3D Stagger model atmospheres with FreeEOS

Zhou, Yixiao; Amarsi, Anish M.; Aguirre Børsen-Koch, Victor; Karlsmose, Klara G.; Collet, Remo; Nordlander, Thomas

doi:10.1051/0004-6361/202346398

Cited by 7 publications

(2 citation statements)

References 110 publications

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“…Line opacities are taken from the MARCS opacity sampling data covering wavelength from 91 nm to 20 μm (Gustafsson et al 2008;Plez 2008). In order to reduce the computational cost, monochromatic opacities at a vast number of wavelengths are grouped into 12 "opacity bins" based on their approximate formation height (reflecting the strength of opacity) and wavelength (Nordlund 1982;Magic et al 2013;Collet et al 2018;Zhou et al 2023). The organization of opacity bins is carefully adjusted such that the predicted radiative cooling rates resemble those from monochromatic calculations.…”

Section: D Stellar Atmosphere Modelsmentioning

confidence: 99%

Does the νmax Scaling Relation Depend on Metallicity? Insights from 3D Convection Simulations

Zhou,

Christensen-Dalsgaard,

Asplund

et al. 2024

ApJ

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Solar-like oscillations have been detected in thousands of stars thanks to modern space missions. These oscillations have been used to measure stellar masses and ages, which have been widely applied in Galactic archeology. One of the pillars of such applications is the ν max scaling relation: the frequency of maximum power ν max , assumed to be proportional to the acoustic cutoff frequency, ν ac, scales with effective temperature and surface gravity. However, the theoretical basis of the ν max scaling relation is uncertain, and there is an ongoing debate about whether it can be applied to metal-poor stars. We investigate the metallicity dependence of the ν max scaling relation by carrying out 3D near-surface convection simulations for solar-type stars with [Fe/H] between −3 and 0.5 dex. First, we found a negative correlation between ν ac and metallicity from the 3D models. This is in tension with the positive correlation identified by studies using 1D models. Second, we estimated theoretical ν max values using velocity amplitudes determined from first principles, by quantifying the mode excitation and damping rates with methods validated in our previous works. We found that ν max does not show correlation with metallicity at solar effective temperature and surface gravity. This study opens an exciting prospect of testing the asteroseismic scaling relations against realistic 3D hydrodynamical stellar models.

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Section: D Stellar Atmosphere Modelsmentioning

confidence: 99%

Does the νmax Scaling Relation Depend on Metallicity? Insights from 3D Convection Simulations

Zhou,

Christensen-Dalsgaard,

Asplund

et al. 2024

ApJ

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“…Recently, Zhou et al (2023) implemented the Free EOS by Irwin (2012), which is constructed to emulate various commonly used EOSs, including the MHD EOS described in Section 8.2. The Free EOS is simpler and faster than the MHD EOS, and the code is publicly available, enabling calculation of tables for custom abundances.…”

Section: Free Eos and Blue Opacitiesmentioning

confidence: 99%

The Stagger Code for Accurate and Efficient, Radiation-coupled Magnetohydrodynamic Simulations

Stein,

Nordlund,

Collet

et al. 2024

ApJ

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We describe the Stagger code for simulations of magnetohydrodynamic (MHD) systems. This is a modular code with a variety of physics modules that will let the user run simulations of deep stellar atmospheres, sunspot formation, stellar chromospheres and coronae, proto-stellar disks, star formation from giant molecular clouds, and even galaxy formation. The Stagger code is efficiently and highly parallelizable, enabling such simulations with large ranges of both spatial and temporal scales. We describe the methodology of the code and present the most important of the physics modules, as well as its input and output variables. We show results of a number of standard MHD tests to enable comparison with other, similar codes. In addition, we provide an overview of tests that have been carried out against solar observations, ranging from spectral line shapes, spectral flux distribution, limb darkening, intensity and velocity distributions of granulation, to seismic power spectra and the excitation of p-modes. The Stagger code has proven to be a high-fidelity code with a large range of uses.

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Titanium abundances in late-type stars

Mallinson,

Lind,

Amarsi

et al. 2024

A&A

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Rapidly growing datasets from stellar spectroscopic surveys are providing unprecedented opportunities to analyse the chemical evolution history of our Galaxy. However, spectral analysis requires accurate modelling of synthetic stellar spectra for late-type stars, for which the assumption of local thermodynamic equilibrium (LTE) has been shown to be insufficient in many cases. Errors associated with LTE can be particularly large for Ti I which is susceptible to over-ionisation, particularly in metal-poor stars. The aims of this work are to study and quantify the 1D non-LTE effects on titanium abundances across the Hertzsprung-Russell diagram for a large sample of stars. A large grid of departure coefficients, $ were computed on standard MARCS model atmospheres. The grid extends from $3000\ K $ to $8000\ K $ in teff , $-0.5\ to $+5.5\ in logg , and $-5.0$ to $+1.0$ in feh , with non-LTE effects in this grid reaching up to 0.4 dex. This was used to compute abundance corrections that were subsequently applied to the LTE abundances of over 70$\,$000 stars selected from the GALAH survey in addition to a smaller sample of literature Keck data for metal-poor dwarfs. The non-LTE effects grow towards lower feh , lower logg , and higher teff , with a minimum and maximum $ A(Ti)_ Ti\,I $ of $0.02$ and $0.19$ in the GALAH sample. For metal-poor giants, the non-LTE modelling reduces the average ionisation imbalance ( from $-0.11\ to $-0.01\ at Fe/H = $-1.7$, and the enhancement in titanium abundances from Ti I lines results in a tife versus feh trend that more closely resembles the behaviour of Ti II at low metallicities. At higher metallicities, the results are limited by the precision of the GALAH DR3 LTE abundances and the effects are within the errors. For the most metal-poor dwarfs from the Keck sample, the average ionisation imbalance increases from $-0.1$ dex to $+0.2$ dex, a shortcoming that is consistent with previous 1D non-LTE studies and which we speculate could be related to 3D effects. Non-LTE effects on titanium abundances are significant. Neglecting them may alter our understanding of Galactic chemical evolution. We have made our grid of departure coefficients publicly available, with the caveat that the Ti abundances of metal-poor dwarfs need further study in 3D non-LTE.

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3D Stagger model atmospheres with FreeEOS

Cited by 7 publications

References 110 publications

Does the νmax Scaling Relation Depend on Metallicity? Insights from 3D Convection Simulations

Does the νmax Scaling Relation Depend on Metallicity? Insights from 3D Convection Simulations

The Stagger Code for Accurate and Efficient, Radiation-coupled Magnetohydrodynamic Simulations

Titanium abundances in late-type stars

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