Atomic diffusion in stars can create systematic trends of surface abundances
with evolutionary stage. Globular clusters offer useful laboratories to put
observational constraints on this theory as one needs to compare abundances in
unevolved and evolved stars, all drawn from the same stellar population. In
this paper, we show the results of an abundance study of stars in the globular
cluster NGC6752 which shows weak but systematic abundances trends with
evolutionary phase for Fe, Sc, Ti and Ca. The trends are best explained by a
stellar structure model including atomic diffusion with efficient additional
mixing. The model allows to correct for sub-primordial stellar lithium
abundances of the stars on the Spite plateau, and to match it to the
WMAP-calibrated Big-Bang nucleosynthesis predictions to within the mutual
1-sigma errors.Comment: 15 pages, 4 figures and 8 table

Barklem, Paul S.

Collet, Remo

Grundahl, Frank

Gruyters, Pieter

Korn, Andreas J.

Mashonkina, Lyudmila I.

Osorio, Yeisson

Richard, Olivier

Astronomy and Astrophysics

English

arXiv

Context. Atomic diffusion in stars can create systematic trends of surface abundances with evolutionary stage. Globular clusters offer useful laboratories to put observational constraints on this theory as one needs to compare abundances in unevolved and evolved stars, all drawn from the same stellar population. Aims. Atomic diffusion and additional mixing has been shown to be at work in the globular cluster NGC 6397 at a metallicity of [Fe/H] ∼ −2.1. We investigate possible abundance trends in Li, Mg, Ca, Ti, Sc, and Fe with evolutionary stage in another globular cluster NGC 6752 at a metallicity of [Fe/H] ∼ −1.6. This in order to better constrain stellar structure models including atomic diffusion and additional mixing. Methods. We performed a differential abundance analysis on VLT/FLAMES-UVES data of 16 stars in four groups between the turnoff point and the red giant branch. Continuum normalisation of the stellar spectra was performed in an automated way using DAOSPEC. Differential abundances relative to the sun were derived by fitting synthetic spectra to individual lines in the stellar spectrum. Results. We find weak systematic abundance trends with evolutionary phase for Fe, Sc, Ti, and Ca. The individual trends are weaker than the trends in NGC 6397 and only significant at the 1-σ level. However, the combined trend shows a significance on the 2-σ level

Pieter Gruyters

Andreas J. Korn

Olivier Richard

Frank Grundahl

Remo Collet

Lyudmila I. Mashonkina

Yeisson Osorio

Paul S. Barklem

CiteSeerX

Atomic diffusion and mixing in old stars IV: Weak abundance trends in the globular cluster NGC6752?

Gruyters, P.

Korn, A.

Richard, O.

Grundahl, F.

Collet, R.

Mashonkina, L.

Osorio, Y.

Barklem, P.

HAL Descartes

Atomic diffusion and mixing in old stars IV. Weak abundance trends in the globular cluster NGC6752

HAL: Hyper Article en Ligne

P. Gruyters

A. J. Korn

O. Richard

F. Grundahl

R. Collet

L. I. Mashonkina

Y. Osorio

P. S. Barklem

Crossref

Atomic diffusion and mixing in old stars

Korn, A. J.

Mashonkina, L. I.

Barklem, P. S.

Copenhagen University Research Information System

Atomic diffusion and mixing in old stars:IV. Weak abundance trends in the globular cluster NGC 6752

HAL-IN2P3

Archive Ouverte en Sciences de l'Information et de la Communication

Context. Atomic diffusion in stars can create systematic trends of surface abundances with evolutionary stage. Globular clusters offer useful laboratories to put observational constraints on this theory as one needs to compare abundances in unevolved and evolved stars, all drawn from the same stellar population. 
        Aims. Atomic diffusion and additional mixing has been shown to be at work in the globular cluster NGC 6397 at a metallicity of [Fe/H] ~ −2.1. We investigate possible abundance trends in Li, Mg, Ca, Ti, Sc, and Fe with evolutionary stage in another globular cluster NGC 6752 at a metallicity of [Fe/H] ~ −1.6. This in order to better constrain stellar structure models including atomic diffusion and additional mixing. 
        Methods. We performed a differential abundance analysis on VLT/FLAMES-UVES data of 16 stars in four groups between the turnoff point and the red giant branch. Continuum normalisation of the stellar spectra was performed in an automated way using DAOSPEC. Differential abundances relative to the sun were derived by fitting synthetic spectra to individual lines in the stellar spectrum.
        Results. We find weak systematic abundance trends with evolutionary phase for Fe, Sc, Ti, and Ca. The individual trends are weaker than the trends in NGC 6397 and only significant at the 1-σ level. However, the combined trend shows a significance on the 2-σ level. The trends are best explained by stellar-structure models including atomic diffusion with more efficient additional mixing than needed in NGC 6397. The model allows to correct for sub-primordial stellar lithium abundances of the stars on the Spite plateau.
        Conclusions. Abundance trends for groups of elements, differently affected by atomic diffusion and additional mixing, are identified. Although the significance of the trends is weak, they all seem to indicate that atomic diffusion is operational along the evolutionary sequence of NGC 6752. The trends are weaker than those observed in NGC 6397, which is perhaps due to more efficient mixing. Using models of atomic diffusion including efficient additional mixing, we find a diffusion-corrected primordial lithium abundance of log ε(Li) = 2.58 ± 0.10, in agreement with WMAP-calibrated Big-Bang nucleosynthesis predictions within the mutual 1-σ uncertainties

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Atomic diffusion and mixing in old stars IV: Weak abundance trends in
  the globular cluster NGC 6752

Atomic diffusion and mixing in old stars IV: Weak abundance trends in the globular cluster NGC 6752

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