Implications of<i>WMAP</i>Observations on Li Abundance and Stellar Evolution Models

Richard, Olivier; Michaud, G.; Richer, Jacques

doi:10.1086/426470

Cited by 299 publications

(524 citation statements)

References 65 publications

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“…Richard et al 2005), we find strong support for the need of some turbulence, with strict limits to its efficiency (cf. figure 10 in Lind et al 2009b).…”

Section: Results and Implicationsmentioning

confidence: 55%

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The lithium history of NGC 6397

et al. 2009

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Abstract. The primordial lithium abundance inferred from WMAP and standard Big Bang nucleosysnthesis is approximately three times higher than the plateau value measured in old metal-poor Population II stars, suggesting that these stars have undergone atmospheric Li depletion. To constrain the physics responsible for such depletion, we conducted a homogeneous analysis of a large sample of stars in the metal-poor globular cluster NGC 6397, covering all evolutionary phases from below the main-sequence turnoff to high up the red-giant branch (RGB). The dwarf, turnoff, and early subgiant stars form a thin abundance plateau, with a sharpe edge in the middle of the subgiant branch, where Li dilution caused by the inward extension of the convective envelope starts (the beginning of the so-called first dredge up). A second steep abundance drop is seen at the RGB bump, again highlighting the need for the onset of nonstandard mixing in this evolutionary phase. Moreover, by also measuring the sodium abundances of the targets, we have gained insight into the degree of pollution by early cluster self-enrichement, and may separate highly polluted, Li-poor and Na-rich stars from stars formed from pristine material. Our observational findings strictly limit both the extent of lithium surface depletion, which in turn constrains the efficiency of mixing below the outer convection zone, and the resulting spread in lithium abundance in metal-poor turn-off stars.

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“…Richard et al 2005), we find strong support for the need of some turbulence, with strict limits to its efficiency (cf. figure 10 in Lind et al 2009b).…”

Section: Results and Implicationsmentioning

confidence: 55%

“…However, without the existence of macroscopic mixing acting below the outer convection zone, a thin and close-to-flat Spite plateau cannot be reproduced by stellar-structure models (Richard et al 2005). As of today, the physical process behind the mixing has yet to be identified.…”

Section: Introductionmentioning

confidence: 99%

The lithium history of NGC 6397

et al. 2009

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“…With some fine-tuning, this could be achieved by the combined effects of atomic diffusion and turbulence in the outer layers of these stars [38], or by lithium destruction, followed by a self-regulated re-enrichment of lithium by late time accretion [39].…”

Section: Discussionmentioning

confidence: 99%

Primordial Nucleosynthesis

Coc

2017

Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016)

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Primordial or big bang nucleosynthesis (BBN) is now a parameter free theory whose predictions are in good overall agreement with observations. However, the 7 Li calculated abundance is significantly higher than the one deduced from spectroscopic observations. Most solutions to this lithium problem involve a source of extra neutrons that inevitably leads to an increase of the deuterium abundance. This seems now to be excluded by recent deuterium observations that have drastically reduced the uncertainty on D/H and also calls for improved precision on thermonuclear reaction rates.

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“…Some calculations have been made (e.g. Richard et al, 2005): a depletion such as figured in Fig, 3, could be matched by a diffusion carefully moderated by some turbulence. The very low scatter of the data around the mean (0.05 dex) in the interval 2 × 10 −3 <…”

Section: Depletion In the Stellar Atmospheresmentioning

confidence: 99%

Li isotopes in metal-poor halo dwarfs: a more and more complicated story

Spite¹,

Spite²

2009

Proc. IAU

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Abstract. The nuclei of the lithium isotopes are fragile, easily destroyed, so that, at variance with most of the other elements, they cannot be formed in stars through steady hydrostatic nucleosynthesis.The 7 Li isotope is synthesized during primordial nucleosynthesis in the first minutes after the Big Bang and later by cosmic rays, by novae and in pulsations of AGB stars (possibly also by the ν process). 6 Li is mainly formed by cosmic rays. The oldest (most metal-deficient) warm galactic stars should retain the signature of these processes if, (as it had been often expected) lithium is not depleted in these stars. The existence of a "plateau" of the abundance of 7 Li (and of its slope) in the warm metal-poor stars is discussed. At very low metallicity ([Fe/H] < −2.7dex) the star to star scatter increases significantly towards low Li abundances. The highest value of the lithium abundance in the early stellar matter of the Galaxy (log (Li) = A( 7 Li) = 2.2 dex † ) is much lower than the the value (log (Li) = 2.72) predicted by the standard Big Bang nucleosynthesis, according to the specifications found by the satellite WMAP. After gathering a homogeneous stellar sample, and analysing its behaviour, possible explanations of the disagreement between Big Bang and stellar abundances are discussed (including early astration and diffusion). On the other hand, possibilities of lower productions of 7 Li in the standard and/or non-standard Big Bang nucleosyntheses are briefly evoked.A surprisingly high value (A( 6 Li) = 0.8 dex) of the abundance of the 6 Li isotope has been found in a few warm metal-poor stars. Such a high abundance of 6 Li independent of the mean metallicity in the early Galaxy cannot be easily explained. But are we really observing 6 Li ?

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Implications ofWMAPObservations on Li Abundance and Stellar Evolution Models

Cited by 299 publications

References 65 publications

The lithium history of NGC 6397

The lithium history of NGC 6397

Primordial Nucleosynthesis

Li isotopes in metal-poor halo dwarfs: a more and more complicated story

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