Absorption Coefficients and Hydrogen Line Intensities.⋆

Menzel, Donald H.; Pekeris, C. L.

doi:10.1093/mnras/96.3.268

Cited by 85 publications

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“…We have also shifted the cross-sections to the ob- served edge energies of Cr i states from the NIST 2 database, because the latter are more accurate than the calculated LS term energies from Nahar (2009). Photoionization from the other Cr i and Cr ii states is computed with a formula of Kramer (Menzel & Pekeris 1935) corrected for the ion charge (Rutten 2003) and using the effective hydrogen-like principle quantum number n * . The use of effective quantum number increases the cross-sections at the ionization edge for low-lying levels and reduces them for some levels of high excitation that is more realistic than the original hydrogenic approximation.…”

Section: Statistical Equilibrium Calculationsmentioning

confidence: 99%

Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy

Bergemann¹

2011

Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI)

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Aims. We investigate statistical equilibrium of Cr in the atmospheres of late-type stars to show whether the systematic abundance discrepancy between Cr I and Cr II lines, as often encountered in the literature, is due to deviations from LTE. Furthermore, we attempt to interpret the NLTE trend of [Cr/Fe] with [Fe/H] using chemical evolution models for the solar neighborhood. Methods. NLTE calculations are performed for the model of Cr atom, comprising 340 levels and 6806 transitions in total. We make use of the quantum-mechanical photoionization cross-sections of Nahar (2009) and investigate sensitivity of the model to uncertain cross-sections for H I collisions. NLTE line formation is performed for the MAFAGS-ODF model atmospheres of the Sun and 10 metal-poor stars with −3.2 < [Fe/H] < −0.5, and abundances of Cr are derived by comparison of the synthetic and observed flux spectra. Results. We achieve good ionization equilibrium of Cr for the models with different stellar parameters, if inelastic collisions with H I atoms are neglected. The solar NLTE abundance based on Cr I lines is 5.74 dex with σ = 0.05 dex; it is ∼ 0.1 higher than the LTE abundance. For the metal-poor stars, the NLTE abundance corrections to Cr I lines range from +0.3 to +0.5 dex. The resulting [Cr/Fe] ratio is roughly solar for the range of metallicities analyzed here, which is consistent with current views on production of these iron peak elements in supernovae. Conclusions. The tendency of Cr to become deficient with respect to Fe in metal-poor stars is an artifact due to neglect of NLTE effects in the line formation of Cr i, and it has no relation to peculiar physical conditions in the Galactic ISM or deficiencies of nucleosynthesis theory.

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Section: Statistical Equilibrium Calculationsmentioning

confidence: 99%

Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy

Bergemann¹

2011

Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI)

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“…Instead, a simpler formula was used and is based on the assumption that each perturbation energy level is far away from the line being analyzed [22]. Under this assumption, the full width at half maximum due to stark broadening can be expressed as, …”

Section: Line Emission (Bound-bound Transitions)mentioning

confidence: 99%

Radiative cooling of laser ablated vapor plumes: Experimental and theoretical analyses

Wen

Mao

Greif

et al. 2006

Journal of Applied Physics

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A study was made of the cooling of the laser induced vapor plume in background air.The temperature and size variations of the vapor plume were determined from spectroscopic measurements during the first few tens of micro-seconds after the laser pulse. Experiments were carried out over a range of laser spot sizes and energies ------------------------------------------------------------------------------------------- Keywords Laser ablation, plasma cooling, thermal radiation decrease of the vapor plume was independent of the plume size, shape, and position. For 1 larger optical thicknesses of the vapor plume, the calculations showed that the reflectivity of the sample surface and the size of the vapor plume would dramatically affect cooling of the vapor plume.2

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“…are n1/2 Rn 1)n -t Extensive tables of the exact hydrogen cross sections have been given by Burgess (1964) A formula for gff given by Menzel and Pekeris (1935), Eq. (3.2-221), has frequently been .sed in opacity calculations (e.g., Mayer, 1948;Moszkowski and Meyerott, 1951 Moszkowski and Meyerott, 1951.…”

