Non local-thermodynamical-equilibrium effects in the simulation of laser-produced plasmas

1998 ◽  
Vol 5 (5) ◽  
pp. 1919-1926 ◽  
Author(s):  
M. Klapisch ◽  
A. Bar-Shalom ◽  
J. Oreg ◽  
D. Colombant
Keyword(s):  
Thermodynamical Equilibrium ◽  
Non Local ◽  
Local Thermodynamical Equilibrium

scholarly journals A detailed study of lithium in 107 CHEPS dwarf stars

2018 ◽  
Vol 611 ◽  
pp. A27 ◽  
Author(s):  
Ya. V. Pavlenko ◽  
J. S. Jenkins ◽  
O. M. Ivanyuk ◽  
H. R. A. Jones ◽  
B. M. Kaminsky ◽  
...  
Keyword(s):  
Isotopic Ratio ◽  
Small Sample Size ◽  
Small Sample ◽  
Thermodynamical Equilibrium ◽  
Lithium Abundance ◽  
Dwarf Stars ◽  
Upper Limits ◽  
Resonance Doublet ◽  
Non Local ◽  
Local Thermodynamical Equilibrium

Context. We report results from lithium abundance determinations using high resolution spectral analysis of the 107 metal-rich stars from the Calan-Hertfordshire Extrasolar Planet Search programme. Aims. We aim to set out to understand the lithium distribution of the population of stars taken from this survey. Methods. The lithium abundance taking account of non-local thermodynamical equilibrium effects was determined from the fits to the Li I 6708 Å resonance doublet profiles in the observed spectra. Results. We find that a) fast rotators tend to have higher lithium abundances; b) log N(Li) is higher in more massive and hot stars; c) log N(Li) is higher in stars of lower log g; d) stars with the metallicities >0.25 dex do not show the lithium lines in their spectra; e) most of our planet hosts rotate slower; and f) a lower limit of lithium isotopic ratio is 7Li/6Li > 10 in the atmospheres of two stars with planets (SWP) and two non-SWP stars. Conclusions. Measurable lithium abundances were found in the atmospheres of 45 stars located at distances of 20−170 pc from the Sun, for the other 62 stars the upper limits of log N(Li) were computed. We found well defined dependences of lithium abundances on Teff, V sin i, and less pronounced for the log g. In case of V sin i we see two sequences of stars: with measurable lithium and with the upper limit of log N(Li). About 10% of our targets are known to host planets. Only two SWP have notable lithium abundances, so we found a lower proportion of stars with detectable Li among known planet hosts than among stars without planets. However, given the small sample size of our planet-host sample, our analysis does not show any statistically significant differences in the lithium abundance between SWP and stars without known planets.

Non-local thermodynamical equilibrium abundance analysis of singly ionized praseodymium for the Sun

2020 ◽  
Vol 496 (4) ◽  
pp. 5361-5371
Author(s):  
Abdelrazek M K Shaltout ◽  
Ali G A Abdelkawy ◽  
M M Beheary
Keyword(s):  
Spectral Lines ◽  
Oscillator Strengths ◽  
Atomic Data ◽  
Dimensional Model ◽  
Thermodynamical Equilibrium ◽  
Solar Abundance ◽  
One Dimensional ◽  
Microturbulent Velocity ◽  
Non Local ◽  
Local Thermodynamical Equilibrium

ABSTRACT Determinations of the solar abundance of praseodymium (Pr) depend critically on the local thermodynamical equilibrium (LTE) and non-local thermodynamical equilibrium (NLTE) techniques beyond the capabilities of a classical one-dimensional model atmosphere. Here, in this analysis, we adopt an atomic model atom of Pr consisting of 105 energy levels and 14 bound–bound transitions of singly ionized praseodymium (Pr ii) and the ground state of the Pr iii continuum limit. We briefly analyse the solar abundance of Pr taking the solar model atmospheres of Holweger & Müller (1974, Solar Physics, 39, 19) with the measured equivalent linewidths and invoking a microturbulent velocity treatment. We succeed in accurately selecting nearby clear sections of the spectrum for 14 spectral lines of Pr ii with the improved atomic data of high-quality oscillator strengths available from the laboratory measurements of several possible sources as well as accurate damping constants successfully determined from the literature. We find a Pr abundance revised to be downwards log ϵPr(NLTE) = 0.75 ± 0.09, which is in good agreement with the meteoritic value (log ϵPr = 0.76 ± 0.03). A comparison of the NLTE abundance corrections with the standard LTE analysis, log ϵPr(LTE) = 0.74 ± 0.08, reveals a positive correction of  +0.01 dex, estimated from the selected solar Pr ii lines. The Pr abundance value is clearly superior following the classical one-dimensional model atmospheres of Holweger & Müller, the absolute scales of gf-values, the microturbulent velocity and the adopted equivalent linewidths.

