Simulations of stellar convection with CO5BOLD

Freytag, B.; Steffen, M.; Ludwig, H.‐G.; Wedemeyer, Sven; Schaffenberger, W.; Steiner, O.

doi:10.1016/j.jcp.2011.09.026

Cited by 389 publications

(465 citation statements)

References 174 publications

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“…It was computed with the CO5BOLD code (Freytag et al 2012) on a Cartesian grid consisting of 140 × 140 grid points horizontally and 150 grid points vertically, spanning 5.6 × 5.6 Mm 2 horizontally and 2.25 Mm vertically ("box-in-a-star" setup). Open boundary conditions were applied vertically, allowing matter and radiation to flow in and out of the computational domain while conserving the total mass of matter inside the box.…”

Section: D Hydrodynamical Co5bold Model Atmospheresmentioning

confidence: 99%

The photospheric solar oxygen project

Steffen

Prakapavičius

Caffau

et al. 2015

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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: D Hydrodynamical Co5bold Model Atmospheresmentioning

confidence: 99%

The photospheric solar oxygen project

Steffen

Prakapavičius

Caffau

et al. 2015

A&A

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109

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“…Our analysis is based on a 3D model atmosphere computed with the CO 5 BOLD code (Freytag et al 2012). The box-size of the CO 5 BOLD 3D solar model atmosphere is 5.6 × 5.6 × 2.25 Mm, with a resolution of 140 × 140 × 150.…”

Section: Atomic Data and Model Atmospheresmentioning

confidence: 99%

The photospheric solar oxygen project

Caffau

Ludwig

Steffen

et al. 2015

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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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“…The red giant model atmosphere used in this work was calculated with the 3D radiation hydrodynamics code CO 5 BOLD (Freytag et al 2012). The CO 5 BOLD code uses a Riemann solver of Roe type to calculate the time evolution of the hydrodynamical flow and the radiation field on a 3D Cartesian grid.…”

Section: Three-dimensional Hydrodynamical Model and 3d Snapshot Selecmentioning

confidence: 99%

Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars

Kučinskas¹,

Steffen²,

Ludwig³

et al. 2012

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Aims. We investigate the role of convection in the formation of atomic and molecular lines in the atmosphere of a red giant star. For this purpose we study the formation properties of spectral lines that belong to a number of astrophysically important tracer elements, including neutral and singly ionized atoms (Li Ba ii, and Eu ii), and molecules (CH, CO, C 2 , NH, CN, and OH).Methods. We focus our investigation on a prototypical red giant located close to the red giant branch (RGB) tip (T eff = 3660 K, log g = 1.0, [M/H] = 0.0). We used two types of model atmospheres, 3D hydrodynamical and classical 1D, calculated with the CO 5 BOLD and LHD stellar atmosphere codes, respectively. Both codes share the same atmospheric parameters, chemical composition, equation of state, and opacities, which allowed us to make a strictly differential comparison between the line formation properties predicted in 3D and 1D. The influence of convection on the spectral line formation was assessed with the aid of 3D-1D abundance corrections, which measure the difference between the abundances of chemical species derived with the 3D hydrodynamical and 1D classical model atmospheres. Results. We find that convection plays a significant role in the spectral line formation in this particular red giant. The derived 3D-1D abundance corrections rarely exceed ±0.1 dex when lines of neutral atoms and molecules are considered, which is in line with the previous findings for solar-metallicity red giants located on the lower RGB. The situation is different with lines that belong to ionized atoms, or to neutral atoms with high ionization potential. In both cases, the corrections for high-excitation lines (χ > 8 eV) may amount to Δ 3D−1D ∼ −0.4 dex. The 3D-1D abundance corrections generally show a significant wavelength dependence; in most cases they are smaller in the near-infrared, at 1600-2500 nm.

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Simulations of stellar convection with CO5BOLD

Cited by 389 publications

References 174 publications

The photospheric solar oxygen project

The photospheric solar oxygen project

The photospheric solar oxygen project

Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars

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Simulations of stellar convection with CO5BOLD

Cited by 389 publications

References 174 publications

The photospheric solar oxygen project

The photospheric solar oxygen project

The photospheric solar oxygen project

Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars

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Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars