Accurate potential energy functions and non-adiabatic couplings in the Mg+H system

Guitou, Marie; Spielfiedel, A.; Feautrier, N.

doi:10.1016/j.cplett.2010.02.031

Cited by 39 publications

(45 citation statements)

References 16 publications

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“…with a magnitude of around 0.4 a.u. (Guitou et al 2010), while Li and Na both have peaks at around 7 a.u. with magnitudes of around 0.25 a.u.…”

Section: Discussionmentioning

confidence: 99%

“…Quantum chemical calculations of the potentials and couplings have now been done for MgH including excited states (Guitou et al 2010). These were then used in full quantum scattering calculations, initially testing on a small number of states , and later applying them to the seven lowest states of symmetry 2 Σ + plus the ionic channel (Belyaev et al 2012).…”

Section: Introductionmentioning

confidence: 99%

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Inelastic Mg+H collision data for non-LTE applications in stellar atmospheres

Barklem

Belyaev

Spielfiedel

et al. 2012

A&A

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Rate coefficients for inelastic Mg+H collisions are calculated for all transitions between the lowest seven levels and the ionic state (charge transfer), namely Mg(3s 2 1 S, 3s3p 3 P, 3s3p 1 P, 3s4s 3 S, 3s4s 1 S, 3s3d 1 D, 3s4p 3 P)+H(1s) and Mg + (3s 2 S)+H − . The rate coefficients are based on cross-sections from full quantum scattering calculations, which are themselves based on detailed quantum chemical calculations for the MgH molecule. The data are needed for non-LTE applications in cool astrophysical environments, especially cool stellar atmospheres, and are presented for a temperature range of 500−8000 K. From consideration of the sensitivity of the cross-sections to various uncertainties in the calculations, most importantly input quantum chemical data and the numerical accuracy of the scattering calculations, a measure of the possible uncertainties in the rate coefficients is estimated.

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“…with a magnitude of around 0.4 a.u. (Guitou et al 2010), while Li and Na both have peaks at around 7 a.u. with magnitudes of around 0.25 a.u.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Inelastic Mg+H collision data for non-LTE applications in stellar atmospheres

Barklem

Belyaev

Spielfiedel

et al. 2012

A&A

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“…are taken from Barklem et al (2012), which are based on calculations of Belyaev et al (2012); see also Guitou et al (2010Guitou et al ( , 2011. These ab initio quantum chemical calculations on which the scattering calculations are based were obtained using the code MOLPRO (Werner et al 2009) and cover the seven lowest lying states of Mg i and the ground state of Mg ii.…”

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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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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“…We adopt hydrogen collision rates from Barklem et al (2012), based on quantum mechanical crosssections Belyaev et al 2012) for low-lying states of Mg i, based on quantum chemical data for the MgH molecule from Guitou et al (2010). For Rydberg transitions we computed rates based on the free electron model of Kaulakys (1985Kaulakys ( , 1991 using the implementation of Barklem (2016a).…”

Section: Magnesiummentioning

confidence: 99%

3D NLTE analysis of the most iron-deficient star, SMSS0313-6708

Nordlander

Amarsi

Lind

et al. 2016

A&A

104

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Context. Models of star formation in the early universe require a detailed understanding of accretion, fragmentation and radiative feedback in metal-free molecular clouds. Different simulations predict different initial mass functions of the first stars, ranging from predominantly low-mass (0.1−10 M ), to massive (10−100 M ), or even supermassive (100−1000 M ). The mass distribution of the first stars should lead to unique chemical imprints on the low-mass second and later generation metal-poor stars still in existence. The chemical composition of SMSS0313-6708, which has the lowest abundances of Ca and Fe of any star known, indicates it was enriched by a single massive supernova. Aims. The photospheres of metal-poor stars are relatively transparent in the UV, which may lead to large three-dimensional (3D) effects as well as departures from local thermodynamical equilibrium (LTE), even for weak spectral lines. If 3D effects and departures from LTE (NLTE) are ignored or treated incorrectly, errors in the inferred abundances may significantly bias the inferred properties of the polluting supernovae. We redetermine the chemical composition of SMSS0313-6708 by means of the most realistic methods available, and compare the results to predicted supernova yields. Methods. A 3D hydrodynamical Stagger model atmosphere and 3D NLTE radiative transfer were applied to obtain accurate abundances for Li, Na, Mg, Al, Ca and Fe. The model atoms employ realistic collisional rates, with no calibrated free parameters. Results. We find significantly higher abundances in 3D NLTE than 1D LTE by 0.8 dex for Fe, and 0.5 dex for Mg, Al and Ca, while Li and Na are unaffected to within 0.03 dex. In particular, our upper limit for [Fe/H] is now a factor ten larger, at [Fe/H] < −6.53 (3σ), than previous estimates based on 3D NLTE (i.e., using averaged 3D models). This higher estimate is due to a conservative upper limit estimation, updated NLTE data, and 3D− 3D NLTE differences, all of which lead to a higher abundance determination. Conclusions. We find that supernova yields for models in a wide range of progenitor masses reproduce the revised chemical composition. In addition to massive progenitors of 20−60 M exploding with low energies (1−2 B, where 1 B = 10 51 erg), we also find good fits for progenitors of 10 M , with very low explosion energies (<1 B). We cannot reconcile the new abundances with supernovae or hypernovae with explosion energies above 2.5 B, nor with pair-instability supernovae.

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Accurate potential energy functions and non-adiabatic couplings in the Mg+H system

Cited by 39 publications

References 16 publications

Inelastic Mg+H collision data for non-LTE applications in stellar atmospheres

Inelastic Mg+H collision data for non-LTE applications in stellar atmospheres

Mg line formation in late-type stellar atmospheres

3D NLTE analysis of the most iron-deficient star, SMSS0313-6708

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