Section: F Nlmentioning

confidence: 99%

“…This can be done by such techniques as approximating the sum over discrete states by integrals, by using the Saha equation (perhaps restricted to two states of ionization) to evaluate the occupation numbers, and noting the close relation between the expressions for the bound-free and free-free cross sections. Menzel and Pekeris (1935) derive the approximate formula for the combination of bound-free and free-free absorption coefficients: Pappert and Penner, 1961;Penner and Thomas, 1964;Stewart and Pyatt, 1961;Bond, Watson, and Welch, 1965, Sec. 11-4.2;Unsold, 1955, Sec.…”

Section: '(V)mentioning

confidence: 99%

“…The next important development was the paper of Menzel and Pekeris (1935) which provided a very extensive analysis of hydrogenic matrix element formulae with tables of numerical values to correct the Kramers' semiclassical approximation. In addition, they discussed, analyzed, and made improvements to previous approximate formulae for the spectral and mean absorption coefPcients.…”

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confidence: 99%

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Thermal Radiation Phenomena. Volume Ii. The Equilibrium Radiative Properties of Air - Theory

Armstrong¹,

Nicholls²

1967

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INTRODUCTIONThis volume is one of a set which is concerned with all aspects of thermal radiation phenomena in heated air, over a wide range of temperature and density. Thermal radiation phenomena are meant to be those which arise due to or are related to, the passage of electromagnetic energy through an atmosphere of some type when significant interaction occurs between the radiation stream and the atmosphere. It is usually implied that some type of partial thermal equilibrium is produced by this interaction, although not a complete one, of course. In the case of complete thermal equilibrium, there can be only an uninteresting homogeneous system with no net transport of radiation at all. Radiation is a significant mode of energy transfer in all gases at sufficiently high temperatures, and in many situations at low temperatures as well. Since radiative energy transfer is controlled by the absorption coefficient which is, in turn determined by the microscopic atomic and molecular, and the statistical/thermodynamic properties of the medium, much of these volumes are concerned with these underlying properties. In particular, after a brief introduction to the theory of radiative transfer limited to conditions of local thermodynamic equilibrium, the present volume is mainly concerned with the detailed application of the basic quantum theory of radiation to real atomic and molecular systems. The transfer problem only reappears occasionally to guide this application into the practical channels which constitute the raison d'etre of the book.Although radiation transport is now of wide interdisciplinary application, most of its basic developments were made in an astrophysical milieu. Some of its contemporary applications are in stellar, solar and planetary atmospheres and aeronomy, in meteor, missile and rocket re-entry phenomena, in F combustion physics and chemistry, and in plasma and weapons physics.Towards very high temperatures there are fewer contributing effects and therefore the situation is conceptually somewhat simpler. Fig. 1.1 illustrates some significant subdivisions and interrelations towards the high-temperature limit of our considerations. As one progresses downwards in temperature, the effects and interactions proliferate and become, at our present state of knowledge, more fragmented and diverse, so that we will not attempt an illustration in this case,A large fraction of the work dating from World War II on specific problems in the above fields of application has been motivated by defense needs and financed by government contracts. As a result, much of the literature on the subject is comprised of unpublished and therefore unrefereed contract reports which are not universally available to the scientific community. Much of the work described in this "grey" literature (Goody, 1964) is important, but some obscurities and errors in an already complex field have propagated through these reports. Other problems due to the particular history of this field have also occurred. For example, a perusal of the reports...

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Absorption Coefficients and Hydrogen Line Intensities.⋆

Cited by 85 publications

References 0 publications

Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy

Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy

Radiative cooling of laser ablated vapor plumes: Experimental and theoretical analyses

Thermal Radiation Phenomena. Volume Ii. The Equilibrium Radiative Properties of Air - Theory

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