Inelastic H+Li and H<sup>-</sup>+Li<sup>+</sup>collisions and non-LTE Li I line formation in stellar atmospheres

Barklem, P. S.; Belyaev, Andrey K.; Asplund, Martin

doi:10.1051/0004-6361:20031199

Cited by 129 publications

(166 citation statements)

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“…Thus, the new RM data for electron collisions did not have a strong effect on non-LTE modelling, since the existing data were relatively good; see Osorio et al (2011) for Li, Lind et al (2011) for Na. Data for hydrogen collision processes, including charge transfer, have been calculated for Li by Barklem et al (2003), and for Na by Barklem et al (2010), and used in non-LTE studies by Barklem et al and Lind et al (2009) in the case of Li and Lind et al (2011) for Na. These studies found for both elements that CH processes have practically no effect on the non-LTE modelling, while CH0, in particular that involving the first excited S -state, had a significant effect because it brought this level into closer detailed balance with the continuum.…”

Section: Discussionmentioning

confidence: 99%

“…We wish to emphasize that with regard to hydrogen collisions in general, the accurate quantum (Barklem et al 2003;Barklem et al 2010Barklem et al , 2012 as well as the more approximate model calculations (Belyaev 2013;Belyaev et al 2014), based on a correct physical background, provide non-zero rate coefficients for both optically allowed and optically forbidden transitions, as well as for charge transfer processes, which generally have the highest rate coefficients among all hydrogen collision processes. Thus, the Drawin formula fails to provide reliable estimates for important inelastic processes in collisions with hydrogen.…”

Section: Hydrogen Atomsmentioning

confidence: 99%

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Mg line formation in late-type stellar atmospheres

Osorio

Barklem

Lind

et al. 2015

A&A

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130

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Context. Magnesium is an element of significant astrophysical importance, often traced in late-type stars using lines of neutral magnesium, which is expected to be subject to departures from local thermodynamic equilibrium (LTE). The importance of Mg, together with the unique range of spectral features in late-type stars probing different parts of the atom, as well as its relative simplicity from an atomic physics point of view, makes it a prime target and test bed for detailed ab initio non-LTE modelling in stellar atmospheres. Previous non-LTE modelling of spectral line formation has, however, been subject to uncertainties due to lack of accurate data for inelastic collisions with electrons and hydrogen atoms. Aims. In this paper we build and test a Mg model atom for spectral line formation in late-type stars with new or recent inelastic collision data and no associated free parameters. We aim to reduce these uncertainties and thereby improve the accuracy of Mg non-LTE modelling in late-type stars.Methods. For the low-lying states of Mg i, electron collision data were calculated using the R-matrix method. Hydrogen collision data, including charge transfer processes, were taken from recent calculations by some of us. Calculations for collisional broadening by neutral hydrogen were also performed where data were missing. These calculations, together with data from the literature, were used to build a model atom. This model was then employed in the context of standard non-LTE modelling in 1D (including average 3D) model atmospheres in a small set of stellar atmosphere models. First, the modelling was tested by comparisons with observed spectra of benchmark stars with well-known parameters. Second, the spectral line behaviour and uncertainties were explored by extensive experiments in which sets of collisional data were changed or removed. Results. The modelled spectra agree well with observed spectra from benchmark stars, showing much better agreement with line profile shapes than with LTE modelling. The line-to-line scatter in the derived abundances shows some improvements compared to LTE (where the cores of strong lines must often be ignored), particularly when coupled with averaged 3D models. The observed Mg emission features at 7 and 12 μm in the spectra of the Sun and Arcturus, which are sensitive to the collision data, are reasonably well reproduced. Charge transfer with H is generally important as a thermalising mechanism in dwarfs, but less so in giants. Excitation due to collisions with H is found to be quite important in both giants and dwarfs. The R-matrix calculations for electron collisions also lead to significant differences compared to when approximate formulas are employed. The modelling predicts non-LTE abundance corrections ΔA(Mg) NLTE−LTE in dwarfs, both solar metallicity and metal-poor, to be very small (of order 0.01 dex), even smaller than found in previous studies. In giants, corrections vary greatly between lines, but can be as large as 0.4 dex. Conclusions. Our results emphasise ...

