Influence of inelastic collisions with hydrogen atoms on the formation of AlI and SiI lines in stellar spectra

Mashonkina, L.; Belyaev, Andrey K.; Shi, Jianrong

doi:10.1134/s1063773716050078

Cited by 22 publications

(31 citation statements)

References 29 publications

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“…For silicon, also an important electron donor in particular for stars slightly hotter than the Sun, statistical-equilibrium calculations by Bergemann et al (2013) and Mashonkina et al (2016) suggest that the differential non-LTE effects are very small for solar-type stars (see also Nissen et al 2017). We also note that Amarsi and Asplund (2017) find small 3D effects in the solar case, using statisticalequilibrium calculations and 3D models.…”

Section: Differential Analysesmentioning

confidence: 56%

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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Section: Differential Analysesmentioning

confidence: 56%

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

Nissen

Gustafsson

2018

Astron Astrophys Rev

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“…The effects are most significant when the lines are saturated (sensitive to, e.g., line broadening), very weak (blending and normalization) or very strong (EW wavelength interval). With these shortcomings in mind, we note that our modeling indicates a stronger variation of NLTE corrections with log g at [Fe/H] = −1, and significantly larger corrections for T eff < 5000 K, as compared to Mashonkina et al (2016). The most significant differences are found for the resonance line at low log g, T eff and [Fe/H], e.g., T eff = 4500 K, log g = 3, [Fe/H] ≤ −2, where our abundance corrections are very large, +0.6 dex, while they find negligibly small corrections of the order 0.05 dex.…”

Section: Comparison To Previous Workmentioning

confidence: 72%

“…Transition rates for the low-lying excited states are very large, introducing an efficient thermalizing mechanism which was not predicted by the Drawin formula. These transition rates have previously been used in the work of Mashonkina et al (2016). They found that in the solar photosphere, excitation rates due to collisions with electrons were much higher than those with hydrogen atoms for transition energies greater than 3 eV, but comparable for transition energies smaller than 2 eV.…”

Section: Collisional Transitionsmentioning

confidence: 98%

Non-LTE aluminium abundances in late-type stars

Nordlander

Lind

2017

A&A

119

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Aims. Aluminium plays a key role in studies of the chemical enrichment of the Galaxy and of globular clusters. However, strong deviations from LTE (non-LTE) are known to significantly affect the inferred abundances in giant and metal-poor stars. Methods. We present NLTE modeling of aluminium using recent and accurate atomic data, in particular utilizing new transition rates for collisions with hydrogen atoms, without the need for any astrophysically calibrated parameters. For the first time, we perform 3D NLTE modeling of aluminium lines in the solar spectrum. We also compute and make available extensive grids of abundance corrections for lines in the optical and near-infrared using one-dimensional model atmospheres, and apply grids of precomputed departure coefficients to direct line synthesis for a set of benchmark stars with accurately known stellar parameters. Results. Our 3D NLTE modeling of the solar spectrum reproduces observed center-to-limb variations in the solar spectrum of the 7835 Å line as well as the mid-infrared photospheric emission line at 12.33 µm. We infer a 3D NLTE solar photospheric abundance of A(Al) = 6.43 ± 0.03, in exact agreement with the meteoritic abundance. We find that abundance corrections vary rapidly with stellar parameters; for the 3961 Å resonance line, corrections are positive and may be as large as +1 dex, while corrections for subordinate lines generally have positive sign for warm stars but negative for cool stars. Our modeling reproduces the observed line profiles of benchmark K-giants, and we find abundance corrections as large as −0.3 dex for Arcturus. Our analyses of four metal-poor benchmark stars yield consistent abundances between the 3961 Å resonance line and lines in the UV, optical and near-infrared regions. Finally, we discuss implications for the galactic chemical evolution of aluminium.

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“…Estimates for NLTE of Si have been published for various stellar spectra (e.g. Bergemann et al 2013;Mashonkina et al 2016a;Zhang et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Probing 3D and NLTE models using APOGEE observations of globular cluster stars

Masseron

Osorio

García-Hernández

et al. 2021

A&A

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Context. Hydrodynamical (or 3D) and non-local thermodynamic equilibrium (NLTE) effects are known to affect abundance analyses. However, there are very few observational abundance tests of 3D and NLTE models. Aims. We developed a new way of testing the abundance predictions of 3D and NLTE models, taking advantage of large spectroscopic survey data. Methods. We use a line-by-line analysis of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra (H band) with the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS). We compute line-by-line abundances of Mg, Si, Ca, and Fe for a large number of globular cluster K giants in the APOGEE survey. We compare this line-by-line analysis against NLTE and 3D predictions. Results. While the 1D–NLTE models provide corrections in the right direction, there are quantitative discrepancies between different models. We observe a better agreement with the data for the models including reliable collisional cross-sections. The agreement between data and models is not always satisfactory when the 3D spectra are computed in LTE. However, we note that for a fair comparison, 3D corrections should be computed with self-consistently derived stellar parameters, and not on 1D models with identical stellar parameters. Finally, we focus on 3D and NLTE effects on Fe lines in the H band, where we observe a systematic difference in abundance relative to the value from the optical. Our results suggest that the metallicities obtained from the H band are more accurate in metal-poor giants. Conclusions. Current 1D–NLTE models provide reliable abundance corrections, but only when the atom data and collisional cross-sections are accurate and complete. Therefore, we call for more atomic data for NLTE calculations. In contrast, we show that 3D corrections in LTE conditions are often not accurate enough, thus confirming that 3D abundance corrections are only valid when NLTE is taken into account. Consequently, more extended self-consistent 3D–NLTE computations need to be made. The method we have developed for testing 3D and NLTE models could be extended to other lines and elements, and is particularly suited for large spectroscopic surveys.

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Influence of inelastic collisions with hydrogen atoms on the formation of AlI and SiI lines in stellar spectra

Cited by 22 publications

References 29 publications

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

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

Non-LTE aluminium abundances in late-type stars

Probing 3D and NLTE models using APOGEE observations of globular cluster stars

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