On inelastic hydrogen atom collisions in stellar atmospheres

Barklem, P. S.; Belyaev, Andrey K.; Guitou, Marie; Feautrier, N.; Gadéa, Florent Xavier; Spielfiedel, A.

doi:10.1051/0004-6361/201116745

Cited by 108 publications

(98 citation statements)

References 61 publications

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“…In fact, such nonuniform scaling has recently been demonstrated for Mg + H by Barklem et al (2012). In principle, S H should depend on temperature (see Barklem et al 2011) and, because the different triplet lines form at different atmospheric heights, S H could be expected to vary slightly from line to line. Our analysis allows for this possibility, since we treat each of the triplet components separately.…”

Section: Assumption Of a Universal S Hmentioning

confidence: 91%

The photospheric solar oxygen project

Steffen

Prakapavičius

Caffau

et al. 2015

A&A

109

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Context. The solar photospheric oxygen abundance is still widely debated. Adopting the solar chemical composition based on the "low" oxygen abundance, as determined with the use of three-dimensional (3D) hydrodynamical model atmospheres, results in a well-known mismatch between theoretical solar models and helioseismic measurements that is so far unresolved. Aims. We carry out an independent redetermination of the solar oxygen abundance by investigating the center-to-limb variation of the O i IR triplet lines at 777 nm in different sets of spectra.Methods. The high-resolution and high signal-to-noise solar center-to-limb spectra are analyzed with the help of detailed synthetic line profiles based on 3D hydrodynamical CO5BOLD model atmospheres and 3D non-LTE line formation calculations with NLTE3D. The idea is to exploit the information contained in the observations at different limb angles to simultaneously derive the oxygen abundance, A(O), and the scaling factor S H that describes the cross-sections for inelastic collisions with neutral hydrogen relative to the classical Drawin formula. Using the same codes and methods, we compare our 3D results with those obtained from the semiempirical Holweger-Müller model atmosphere as well as from different one-dimensional (1D) reference models. Results. With the CO5BOLD 3D solar model, the best fit of the center-to-limb variation of the triplet lines is obtained when the collisions by neutral hydrogen atoms are assumed to be efficient, i.e., when the scaling factor S H is between 1.2 and 1.8, depending on the choice of the observed spectrum and the triplet component used in the analysis. The line profile fits achieved with standard 1D model atmospheres (with fixed microturbulence, independent of disk position μ) are clearly of inferior quality compared to the 3D case, and give the best match to the observations when ignoring collisions with neutral hydrogen (S H = 0). The results derived with the Holweger-Müller model are intermediate between 3D and standard 1D. Conclusions. The analysis of various observations of the triplet lines with different methods yields oxygen abundance values (on a logarithmic scale where A(H) = 12) that fall in the range 8.74 < A(O) < 8.78, and our best estimate of the 3D non-LTE solar oxygen abundance is A(O) = 8.76 ± 0.02. All 1D non-LTE models give much lower oxygen abundances, by up to −0.15 dex. This is mainly a consequence of the assumption of a μ-independent microturbulence. An independent determination of the relevant collisional cross-sections is essential to substantially improve the accuracy of the oxygen abundance derived from the O i IR triplet.

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Section: Assumption Of a Universal S Hmentioning

confidence: 91%

The photospheric solar oxygen project

Steffen

Prakapavičius

Caffau

et al. 2015

A&A

109

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“…An enhancement factor SH to the Drawin formula was calibrated by studying the centre-to-limb variation in the Sun, following Pereira et al (2009) The dominant systematic errors in the non-LTE calculations likely arise from the errors in the rate of excitation via neutral hydrogen collisions. As discussed in Barklem et al (2011), the approach of calibrating the Drawin formula using a single parameter SH cannot correct any errors in the relative rates, and can mask other deficiencies in the models. One can get a feeling for the sensitivity of the results on the neutral hydrogen collisions by comparing the results with those obtained when SH is reduced to nought, thereby neglecting them altogether.…”

Section: Model Atommentioning

confidence: 99%

The Galactic chemical evolution of oxygen inferred from 3D non-LTE spectral-line-formation calculations

Amarsi

Asplund

Collet

et al. 2015

Monthly Notices of the Royal Astronomical Society: Letters

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We revisit the Galactic chemical evolution of oxygen, addressing the systematic errors inherent in classical determinations of the oxygen abundance that arise from the use of one dimensional hydrostatic (1D) model atmospheres and from the assumption of local thermodynamic equilibrium (LTE). We perform detailed 3D non-LTE radiative transfer calculations for atomic oxygen lines across a grid of 3D hydrodynamic stagger model atmospheres for dwarfs and subgiants. We apply our grid of predicted line strengths of the [OI]

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“…Only for a few atoms do we know the cross sections of inelastic collisions with neutral hydrogen from either experiments or quantum-mechanical computations. The use of the Drawin approximation (Drawin 1969;Steenbock & Holweger 1984) has been seriously criticised by Barklem et al (2011). For further discussion on this point see also Steffen et al (2015).…”

Section: Introductionmentioning

confidence: 99%

The photospheric solar oxygen project

Caffau

Ludwig

Steffen

et al. 2015

A&A

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Context. The solar photospheric abundance of oxygen is still a matter of debate. For about ten years some determinations have favoured a low oxygen abundance which is at variance with the value inferred by helioseismology. Among the oxygen abundance indicators, the forbidden line at 630 nm has often been considered the most reliable even though it is blended with a Ni i line. In Papers I and II of this series we reported a discrepancy in the oxygen abundance derived from the 630 nm and the subordinate [O I] line at 636 nm in dwarf stars, including the Sun. Aims. Here we analyse several, in part new, solar observations of the centre-to-limb variation of the spectral region including the blend at 630 nm in order to separate the individual contributions of oxygen and nickel. Methods. We analyse intensity spectra observed at different limb angles in comparison with line formation computations performed on a CO5BOLD 3D hydrodynamical simulation of the solar atmosphere. Results. The oxygen abundances obtained from the forbidden line at different limb angles are inconsistent if the commonly adopted nickel abundance of 6.25 is assumed in our local thermodynamic equilibrium computations. With a slightly lower nickel abundance, A(Ni) ≈ 6.1, we obtain consistent fits indicating an oxygen abundance of A(O) = 8.73 ± 0.05. At this value the discrepancy with the subordinate oxygen line remains. Conclusions. The derived value of the oxygen abundance supports the notion of a rather low oxygen abundance in the solar photosphere. However, it is disconcerting that the forbidden oxygen lines at 630 and 636 nm give noticeably different results, and that the nickel abundance derived here from the 630 nm blend is lower than expected from other nickel lines.

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On inelastic hydrogen atom collisions in stellar atmospheres

Cited by 108 publications

References 61 publications

The photospheric solar oxygen project

The photospheric solar oxygen project

The Galactic chemical evolution of oxygen inferred from 3D non-LTE spectral-line-formation calculations

The photospheric solar oxygen project

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