Aims. Rate coefficients for inelastic Al + H and Al+ + H− collisions are calculated for all transitions between the seven low-lying levels up to and including the ionic state, namely ...Al(3p,4s,3d,4p,5s,nd)+H(1s) and Al+ + H−. The data are needed for non-LTE applications in stellar atmospheres and are presented for a temperature range of 1000–10 000 K. Methods. The calculations were obtained by means of the recently proposed model approach based on the asymptotic method for electronic molecular structure determination and on the branching probability current method for the nonadiabatic nuclear dynamics. Results. It is shown that the processes with the highest rates are the excitation and de-excitation ones between the Al(3d), Al(4p) and Al(4s) states in collisions with H, as well as the ion-pair formation and the mutual neutralization processes between these states and the ionic state.
Manganese (Mn) is a key Fe-group element, commonly employed in stellar population and nucleosynthesis studies to explore the role of SN Ia. We have developed a new non-local thermodynamic equilibrium ...(NLTE) model of Mn, including new photo-ionisation cross-sections and new transition rates caused by collisions with H and H
−
atoms. We applied the model in combination with one-dimensional (1D) LTE model atmospheres and 3D hydrodynamical simulations of stellar convection to quantify the impact of NLTE and convection on the line formation. We show that the effects of NLTE are present in Mn I and, to a lesser degree, in Mn II lines, and these increase with metallicity and with the effective temperature of a model. Employing 3D NLTE radiative transfer, we derive a new abundance of Mn in the Sun,
A
(Mn) = 5.52 ± 0.03 dex, consistent with the element abundance in C I meteorites. We also applied our methods to the analysis of three metal-poor benchmark stars. We find that 3D NLTE abundances are significantly higher than 1D LTE. For dwarfs, the differences between 1D NLTE and 3D NLTE abundances are typically within 0.15 dex, however, the effects are much larger in the atmospheres of giants owing to their more vigorous convection. We show that 3D NLTE successfully solves the ionisation and excitation balance for the RGB star HD 122563 that cannot be achieved by 1D LTE or 1D NLTE modelling. For HD 84937 and HD 140283, the ionisation balance is satisfied, however, the resonance Mn I triplet lines still show somewhat lower abundances compared to the high-excitation lines. Our results for the benchmark stars confirm that 1D LTE modelling leads to significant systematic biases in Mn abundances across the full wavelength range from the blue to the IR. We also produce a list of Mn lines that are not significantly biased by 3D and can be reliably, within the 0.1 dex uncertainty, modelled in 1D NLTE.
Solar oxygen abundance Bergemann, Maria; Hoppe, Richard; Semenova, Ekaterina ...
Monthly notices of the Royal Astronomical Society,
12/2021, Letnik:
508, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Motivated by the controversy over the surface metallicity of the Sun, we present a re-analysis of the solar photospheric oxygen (O) abundance. New atomic models of O and Ni are used to ...perform non-local thermodynamic equilibrium (NLTE) calculations with 1D hydrostatic (MARCS) and 3D hydrodynamical (Stagger and Bifrost) models. The Bifrost 3D MHD simulations are used to quantify the influence of the chromosphere. We compare the 3D NLTE line profiles with new high-resolution, R$\approx 700\, 000$, spatially resolved spectra of the Sun obtained using the IAG FTS instrument. We find that the O i lines at 777 nm yield the abundance of log A(O) = 8.74 ± 0.03 dex, which depends on the choice of the H-impact collisional data and oscillator strengths. The forbidden O i line at 630 nm is less model dependent, as it forms nearly in LTE and is only weakly sensitive to convection. However, the oscillator strength for this transition is more uncertain than for the 777 nm lines. Modelled in 3D NLTE with the Ni i blend, the 630 nm line yields an abundance of log A(O) = 8.77 ± 0.05 dex. We compare our results with previous estimates in the literature and draw a conclusion on the most likely value of the solar photospheric O abundance, which we estimate at log A(O) = 8.75 ± 0.03 dex.
The nonadiabatic nuclear dynamics for the 17 low-lying molecular states of the collisional system is studied by the probabilistic version of the hopping probability current method based on the ...accurate ab initio adiabatic potentials. Inelastic Ca+ + H, Ca + H+, and Ca2+ + H− collisions are treated, and partial cross sections and rate coefficients for all transitions between the considered scattering channels are calculated for excitation, de-excitation, charge exchange, ion-pair formation, and neutralization processes. The cross sections and the rate coefficients for the 272 partial inelastic processes are computed. It is found that the reaction mechanism for the partial processes with high-valued rates is due to the long-range ionic-covalent interaction, while for some processes with moderate-valued rates it is due to short-range nonadiabatic regions. It is shown that the largest rate coefficients correspond to the neutralization and also charge exchange processes from the optimal window. The largest rate coefficient exceeds the value . It is also found that some two-electron-transition charge exchange processes have rate coefficients as large as one-electron-transition processes. The processes with large and moderate values of rate coefficients are likely to be important for stellar spectra modeling.
