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**Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation.** / Amarsi, A. M.; Nordlander, T.; Barklem, P. S.; Asplund, M.; Collet, R.; Lind, K.

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review

Amarsi, AM, Nordlander, T, Barklem, PS, Asplund, M, Collet, R & Lind, K 2018, 'Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation', *Astronomy & Astrophysics*, vol. 615, 139. https://doi.org/10.1051/0004-6361/201732546

Amarsi, A. M., Nordlander, T., Barklem, P. S., Asplund, M., Collet, R., & Lind, K. (2018). Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation. *Astronomy & Astrophysics*, *615*, [139]. https://doi.org/10.1051/0004-6361/201732546

Amarsi AM, Nordlander T, Barklem PS, Asplund M, Collet R, Lind K. 2018. Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation. Astronomy & Astrophysics. 615. https://doi.org/10.1051/0004-6361/201732546

Amarsi, A. M. et al. "Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation". *Astronomy & Astrophysics*. 2018. 615. https://doi.org/10.1051/0004-6361/201732546

Amarsi AM, Nordlander T, Barklem PS, Asplund M, Collet R, Lind K. Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation. Astronomy & Astrophysics. 2018 Jul 27;615. 139. https://doi.org/10.1051/0004-6361/201732546

Amarsi, A. M. ; Nordlander, T. ; Barklem, P. S. ; Asplund, M. ; Collet, R. ; Lind, K. / **Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation**. In: Astronomy & Astrophysics. 2018 ; Vol. 615.

@article{a39e7b384b8643dfbbb3eccbee1bee35,

title = "Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation",

abstract = "Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, reliable inferences require accurate model spectra, and the absolute accuracy of classical methods that are based on one-dimensional (1D) hydrostatic model atmospheres and local thermodynamic equilibrium (LTE) is still unclear. To investigate this, we carry out 3D non-LTE calculations for the Balmer lines, performed, for the first time, over an extensive grid of 3D hydrodynamic STAGGER model atmospheres. For H alpha, H beta, and H gamma we find significant 1D non-LTE versus 3D non-LTE differences (3D effects): the outer wings tend to be stronger in 3D models, particularly for H gamma, while the inner wings can be weaker in 3D models, particularly for H alpha. For H alpha, we also find significant 3D LTE versus 3D non-LTE differences (non-LTE effects): in warmer stars (T-eff approximate to 6500 K) the inner wings tend to be weaker in non-LTE models, while at lower effective temperatures (T-eff approximate to 4500 K) the inner wings can be stronger in non-LTE models; the non-LTE effects are more severe at lower metallicities. We test our 3D non-LTE models against observations of well-studied benchmark stars. For the Sun, we infer concordant effective temperatures from H alpha, H beta, and H gamma; however the value is too low by around 50 K which could signal residual modelling shortcomings. For other benchmark stars, our 3D non-LTE models generally reproduce the effective temperatures to within 1 sigma uncertainties. For H alpha, the absolute 3D effects and non-LTE effects can separately reach around 100 K, in terms of inferred effective temperatures. For metal-poor turn-off stars, 1D LTE models of H alpha can underestimate effective temperatures by around 150 K. Our 3D non-LTE model spectra are publicly available, and can be used for more reliable spectroscopic effective temperature determinations.",

keywords = "radiative transfer, line: formation, line: profiles, stars: atmospheres, stars: late-type, COOL DWARF STARS, ELECTRON-IMPACT IONIZATION, MODEL STELLAR ATMOSPHERES, ATOM-ATOM COLLISIONS, METAL-POOR STARS, SOLAR-TYPE STARS, RADIATIVE-TRANSFER, CHEMICAL-COMPOSITION, EXCITED ATOMS, CROSS-SECTION",

author = "Amarsi, {A. M.} and T. Nordlander and Barklem, {P. S.} and M. Asplund and R. Collet and K. Lind",

year = "2018",

month = "7",

day = "27",

doi = "10.1051/0004-6361/201732546",

language = "English",

volume = "615",

journal = "Astronomy & Astrophysics",

issn = "0004-6361",

publisher = "E D P Sciences",

}

TY - JOUR

T1 - Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation

AU - Amarsi, A. M.

AU - Nordlander, T.

