Super and massive AGB stars – III. Nucleosynthesis in metal-poor and very metal-poor stars – Z = 0.001 and 0.0001

Doherty, Carolyn; Gil‐Pons, Pilar; Lau, Herbert H. B.; Lattanzio, John C.; Siess, Lionel; Campbell, Simon

doi:10.1093/mnras/stu571

Cited by 106 publications

(86 citation statements)

References 99 publications

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“…While the FRMS scenario predicts that 2P stars can start their life with an helium mass fraction of between that of 1P stars (i.e., typically 0.248 for the metallicity presented in this study) and 0.8, the maximum helium enrichment provided by the AGB scenario amounts to at most ∼0.36−0.38 in mass fraction (e.g., Siess 2010;Doherty et al 2014). Since the initial helium content is an important ingredient for the evolution of stars (e.g., Iben & Rood 1969;Demarque et al 1971;Sweigart 1978;Maeder 2009;Chantereau et al 2015), it is mandatory to quantify the effect of these differences on the expected properties of GC multiple populations (e.g., D'Antona et al 2002;Salaris et al 2006;Pietrinferni et al 2009;Sbordone et al 2011;Valcarce et al 2012;Cassisi et al 2013a).…”

Section: Introductionmentioning

confidence: 78%

“…Moreover, only 9% (3%) of the HB stars have an initial helium mass fraction between 0.36 and 0.41 (between 0.38 and 0.41). It is important to recall that the AGB scenario predicts a maximum helium enrichment of 2P stars of Y ini,max ∼ 0.36−0.38 (Siess 2010;Doherty et al 2014). This means that the AGB and the FRMS scenario predict a similar maximum extension of the initial helium content on the HB for analogous ages and metallicities, hence it is impossible to use this evolution phase to distinguish between these two frameworks.…”

Section: Highest Helium Content On the Horizontal Branchmentioning

confidence: 99%

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Evolution of long-lived globular cluster stars

Chantereau

Charbonnel

Meynet

2016

A&A

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Context. Globular clusters host multiple populations of long-lived low-mass stars whose origin remains an open question. Several scenarios have been proposed to explain the associated photometric and spectroscopic peculiarities. They differ, for instance, in the maximum helium enrichment they predict for stars of the second population, which these stars can inherit at birth as the result of the internal pollution of the cluster by different types of stars of the first population. Aims. We present the distribution of helium-rich stars in present-day globular clusters as it is expected in the original framework of the fast-rotating massive stars scenario (FRMS) as first-population polluters. We focus on NGC 6752. Methods. We completed a grid of 330 stellar evolution models for globular cluster low-mass stars computed with different initial chemical compositions corresponding to the predictions of the original FRMS scenario for [Fe/H] = −1.75. Starting from the initial helium-sodium relation that allows reproducing the currently observed distribution of sodium in NGC 6752, we deduce the helium distribution expected in that cluster at ages equal to 9 and 13 Gyr. We distinguish the stars that are moderately enriched in helium from those that are very helium-rich (initial helium mass fraction below and above 0.4, respectively), and compare the predictions of the FRMS framework with other scenarios for globular cluster enrichment. Results. The effect of helium enrichment on the stellar lifetime and evolution reduces the total number of very helium-rich stars that remain in the cluster at 9 and 13 Gyr to only 12% and 10%, respectively, from an initial fraction of 21%. Within this age range, most of the stars still burn their hydrogen in their core, which widens the MS band significantly in effective temperature. The fraction of very helium-rich stars drops in the more advanced evolution phases, where the associated spread in effective temperature strongly decreases. These stars even disappear from the horizontal branch and the asymptotic giant branch at 13 Gyr. Conclusions. The helium constraint is no suitable criterion for clearly distinguishing between the scenarios for GC self-enrichment because only few very helium-rich stars are predicted in the investigated framework and because it is difficult to derive the helium content of GC stars observationally. However, the helium constraint indicates some difficulties of the original FRMS scenario that require the exploration of alternatives.

