The impact of surface dynamo magnetic fields on the solar iron abundance

Shchukina, N. G.; Bueno, J. Trujillo

doi:10.1051/0004-6361/201425569

Cited by 16 publications

(11 citation statements)

References 61 publications

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“…We note, that the mean temperature in the MHD snapshot models of Rempel (2014) and Vögler & Schüssler (2007) agree very well with the temperature of the 1D semi-empirical model MACKKL (Maltby et al 1986) based on observations of the continuum radiation. As a result, the absolute continuum intensities at different wavelengths computed in the 3D snapshot model of Rempel (2014) are consistent with those calculated in the MACKKL model (see Shchukina & Trujillo Bueno 2015). At heights above log 10 τ 5 > −0.5, the above-mentioned 3D MHD snapshot models are significantly cooler compared to the MACKKL model.…”

Section: Model Atmospheresupporting

confidence: 82%

A Si I atomic model for NLTE spectropolarimetric diagnostics of the 10 827 Å line

Shchukina

Sukhorukov

Bueno

2017

A&A

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Aims. The Si i 10 827 Å line is commonly used for spectropolarimetric diagnostics of the solar atmosphere. First, we aim at quantifying the sensitivity of the Stokes profiles of this line to non-local thermodynamic equilibrium (NLTE) effects. Second, we aim at facilitating NLTE diagnostics of the Si i 10 827 Å line. To this end, we propose the use of a relatively simple silicon model atom, which allows a fast and accurate computation of Stokes profiles. The NLTE Stokes profiles calculated using this simple model atom are very similar to those obtained via the use of a very comprehensive silicon model atom. Methods. We investigate the impact of the NLTE effects on the Si i 10 827 Å line by means of multilevel radiative transfer calculations in a three-dimensional (3D) model atmosphere taken from a state-of-the-art magneto-convection simulation with small-scale dynamo action. We calculate the emergent Stokes profiles for this line at the solar disk center and for every vertical column of the 3D snapshot model, neglecting the effects of horizontal radiative transfer. Results. We find significant departures from LTE in the Si i 10 827 Å line, not only in the intensity but also in the linearly and circularly polarized profiles. At wavelengths around 0.1 Å, where most of the Stokes Q, U, and V peaks of the Si i 10 827 Å line occur, the differences between the NLTE and LTE profiles are comparable with the Stokes amplitudes themselves. The deviations from LTE increase with increasing Stokes Q, U, and V signals. Concerning the Stokes V profiles, the NLTE effects correlate with the magnetic field strength in the layers where such circular polarization signals are formed. Conclusions. The NLTE effects should be taken into account when diagnosing the emergent Stokes I profiles as well as the Stokes Q, U, and V profiles of the Si i 10 827 Å line. The sixteen-level silicon model atom proposed here, with six radiative bound-bound transitions, is suitable to account for the physics of formation of the Si i 10 827 Å line and for modeling and inverting its Stokes profiles without assuming LTE.

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Section: Model Atmospheresupporting

confidence: 82%

A Si I atomic model for NLTE spectropolarimetric diagnostics of the 10 827 Å line

Shchukina

Sukhorukov

Bueno

2017

A&A

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“…For the iron ions, we obtained N(Fe i)=-4.42±0.03 dex and N(Fe ii)=-4.46±0.02 dex, which again highlights the known problem of the measured difference between Fe i and Fe ii abundances obtained in the framework of the classical approach (see Holweger, Heise & Kock 1990, Shchukina & Trujillo 2015, Shchukina, Sukhorukov & Trujillo 2016. The abundances for the other elements (see the first column of Table 2) are in agreement with those in the literature (e.g.…”

Section: Solar Abundancesmentioning

confidence: 56%

The metal-rich abundance pattern – spectroscopic properties and abundances for 107 main-sequence stars

Ivanyuk

Jenkins

Pavlenko

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We report results from the high resolution spectral analysis of the 107 metal rich (mostly [Fe/H] 7.67 dex) target stars from the Calan-Hertfordshire Extrasolar Planet Search program observed with HARPS. Using our procedure of finding the best fit to the absorption line profiles in the observed spectra, we measure the abundances of Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zn, and we then compare them with known results from different authors. Most of our abundances agree with these works at the level of ±0.05 dex or better for the stars we have in common. However, we do find systematic differences that make direct inferences difficult. Our analysis suggests that the selection of line lists and atomic line data along with the adopted continuum level influence these differences the most. At the same time, we confirm the positive trends of abundances versus metallicity for Na, Mn, Ni, and to a lesser degree, Al. A slight negative trend is observed for Ca, whereas Si and Cr tend to follow iron. Our analysis allows us to determine the positively skewed normal distribution of projected rotational velocities with a maximum peaking at 3 km s −1 . Finally, we obtained a Gaussian distribution of microturbulent velocities that has a maximum at 1.2 km s −1 and a full width at half maximum ∆v 1/2 =0.35 km s −1 , indicating that metal rich dwarfs and subgiants in our sample have a very restricted range in microturbulent velocity.

