On the Possibility of Nova Enrichment of Globular Clusters

Smith, Graeme H.; Kraft, Robert P.

doi:10.1086/133728

Cited by 14 publications

(11 citation statements)

References 57 publications

(103 reference statements)

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“…Classical novae could thus be interesting polluter candidates, as previously proposed by Smith & Kraft (1996). Recent work also suggested novae involving isolated white dwarfs, i.e., white dwarfs that accrete directly from the intracluster medium, as polluters (Maccarone & Zurek 2012).…”

Section: Novaementioning

confidence: 77%

“…For the cluster NGC 6752, the measured stellar abundance anomalies involving O, Na, Mg, and Al can be explained by hydrogen burning at moderate temperatures, near 75 MK, as was shown by Prantzos, Charbonnel & Iliadis (2007). Candidate sources for the first-generation polluter stars include rapidly rotating massive stars (Decressin et al 2007), massive stars in interacting binary systems (de Mink et al 2009), stellar collisions (Sills & Glebbeek 2010), supermassive stars with M ≈ 10 4 M (Denissenkov & Hartwick 2014), intermediate-mass asymptotic giant branch (AGB) stars (D'Antona et al 2002), superasymptotic giant branch stars (SAGB) (Ventura et al 2012), and novae (Smith & Kraft 1996;Maccarone & Zurek 2012), but detailed stellar models fail to account for all observations.…”

Section: Introductionmentioning

confidence: 95%

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On Potassium and Other Abundance Anomalies of Red Giants in NGC 2419

Iliadis

Karakas

Prantzos

et al. 2016

ApJ

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Globular clusters are of paramount importance for testing theories of stellar evolution and early galaxy formation. Strong evidence for multiple populations of stars in globular clusters derives from observed abundance anomalies. A puzzling example is the recently detected Mg-K anticorrelation in NGC 2419. We perform Monte Carlo nuclear reaction network calculations to constrain the temperature-density conditions that gave rise to the elemental abundances observed in this elusive cluster. We find a correlation between stellar temperature and density values that provide a satisfactory match between simulated and observed abundances in NGC 2419 for all relevant elements (Mg, Si, K, Ca, Sc, Ti, and V). Except at the highest densities (ρ 10 8 g/cm 3 ), the acceptable conditions range from ≈ 100 MK at ≈ 10 8 g/cm 3 to ≈ 200 MK at ≈ 10 −4 g/cm 3 . This result accounts for uncertainties in nuclear reaction rates and variations in the assumed initial composition. We review hydrogen burning sites and find that low-mass stars, AGB stars, massive stars, or supermassive stars cannot account for the observed abundance anomalies in NGC 2419. Super-AGB stars could be viable candidates for the polluter stars if stellar model parameters can be fine-tuned to produce higher temperatures. Novae, either involving CO or ONe white dwarfs, could be interesting polluter candidates, but a current lack of low-metallicity nova models precludes firmer conclusions. We also discuss if additional constraints for the firstgeneration polluters can be obtained by future measurements of oxygen, or by evolving models of second-generation low-mass stars with a non-canonical initial composition.

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Section: Novaementioning

confidence: 77%

Section: Introductionmentioning

confidence: 95%

On Potassium and Other Abundance Anomalies of Red Giants in NGC 2419

Iliadis

Karakas

Prantzos

et al. 2016

ApJ

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“…In general, the GC chemical composition seems to be compatible with enrichment due to core‐collapse supernovae and may be some late pollution by nova outbursts and winds from asymptotic giant branch (AGB) stars (Smith & Kraft 1996; Jehin et al 1999). One may ask why the distribution of iron is homogeneous and the distribution of light elements is not, if both originate from the same massive stars.…”

