Atomic Diffusion in Stars

Michaud, G.; Alecian, G.; Richer, Jacques

doi:10.1007/978-3-319-19854-5

Cited by 128 publications

(125 citation statements)

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“…In principle, the higher atomic mass of 4 He leads to a faster gravitational settling for it than for 3 He. Therefore, the 4 He/ 3 He abundance ratio decreases with time (Michaud et al 2015). By applying the simplistic diffusion theory model, Vauclair et al (1974) showed that the time needed to result in the observed 3 He overabundances is much longer than the stellar lifetime.…”

Section: Introductionmentioning

confidence: 99%

On the 3He anomaly in hot subdwarf B stars

Schneider¹,

Irrgang²,

Heber³

et al. 2017

Open Astronomy

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Decades ago, 3 He isotope enrichment in helium-weak B-type main-sequence, in blue horizontal branch and in hot subdwarf B (sdB) stars, i.e., helium-core burning stars of the extreme horizontal branch, were discovered. Diffusion processes in the atmosphere of these stars lead to the observed abundance anomalies. Quantitative spectral analyses of high-resolution spectra to derive photospheric isotopic helium abundance ratios for known 3 He sdBs have notbeen performed yet. We present preliminary results of high-resolution and high S/N spectra to determine the 3 He and 4 He abundances of nine known 3 He sdBs. We used a hybrid local/non-local thermodynamic equilibrium (LTE/NLTE) approach for B-type stars investigating multiple He lines, including λ4922 Å and λ6678 Å, which show the strongest isotopic shifts in the optical spectral range. We also report the discovery of four new 3 He sdBs from the ESO SupernovaProgenitor survey. Most of the 3 He sdBs cluster in a narrow temperature strip between ∼ 26000 K and ∼ 30000 K and have almost no atmospheric 4 He at all. Interestingly, three 3 He sdBs show evidence for vertical helium stratification.

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Section: Introductionmentioning

confidence: 99%

On the 3He anomaly in hot subdwarf B stars

Schneider¹,

Irrgang²,

Heber³

et al. 2017

Open Astronomy

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“…CP stars rotate slowly and show extreme chemical anomalies in their atmospheres, often corresponding to deviations from the solar chemical composition by several orders of magnitude for some heavy elements. This unusual surface chemistry is attributed to the processes of radiative levitation and gravitational settling, commonly referred to as atomic diffusion (Michaud 1970;Michaud et al 2015), operating in stably stratified stellar atmospheres.…”

Section: Introductionmentioning

confidence: 99%

Doppler imaging of chemical spots on magnetic Ap/Bp stars

Kochukhov

2016

A&A

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Context. Doppler imaging (DI) is a powerful spectroscopic inversion technique that enables conversion of a line profile time series into a two-dimensional map of the stellar surface inhomogeneities. DI has been repeatedly applied to reconstruct chemical spot topologies of magnetic Ap/Bp stars with the goal of understanding variability of these objects and gaining an insight into the physical processes responsible for spot formation. Aims. In this paper we investigate the accuracy of chemical abundance DI and assess the impact of several different systematic errors on the reconstructed spot maps. Methods. We have simulated spectroscopic observational data for two different Fe spot distributions with a surface abundance contrast of 1.5 dex in the presence of a moderately strong dipolar magnetic field. We then reconstructed chemical maps using different sets of spectral lines and making different assumptions about line formation in the inversion calculations. Results. Our numerical experiments demonstrate that a modern DI code successfully recovers the input chemical spot distributions comprised of multiple circular spots at different latitudes or an element overabundance belt at the magnetic equator. For the optimal reconstruction based on half a dozen spectral intervals, the average reconstruction errors do not exceed ∼0.10 dex. The errors increase to about 0.15 dex when abundance distributions are recovered from a few and/or blended spectral lines. Ignoring a 2.5 kG dipolar magnetic field in chemical abundance DI leads to an average relative error of 0.2 dex and maximum errors of 0.3 dex. Similar errors are encountered if a DI inversion is carried out neglecting a non-uniform continuum brightness distribution and variation of the local atmospheric structure. None of the considered systematic effects lead to major spurious features in the recovered abundance maps.Conclusions. This series of numerical DI simulations proves that inversions based on one or two spectral lines with simplifying assumptions of the non-magnetic radiative transfer and a single model atmosphere are generally reliable provided that the stellar magnetic field is not much stronger than 2-3 kG and the recovered spot map has a contrast of at least ∼0.3 dex. In the light of these findings, we assess magnetic field strengths of several dozen Ap/Bp stars previously studied with DI methods, concluding that the vast majority of the published chemical spot maps are unaffected by the systematic errors addressed in this paper.

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“…Quantitative high-resolution spectroscopic analyses can be used to reveal if there are chemical abundance differences between the M67 members in the different evolutionary phases, as well as determining whether these differences are real or if they reveal systematic differences induced by the analysis techniques themselves. Accurate chemical abundances of a large number of elements can be used to test models of chemical diffusion in stars (e.g., Michaud et al 2015). The recent studies by Önehag et al (2014), Blanco-Cuaresma et al (2015), and Bertelli Motta et al…”

Section: Introductionmentioning

confidence: 99%

Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. I. Signatures of Diffusion in the Open Cluster M67

Souto

Cunha

Smith

et al. 2018

ApJ

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Detailed chemical abundance distributions for 14 elements are derived for eight high-probability stellar members of the solar metallicity old open cluster M67 with an age of ∼4 Gyr. The eight stars consist of four pairs, with each pair occupying a distinct phase of stellar evolution: two G dwarfs, two turnoff stars, two G subgiants, and two red clump (RC) K giants. The abundance analysis uses near-IR high-resolution spectra (λ1.5-1.7 μm) from the Apache Point Observatory Galactic Evolution Experiment survey and derives abundances for C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe. Our derived stellar parameters and metallicity for 2M08510076+1153115 suggest that this star is a solar twin, exhibiting abundance differences relative to the Sun of 0.04 dex for all elements. Chemical homogeneity is found within each class of stars (∼0.02 dex), while significant abundance variations (∼0.05-0.20 dex) are found across the different evolutionary phases; the turnoff stars typically have the lowest abundances, while the RCs tend to have the largest. Non-LTE corrections to the LTE-derived abundances are unlikely to explain the differences. A detailed comparison of the derived Fe, Mg, Si, and Ca abundances with recently published surface abundances from stellar models that include chemical diffusion provides a good match between the observed and predicted abundances as a function of stellar mass. Such agreement would indicate the detection of chemical diffusion processes in the stellar members of M67.

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Atomic Diffusion in Stars

Cited by 128 publications

References 0 publications

On the 3He anomaly in hot subdwarf B stars

On the 3He anomaly in hot subdwarf B stars

Doppler imaging of chemical spots on magnetic Ap/Bp stars

Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. I. Signatures of Diffusion in the Open Cluster M67

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