Stellar populations in star clusters

Abstract

Stellar populations contain the most important information about star clus- ter formation and evolution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar populations (SSPs). However, discoveries of multiple stellar populations in Galactic globular clusters have expanded our view on stellar populations in star clusters. They have simultaneously generated a number of controversies, particularly as to whether young star clusters may have the same origin as old globular clusters. In addition, extensive studies have revealed that the SSP scenario does not seem to hold for some intermediate-age and young star clusters either, thus making the origin of multiple stellar populations in star clusters even more complicated. Stellar population anomalies in numerous star clusters are well-documented, implying that the notion of star clusters as true SSPs faces serious challenges. In this review, we focus on stellar populations in massive clusters with different ages. We present the history and progress of research in this active field, as well as some of the most recent improvements, including observational results and scenar- ios that have been proposed to explain the observations. Although our current ability to determine the origin of multiple stellar populations in star clusters is unsatisfactory, we propose a number of promising projects that may contribute to a significantly improved understanding of this subject.

27 pages, 10 figures. Invited review for Research in Astronomy and Astrophysics

References in corpus (107)

• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Embedded Clusters in Molecular Clouds
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Young massive star clusters
• The evolution of rotating stars
• Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
• Na-O Anticorrelation and HB. VII. The chemical composition of first and second-generation stars in 15 globular clusters from GIRAFFE spectra
• The Formation of a Star Cluster: Predicting the Properties of Stars and Brown Dwarfs
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• A Triple Main Sequence in the Globular Cluster NGC 2808
• The Ages of Stars
• The O-Na and Mg-Al Anticorrelations in Turn-Off and early Subgiants in Globular Clusters
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• Massive binaries as the source of abundance anomalies in globular clusters
• A comprehensive set of simulations studying the influence of gas expulsion on star cluster evolution
• Grids of stellar models with rotation - III. Models from 0.8 to 120 Msun at a metallicity Z = 0.002
• A helium spread among the main sequence stars in NGC 2808
• The Dynamics of Radiation Pressure-Dominated HII Regions
• Evidence for the Strong Effect of Gas Removal on the Internal Dynamics of Young Stellar Clusters
• Dynamical mass segregation on a very short timescale
• Multiple stellar populations in 47 Tucanae
• Rotational velocities of A-type stars. III. Velocity distributions
• Evolution and fate of very massive stars
• The Effect of Stellar Rotation on Colour-Magnitude Diagrams: On the apparent presence of multiple populations in intermediate age stellar clusters
• A double main sequence turn-off in the rich star cluster NGC 1846 in the Large Magellanic Cloud
• Massive AGB models of low metallicity: the implications for the self-enrichment scenario in metal poor Globular Clusters
• Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members. II. age dependencies and new insights
• Multiple stellar populations in three rich Large Magellanic Cloud star clusters
• A unique model for the variety of multiple populations formation(s) in globular clusters: a temporal sequence
• The double Subgiant Branch of NGC 1851: the role of the CNO abundance
• Gravitational fragmentation and the formation of brown dwarfs in stellar clusters
• On the Formation of Multiple Stellar Populations in Globular Clusters
• Helium enhanced stars and multiple populations along the horizontal branch of NGC2808: direct spectroscopic measurements
• Mg isotopic ratios in giant stars of the globular cluster NGC 6752
• MOCCA code for star cluster simulations - I. Blue Stragglers, first results
• Iron and neutron-capture element abundance variations in the globular cluster M2 (NGC 7089)
• Studying the YMC population of M83: how long clusters remain embedded, their interaction with the ISM and implications for GC formation theories
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. II. The seven stellar populations of NGC7089 (M2)
• A General Abundance Problem for All Self-Enrichment Scenarios for the Origin of Multiple Populations in Globular Clusters
• Mixed Populations in Globular Clusters: Et Tu, 47 Tuc?
• Chemical Compositions of Red Giant Stars in Old Large Magellanic Cloud Globular Clusters
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity
• Mining SDSS in search of Multiple Populations in Globular Clusters
• Abundance Analysis of Turn-Off and Early Subgiant Stars in the Globular Cluster 47 Tuc (NGC 104)
• Globular cluster systems in nearby dwarf galaxies - II. Nuclear star clusters and their relation to massive Galactic globular clusters
• Abundances for a large sample of red giants in NGC 1851: hints for a merger of two clusters?
• HST/STIS Spectroscopy of Five Super Star Clusters in the Starburst Galaxy M82
• Populations of rotating stars III. SYCLIST, the new Geneva Population Synthesis code
• Shaping the Globular Cluster Mass Function by Stellar-Dynamical Evaporation
• Constraining Globular Cluster Formation Through Studies of Young Massive Clusters: I. A lack of ongoing star formation within young clusters
• The chemical composition of the Orion star-forming region. III. C, N, Ne, Mg and Fe abundances in B-type stars revisited
• Discovery of two distinct red clumps in NGC419: a rare snapshot of a cluster at the onset of degeneracy
• Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. III. The Antennae
• Importance of the Initial Conditions for Star Formation - III: Statistical Properties of Embedded Protostellar Clusters
• Multiple stellar populations in Magellanic Cloud clusters. IV. The double main sequence of the young cluster NGC1755