Collisional (de-)excitation of protonated cyanoacetylene (HC3NH+) by helium at low and moderate temperatures

2021 ◽  
Vol 503 (2) ◽  
pp. 2902-2912
Author(s):  
M Mogren Al Mogren ◽  
D Ben Abdallah ◽  
S Dhaif Allah Al Harbi ◽  
M S Al Salhi ◽  
M Hochlaf
Keyword(s):  
Cross Sections ◽  
Quantum Scattering ◽  
Thermodynamical Equilibrium ◽  
Close Coupling ◽  
Molecular Chemistry ◽  
Excitation Cross Sections ◽  
Non Local ◽  
Total Energies ◽  
Highly Correlated ◽  
Local Thermodynamical Equilibrium

ABSTRACT Protonated cyanoacetylene, HC3NH+, is detected in astrophysical media, where it plays a key role as an intermediate in the chemistries of HCN/HNC and of cyanopolyynes. We first generated a potential energy surface (PES) describing the intermonomer interaction between HC3NH+ and He in Jacobi coordinates using the highly correlated CCSD(T)-F12/aug-cc-pVTZ ab initio methodology. Then, scattering calculations based on an exact close-coupling quantum-scattering technique were done to obtain pure rotational cross-sections for the rotational (de-)excitation of HC3NH+ after collision with He for total energies up to 2500 cm−1. These cross-sections are used to deduce the collision rates in the 5–350 K temperature range for the low-lying rotational levels of HC3NH+ (up to $j\,\, = \,\,15$). In addition, we generated an average PES for the HC3NH+–H2 system. The preliminary results show that the H2($j_{\mathrm{H_2}} = 0$) and He state-to-state de-excitation cross-sections have similar magnitudes, even though the H2 cross-sections are larger by a factor of 2–2.5. This work should help with the accurate derivation of protonated cyanoacetylene abundances in non-local thermodynamical equilibrium astrophysical media. These will put more constraints on the chemical pathways involving the formation and destruction of HC3NH+ while going back to the cyanopolyyne family and more generally those parts of nitrogen-containing molecular chemistry.

scholarly journals Possibility of chromospheric back-radiation influencing the lithium line formation in Spite plateau stars

2019 ◽  
Vol 622 ◽  
pp. A107 ◽  
Author(s):  
Y. Takeda
Keyword(s):  
Uv Radiation ◽  
Incident Radiation ◽  
Surface Boundary ◽  
Thermodynamical Equilibrium ◽  
Surface Boundary Condition ◽  
Non Local ◽  
Standard Cosmological Model ◽  
Equilibrium Calculations ◽  
Abundance Determination ◽  
Local Thermodynamical Equilibrium

Context. Spectroscopically determined lithium abundances of metal-poor turn-off dwarfs are known to be nearly constant (Spite plateau), but manifestly lower than the primordial value expected from the standard cosmological model. However, abundance determination by using conventional model atmospheres may not necessarily be correct since the existence of high-temperature chromosphere even in very old stars has been confirmed. Aims. The aim of this study is to examine how the extra UV flux possibly irradiated from the chromosphere could affect the formation of the Li I 6708 line, and whether or not its influence might lead to a solution of the Li abundance discrepancy. Methods. A simple model chromosphere of a uniform thin gray slab emitting only thermal radiation is assumed, characterized by optical thickness and temperature. By taking into account this incident radiation in the surface boundary condition, non-local thermodynamical equilibrium calculations for neutral Li atoms are carried out in order to see how the equivalent widths and the resulting abundances are affected by these parameters. Results. If the parameters are appropriately chosen, the strength of the Li I 6708 line can be reduced by a factor of ~2–3 due to overionization caused by enhanced UV radiation, leading to an apparent lowering of the abundance by ~0.3–0.5 dex, which is consistent with the discrepancy in question. Moreover, the observed slight metallicity-dependent trend of the plateau can also be reproduced as a result of the change in atmospheric transparency. Conclusions. Superficial underestimation of Li abundances due to considerable overionization caused by chromospheric radiation may be regarded as a ponderable interpretation for the cosmological Li problem. The touchstone to verify this model would be to check the existence of significantly enhanced UV radiation in these Spite plateau stars, which should be detected if this scenario is valid, although very few such UV spectrophotometric observations have been done to date.