AU - Barklem, P. S.

AU - Asplund, M.

AU - Collet, R.

AU - Lind, K.

PY - 2018/7/27

Y1 - 2018/7/27

N2 - Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, reliable inferences require accurate model spectra, and the absolute accuracy of classical methods that are based on one-dimensional (1D) hydrostatic model atmospheres and local thermodynamic equilibrium (LTE) is still unclear. To investigate this, we carry out 3D non-LTE calculations for the Balmer lines, performed, for the first time, over an extensive grid of 3D hydrodynamic STAGGER model atmospheres. For H alpha, H beta, and H gamma we find significant 1D non-LTE versus 3D non-LTE differences (3D effects): the outer wings tend to be stronger in 3D models, particularly for H gamma, while the inner wings can be weaker in 3D models, particularly for H alpha. For H alpha, we also find significant 3D LTE versus 3D non-LTE differences (non-LTE effects): in warmer stars (T-eff approximate to 6500 K) the inner wings tend to be weaker in non-LTE models, while at lower effective temperatures (T-eff approximate to 4500 K) the inner wings can be stronger in non-LTE models; the non-LTE effects are more severe at lower metallicities. We test our 3D non-LTE models against observations of well-studied benchmark stars. For the Sun, we infer concordant effective temperatures from H alpha, H beta, and H gamma; however the value is too low by around 50 K which could signal residual modelling shortcomings. For other benchmark stars, our 3D non-LTE models generally reproduce the effective temperatures to within 1 sigma uncertainties. For H alpha, the absolute 3D effects and non-LTE effects can separately reach around 100 K, in terms of inferred effective temperatures. For metal-poor turn-off stars, 1D LTE models of H alpha can underestimate effective temperatures by around 150 K. Our 3D non-LTE model spectra are publicly available, and can be used for more reliable spectroscopic effective temperature determinations.

AB - Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, reliable inferences require accurate model spectra, and the absolute accuracy of classical methods that are based on one-dimensional (1D) hydrostatic model atmospheres and local thermodynamic equilibrium (LTE) is still unclear. To investigate this, we carry out 3D non-LTE calculations for the Balmer lines, performed, for the first time, over an extensive grid of 3D hydrodynamic STAGGER model atmospheres. For H alpha, H beta, and H gamma we find significant 1D non-LTE versus 3D non-LTE differences (3D effects): the outer wings tend to be stronger in 3D models, particularly for H gamma, while the inner wings can be weaker in 3D models, particularly for H alpha. For H alpha, we also find significant 3D LTE versus 3D non-LTE differences (non-LTE effects): in warmer stars (T-eff approximate to 6500 K) the inner wings tend to be weaker in non-LTE models, while at lower effective temperatures (T-eff approximate to 4500 K) the inner wings can be stronger in non-LTE models; the non-LTE effects are more severe at lower metallicities. We test our 3D non-LTE models against observations of well-studied benchmark stars. For the Sun, we infer concordant effective temperatures from H alpha, H beta, and H gamma; however the value is too low by around 50 K which could signal residual modelling shortcomings. For other benchmark stars, our 3D non-LTE models generally reproduce the effective temperatures to within 1 sigma uncertainties. For H alpha, the absolute 3D effects and non-LTE effects can separately reach around 100 K, in terms of inferred effective temperatures. For metal-poor turn-off stars, 1D LTE models of H alpha can underestimate effective temperatures by around 150 K. Our 3D non-LTE model spectra are publicly available, and can be used for more reliable spectroscopic effective temperature determinations.

KW - radiative transfer

KW - line: formation

KW - line: profiles

KW - stars: atmospheres

KW - stars: late-type

KW - COOL DWARF STARS

KW - ELECTRON-IMPACT IONIZATION

KW - MODEL STELLAR ATMOSPHERES

KW - ATOM-ATOM COLLISIONS

KW - METAL-POOR STARS

KW - SOLAR-TYPE STARS

KW - RADIATIVE-TRANSFER

KW - CHEMICAL-COMPOSITION

KW - EXCITED ATOMS

KW - CROSS-SECTION

U2 - 10.1051/0004-6361/201732546

DO - 10.1051/0004-6361/201732546

M3 - Journal article

VL - 615

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

M1 - 139

ER -