• Multiple stellar populations in Magellanic Cloud clusters. III. The first evidence of an extended main sequence turn-off in a young cluster: NGC1856
• Rotating Stellar Models Can Account for the Extended Main Sequence Turnoffs in Intermediate Age Clusters
• The Gaia-ESO Survey: Stellar content and elemental abundances in the massive cluster NGC 6705
• Can rotation explain the multiple main sequence turn-offs of Magellanic Cloud star clusters?
• NGC 362: another globular cluster with a split red giant branch
• Formation of Multiple Populations in Globular Clusters: Another Possible Scenario
• No Evidence for Significant Age Spreads in Young Massive LMC Clusters
• The effects of rotation on the main-sequence turnoff of intermediate-age massive star clusters
• Search for Associations Containing Young stars (SACY): Chemical tagging IC 2391 & the Argus association
• Population Parameters of Intermediate-Age Star Clusters in the Large Magellanic Cloud. III. Dynamical Evidence for a Range of Ages Being Responsible for Extended Main Sequence Turnoffs
• Constraining globular cluster formation through studies of young massive clusters - II. A Single Stellar Population Young Massive Cluster in NGC 34
• No evidence of chemical anomalies in the bimodal turnoff cluster NGC 1806 in the LMC
• The Unique Na:O Abundance Distribution in NGC 6791: The First Open(?) Cluster with Multiple Populations
• Searching for Chemical Signatures of Multiple Stellar Populations in the Old, Massive Open Cluster NGC 6791
• MHD and deep mixing in evolved stars. 1. 2D and 3D analytical models for the AGB
• The primordial and evolutionary abundance variations in globular-cluster stars: a problem with two unknowns
• Chemical composition of the young open clusters IC2602 and IC2391
• The exclusion of a significant range of ages in a massive star cluster
• Constraining globular cluster formation through studies of young massive clusters - V. ALMA observations of clusters in the Antennae
• The star formation history of the SMC star cluster NGC419
• Constraining Globular Cluster Formation Through Studies of Young Massive Clusters - IV. Testing the Fast Rotating Massive Star Scenario
• Constraining globular cluster formation through studies of young massive clusters - III. A lack of gas and dust in massive stellar clusters in the LMC and SMC
• A Young Cluster With an Extended Main Sequence Turnoff: Confirmation of a Prediction of the Stellar Rotation Scenario
• On the origin of double main-sequence turn-offs in star clusters of the Magellanic Clouds
• Multi-wavelength Hubble Space Telescope photometry of stellar populations in NGC288
• The star formation history of the Large Magellanic Cloud star cluster NGC1751
• An extended main sequence turn-off in the Small Magellanic Cloud star cluster NGC411
• Star-to-star Na and O abundance variations along the red giant branch in NGC 2808
• Lithium depleted stars in the young sigma Ori cluster
• Controversial Age Spreads from the Main Sequence Turn-Off and Red Clump in Intermediate-Age Clusters in the LMC
• A revolution in star cluster research: setting the scene
• The Morphology of the Sub-Giant Branch and Red Clump Reveal No Sign of Age Spreads in Intermediate Age Clusters
• Is the Escape Velocity in Star Clusters Linked to Extended Star Formation Histories? Using NGC 7252: W3 as a Test Case
• Formation of new stellar populations from gas accreted by massive young star clusters
• On the Interpretation of Sub-Giant Branch Morphologies of Intermediate-Age Star Clusters with Extended Main Sequence Turnoffs
• Variations in the Na-O anticorrelation in globular clusters: Evidence for a deep mixing episode in red giant branch stars
• New Constraints on the Star Formation History of the Star Cluster NGC 1856
• The difficult early stages of embedded star clusters and the importance of the pre-gas expulsion virial ratio
• Deep near-infrared imaging of W3 Main: constraints on stellar cluster formation
• Not-So-Simple Stellar Populations in the Intermediate-age Large Magellanic Cloud Star Clusters NGC 1831 and NGC 1868
• High-resolution elemental abundance analysis of the open cluster IC 4756
• External Mass Accumulation onto Core Potentials: Implications for Star Clusters, Galaxies and Galaxy Clusters
• Spectroscopic abundance analysis of dwarfs in young open cluster IC 4665
• Mergers of multi-metallic globular clusters: The role of dynamics
• The VMC Survey. XI. Radial Stellar Population Gradients in the Galactic Globular Cluster 47 Tucanae
• No evidence for younger stellar generations within the intermediate age massive clusters NGC 1783, NGC 1696 and NGC 411
• Binary interactions as a possible scenario for the formation of multiple stellar populations in globular clusters
• The tight subgiant branch of the intermediate-age star cluster NGC 411 implies a single-aged stellar population
• The Young Open Clusters King 12, NGC 7788, and NGC 7790: Pre-Main Sequence Stars and Extended Stellar Halos
• First Observational Signature of Rotational Deceleration in a Massive, Intermediate-age Star Cluster in the Magellanic Clouds
• Probing embedded star clusters in the HII complex NGC 6357 with VVV
• Comparison of Convective Overshooting Models and Their Impact on Abundances from Integrated Light Spectroscopy of Young ($<$ 3 Gyr) Star Clusters

Cited by in corpus (11)

• Discovery of Extended Main Sequence Turn-offs in Four Young Massive Clusters in the Magellanic Clouds
• The radial distributions of the two main-sequence components in the young massive star cluster NGC 1856
• The effects of the overshooting of the convective core on main-sequence turnoffs of young- and intermediate-age star clusters
• No Evidence for Chemical Abundance Variations in the Intermediate-age Cluster NGC 1783
• Lifting the dust veil from the Globular Cluster Palomar2
• Mass transfer of low-mass binaries and chemical anomalies among unevolved stars in globular clusters
• The Origin of Young Stellar Populations in NGC 1783: Accretion of External Stars
• Studying the interstellar medium to look for relics of triggered star formation among stellar clusters
• Impact of radiation feedback on the assembly of star clusters in galactic context
• Extended Main Sequences in Star Clusters
• Searching for chemical abundance variations in young star clusters in the Magellanic Clouds: NGC 411, NGC 1718 and NGC 2213