Atomic diffusion and mixing in old stars

Gruyters, Pieter; Nordlander, Thomas; Korn, A. J.

doi:10.1051/0004-6361/201423590

Cited by 57 publications

(56 citation statements)

References 85 publications

(130 reference statements)

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“…The lower estimate to the initial Li abundance based on the T6.00 model does not fully agree with the latest predictions from BBNS by Cyburt et al (2015) Gruyters et al 2016). We note that these Li values are derived from predictions by the stellar structure model including AD and AddMix, which represents the observations best, and thus from models with different efficiencies of AddMix.…”

Section: Comparison To Atomic Diffusion Modelscontrasting

confidence: 76%

“…The result is a Li-depleted surface layer. Similar lithium trends are observed in other metal-poor clusters such as NGC 6397 (Lind et al 2009b;Nordlander et al 2012), NGC 6752 (Gruyters et al 2013(Gruyters et al , 2014, and M4 (Mucciarelli et al 2012;Gruyters et al 2016), as well as in halo field stars (Gratton et al 2000). Notes.…”

Section: LIsupporting

confidence: 65%

“…And although the surface metallicities observed today may vary between stars in different evolutionary phases, due to the effects of atomic diffusion, e.g. Korn et al (2007), Lind et al (2008), Nordlander et al (2012), Gruyters et al (2013Gruyters et al ( , 2014, all stars were also born with the same (iron-peak) metallicity.…”

Section: Introductionmentioning

confidence: 99%

“…As Na also theoretically anticorrelates with Li, the same mechanism will lower the Li abundance in second-generation stars as the more massive stars are hotter and thus burn the Li before it is returned to the interstellar medium. Thus, if we wish to obtain the primordial value of Li, we have to find a way to disentangle the effects of atomic diffusion and intrinsic stellar depletion from early cluster pollution (Lind et al 2009b;Nordlander et al 2012;Gruyters et al 2014).…”

Section: Introductionmentioning

confidence: 99%

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Atomic diffusion and mixing in old stars

Gruyters

Lind

Richard

et al. 2016

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Context. The prediction of the Planck-constrained primordial lithium abundance in the Universe is in discordance with the observed Li abundances in warm Population II dwarf and subgiant stars. Among the physically best motivated ideas, it has been suggested that this discrepancy can be alleviated if the stars observed today had undergone photospheric depletion of lithium. Aims. The cause of this depletion is investigated by accurately tracing the behaviour of the lithium abundances as a function of effective temperature. Globular clusters are ideal laboratories for such an abundance analysis as the relative stellar parameters of their stars can be precisely determined. Methods. We performed a homogeneous chemical abundance analysis of 144 stars in the metal-poor globular cluster M30, ranging from the cluster turnoff point to the tip of the red giant branch. Non-local thermal equilibrium (NLTE) abundances for Li, Ca, and Fe were derived where possible by fitting spectra obtained with VLT/FLAMES-GIRAFFE using the quantitative-spectroscopy package SME. Stellar parameters were derived by matching isochrones to the observed V vs. V − I colour-magnitude diagram. Independent effective temperatures were obtained from automated profile fitting of the Balmer lines and by applying colour-T eff calibrations to the broadband photometry. Results. Li abundances of the turnoff and early subgiant stars form a thin plateau that is broken off abruptly in the middle of the SGB as a result of the onset of Li dilution caused by the first dredge-up. Abundance trends with effective temperature for Fe and Ca are observed and compared to predictions from stellar structure models including atomic diffusion and ad hoc additional mixing below the surface convection zone. The comparison shows that the stars in M30 are affected by atomic diffusion and additional mixing, but we were unable to determine the efficiency of the additional mixing precisely. This is the fourth globular cluster (after NGC 6397, NGC 6752, and M4) in which atomic diffusion signatures are detected. After applying a conservative correction (T6.0 model) for atomic diffusion, we find an initial Li abundance of A(Li) = 2.48 ± 0.10 for the globular cluster M30. We also detected a Li-rich SGB star with a Li abundance of A(Li) = 2.39. The finding makes Li-rich mass transfer a likely scenario for this star and rules out models in which its Li enhancement is created during the RGB bump phase.

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Section: Comparison To Atomic Diffusion Modelscontrasting

confidence: 76%

Section: LIsupporting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Atomic diffusion and mixing in old stars

Gruyters

Lind

Richard

et al. 2016

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“…Fig. 6 in Korn et al 2007) with the magnitudes of non-LTE effects seen, underlines the necessity to include accurate non-LTE corrections in order to study changes in atmospheric abundances with evolutionary status (see also Gruyters et al 2013Gruyters et al , 2014. Figure 5 shows the Mg abundance one would derive in LTE as function of T eff for various values of log g for a constant non-LTE abundance.…”

Section: Differential Effectsmentioning

confidence: 92%

Mg line formation in late-type stellar atmospheres

Osorio

Barklem

2016

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Context. Mg is the α element of choice for Galactic population and chemical evolution studies because it is easily detectable in all late-type stars. Such studies require precise elemental abundances, and thus departures from local thermodynamic equilibrium (LTE) need to be accounted for. Aims. Our goal is to provide reliable departure coefficients and equivalent widths in non-LTE, and for reference in LTE, for diagnostic lines of Mg studied in late-type stars. These can be used, for example, to correct LTE spectra and abundances.Methods. Using the model atom built and tested in the preceding paper in this series, we performed non-LTE radiative transfer calculations in a grid of 3945 stellar 1D atmospheric models. We used a sub-grid of 86 models to explore the propagation of errors in the recent atomic collision calculations to the radiative transfer results. Results. We obtained departure coefficients for all the levels and equivalent widths (in LTE and non-LTE) for all the radiative transitions included in the "final" model atom presented in Paper I. Here we present and describe our results and show some examples of applications of the data. The errors that result from uncertainties in the collisional data are investigated and tabulated. The results for equivalent widths and departure coefficients are made freely available. Conclusions. Giants tend to have negative abundance corrections while dwarfs have positive, though small, corrections. Error analysis results show that uncertainties related to the atomic collision data are typically on the order of 0.01 dex or less, although for few stellar models in specific lines uncertainties can be as large as 0.03 dex. As these errors are less than or on the same order as typical corrections, we expect that we can use these results to extract Mg abundances from high-quality spectra more reliably than from classical LTE analysis.

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