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Section: Discussionmentioning

confidence: 99%

Section: Hydrogen Atomsmentioning

confidence: 99%

Mg line formation in late-type stellar atmospheres

Osorio

Barklem

Lind

et al. 2015

A&A

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130

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“…Kurucz 1993;Plez 1998;Johansson et al 2003;Lawler et al 2006) and photoionization rates (e.g. Badnell et al 2005) The progress for the important collisional data is less satisfactory in spite of some recent advances (Barklem et al 2003;Barklem 2007a). Non-LTE calculations therefore still normally employ various recipes based on classical physics for electron and hydrogen collisions, often with a scaling factor somehow calibrated.…”

Section: Ingredients For Solar Spectroscopic Analysesmentioning

confidence: 99%

“…It is important to realize that such empirical calibrations of S H is certainly no substitute to having real quantum mechanical or laboratory estimates, since the necessary thermalization may well come from other atomic processes than H collisions, as in the case of charge transfer reactions in Li (Barklem et al 2003). Furthermore, the observations of Allende Prieto et al were not optimal.…”

Section: Caffau Et Al (2008)mentioning

confidence: 99%

Does the Sun have a subsolar metallicity?

Asplund¹

2008

Proc. IAU

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Abstract. The solar chemical composition has recently undergone a drastic revision, in particular in terms of the C, N, O and Ne abundances that have been lowered by almost a factor of two. In this invited review I will describe the different compounding reasons for this change (3D model atmospheres, non-LTE line formation, improved atomic/molecular data) and discuss some astrophysical implications thereof, which fall under both good (solar neighborhood) and bad (helioseismology) news. The most recent literature regarding the solar O abundance is surveyed and a critical evaluation whether or not these support the low solar abundance scale is presented. Finally I venture to make some predictions to what the real solar O abundance may be.

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“…They are, however, included in this study because (Li + He + ) collision pairs are obtained here via charge transfer processes in (Li + + He) collisions. In addition, even if lithium is rather rare compared to the other primordial elements synthesized in the early Universe, inelastic collisional processes of neutral lithium with hydrogen and other atomic or ionic species are of high interest in modeling stellar atmospheres (Carlsson et al 1994;Barklem et al 2003;.…”

Section: Introductionmentioning

confidence: 99%

Non-radiative inelastic processes in lithium-helium ion-atom collisions

Belyaev

Augustovičová

Soldán

et al. 2014

A&A

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Aims. The aims are to estimate efficiencies of non-radiative inelastic processes in lithium-helium ion-atom collisions and to compare them to those for radiative processes. Methods. Non-radiative inelastic cross-sections and rate coefficients for different lithium-helium ion-atom collisions are estimated by means of the recently proposed branching probability current method, which is based on the accurate ab initio adiabatic BornOppenheimer potentials that have been recently calculated for the low-lying 1,3 Σ + and 1,3 Π states of the LiHe + ion. Results. It is shown that at low temperatures the radiative depopulation in Li + + He and Li + He + collisions dominates over the non-radiative processes, while in Li + + He(2s 3 S) collisions the non-radiative processes dominate over the radiative association at temperatures above 3000 K, which can be expected to have some influence on depopulations of metastable He in high temperature astrophysical environments.

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Inelastic H+Li and H^-+Li⁺collisions and non-LTE Li I line formation in stellar atmospheres

Cited by 129 publications

References 21 publications

Mg line formation in late-type stellar atmospheres

Mg line formation in late-type stellar atmospheres

Does the Sun have a subsolar metallicity?

Non-radiative inelastic processes in lithium-helium ion-atom collisions

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Inelastic H+Li and H-+Li+collisions and non-LTE Li I line formation in stellar atmospheres

Cited by 129 publications

References 21 publications

Mg line formation in late-type stellar atmospheres

Mg line formation in late-type stellar atmospheres

Does the Sun have a subsolar metallicity?

Non-radiative inelastic processes in lithium-helium ion-atom collisions

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Inelastic H+Li and H^-+Li⁺collisions and non-LTE Li I line formation in stellar atmospheres