3D non-LTE iron abundances in FG-type dwarfs

Amarsi, A. M.; Liljegren, S.; Nissen, P. E.

doi:10.1051/0004-6361/202244542

Cited by 21 publications

(13 citation statements)

References 71 publications

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“…This can be explained by the stellar parameter differences adopted in both studies, as well as the difference between line lists. However, as noted in Amarsi et al (2016), Amarsi et al (2022), 3D corrections can nevertheless be smaller than the NLTE corrections determined for low metallicity evolved stars. Therefore, including 1D, NLTE corrections in the determination of Fe I and Fe II lines can significantly improve the derived stellar parameters as compared to 1D, LTE.…”

Section: Caveatsmentioning

confidence: 68%

LOTUS: A (Non-) LTE Optimization Tool for Uniform Derivation of Stellar Atmospheric Parameters

Ezzeddine

2023

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Precise fundamental atmospheric stellar parameters and abundance determination of individual elements in stars are important for all stellar population studies. Non–local thermodynamic equilibrium (non-LTE; hereafter NLTE) models are often important for such high precision, however, can be computationally complex and expensive, which renders the models less utilized in spectroscopic analyses. To alleviate the computational burden of such models, we developed a robust 1D, NLTE fundamental atmospheric stellar parameter derivation tool, LOTUS, to determine the effective temperature T eff, surface gravity log g , metallicity [Fe/H], and microturbulent velocity v mic for FGK-type stars, from equivalent width (EW) measurements of Fe i and Fe ii lines. We utilize a generalized curve of growth method to take into account the EW dependencies of each Fe i and Fe ii line on the corresponding atmospheric stellar parameters. A global differential evolution optimization algorithm is then used to derive the fundamental parameters. Additionally, LOTUS can determine precise uncertainties for each stellar parameter using a Markov Chain Monte Carlo algorithm. We test and apply LOTUS on a sample of benchmark stars, as well as stars with available asteroseismic surface gravities from the K2 survey, and metal-poor stars from the Gaia-ESO and R-Process Alliance surveys. We find very good agreement between our NLTE-derived parameters in LOTUS to nonspectroscopic values on average within T eff = ±30 K, and log g = ±0.10 dex for benchmark stars. We provide open access of our code, as well as of the interpolated precomputed NLTE EW grids available on Github (the software is available on GitHub 3 3 https://github.com/Li-Yangyang/LOTUS under an MIT License, and version 0.1.1 (as the persistent version) is archived in Zenodo) and documentation with working examples on the Readthedocs book.

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Section: Caveatsmentioning

confidence: 68%

LOTUS: A (Non-) LTE Optimization Tool for Uniform Derivation of Stellar Atmospheric Parameters

Ezzeddine

2023

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“…The full 3D non-LTE analysis increased the upper limit on the Fe abundance for this star to [Fe/H] < −6.53 as compared to the previous non-LTE upper limit of [Fe/H] < −7.52 computed using averaged 3D (⟨3D⟩) model atmospheres (Bessell et al 2015). Additionally, recent work on C and O (Amarsi et al 2016a), Li (Wang et al 2021), and Fe (Amarsi et al 2016b(Amarsi et al , 2022 have also demonstrated significant 1D LTE-3D non-LTE abundance corrections for metal-poor stars.…”

Section: Introductionmentioning

confidence: 67%

“…These analyses are strongly sensitive to the approximations employed when modelling the synthetic spectra. The abundance offsets introduced by the simplifying assumptions of one-dimensional (1D) hydrostatic atmospheres and local thermodynamic equilibrium (LTE) have been shown to be particularly severe at lower metallicities (Amarsi et al 2016b(Amarsi et al , 2022Bergemann et al 2012Bergemann et al , 2019Ezzeddine et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Raising the observed metallicity floor with a 3D non-LTE analysis of SDSS J102915.14+172927.9