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“…In a subsequent paper Fabbian and Moreno-Insertis (2015) studied the case of the O i lines and again found that an abundance determination using non-magnetic models would lead to underestimates by a few to several centi-dex. Shchukina and Trujillo Bueno (2015) challenged the results of Fabbian et al by a study of Fe spectra from 3D models with and without magnetic fields assuming that the former are dominated by small-scale dynamo action (with the net magnetic flux being zero). Also for solar C, N, and O spectra the effects were found to be negligible (Shchukina et al 2016).…”

Section: Effects Of Magnetic Fieldsmentioning

confidence: 82%

“…We also note that the small corrections on derived solar Fe abundances from including small scale magnetic fields with no net magnetic flux are not totally negligible in discussions of very precise abundances of solar twins. Shchukina and Trujillo Bueno (2015) found an average correction of +0.016 dex for Fe i lines, but for low-excitation lines formed in the upper photosphere the correction reaches ∼ +0.05 dex. Considering that the magnetic field configuration and strength may vary between solar twins, there could be significant magnetic effects on derived differential abundances.…”

Section: Effects Of Magnetic Fieldsmentioning

confidence: 94%

High-precision stellar abundances of the elements: methods and applications

Nissen

Gustafsson

2018

Astron Astrophys Rev

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Efficient spectrographs at large telescopes have made it possible to obtain high-resolution spectra of stars with high signal-to-noise ratio and advances in model atmosphere analyses have enabled estimates of high-precision differential abundances of the elements from these spectra, i.e. with errors in the range 0.01 -0.03 dex for F, G, and K stars.Methods to determine such high-precision abundances together with precise values of effective temperatures and surface gravities from equivalent widths of spectral lines or by spectrum synthesis techniques are outlined, and effects on abundance determinations from using a 3D non-LTE analysis instead of a classical 1D LTE analysis are considered.The determination of high-precision stellar abundances of the elements have led to the discovery of unexpected phenomena and relations with important bearings on the astrophysics of galaxies, stars, and planets, i.e. i) Existence of discrete stellar populations within each of the main Galactic components (disk, halo, and bulge) providing new constraints on models for the formation of the Milky Way. ii) Differences in the relation between abundances and elemental condensation temperature for the Sun and solar twins suggesting dust-cleansing effects in proto-planetary disks and/or engulfment of planets by stars; iii) Differences in chemical composition between binary star components and between members of open or globular clusters showing that star-and cluster-formation processes are more complicated than previously thought; iv) Tight relations between some abundance ratios and age for solar-like stars providing new constraints on nucleosynthesis and Galactic chemical evolution models as well as the composition of terrestrial exoplanets.We conclude that if stellar abundances with precisions of 0.01 -0.03 dex can be achieved in studies of more distant stars and stars on the giant and supergiant branches, many more interesting future applications, of great relevance to stellar and galaxy evolution, are probable. Hence, in planning abundance surveys, it is important to carefully balance the need for large samples of stars against the spectral resolution and signal-to-noise ratio needed to obtain high-precision abundances. Furthermore, it is an advantage to work differentially on stars with similar atmospheric parameters, because then a simple 1D LTE analysis of stellar spectra may be sufficient. However, when determining high-precision absolute abundances or differential abundance between stars having more widely different parameters, e.g. metal-poor stars compared to the Sun or giants to dwarfs, then 3D non-LTE effects must be taken into account.

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The impact of surface dynamo magnetic fields on the solar iron abundance

Cited by 16 publications

References 61 publications

A Si I atomic model for NLTE spectropolarimetric diagnostics of the 10 827 Å line

A Si I atomic model for NLTE spectropolarimetric diagnostics of the 10 827 Å line

The metal-rich abundance pattern – spectroscopic properties and abundances for 107 main-sequence stars

High-precision stellar abundances of the elements: methods and applications

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