Revisiting nucleosynthesis in globular clusters

Prantzos, Nikos; Charbonnel, C.; Iliadis, Christian

doi:10.1051/0004-6361/201731528

Cited by 59 publications

(79 citation statements)

References 132 publications

(155 reference statements)

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“…In contrast, the NGC 6402 E population data are better fit with a burning temperature of ∼70 MK. A higher burning temperature for the E population in NGC 2808 is also consistent with its larger Si enhancements since 28 Si production is a relatively monotonic function of temperature in the ∼65−125 MK range (e.g., Prantzos et al 2017). As a consequence of the very high temperatures required to modify elements heavier than Si, the Al-Ca correlation signature observed in NGC 6402, but not NGC 2808, seems likely to be a spurious result.…”

Section: Nucleosynthesis Implications From Amentioning

confidence: 54%

“…Temperatures exceeding 80 MK also lower the Na and Al yields but may destroy too much Mg and produce too much Si to fit the observations (e.g., see Fig. 3 of Prantzos et al 2017). Further inspection of Fig.…”

Section: Nucleosynthesis Implications From Amentioning

confidence: 86%

“…values can also fit the data, but at least for NGC 6402 such a scenario would require additional dilution to decrease the maximum ∆[Na/Fe] and ∆[Al/Fe] ratios. We note that Prantzos et al (2017) did include a small initial dilution of 4−5 per cent pristine material to explain the light element variations in NGC 2808. Small H ex.…”

Section: Nucleosynthesis Implications From Amentioning

confidence: 99%

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Light element discontinuities suggest an early termination of star formation in the globular cluster NGC 6402 (M14)

Johnson

Caldwell

Rich

et al. 2019

Monthly Notices of the Royal Astronomical Society

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NGC 6402 is among the most massive globular clusters in the Galaxy, but little is known about its detailed chemical composition. Therefore, we obtained radial velocities and/or chemical abundances of 11 elements for 41 red giant branch cluster members using high resolution spectra obtained with the Magellan-M2FS instrument. We find NGC 6402 to be only moderately metal-poor with [Fe/H] = −1.13 dex (σ = 0.05 dex) and to have a mean heliocentric radial velocity of −61.1 km s −1 (σ = 8.5 km s −1 ). In general, NGC 6402 exhibits mean composition properties that are similar to other inner Galaxy clusters, such as [α/Fe] ∼ +0.3 dex, [Cr,Ni/Fe] ∼ 0.0 dex, and [La/Eu] = −0.08 dex. Similarly, we find large star-to-star abundance variations for O, Na, Mg, Al, and Si that are indicative of gas that experienced high temperature proton-capture burning. Interestingly, we detect three distinct populations, but also find large gaps in the [O/Fe], [Na/Fe], and [Al/Fe] distributions that may provide the first direct evidence of delayed formation for intermediate composition stars. A qualitative enrichment model is discussed where clusters form stars through an early ( < ∼ 5−10 Myr) phase, which results in first generation and "extreme" composition stars, and a delayed phase ( > ∼ 40 Myr), which results in the dilution of processed and pristine gas and the formation of intermediate composition stars. For NGC 6402, the missing intermediate composition stars suggest the delayed phase terminated prematurely, and as a result the cluster may uniquely preserve details of the chemical enrichment process.

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Section: Nucleosynthesis Implications From Amentioning

confidence: 54%

Section: Nucleosynthesis Implications From Amentioning

confidence: 86%

Section: Nucleosynthesis Implications From Amentioning

confidence: 99%

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Light element discontinuities suggest an early termination of star formation in the globular cluster NGC 6402 (M14)

Johnson

Caldwell

Rich

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…The chemical abundances in light elements obey to specific patterns, such as the mass of the polluters (e.g. Prantzos, Charbonnel & Iliadis 2017). The most acknowledged scenarios predict that second generations (2G) of stars form from material processed in 1G polluters, so filling the Na-N-enhanced and O-C-depleted regions of the common (anti)correlations abundance plots.…”

Section: Introductionmentioning

confidence: 99%

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters – XIX. A chemical tagging of the multiple stellar populations over the chromosome maps

