Radiative transfer with scattering for domain-decomposed 3D MHD simulations of cool stellar atmospheres

Hayek, Wolfgang; Asplund, Martin; Carlsson, Mats; Trampedach, Regner; Collet, Remo; Gudiksen, B. V.; Hansteen, V. H.; Leenaarts, J.

doi:10.1051/0004-6361/201014210

Cited by 147 publications

(180 citation statements)

References 69 publications

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“…We therefore assume a static medium and LTE for the gas opacity, which thus depends only on the local gas temperature and the gas density, and which can therefore be precomputed and tabulated. Skartlien (2000) and Hayek et al (2010) showed the importance of photon scattering in simulations of the higher solar atmosphere; we therefore include a coherent scattering contribution in the gas emission, which requires an iterative solution of the radiative transfer equation to obtain a consistent radiation field. The vast number of spectral lines encountered in a stellar atmosphere requires, in principle, the solution of a large number of radiative transfer problems.…”

Section: Full Radiative Transfermentioning

confidence: 99%

“…If the hydrodynamical timesteps are sufficiently short that changes in the radiative energy flux are small, full radiative transfer only needs to be computed in a fraction of the hydrodynamical timesteps. A detailed description of the numerical methods and the parallelization techniques used for the full radiative transfer module in Bifrost can be found in Hayek et al (2010).…”

Section: Full Radiative Transfermentioning

confidence: 99%

“…The full radiative transfer module of the Bifrost code operates on a static 3D atmosphere with a resolution of 50 × 50×120 grid points and with a horizontally homogeneous isothermal stratification; other physics modules are not used during the computation. The interpolation algorithms needed for radiative transfer in 3D simulations are validated separately with the searchlight test described in Hayek et al (2010). Optical depths are preset on a grid that is equidistant in log 10 τ with 10 grid points per decade.…”

Section: Full Radiative Transfer Test In An Isothermal Scattering Atmmentioning

confidence: 99%

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The stellar atmosphere simulation codeBifrost

Gudiksen

Carlsson

Hansteen

et al. 2011

A&A

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Context. Numerical simulations of stellar convection and photospheres have been developed to the point where detailed shapes of observed spectral lines can be explained. Stellar atmospheres are very complex, and very different physical regimes are present in the convection zone, photosphere, chromosphere, transition region and corona. To understand the details of the atmosphere it is necessary to simulate the whole atmosphere since the different layers interact strongly. These physical regimes are very diverse and it takes a highly efficient massively parallel numerical code to solve the associated equations. Aims. The design, implementation and validation of the massively parallel numerical code Bifrost for simulating stellar atmospheres from the convection zone to the corona. Methods. The code is subjected to a number of validation tests, among them the Sod shock tube test, the Orzag-Tang colliding shock test, boundary condition tests and tests of how the code treats magnetic field advection, chromospheric radiation, radiative transfer in an isothermal scattering atmosphere, hydrogen ionization and thermal conduction. Results. Bifrost completes the tests with good results and shows near linear efficiency scaling to thousands of computing cores.

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Section: Full Radiative Transfermentioning

confidence: 99%

Section: Full Radiative Transfermentioning

confidence: 99%

Section: Full Radiative Transfer Test In An Isothermal Scattering Atmmentioning

confidence: 99%

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The stellar atmosphere simulation codeBifrost

Gudiksen

Carlsson

Hansteen

et al. 2011

A&A

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468

522

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“…Opacities were based on OSMARCS model opacities (these models are used in Appendix A), which were binned into 14 opacity groups (Nordlund 1982;Ludwig et al 1994). The effect of scattering was treated according to the Hayek et al (2010) approximation as explored by Collet et al (2011); scattering opacities in the deeper layers of the model are treated as true absorption and ignored in the outer regions of the model atmosphere (see Ludwig & Steffen 2013, for a full description). As all models used are metal poor, the alpha elements were enhanced so that [α/Fe] = +0.4.…”

Section: Co 5 Bold Model Computationsmentioning

confidence: 99%

An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres

Gallagher

Caffau

Bonifacio

et al. 2017

A&A

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Context. Tighter constraints on metal-poor stars we observe are needed to better understand the chemical processes of the early Universe. Computing a stellar spectrum in 3D allows one to model complex stellar behaviours, which cannot be replicated in 1D. Aims. We examine the effect that the intrinsic CNO abundances have on a 3D model structure and the resulting 3D spectrum synthesis. Methods. Model atmospheres were computed in 3D for three distinct CNO chemical compositions using the CO 5 BOLD model atmosphere code, and their internal structures were examined. Synthetic spectra were computed from these models using Linfor3D and they were compared. New 3D abundance corrections for the G-band and a selection of UV OH lines were also computed. Results. The varying CNO abundances change the metal content of the 3D models. This had an effect on the model structure and the resulting synthesis. However, it was found that the C/O ratio had a larger effect than the overall metal content of a model. Conclusions. Our results suggest that varying the C/O ratio has a substantial impact on the internal structure of the 3D model, even in the hot turn-off star models explored here. This suggests that bespoke 3D models, for specific CNO abundances should be sought. Such effects are not seen in 1D at these temperature regimes.

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“…Recently Hayek et al (2010) have introduced a proper treatment of scattering in their magneto-hydrodynamical simulation code, BIFROST. For the Sun and solar-type stars they do not find a significant impact of continuum scattering on the temperature structure.…”

Section: Hydrodynamical Models and Spectrum Synthesismentioning

confidence: 99%

Cu i resonance lines in turn-off stars of NGC 6752 and NGC 6397

Bonifacio

Caffau

Ludwig

2010

A&A

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Context.Copper is an element whose interesting evolution with metallicity is not fully understood. Observations of copper abundances rely on a very limited number of lines, the strongest are the Cu i lines of Mult. 1 at 324.7 nm and 327.3 nm which can be measured even at extremely low metallicities. Aims. We investigate the quality of these lines as abundance indicators. Methods. We measure these lines in two turn-off (TO) stars in the Globular Cluster NGC 6752 and two TO stars in the Globular Cluster NGC 6397 and derive abundances with 3D hydrodynamical model atmospheres computed with the CO5BOLD code. These abundances are compared to the Cu abundances measured in giant stars of the same clusters, using the lines of Mult. 2 at 510.5 nm and 578.2 nm. Results. The abundances derived from the lines of Mult. 1 in TO stars differ from the abundances of giants of the same clusters. This is true both using CO5BOLD models and using traditional 1D model atmospheres. The LTE 3D corrections for TO stars are large, while they are small for giant stars.Conclusions. The Cu i resonance lines of Mult. 1 are not reliable abundance indicators. It is likely that departures from LTE should be taken into account to properly describe these lines, although it is not clear if these alone can account for the observations. An investigation of these departures is indeed encouraged for both dwarfs and giants. Our recommendation to those interested in the study of the evolution of copper abundances is to rely on the measurements in giants, based on the lines of Mult. 2. We caution, however, that NLTE studies may imply a revision in all the Cu abundances, both in dwarfs and giants.

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Radiative transfer with scattering for domain-decomposed 3D MHD simulations of cool stellar atmospheres

Cited by 147 publications

References 69 publications

The stellar atmosphere simulation codeBifrost

The stellar atmosphere simulation codeBifrost

An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres

Cu i resonance lines in turn-off stars of NGC 6752 and NGC 6397

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