Excitation and charge transfer in low-energy hydrogen atom collisions with neutral carbon and nitrogen

Amarsi, A. M.; Barklem, P. S.

doi:10.1051/0004-6361/201935101

Cited by 12 publications

(2 citation statements)

References 47 publications

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“…In late-type stars, carbon and oxygen abundances can be measured using atomic lines (although carbon abundances are more commonly measured using lines of CH). Improved atomic models have recently been developed for C I (Amarsi et al 2019b) and O I (Amarsi et al 2018a), that utilise ab initio calculations for inelastic collisions with atomic hydrogen (Barklem 2018;Amarsi & Barklem 2019) such data typically being the largest source of uncertainty in non-LTE modelling (e.g. Barklem et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Carbon, oxygen, and iron abundances in disk and halo stars

Amarsi

Nissen

Skúladóttir

2019

A&A

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136

106

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The abundances of carbon, oxygen, and iron in late-type stars are important parameters in exoplanetary and stellar physics, as well as key tracers of stellar populations and Galactic chemical evolution. However, standard spectroscopic abundance analyses can be prone to severe systematic errors, based on the assumption that the stellar atmosphere is one-dimensional (1D) and hydrostatic, and by ignoring departures from local thermodynamic equilibrium (LTE). In order to address this, we carried out three-dimensional (3D) non-LTE radiative transfer calculations for C I and O I, and 3D LTE radiative transfer calculations for Fe II, across the STAGGER-grid of 3D hydrodynamic model atmospheres. The absolute 3D non-LTE versus 1D LTE abundance corrections can be as severe as − 0.3 dex for C I lines in low-metallicity F dwarfs, and − 0.6 dex for O I lines in high-metallicity F dwarfs. The 3D LTE versus 1D LTE abundance corrections for Fe II lines are less severe, typically less than + 0.15 dex. We used the corrections in a re-analysis of carbon, oxygen, and iron in 187 F and G dwarfs in the Galactic disk and halo. Applying the differential 3D non-LTE corrections to 1D LTE abundances visibly reduces the scatter in the abundance plots. The thick disk and high-α halo population rise in carbon and oxygen with decreasing metallicity, and reach a maximum of [C/Fe] ≈ 0.2 and a plateau of [O/Fe] ≈ 0.6 at [Fe/H] ≈ −1.0. The low-α halo population is qualitatively similar, albeit offset towards lower metallicities and with larger scatter. Nevertheless, these populations overlap in the [C/O] versus [O/H] plane, decreasing to a plateau of [C/O] ≈ −0.6 below [O/H] ≈ −1.0. In the thin-disk, stars having confirmed planet detections tend to have higher values of C∕O at given [O/H]; this potential signature of planet formation is only apparent after applying the abundance corrections to the 1D LTE results. Our grids of line-by-line abundance corrections are publicly available and can be readily used to improve the accuracy of spectroscopic analyses of late-type stars.

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Section: Introductionmentioning

confidence: 99%

Carbon, oxygen, and iron abundances in disk and halo stars

Amarsi

Nissen

Skúladóttir

2019

A&A

Self Cite

136

106

View full text Add to dashboard Cite

show abstract

“…In late-type stars, carbon and oxygen abundances can be measured using atomic lines (although carbon abundances are more commonly measured using lines of CH). Improved atomic models have recently been developed for C i (Amarsi et al 2019a) and O i (Amarsi et al 2018a), that utilise ab initio calculations for inelastic collisions with atomic hydrogen (Barklem 2018;Amarsi & Barklem 2019) such data typically being the largest source of uncertainty in non-LTE modelling (e.g. Barklem et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Carbon, oxygen, and iron abundances in disk and halo stars. Implications of 3D non-LTE spectral line formation

Amarsi,

Nissen,

Skúladóttir

2019

Preprint

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The abundances of carbon, oxygen, and iron in late-type stars are important parameters in exoplanetary and stellar physics, as well as key tracers of stellar populations and Galactic chemical evolution. However, standard spectroscopic abundance analyses can be prone to severe systematic errors, based on the assumption that the stellar atmosphere is one-dimensional (1D) and hydrostatic, and by ignoring departures from local thermodynamic equilibrium (LTE). In order to address this, we carried out three-dimensional (3D) non-LTE radiative transfer calculations for C i and O i, and 3D LTE radiative transfer calculations for Fe ii, across the staggergrid of 3D hydrodynamic model atmospheres. The absolute 3D non-LTE versus 1D LTE abundance corrections can be as severe as −0.3 dex for C i lines in low-metallicity F dwarfs, and −0.6 dex for O i lines in high-metallicity F dwarfs. The 3D LTE versus 1D LTE abundance corrections for Fe ii lines are less severe, typically less than +0.15 dex. We used the corrections in a re-analysis of carbon, oxygen, and iron in 187 F and G dwarfs in the Galactic disk and halo. Applying the differential 3D non-LTE corrections to 1D LTE abundances visibly reduces the scatter in the abundance plots. The thick disk and high-α halo population rise in carbon and oxygen with decreasing metallicity, and reach a maximum of [C/Fe] ≈ 0.2 and a plateau of [O/Fe] ≈ 0.6 at [Fe/H] ≈ −1.0. The low-α halo population is qualitatively similar, albeit offset towards lower metallicities and with larger scatter. Nevertheless, these populations overlap in the [C/O] versus [O/H] plane, decreasing to a plateau of [C/O] ≈ −0.6 below [O/H] ≈ −1.0. In the thin-disk, stars having confirmed planet detections tend to have higher values of C/O at given [O/H]; this potential signature of planet formation is only apparent after applying the abundance corrections to the 1D LTE results. Our grids of line-by-line abundance corrections are publicly available and can be readily used to improve the accuracy of spectroscopic analyses of late-type stars.

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Excitation and charge transfer in low-energy hydrogen atom collisions with neutral manganese and titanium

Grumer

Barklem

2020

A&A

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Data for inelastic processes due to hydrogen atom collisions with manganese and titanium are needed for accurate modeling of the corresponding spectra in late-type stars. Excitation and charge transfer in low-energy Mn+H and Ti+H collisions is studied theoretically using a method based on an asymptotic two-electron linear combination of atomic orbitals model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multi-channel Landau-Zener model to treat the dynamics. Extensive calculations of charge transfer (mutual neutralization, ion-pair production), excitation and de-excitation processes in the two collisional systems are carried out for all transitions between covalent states dissociating to energies below the first ionic limit, and the dominating ionic states. Rate coefficients are determined for temperatures in the range 1000 -20 000 K in steps of 1000 K. Like for earlier studies of other atomic species, charge transfer processes are found to lead to much larger rate coefficients than excitation processes.

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Excitation and charge transfer in low-energy hydrogen atom collisions with neutral carbon and nitrogen

Cited by 12 publications

References 47 publications

Carbon, oxygen, and iron abundances in disk and halo stars

Carbon, oxygen, and iron abundances in disk and halo stars

Carbon, oxygen, and iron abundances in disk and halo stars. Implications of 3D non-LTE spectral line formation

Excitation and charge transfer in low-energy hydrogen atom collisions with neutral manganese and titanium

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