ABSTRACT
This paper reports the results of investigations of inelastic processes in B + H and B+ + H− collisions with accounting for the fine structure. The calculations of the cross-sections and ...rate coefficients for excitation, de-excitation, ion-pair formation, and mutual neutralization processes (240 in total) are performed by using the quantum asymptotic method, which is modified in this paper for accounting of the fine structure, and by the multichannel approach within the framework of the Born–Oppenheimer formalism. It is found that accounting for the fine structure may change the rate coefficients significantly, and the rates calculated with accounting for the fine structure cannot be obtained by a simple redistribution of the non-relativistic rates. The processes important for non-local thermodynamic equilibrium modelling of stellar atmospheres are designated.
Abstract
The cross sections and rate coefficients for inelastic processes in low-energy collisions of nickel atoms and positive ions with hydrogen atoms and negative ions are calculated for the ...collisional energy range 10
−4
–100 eV and for the temperature range 1000–10,000 K. 74 covalent and three ionic states correlated to 11 molecular symmetries are considered. 3380 partial inelastic processes are treated in total. The study of nickel–hydrogen collisions is performed by the quantum model methods within the Born–Oppenheimer formalism. The electronic structure of the collisional quasimolecule is calculated by the semiempirical asymptotic method for each considered molecular symmetry. For nuclear dynamic calculations the simplified method in combination with the Landau–Zener model is used. Nuclear dynamics within each considered symmetry is treated separately, and the total rate coefficients for each inelastic process have been summed over all symmetries. The largest values of the rate coefficients (exceeding 10
−8
cm
3
s
−1
) correspond to the mutual neutralization processes in collisions Ni
+
(3
d
9
2
D
) + H
−
(1
s
2
1
S
) (the ground ionic state being the initial state), as well as in Ni
+
(3
d
8
4
s
4,2
F
) + H
−
(1
s
2
1
S
) (the first excited and the second excited ionic states being the initial states) collisions. At the temperature of 6000 K, the rate coefficients with large magnitudes have the values from the ranges (1.35−5.87) × 10
−8
cm
3
s
−1
and (1.02−6.77) × 10
−8
cm
3
s
−1
, respectively. The calculated rate coefficients with large and moderate values are important for non–local thermodynamic equilibrium stellar atmosphere modeling.
The cross sections and the rate coefficients for mutual neutralization, ion-pair formation, excitation, and de-excitation processes in low-energy Li + H and Li+ + H− collisions are calculated for all ...transitions between the seven lowest-lying atomic lithium states and the ionic state for the collision energy range 0.01-100 eV and the temperature range 1000-10,000 K. The calculations are performed by the quantum probability current method based on the accurate adiabatic potentials. The present rate coefficients for the mutual neutralization processes are in perfect agreement with the available full quantum data. For the excitation and de-excitation processes, the present data are more accurate than the previous rates. The processes with large and moderate rates are singled out. Additional calculations made by the quantum multichannel approach show that the reaction mechanism of these processes is mainly based on the long-range ionic-covalent interaction. The processes with large and moderate rates are important for astrophysical applications.
Aims. Inelastic processes in low-energy Si + H and Si+ + H− collisions are treated for the states from the ground state up to the ionic state, in order to provide rate coefficients needed for non-LTE ...modeling of Si in cool stellar atmospheres. Methods. Electronic molecular structure is determined using a recently proposed model approach based on an asymptotic method in combination with available ab initio potentials. Nonadiabatic nuclear dynamics are treated by means of a combination of multichannel formulas and the branching-probability-current method, based on the Landau-Zener model for nonadiabatic transition probabilities. Results. Cross sections and rate coefficients for inelastic processes in Si + H and Si+ + H− collisions for all transitions between 26 low-lying states plus the ionic state are calculated. It is shown that the highest rate coefficient values correspond to the excitation, de-excitation, ion-pair formation, and mutual neutralization processes involving the Si(3p4p 3D), Si(3p3d 3F), Si(3p4p 1D), Si(3p3d 3P), Si(3p4p 1S), and the ionic Si+ + H− states. These processes are likely to be important in non-LTE modeling.
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