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Section: Introductionmentioning

confidence: 78%

Section: Highest Helium Content On the Horizontal Branchmentioning

confidence: 99%

Evolution of long-lived globular cluster stars

Chantereau

Charbonnel

Meynet

2016

A&A

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“…The SDU is deeper than the FDU in every model with FDU, and the depth of the SDU decreases with increasing He abundance. However, due to the increased core mass in the 6 M model with Y = 0.40, a "corrosive SDU" takes place (Gil-Pons et al 2013;Doherty et al 2014). In this model, the inner edge of the convective envelope reaches below the top of the CO core, which dredges up C and O to the surface.…”

Section: The First and Second Dredge-upmentioning

confidence: 99%

Evolution and nucleosynthesis of helium-rich asymptotic giant branch models

Shingles

Doherty

Karakas

et al. 2015

Mon. Not. R. Astron. Soc.

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There is now strong evidence that some stars have been born with He mass fractions as high as Y ≈ 0.40 (e.g., in ω Centauri). However, the advanced evolution, chemical yields, and final fates of He-rich stars are largely unexplored. We investigate the consequences of He-enhancement on the evolution and nucleosynthesis of intermediatemass asymptotic giant branch (AGB) models of 3, 4, 5, and 6 M with a metallicity of Z = 0.0006 ([Fe/H] ≈ −1.4). We compare models with He-enhanced compositions (Y = 0.30, 0.35, 0.40) to those with primordial He (Y = 0.24). We find that the minimum initial mass for C burning and super-AGB stars with CO(Ne) or ONe cores decreases from above our highest mass of 6 M to ∼ 4-5 M with Y = 0.40. We also model the production of trans-Fe elements via the slow neutron-capture process (s-process). He-enhancement substantially reduces the third dredge-up efficiency and the stellar yields of s-process elements (e.g., 90% less Ba for 6 M , Y = 0.40). An exception occurs for 3 M , where the near-doubling in the number of thermal pulses with Y = 0.40 leads to ∼ 50% higher yields of Ba-peak elements and Pb if the 13 C neutron source is included. However, the thinner intershell and increased temperatures at the base of the convective envelope with Y = 0.40 probably inhibit the 13 C neutron source at this mass. Future chemical evolution models with our yields might explain the evolution of s-process elements among He-rich stars in ω Centauri.

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“…However, the available data make differentiating various pollution scenarios difficult. To date, none of the proposed nucleosynthesis sources, which include intermediate mass (∼5-8 M e ) AGB stars (e.g., Fenner et al 2004;Karakas et al 2006;Ventura & D'Antona 2009;D'Ercole et al 2010;Ventura et al 2013;Doherty et al 2014), massive rapidly rotating main-sequence stars (e.g., Decressin et al 2007Decressin et al , 2010, interacting massive binary stars (de Mink et al 2009;Izzard et al 2013), and very massive (∼10 4 M e ) stars (Denissenkov & Hartwick 2014), are able to fully explain all observed abundance patterns. Additionally, no combination of the previously proposed sources seems able to reproduce all abundance patterns either (Bastian et al 2015).…”

Section: Introductionmentioning

confidence: 99%

A Spectroscopic Analysis of the Galactic Globular Cluster NGC 6273 (M19)

et al. 2015

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A combined effort utilizing spectroscopy and photometry has revealed the existence of a new globular cluster class. These "anomalous" clusters, which we refer to as "iron-complex" clusters, are differentiated from normal clusters by exhibiting large (0.10 dex) intrinsic metallicity dispersions, complex sub-giant branches, and correlated [Fe/H] and s-process enhancements. In order to further investigate this phenomenon, we have measured radial velocities and chemical abundances for red giant branch stars in the massive, but scarcely studied, globular cluster NGC 6273. The velocities and abundances were determined using high resolution (R ∼ 27,000) spectra obtained with the Michigan/ Magellan Fiber System (M2FS) and MSpec spectrograph on the Magellan-Clay 6.5 m telescope at Las Campanas Observatory. We find that NGC 6273 has an average heliocentric radial velocity of +144.49 km s −1 (σ = 9.64 km s

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Super and massive AGB stars – III. Nucleosynthesis in metal-poor and very metal-poor stars – Z = 0.001 and 0.0001

Cited by 106 publications

References 99 publications

Evolution of long-lived globular cluster stars

Evolution of long-lived globular cluster stars

Evolution and nucleosynthesis of helium-rich asymptotic giant branch models

A Spectroscopic Analysis of the Galactic Globular Cluster NGC 6273 (M19)

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