symposium - International Astronomical Union ◽

10.1017/s0074180900001613 ◽

1996 ◽

Vol 174 ◽

pp. 273-282 ◽

Cited By ~ 2

Author(s):

Rosemary A. Mardling

Keyword(s):

Globular Clusters ◽

Star Clusters ◽

Orbital Evolution ◽

Open Clusters ◽

Capture Process ◽

X Ray ◽

Low Mass ◽

The Rich ◽

X Ray Binaries

We review the tidal capture process and in particular the chaotic orbital evolution which follows capture. We discuss the formation of low-mass X-ray binaries in globular clusters via tidal capture and speculate on the possibility that some field low-mass X-ray binaries were formed this way in open clusters which have since dispersed, or in existing old open clusters which are not accessible to observation because of obscuration by dust or because they are indistinguishable from the rich background of galactic stars.

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Theoretical evolutionary framework for low-mass stars in massive star clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315008881 ◽

2015 ◽

Vol 12 (S316) ◽

pp. 320-327

Author(s):

Santi Cassisi

Keyword(s):

Energy Distribution ◽

Globular Clusters ◽

Massive Star ◽

Spectral Energy Distribution ◽

Star Clusters ◽

Spectral Energy ◽

Stellar Systems ◽

Low Mass Stars ◽

Specific Chemical ◽

Low Mass

AbstractRecent spectroscopic and photometric surveys of Galactic Globular Clusters have shown that these stellar systems host distinct sub-populations of stars characterised by peculiar chemical patterns. In the following we wish to address the issue of how these specific chemical patterns affect both the structural and evolutionary properties of stars as well as their spectral energy distribution. The implications of these effects on the photometric appearance of multiple stellar populations in different photometric planes are also briefly discussed.

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Ages of Galactic and Extragalactic Star Clusters of Various Abundances

Highlights of Astronomy ◽

10.1017/s1539299600005025 ◽

1983 ◽

Vol 6 ◽

pp. 109-117 ◽

Cited By ~ 3

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.

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