Effective collision strengths between Mg i and electrons

Merle, Thibault; Thévenin, F.; Zatsarinny, Oleg

doi:10.1051/0004-6361/201525914

Cited by 7 publications

(11 citation statements)

References 8 publications

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“…Comparisons with the data of Merle et al (2015) and Osorio et al (2015) were also performed, but for the sake of simplicity of presentation, we have chosen not to present or analyse these in detail. It suffices to say that these datasets compare significantly better than M88 with the new data, with agreement to better than a factor of two.…”

Section: Resultsmentioning

confidence: 99%

Inelastic e+Mg collision data and its impact on modelling stellar and supernova spectra

Barklem

Osorio

Fursa

et al. 2017

A&A

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Results of calculations for inelastic e+Mg effective collision strengths for the lowest 25 physical states of Mg i (up to 3s6p 1 P), and thus 300 transitions, from the convergent close-coupling (CCC) and the B-spline R-matrix (BSR) methods are presented. At temperatures of interest, ∼5000 K, the results of the two calculations differ on average by only 4%, with a scatter of 27%. As the methods are independent, this suggests that the calculations provide datasets for e+Mg collisions accurate to this level. Comparison with the commonly used dataset compiled by Mauas et al. (1988, ApJ, 330, 1008, covering 25 transitions among 12 states, suggests the Mauas et al. data are on average ∼57% too low, and with a very large scatter of a factor of ∼6.5. In particular the collision strength for the transition corresponding to the Mg i intercombination line at 457 nm is significantly underestimated by Mauas et al., which has consequences for models that employ this dataset. In giant stars the new data leads to a stronger line compared to previous non-LTE calculations, and thus a reduction in the non-LTE abundance correction by ∼0.1 dex (∼25%). A non-LTE calculation in a supernova ejecta model shows this line becomes significantly stronger, by a factor of around two, alleviating the discrepancy where the 457 nm line in typical models with Mg/O ratios close to solar tended to be too weak compared to observations.

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Section: Resultsmentioning

confidence: 99%

Inelastic e+Mg collision data and its impact on modelling stellar and supernova spectra

Barklem

Osorio

Fursa

et al. 2017

A&A

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“…Collisional data. For all the transitions between the lowest 17 energy levels of Mg i (up to 5p 1 P • ) and transitions from these levels to the more excited levels up to 3p 2 1 S, in total 369 transitions, we adopted accurate electron-impact excitation data from Merle et al (2015). Sigut & Pradhan (1995) provided accurate electron collision strengths for transitions between the lowest 10 levels of Mg ii (up to 5d 2 D).…”

Section: Model Atom and Atomic Datamentioning

confidence: 99%

“…In this study, accurate data on electron-impact excitation are used for a larger number of transitions compared with that of Osorio et al (2015), that is, 369 transitions against 45 ones. From the other hand side, we use more simple approch compared with that of Osorio et al (2015) to treat electron-impact excitation of those forbidden transitions, which are not available in Merle et al (2015), and we neglect the hydrogen-impact excitation of the Rydberg levels in Mg i.…”