Marino

Milone

Renzini

et al. 2019

Monthly Notices of the Royal Astronomical Society

130

181

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The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters (GCs) has investigated GCs and their stellar populations. In previous papers of this series we have introduced a pseudo two-colour diagram, or "chromosome map" (ChM) that maximises the separation between the multiple populations. We have identified two main classes of GCs: Type I, including ∼83% of the objects, and Type II clusters. Both classes host two main groups of stars, referred to in this series as first (1G) and second generation (2G). Type II clusters host more-complex ChMs, exhibiting two or more parallel sequences of 1G and 2G stars. We exploit spectroscopic elemental abundances from literature to assign the chemical composition to the distinct populations as identified on the ChMs of 29 GCs. We find that stars in different regions of the ChM have different composition: 1G stars share the same light-element content as field stars, while 2G stars are enhanced in N, Na and depleted in O. Stars with enhanced Al, as well as stars with depleted Mg populate the extreme regions of the ChM. We investigate the intriguing colour spread among 1G stars observed in many Type I GCs, and find no evidence for internal variations in light elements among these stars, whereas either a ∼ 0.1 dex iron spread or a variation in He among 1G stars remain to be verified. In the attempt of analysing the global properties of the multiple populations phenomenon, we have constructed a universal ChM, which highlights that, though very variegate, the phenomenon has some common pattern among all the analysed GCs. The universal ChM reveals a tight connection with Na abundances, for which we have provided an empirical relation. The additional ChM sequences observed in Type II GCs, are enhanced in metallicity and, in some cases, s-process elements. Omega Centauri can be classified as an extreme Type II GC, with a ChM displaying three main extended "streams", each with its own variations in chemical abundances. One of the most noticeable differences is found between the lower and upper streams, with the latter, associated with higher He, being also shifted towards higher Fe and lower Li abundances. We publicly release the ChMs.

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“…comm. seePrantzos et al 2017). The vertical dashed lines show the mass limits that are allowed for nucleosynthesis; see text.…”

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confidence: 99%

Spectral properties and detectability of supermassive stars in protoglobular clusters at high redshift

Martins

Haemmerlé

Charbonnel

2019

A&A

Self Cite

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Context. Globular clusters (GCs) contain multiple stellar populations with peculiar chemical compositions. Pollution of the intracluster gas by an early population of fast-evolving stars is the most common scenario for explaining the observations. Stars with masses in excess of 1000 M have recently been suggested as potential polluters. Aims. We investigate the spectral properties of proto-GCs that would host a supermassive star (SMS). Our main goal is to quantify how such a star would affect the integrated light of the cluster, and to study the detectability of such objects. Methods. We computed nonlocal thermal equilibirum atmosphere models for SMS with various combinations of stellar parameters (luminosity, effective temperature, and mass) and metallicities appropriate for GCs, and we predict their emergent spectra. Using these spectra, we calculated the total emission of young proto-GCs with SMS as predicted in a previously reported scenario, and we computed synthetic photometry in UV, optical, and near-IR bands, in particular for the James Webb Space Telescope (JWST).Results. At an effective temperature of 10000 K, the spectrum of SMSs shows a Balmer break in emission. This feature is due to strong nonlocal thermal equilibrium effects (implied by the high luminosity) and is not observed in "normal" stars. The hydrogen lines also show a peculiar behavior, with Balmer lines in emission while higher series lines are in absorption. At 7000 K, the Balmer break shows a strong absorption. At high effective temperatures, the Lyman break is found in emission. Cool and luminous SMSs are found to dominate the integrated spectrum of the cluster, except for the UV range. The predicted magnitudes of these proto-GCs are mag AB ∼28-30 between 0.7 and 8 µm and for redshifts z ∼ 4 − 10, which is detectable with the JWST. The peculiar observational features of cool SMSs imply that they might in principle be detected in color-color diagrams that probe the spectral energy distribution below and above the Balmer break. Conclusions.Our results show that SMSs should be detectable in proto-GCs if they are luminous and relatively cool. They may be found through deep imaging with the JWST.

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Revisiting nucleosynthesis in globular clusters

Cited by 59 publications

References 132 publications

Light element discontinuities suggest an early termination of star formation in the globular cluster NGC 6402 (M14)

Light element discontinuities suggest an early termination of star formation in the globular cluster NGC 6402 (M14)

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters – XIX. A chemical tagging of the multiple stellar populations over the chromosome maps

Spectral properties and detectability of supermassive stars in protoglobular clusters at high redshift

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