Section: Discussionmentioning

confidence: 99%

First supernovae in Galactic globular clusters

Шустов

Wiebe

2000

Monthly Notices of the Royal Astronomical Society

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We address the question of whether globular clusters (GC) in a protogalaxy could evolve chemically for some time as isolated systems, enriching themselves with heavy elements produced in the first supernova events that follow initial star formation. We determine both the critical mass of a protoglobular cluster (proto‐GC) that is needed to retain the ejecta of the very first supernova, and the critical energy (i.e. number of supernovae) that is needed to expel the residual gas from a cluster of a given mass. We show that the critical mass of a proto‐GC for a wide range of parameters (size, degree of fragmentation, degree of central concentration) does not exceed to 106 M⊙. The critical star formation efficiency (resulting in a certain number of supernova events) that is needed to expel the residual gas is about 1–3 per cent. Assuming that all the star‐forming activity in the cluster stops after the critical number of supernovae have exploded, we reproduce the basic parameters of the present‐day globular clusters, i.e. their final masses and oxygen abundances. A typical globular cluster in our model originates from a cloud with a mass of to 108 M⊙. When all the remaining gas is lost from the cluster, its mass is about a few times 105 M⊙. A significant fraction (∼97 per cent) of an initial protocluster cloud is then available for galactic disc formation. We check our results with the method that is usually applied to elliptical galaxy modelling. The assumption that a protocluster cloud evolves and accumulates metals until the gas thermal energy (increased due to supernova explosions) exceeds its binding energy leads to the same conclusions. We also comment on the observed homogeneity of the iron distribution in globular clusters, which is often considered as a primary argument against self‐enrichment. According to the current paradigm, iron originates mainly in Type Ia supernovae with long‐lived progenitors. If one states that iron has existed in globular clusters prior to their formation, it should have had a pre‐Galactic origin. We argue that it is hard to reconcile this with the observed correlation of average iron abundances in extragalactic GC systems with the luminosities of parent galaxies.

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“…Such a mechanism was discussed by Bell et al (1981) and Briley et al (1994a); a more detailed version, which invokes nova events to explain also certain isotopic abundances in the giants, has been given by Smith & Kraft (1996). An advantage of pollution is that the main-sequence stars can have their surface abundances significantly altered by rather small amounts of accreted matter, since they do not have convective envelopes.…”

Section: Pollutionmentioning

confidence: 99%

Carbon and nitrogen abundance variations on the main sequence of 47 Tucanae

Cannon

Croke

Bell

et al. 1998

Monthly Notices of the Royal Astronomical Society

188

219

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The FOCAP multi‐object fibre optic system on the AAT has been used to obtain spectra for a sample of more than a hundred faint stars in the globular cluster 47 Tuc (NGC 104), from the base of the giant branch to about a magnitude below the main‐sequence turn‐off. The spectra cover the ultraviolet and blue bands of CN and the G band of CH. Quantitative abundances have been derived by comparing the observations with synthetic spectra. The main‐sequence stars can be divided into two approximately equal groups, one having N enhanced by a factor of ∼ 7, and C depleted by 40 per cent, relative to the other, similar to what is inferred for the red giants. The mean heavy‐element abundance, as measured by Ca or Fe, differs between the two groups by no more than 0.01 ± 0.05 dex. All the available abundance data indicate that the atmospheres of 47 Tuc stars contain different amounts of material which has been processed through the CNO cycle, but not through more advanced stages of nucleosynthesis. In the red giants, this could be a result of the convective dredge‐up of processed material from deep within the stars themselves, as occurs in some more metal‐poor clusters. However, stars on the upper main sequence of globular clusters do not have convective envelopes, while any deep mixing there would have consequences incompatible with other observational data. Thus it seems that the main‐sequence C and N variations must be either primordial or caused by a pollution mechanism. The similarity of the bimodal abundance patterns among the dwarfs and giants then suggests that the dredge up of CNO‐cycled material is not the dominant process in the red giants either, at least not in 47 Tuc. The CNO‐processed material seems most likely to have come from intermediate‐mass stars on the asymptotic giant branch; various mechanisms by which such material might appear in the main‐sequence stars are discussed. Explanations involving a truly primordial origin, or having successive generations of stars, seem to require rather special ‘tuning’. A somewhat speculative alternative self‐enrichment process is proposed, in which stellar winds from intermediate‐mass stars were captured by existing low‐mass stars, early in the life of the cluster. Whatever the mechanism, the abundance data presumably contain important clues about the formation and early evolution of globular clusters.

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On the Possibility of Nova Enrichment of Globular Clusters

Cited by 14 publications

References 57 publications

On Potassium and Other Abundance Anomalies of Red Giants in NGC 2419

On Potassium and Other Abundance Anomalies of Red Giants in NGC 2419

First supernovae in Galactic globular clusters

Carbon and nitrogen abundance variations on the main sequence of 47 Tucanae

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