Section: Comparison With Previous Studiesmentioning

confidence: 99%

NLTE Line Formation for Mg i and Mg ii in the Atmospheres of B–A–F–G–K Stars

Alexeeva

Ryabchikova

Mashonkina

et al. 2018

ApJ

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Non-local thermodynamical equilibrium (NLTE) line formation for Mg i and Mg ii lines is considered in classical 1D-LTE model atmospheres of the Sun and 17 stars with reliable atmospheric parameters and in a broad range of spectral types: 3900 ≤ T eff ≤ 17500 K, 1.1 ≤ logg ≤ 4.7, and −2.6 ≤ [Fe/H] ≤ +0.4.We find that, for each star, NLTE leads to smaller line-to-line scatter. For 10 stars, NLTE leads to consistent abundances from Mg i and Mg ii, while the difference in the LTE abundance varies between −0.21 and +0.23 dex. We obtain an abundance discrepancy betweeen Mg i and Mg ii in the two very metal-poor stars, HD 140283 and HD 84937. An origin of these abundance differences remains unclear.Our standard NLTE modelling predicts Mg i emission lines at 7.736, 11.789, 12.224, and 12.321 µm in the atmospheres with T eff ≤ 7000 K. We reproduce well the Mg i 12.2 and 12.3 µm emission lines in Procyon. However, for the Sun and 3 K-giants, the predicted Mg i emission lines are too weak compared with the observations. For stars with 7000 K ≤ T eff ≤ 17500 K, we recommend the Mg ii 3848, 3850, 4384, 4390, 4427, and 4433Å lines for Mg abundance determinations even at the LTE assumption due to their small NLTE effects. The Mg i 4167, 4571, 4702, 5528, 5167, 5172, and 5183Å lines can be safely used in the LTE analysis of stars with 7000 K < T eff ≤ 8000 K. For the hotter stars, with T eff from 8000 to 9500 K, the NLTE effects are minor only for Mg i 4167, 4702, and 4528Å.

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“…All levels in the model atoms are coupled via inelastic collisions with electrons. Quantum calculations for effective collisional strengths Υ e − for electron collisions were implemented for the Mg i model atom following Merle et al (2015). For transitions where no quantum data are available, classical and semiclassical approximations were used.…”

Section: E − Collisional Transitionsmentioning

confidence: 99%

An empirical recipe for inelastic hydrogen-atom collisions in non-LTE calculations

Ezzeddine

Merle

Plez

et al. 2018

A&A

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Context. Determination of high-precision abundances of late-type stars has been and always will be an important goal of spectroscopic studies, which requires accurate modeling of their stellar spectra with non-local thermodynamic equilibrium (NLTE) radiative transfer methods. This entails using up-to-date atomic data of the elements under study, which are still subject to large uncertainties. Aims. We investigate the role of hydrogen collisions in NLTE spectral line synthesis, and introduce a new general empirical recipe to determine inelastic charge transfer (CT) and bound-bound hydrogen collisional rates. This recipe is based on fitting the energy functional dependence of published quantum collisional rate coefficients of several neutral elements (Be i, Na i, Mg i, Al i, Si i and Ca i) using simple polynomial equations. Methods. We perform thorough NLTE abundance calculation tests using our method for four different atoms, Na, Mg, Al and Si, for a broad range of stellar parameters. We then compare the results to calculations computed using the published quantum rates for all the corresponding elements. We also compare to results computed using excitation collisional rates via the commonly used Drawin equation for different fudge factors, S H , applied.Results. We demonstrate that our proposed method is able to reproduce the NLTE abundance corrections performed with the quantum rates for different spectral types and metallicities for representative Na i and Al i lines to within ≤ 0.05 dex and ≤ 0.03 dex, respectively. For Mg i and Si i lines, the method performs better for the cool giants and dwarfs, while larger discrepancies up to 0.2 dex could be obtained for some lines for the subgiants and warm dwarfs. We obtained larger NLTE correction differences between models incorporating Drawin rates relative to the quantum models by up to 0.4 dex. These large discrepancies are potentially due to ignoring either or both CT and ionization collisional processes by hydrogen in our Drawin models. Conclusions. Our general empirical fitting method (EFM) for estimating hydrogen collision rates performs well in its ability to reproduce, within narrow uncertainties, the abundance corrections computed with models incorporating quantum collisional rates. It performs generally best for the cool and warm dwarfs, with slightly larger discrepancies obtained for the giants and subgiants. It could possibly be extended in the future to transitions of the same elements for which quantum calculations do not exist, or, in the absence of published quantum calculations, to other elements as well.

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Effective collision strengths between Mg i and electrons

Cited by 7 publications

References 8 publications

Inelastic e+Mg collision data and its impact on modelling stellar and supernova spectra

Inelastic e+Mg collision data and its impact on modelling stellar and supernova spectra

NLTE Line Formation for Mg i and Mg ii in the Atmospheres of B–A–F–G–K Stars

An empirical recipe for inelastic hydrogen-atom collisions in non-LTE calculations

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