Super and massive AGB stars – II. Nucleosynthesis and yields – Z = 0.02, 0.008 and 0.004

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

doi:10.1093/mnras/stt1877

Cited by 189 publications

(204 citation statements)

References 72 publications

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“…This finding indicates that envelope convection is highly efficient in low-metallicity, massive AGB stars, as predicted by the FST schematisation adopted here. Note that a similar result can be obtained within the traditional Mixing Length Theory description, provided that a mixing length significantly higher than the standard vale used to reproduce the evolution of the Sun is adopted (Doherty et al 2014). Furthermore, the extremely low carbon abundances measured in these stars indicates that TDU has negligible (if any) effects on the evolution of the surface chemistry of these objects, at odds with other models for stars of similar mass and metallicity, which predict much higher quantities of carbon (see Fishlock et al 2014 and references therein).…”

Section: Pne In the Smc: A Further Test For Agb Modellingsupporting

confidence: 62%

Planetary nebulae in the Small Magellanic Cloud

Ventura

Stanghellini

Criscienzo

et al. 2016

Mon. Not. R. Astron. Soc.

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We analyse the planetary nebulae (PNe) population of the Small Magellanic Cloud (SMC), based on evolutionary models of stars with metallicities in the range 10 −3 ≤ Z ≤ 4 × 10 −3 and mass 0.9 M < M < 8 M , evolved through the asymptotic giant branch (AGB) phase. The models used account for dust formation in the circumstellar envelope. To characterise the PNe sample of the SMC, we compare the observed abundances of the various species with the final chemical composition of the AGB models: this study allows us to identify the progenitors of the PNe observed, in terms of mass and chemical composition. According to our interpretation, most of the PNe descend from low-mass (M < 2M ) stars, which become carbon rich, after experiencing repeated third dredge-up episodes, during the AGB phase. A fraction of the PNe showing the signature of advanced CNO processing are interpreted as the progeny of massive AGB stars, with mass above ∼ 6M , undergoing strong hot bottom burning. The differences with the chemical composition of the PNe population of the Large Magellanic Cloud (LMC) is explained on the basis of the diverse star formation history and age-metallicity relation of the two galaxies. The implications of the present study for some still highly debated points regarding the AGB evolution are also commented.

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Section: Pne In the Smc: A Further Test For Agb Modellingsupporting

confidence: 62%

Planetary nebulae in the Small Magellanic Cloud

Ventura

Stanghellini

Criscienzo

et al. 2016

Mon. Not. R. Astron. Soc.

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“…Instead, in the AGB scenario the helium enrichment of 2P stars is limited (maximum Y ini of ∼0.36, Doherty et al 2014 as a result of second dredge-up in intermediate-mass stars), and it is not directly correlated with the sodium enrichment. In this case, therefore, the Na abundance distribution is expected to be the same on the RGB and AGB whatever the age and the metallicity of the cluster.…”

Section: Uncertainties On the Dependency Of The Initial He-na Correlamentioning

confidence: 99%

Evolution of long-lived globular cluster stars

Charbonnel

Chantereau

2016

A&A

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Context. Long-lived stars in globular clusters exhibit chemical peculiarities with respect to their halo counterparts. In particular, sodium-enriched stars are identified as belonging to a second stellar population born from cluster material contaminated by the hydrogen-burning ashes of a first stellar population. Their presence and numbers in different locations of the colour-magnitude diagram provide important constraints on the self-enrichment scenarios. In particular, the ratio of Na-poor to Na-rich stars on the asymptotic giant branch (AGB) has recently been found to vary strongly from cluster to cluster (NGC 6752, 47 Tuc, and NGC 2808), while it is relatively constant on the red giant branch (RGB). Aims. We investigate the impact of both age and metallicity on the theoretical sodium spread along the AGB within the framework of the fast rotating massive star (FRMS) scenario for globular cluster self-enrichment. Methods. We computed evolution models of low-mass stars for four different metallicities ([Fe/H] = −2.2, −1.75, −1.15, −0.5) assuming the initial helium-sodium abundance correlation for second population stars derived from the FRMS models and using mass loss prescriptions on the RGB with two realistic values of the free parameter in the Reimers formula. Results. Based on this grid of models we derive the theoretical critical initial mass for a star born with a given helium, sodium, and metal content that determines whether that star will climb or not the AGB. This allows us to predict the maximum sodium content expected on the AGB for globular clusters as a function of both their metallicity and age. We find that (1) at a given metallicity, younger clusters are expected to host AGB stars exhibiting a larger sodium spread than older clusters and (2) at a given age, higher sodium dispersion along the AGB is predicted in the most metal-poor globular clusters than in the metal-rich ones. We also confirm the strong impact of the mass loss rate in the earlier evolution phases on the Na cut on the AGB: the higher the mass loss, the stronger the trends with age and metallicity. Conclusions. The theoretical trends we obtain provide, in principle, an elegant qualitative explanation to the different sodium spreads that are observed along the AGB in the Galactic globular clusters of different ages and [Fe/H] values. Although it is real, the slope with both age and metallicity is relatively flat, although it steepens when accounting for mass loss variations. Therefore, additional parameters may play a role in inducing cluster to cluster variations, that are difficult to disentangle from existing data.

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“…In the former case, no Li production is found at metallicity Z , a little Li is produced around 4 M at 1/2 Z and important production occurs only at 2 Z . In the study of Doherty et al (2014), some Li is produced only in the most massive stars, around 8 M . In view of the results obtained in Prantzos (2012b), we conclude that in neither case the Li yields are sufficient to reproduce the solar Li abundance, by at least a factor of two.…”

Section: From a Short-lived Sourcementioning

confidence: 99%

The AMBRE project: a study of Li evolution in the Galactic thin and thick discs

Prantzos

Laverny

Guiglion

et al. 2017

A&A

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Context. Recent observations suggest a double-branch behaviour of Li/H versus metallicity in the local thick and thin discs. This is reminiscent of the corresponding O/Fe versus Fe/H behaviour, which has been explained as resulting from radial migration in the Milky Way disc. Aims. We study here the role of radial migration in shaping these observations. Methods. We use a semi-analytical model of disc evolution with updated chemical yields and parameterised radial migration. We explore the cases of long-lived (red giants of a few Gy lifetime) and shorter-lived (asymptotic giant branch stars of several 10 8 yr) stellar sources of Li, as well as those of low and high primordial Li. We show that both factors play a key role in the overall Li evolution. Results. We find that the observed two-branch Li behaviour is only directly obtained in the case of long-lived stellar Li sources and low primordial Li. In all other cases, the data imply systematic Li depletion in stellar envelopes, thus no simple picture of the Li evolution can be obtained. This concerns also the reported Li/H decrease at supersolar metallicities.

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Super and massive AGB stars – II. Nucleosynthesis and yields – Z = 0.02, 0.008 and 0.004

Cited by 189 publications

References 72 publications

Planetary nebulae in the Small Magellanic Cloud

Planetary nebulae in the Small Magellanic Cloud

Evolution of long-lived globular cluster stars

The AMBRE project: a study of Li evolution in the Galactic thin and thick discs

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