Lagae

Amarsi

Díaz

et al. 2023

A&A

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Context. The first stars marked the end of the cosmic dark ages, produced the first heavy elements, and set the stage for the formation of the first galaxies. Accurate chemical abundances of ultra metal-poor stars ([Fe/H] < −4) can be used to infer the properties of the first stars and thus the formation mechanism for low-mass second-generation stars in the early Universe. Spectroscopic studies have shown that most second-generation stars are carbon enhanced. A notable exception is SDSS J102915.14+172927.9, which is the most metal-poor star known to date, largely by virtue of the low upper limits of the carbon abundance reported in earlier studies. Aims. We re-analysed the composition of SDSS J102915.14+172927.9 with the aim of providing improved observational constraints on the lowest metallicity possible for low-mass star formation and constraining the properties of its Population III progenitor star. Methods. We developed a tailored three-dimensional model atmosphere for SDSS J102915.14+172927.9 with the Stagger code, making use of an improved surface gravity estimate based on the Gaia DR3 parallax. Snapshots from the model were used as input in the radiative transfer code Balder to compute 3D non-local thermodynamic equilibrium (non-LTE) synthetic spectra. These spectra were then used to infer abundances for Mg, Si, Ca, Fe, and Ni as well as upper limits on Li, Na, and Al. Synthetic 3D LTE spectra were computed with Scate to infer the abundance of Ti and upper limits on C and N. Results. In contrast to earlier works based on 1D non-LTE corrections applied to 3D LTE results, we are able to achieve ionisation balance for Ca I and Ca II when employing our consistent 3D non-LTE treatment. The elemental abundances are systematically higher than those found in earlier works. In particular, [Fe/H] is increased by 0.57 dex, and the upper limits of C and N are larger by 0.90 dex and 1.82 dex, respectively. Conclusions. We find that Population III progenitors with masses 10–20 M⊙ exploding with energy E ⪅ 3 × 1051 erg can reproduce our 3D non-LTE abundance pattern. Our 3D non-LTE abundances are able to better constrain the progenitor mass and explosion energy as compared to our 1D LTE abundances. Contrary to previous work, we obtain higher upper limits on the carbon abundance that are ‘marginally consistent’ with star formation through atomic line cooling, and consequently, these results prevent us from drawing strong conclusions about the formation mechanism of this low-mass star.

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“…The right panel in Figure 9 shows this in detail, alongside the observed spectrum of HD122563, a star with similar parameters, from GALAH (Buder et al 2021). Given that accurate modeling of H α core requires techniques beyond 1D LTE (e.g., Barklem 2007;Amarsi et al 2018), and that the observational data does not match the prediction of any of the codes, we consider this disagreement permissible.…”

Section: Balmer Seriesmentioning

confidence: 99%

“…Eliminating the former two assumptions means calculating atmospheric structure using the full hydrodynamic equations (e.g., Freytag et al 2012;Magic et al 2015;Schultz et al 2022) or the magnetohydrodynamic equations (e.g., Vögler et al 2005), if the internal magnetic field is strong. Fortunately, corrections to 1D LTE level populations (e.g., Amarsi et al 2020Amarsi et al , 2022, equivalent widths, or abundances (e.g., Lind et al 2011;Bergemann et al 2012;Amarsi et al 2015;Osorio & Barklem 2016) can be calculated from non-LTE (NLTE) simulations. These can be applied to LTE results or codes to produce approximate NLTE spectra at relatively little computational cost.…”

Section: Introductionmentioning

confidence: 99%

Korg: A Modern 1D LTE Spectral Synthesis Package

Wheeler

Abruzzo

Casey

et al. 2023

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We present Korg, a new package for 1D LTE spectral synthesis of FGK stars, which computes theoretical spectra from the near-ultraviolet to the near-infrared, and implements both plane-parallel and spherical radiative transfer. We outline the inputs and internals of Korg, and compare synthetic spectra from Korg, Moog, Turbospectrum, and SME. The disagreements between Korg and the other codes are no larger than those between the other codes, although disagreement between codes is substantial. We examine the case of a C2 band in detail, finding that uncertainties on physical inputs to spectral synthesis account for a significant fraction of the disagreement. Korg is 1–100 times faster than other codes in typical use, compatible with automatic differentiation libraries, and easily extensible, making it ideal for statistical inference and parameter estimation applied to large data sets. Documentation and installation instructions are available at https://ajwheeler.github.io/Korg.jl/stable/.

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3D non-LTE iron abundances in FG-type dwarfs

Cited by 21 publications

References 71 publications

LOTUS: A (Non-) LTE Optimization Tool for Uniform Derivation of Stellar Atmospheric Parameters

LOTUS: A (Non-) LTE Optimization Tool for Uniform Derivation of Stellar Atmospheric Parameters

Raising the observed metallicity floor with a 3D non-LTE analysis of SDSS J102915.14+172927.9

Korg: A Modern 1D LTE Spectral Synthesis Package

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