scholarly journals New insights on Be shell stars from modelling their Hα emission profiles

2014 ◽  
Vol 9 (S307) ◽  
pp. 457-458
Author(s):  
J. Silaj ◽  
C. E. Jones ◽  
T. A. A. Sigut ◽  
C. Tycner
Keyword(s):  
High Resolution ◽  
Radiative Transfer ◽  
Rotation Axis ◽  
Spectral Synthesis ◽  
Be Stars ◽  
Thermodynamical Equilibrium ◽  
Inclination Angles ◽  
Hα Emission ◽  
Non Local ◽  
Local Thermodynamical Equilibrium

AbstractBe shell stars are believed to be ordinary Be stars seen edge-on, which makes them particularly desirable objects for study since the uncertainty in the inclination of the rotation axis is largely eliminated. We have recently modelled high resolution Hα spectroscopic observations for eight Be shell stars, using the non-local thermodynamical equilibrium radiative transfer codeBedisk(Sigut & Jones 2007) and the new spectral synthesis packageBeray(Sigut 2011). Generally, we confirm that these systems are oriented at high inclination angles, although we find that they are not necessarily as close to edge-on as initially expected.

Ammonia in C-rich stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 396-397
Author(s):  
Bartosz Etmański ◽  
Mirosław R. Schmidt ◽  
Bosco H. K. Yung ◽  
Ryszard Szczerba
Keyword(s):  
Quantitative Estimation ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Thermodynamical Equilibrium ◽  
Evolved Stars ◽  
Red Supergiants ◽  
Non Local ◽  
Radiative Transfer Modeling ◽  
Local Thermodynamical Equilibrium

AbstractHIFI instrument onboard the Herschel satellite provided an unprecedented number of detections of rotational transitions of ammonia in circumstellar envelopes of evolved stars including massive red supergiants, Asymptotic Giant Branch (AGB), and post-AGB stars. The chemistry of ammonia formation in the circumstellar envelopes of evolved stars is poorly understood. The mechanisms proposed for its formation are processes behind the shock front, photochemistry in the inner part of the clumpy envelope, and formation on dust grains. We present results of the non-local thermodynamical equilibrium (non-LTE) radiative transfer modeling of ammonia transitions, mainly of the ground-state rotational one NH3 JK = 10 – 00 at 572.5 GHz, in selected AGB stars, aiming at the quantitative estimation of the NH3 abundance. The model of ammonia includes IR radiative pumping via v2 = 1 vibrational band at 10 μm.

scholarly journals Effect of the 3D distribution on water observations made with the SWI

2020 ◽  
Vol 637 ◽  
pp. A90
Author(s):  
E. S. Wirström ◽  
P. Bjerkeli ◽  
L. Rezac ◽  
C. Brinch ◽  
P. Hartogh
Keyword(s):  
Radiative Transfer ◽  
Spectral Lines ◽  
Characteristic Line ◽  
Transfer Model ◽  
Asymmetric Distribution ◽  
Thermodynamical Equilibrium ◽  
Icy Moons ◽  
Non Local ◽  
Phase Angles ◽  
Local Thermodynamical Equilibrium

Context. Characterising and understanding the atmospheres of Jovian icy moons is one of the key exploration goals of the Submillimetre Wave Instrument (SWI), which is to be flown on ESA’s Jupiter Icy Moons Explorer (JUICE) mission. Aims. The aim of this paper is to investigate how and under which conditions a 3D asymmetric distribution of the atmosphere may affect the SWI observations. In this work we target the role of phase angle for both nadir and limb geometries for unresolved and partially resolved disc observations from large distances. Methods. We adapted the LIME software package, a 3D non-local thermodynamical equilibrium radiative transfer model, to evaluate ortho-H2O populations and synthesise the simulated SWI beam spectra for different study cases of Ganymede’s atmosphere. The temperature and density vertical distributions were adopted from a previous work. The study cases presented here were selected according to the distance and operational scenarios of moon monitoring anticipated for SWI during the Jupiter phase of the JUICE mission. Results. We demonstrate that nadir and limb observations at different phase angles will modify the line amplitude and width. Unresolved observations where both absorption against surface continuum and limb emission contributes within the beam will lead to characteristic line wing emission, which may also appear in pure nadir geometry for specific phase angles. We also find that for Ganymede, the 3D non-local thermodynamical equilibrium populations are more highly excited in the upper atmosphere near the sub-solar region than they are in 1D spherically symmetric models. Finally, the 3D radiative transfer is better suited to properly simulate spectral lines for cases where density or population gradients exist along the line of sight.

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