MPS-ATLAS: A fast all-in-one code for synthesising stellar spectra

Witzke, V.; Шапиро, А. И.; Černetič, Miha; Tagirov, Rinat; Костогрыз, Н. М.; Anusha, L. S.; Unruh, Y. C.; Solanki, S. K.; Kurucz, Robert L.

doi:10.1051/0004-6361/202140275

Cited by 30 publications

(39 citation statements)

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“…The opacity contains a contribution from the continuum c and from lines l . Detailed opacity distribution functions (ODFs) were taken from the merged parallelised simplified ATLAS code (Witzke et al 2021), an upgraded version of ATLAS9 (Kurucz 1970). For the continuum, the total and scattering opacities are available through the ATLAS package, tabulated with frequency, temperature and pressure.…”

Section: Appendix A: Lte Equation Of Statementioning

confidence: 99%

Chromospheric extension of the MURaM code

Przybylski

Cameron

Solanki

et al. 2022

A&A

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Context. Detailed numerical models of the chromosphere and corona are required to understand the heating of the solar atmosphere. An accurate treatment of the solar chromosphere is complicated by the effects arising from non-local thermodynamic equilibrium (NLTE) radiative transfer. A small number of strong, highly scattering lines dominate the cooling and heating in the chromosphere. Additionally, the recombination times of ionised hydrogen are longer than the dynamical timescales, requiring a non-equilibrium (NE) treatment of hydrogen ionisation. Aims. We describe a set of necessary additions to the MURaM code that allow it to handle some of the important NLTE effects. We investigate the impact on solar chromosphere models caused by NLTE and NE effects in radiation magnetohydrodynamic simulations of the solar atmosphere. Methods. The MURaM code was extended to include the physical process required for an accurate simulation of the solar chromosphere, as implemented in the Bifrost code. This includes a time-dependent treatment of hydrogen ionisation, a scattering multi-group radiation transfer scheme, and approximations for NLTE radiative cooling. Results. The inclusion of NE and NLTE physics has a large impact on the structure of the chromosphere; the NE treatment of hydrogen ionisation leads to a higher ionisation fraction and enhanced populations in the first excited state throughout cold inter-shock regions of the chromosphere. Additionally, this prevents hydrogen ionisation from buffering energy fluctuations, leading to hotter shocks and cooler inter-shock regions. The hydrogen populations in the ground and first excited state are enhanced by 102–103 in the upper chromosphere and by up to 109 near the transition region. Conclusions. Including the necessary NLTE physics leads to significant differences in chromospheric structure and dynamics. The thermodynamics and hydrogen populations calculated using the extended version of the MURaM code are consistent with previous non-equilibrium simulations. The electron number and temperature calculated using the non-equilibrium treatment of the chromosphere are required to accurately synthesise chromospheric spectral lines.

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Section: Appendix A: Lte Equation Of Statementioning

confidence: 99%

Chromospheric extension of the MURaM code

Przybylski

Cameron

Solanki

et al. 2022

A&A

Self Cite

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show abstract

“…The opacity contains a contribution from the continuum c and from lines l . Detailed Opacity Distribution Functions (ODFs) are taken from the Merged Parallelised Simplified ATLAS code (MPS-ATLAS) (Witzke et al 2021), an upgraded version of ATLAS9 (Kurucz 1970). For the continuum, the total and scattering opacities are available through the ATLAS package, tabulated with frequency, temperature and pressure.…”

