Supermassive stars as a source of abundance anomalies of proton-capture elements in globular clusters

Denissenkov, Pavel A.; Hartwick, F. D. A.

doi:10.1093/mnrasl/slt133

Cited by 281 publications

(287 citation statements)

References 43 publications

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“…This last implication is however in conflict with observations of the number ratio of GC and field stars in nearby dwarf galaxies (Fornax, WLM, IKN), which suggest that GCs in these systems could not have been more than about five times more massive initially (Larsen et al 2012(Larsen et al , 2014. In addition to the two sources of enriched material mentioned above, super-massive stars with M ∼ 10 4 M have also been considered as polluters to explain the detailed abundance patterns observed in GCs (Denissenkov & Hartwick 2014;Denissenkov et al 2015). Bastian et al (2013) also proposed a scenario that does not invoke multiple generations of stars, and in which the enriched material is released by massive interacting binaries (de Mink et al 2009) and accreted onto the circumstellar discs of low-mass pre-main sequence stars from the same stellar generation (although see Wijnen et al 2016, which highlights important limitations regarding the efficiency of such an accretion process).…”

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confidence: 88%

Differences in the rotational properties of multiple stellar populations in M13: a faster rotation for the ‘extreme’ chemical subpopulation

Cordero

Hénault-Brunet

Pilachowski

et al. 2016

Mon. Not. R. Astron. Soc.

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We use radial velocities from spectra of giants obtained with the WIYN telescope, coupled with existing chemical abundance measurements of Na and O for the same stars, to probe the presence of kinematic differences among the multiple populations of the globular cluster (GC) M13. To characterise the kinematics of various chemical subsamples, we introduce a method using Bayesian inference along with an MCMC algorithm to fit a six-parameter kinematic model (including rotation) to these subsamples. We find that the so-called "extreme" population (Na-enhanced and extremely O-depleted) exhibits faster rotation around the centre of the cluster than the other cluster stars, in particular when compared to the dominant "intermediate" population (moderately Na-enhanced and O-depleted). The most likely difference between the rotational amplitude of this extreme population and that of the intermediate population is found to be ∼ 4 km s −1 , with a 98.4% probability that the rotational amplitude of the extreme population is larger than that of the intermediate population. We argue that the observed difference in rotational amplitudes, obtained when splitting subsamples according to their chemistry, is not a product of the long-term dynamical evolution of the cluster, but more likely a surviving feature imprinted early in the formation history of this GC and its multiple populations. We also find an agreement (within uncertainties) in the inferred position angle of the rotation axis of the different subpopulations considered. We discuss the constraints that these results may place on various formation scenarios.

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confidence: 88%

Differences in the rotational properties of multiple stellar populations in M13: a faster rotation for the ‘extreme’ chemical subpopulation

Cordero

Hénault-Brunet

Pilachowski

et al. 2016

Mon. Not. R. Astron. Soc.

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“…In this scenario, chemical abundances between the two generations are different because chemical abundances of gas ejected from fast-rotating massive stars (e.g., Decressin et al 2007), supermassive stars (e.g., Denissenkov & Hartwick 2014), massive interacting binaries (e.g., Bastian et al 2013), and AGB stars (e.g.,D08) are quite different from the averaged ones of FG stars. This scenario has been suggested to have a number of serious problems in explaining the fundamental properties of GCs, for example, the larger fraction of SG stars in GCs with multiple stellar populations.…”

Section: Introductionmentioning

confidence: 99%

Globular cluster formation with multiple stellar populations from hierarchical star cluster complexes

Bekki¹

2017

Mon. Not. R. Astron. Soc.

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Most old globular clusters (GCs) in the Galaxy are observed to have internal chemical abundance spreads in light elements. We discuss a new GC formation scenario based on hierarchical star formation within fractal molecular clouds. In the new scenario, a cluster of bound and unbound star clusters ('star cluster complex', SCC) that have a power-law cluster mass function with a slope (β) of 2 is first formed from a massive gas clump developed in a dwarf galaxy. Such cluster complexes and β = 2 are observed and expected from hierarchical star formation. The most massive star cluster ('main cluster'), which is the progenitor of a GC, can accrete gas ejected from asymptotic giant branch (AGB) stars initially in the cluster and other low-mass clusters before the clusters are tidally stripped or destroyed to become field stars in the dwarf. The SCC is initially embedded in a giant gas hole created by numerous supernovae of the SCC so that cold gas outside the hole can be accreted onto the main cluster later. New stars formed from the accreted gas have chemical abundances that are different from those of the original SCC. Using hydrodynamical simulations of GC formation based on this scenario, we show that the main cluster with the initial mass as large as [2 − 5] × 10 5 M ⊙ can accrete more than 10 5 M ⊙ gas from AGB stars of the SCC. We suggest that merging of hierarchical star cluster complexes can play key roles in stellar halo formation around GCs and self-enrichment processes in the early phase of GC formation.

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“…Within this general framework, four main scenarios have been proposed, differing mainly in the nature of the polluters: (i) asymptotic giant branch stars (D'Ercole et al 2008), (ii) fastrotating massive stars (Decressin et al 2007), (iii) interacting massive binary stars (De Mink et al 2009), and (iv) supermassive stars (Denissenkov & Hartwick 2014;Denissenkov et al 2015). An alternative scenario that does not require an age difference between first-and secondgeneration stars is the so-called early disk accretion scenario (Bastian et al 2013).…”

Section: Introductionmentioning

confidence: 99%

NGC 6362: The Least Massive Globular Cluster With Chemically Distinct Multiple Populations*

Mucciarelli

Dalessandro

Massari

et al. 2016

ApJ

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We present the first measure of Fe and Na abundances in NGC 6362, a low-mass globular cluster (GC) where firstand second-generation stars are fully spatially mixed. A total of 160 member stars (along the red giant branch (RGB) and the red horizontal branch (RHB)) were observed with the multi-object spectrograph FLAMES at the Very Large Telescope. We find that the cluster has an iron abundance of [Fe/H] = −1.09 ± 0.01 dex, without evidence of intrinsic dispersion. On the other hand, the [Na/Fe] distribution turns out to be intrinsically broad and bimodal. The Na-poor and Na-rich stars populate, respectively, the bluest and the reddest RGBs detected in the color-magnitude diagrams including the U filter. The RGB is composed of a mixture of first-and secondgeneration stars in a similar proportion, while almost all the RHB stars belong to the first cluster generation. To date, NGC 6362 is the least massive GC where both the photometric and spectroscopic signatures of multiple populations have been detected.

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Supermassive stars as a source of abundance anomalies of proton-capture elements in globular clusters

Cited by 281 publications

References 43 publications

Differences in the rotational properties of multiple stellar populations in M13: a faster rotation for the ‘extreme’ chemical subpopulation

Differences in the rotational properties of multiple stellar populations in M13: a faster rotation for the ‘extreme’ chemical subpopulation

Globular cluster formation with multiple stellar populations from hierarchical star cluster complexes

NGC 6362: The Least Massive Globular Cluster With Chemically Distinct Multiple Populations*

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