Section: Appendix A: Lte Equation Of Statementioning

confidence: 99%

Chromospheric Extension of the MURaM Code

Przybylski,

Cameron,

Solanki

et al. 2022

Preprint

Self Cite

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Context. Detailed numerical models of chromosphere and corona are required to understand the heating of the solar atmosphere. An accurate treatment of the solar chromosphere is complicated by the effects arising from Non Local Thermodynamic Equilibrium (NLTE) radiative transfer. A small number of strong, highly scattering lines dominate the cooling and heating in the chromosphere. Additionally, the recombination times of ionised hydrogen are longer than the dynamical timescales, requiring a non-equilibrium (NE) treatment of hydrogen ionisation. Aims. We describe a set of necessary additions to the MURaM code so that it might handle some of the important NLTE effects. We investigate the impact on models of the solar chromosphere caused by NLTE and NE effects in radiation magnetohydrodynamic (rMHD) simulations of the solar atmosphere. Methods. The MURaM code is extended to include the physical process required for accurate simulation of the solar chromosphere, as implemented in the Bifrost code. This includes a time-dependent treatment of hydrogen ionisation, a scattering multi-group radiation transfer scheme and approximations for NLTE radiative cooling. Results. The inclusion of NE and NLTE physics has a large impact on the structure of the chromosphere; the NE treatment of hydrogen ionisation leads to a higher ionisation fraction and enhanced populations in the first excited state throughout cold inter-shock regions of the chromosphere. Additionally this prevents hydrogen ioniation from buffering energy fluctuations, leading to hotter shocks and cooler inter-shock regions. The hydrogen populations in the ground and first excited state are enhanced by 10 2 − 10 3 in the upper chromosphere and up to 10 9 near the transition region. Conclusions. Including the necessary NLTE physics leads to significant differences in chromospheric structure and dynamics. The thermodynamics and hydrogen populations calculated using the extended version of the MURaM code are consistent with previous non-equilibrium simulations. The electron number and temperature calculated using the non-equilibrium treatment of the chromosphere are required to accurately synthesise chromospheric spectral lines.

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“…Blue dots depict the MARCS grid from Gustafsson et al (2008) and red dots represents the PHOENIX grid from Husser et al (2013). ity of 2 km/s (see Kurucz 2005;Witzke et al 2021). The continuum opacity is calculated taking into account contributions from both absorption and scattering processes.…”

Section: Model Atmospheresmentioning

confidence: 99%

“…For the scattering contribution we include electron scattering and Rayleigh scattering on HI, HeI, and H 2 . A more detailed description of all physical processes and numerical schemes applied in MPS-ATLAS is given in Witzke et al (2021).…”

Section: Model Atmospheresmentioning

confidence: 99%

“…With this work, we start our effort in producing a new library of stellar limb darkening. Namely, we employ the recently developed 1-D Merged Parallelised Simplified ATLAS (MPS-ATLAS, Witzke et al 2021) code to create a grid of model atmospheres and the corresponding limb darkening for a wide range of stellar fundamental parameters, utilizing most accurate information on stellar abundances and mixing lengths. The code has been intensively tested against solar and stellar observations and incorporates improved molecular and atomic data.…”

Section: Introductionmentioning

confidence: 99%

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Stellar limb darkening. A new MPS-ATLAS library for Kepler, TESS, CHEOPS, and PLATO passbands

Kostogryz,

Witzke,

Shapiro

et al. 2022

Preprint

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Context. The detection of the first exoplanet paved the way into the era of transit photometry space missions with a revolutionary photometric precision that aim at discovering new exoplanetary systems around different types of stars. With this high precision, it is possible to derive very accurately the radii of exoplanets which is crucial for constraining their type and composition. However, it requires an accurate description of host stars, especially their center-to-limb variation of intensities (so called limb darkening) as it affects the planet-to-star radius ratio determination. Aims. We aim at improving the accuracy of limb darkening calculations for stars with a wide range of fundamental parameters. Methods. We used the recently developed 1D Merged Parallelised Simplified ATLAS (MPS-ATLAS) code to compute model atmosphere structures and to synthesize stellar limb darkening on a very fine grid of stellar parameters. For the computations we utilised the most accurate information on chemical element abundances and mixing length parameters including convective overshoot. The stellar limb darkening was fitted using the two most accurate limb darkening laws: the power-2 and 4-parameters non-linear laws.Results. We present a new extensive library of stellar model atmospheric structures, the synthesized stellar limb darkening curves, and the coefficients of parameterized limb-darkening laws on a very fine grid of stellar parameters in the Kepler, TESS, CHEOPS, and PLATO passbands. The fine grid allows overcoming the sizable errors introduced by the need to interpolate. Our computations of solar limb darkening are in a good agreement with available solar measurements at different view angles and wavelengths. Our computations of stellar limb darkening agree well with available measurements of Kepler stars. A new grid of stellar model structures, limb darkening and their fitted coefficients in different broad passbands is provided in online tables (CDS).

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MPS-ATLAS: A fast all-in-one code for synthesising stellar spectra

Cited by 30 publications

References 50 publications

Chromospheric extension of the MURaM code

Chromospheric extension of the MURaM code

Chromospheric Extension of the MURaM Code

Stellar limb darkening. A new MPS-ATLAS library for Kepler, TESS, CHEOPS, and PLATO passbands

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