Parameterization of IR cooling in a middle atmosphere. II Non-LTE radiative transfer and the globally averaged temperature of the mesosphere and lower thermosphere
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Apruzese, J. P.↗
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Departures from LTE Populations Versus Anomalous Abundances: the Effects of Heating
The deposit of nonradiative heat and momentum in the mantle of a hot star affects the interpretation of the stellar spectrum in two ways. First, a superheated and moving plasma should be considered when doing the analysis, and second, a model atom which is appropriate for the physical state of the line forming regions. Some examples are presented for H and He showing how the changes in the electron temperature affect the solution of the equations of statistical equilibrium. The observed spectra of the Wolf-Raynet stars HD 191765, HD 192103, and HD 192163 are compatible with a normal H/He abundance ratio.
Underhill, A. B.↗
Determination of electron density and temperature in non-LTE plasmas from spectral lines of impurity ions
A novel approach for calculating the populations of the excited Li-like ions C IV, N V, O VI, and Ne VIII is presented. The populations of the 2(2P), 3(2S), 3(2P), and 3(2D) electronic levels in these ions in optically thin plasmas with a broad range of electron density, N(e), and temperature, T(e), are determined from the collisional-radiative model by solving the system of rate equations for the production of excited ions; the equations are linear with respect to the excited ion populations, and the N(e) and T(e) are taken as independent variables. These populations are used to determine the ratios of line intensities for dipole allowed transitions between various energy levels. This approach can be applied to impurities other than the lithiumlike ions and is especially useful for diagnostics of systems where nonintrusive spectroscopic techniques must be used.
Kunc, Joseph A.↗
The solution of radiative transfer problems in molecular bands without the LTE assumption by accelerated lambda iteration methods
An iterative method based on the use of approximate transfer operators, which was designed initially to solve multilevel NLTE line formation problems in stellar atmospheres, is adapted and applied to the solution of the NLTE molecular band radiative transfer in planetary atmospheres. The matrices to be constructed and inverted are much smaller than those used in the traditional Curtis matrix technique, which makes possible the treatment of more realistic problems using relatively small computers. This technique converges much more rapidly than straightforward iteration between the transfer equation and the equations of statistical equilibrium. A test application of this new technique to the solution of NLTE radiative transfer problems for optically thick and thin bands (the 4.3 micron CO2 band in the Venusian atmosphere and the 4.7 and 2.3 micron CO bands in the earth's atmosphere) is described.
Kutepov, A. A.↗
Spherically symmetric, expanding, non-LTE model atmospheres for novae during their early stages
In the continuum and line-blanketed models presented here, nova atmospheres are characterized by a very slow decrease of density with increasing radius. This feature leads to very large geometrical extensions so that there are large temperature differences between the inner and outer parts of the line-forming regions. The theoretical spectra show a large IR excess and a small Balmer jump which may be either in absorption or in emission. For the parameters considered (effective temperature of about 10 exp 4 K, L = 2 x 10 exp 4 solar luminosities, outer boundary density of about 3 x 10 exp -15 g cm exp -3, mass-loss rate of 10 exp -5 solar masses/yr), most lines are in absorption. The effects of changes in the abundances of the heavy elements on the emergent spectra are discussed. The strong unidentified features observed in ultraviolet spectra of novae are found in actuality to be regions of transparency within the Fe 'forest'. Ultraviolet spectra obtained from the IUE archives are displayed, and spectral synthesis of these spectra is done using the theoretical atmospheres.
Hauschildt, P. H.↗
H2NEW: Hydrogen (H2) from Next-Generation Electrolyzers of Water LTE Task 9: Liquid Alkaline
This presentation summarizes H2NEW consortium research on liquid alkaline electrolysis (Task 9).
electrolysis↗
LTE Electrolyzer Data Collection
The goal for NREL is to collect, develop and publish performance metrics relative to low temperature electrolyzer installations. This will be done through the development of: Secure storage solution to house the collection of data from multiple projects Standardization of data to be collected and analyzed. This will be done using data templates developed with the help of partners involved with electrolyzer installations. Analysis that produces metrics of interest for all stakeholders Aggregation of results from multiple projects to view industry progress as a whole Publication of aggregated results in the form of composite data products (CDPs) Collaboration with Idaho National Lab and their work with high temperature electrolyzer installations will enable efficient use of storage and analysis tools.
data↗
Non-equilibrium ionized blast wave
The structure of a cylindrical blast wave with ionization at non-LTE conditions was calculated using equations previously developed by Wu and Fu (1970). The degree of ionization was predicted by a modified Saha equation. Temperature profiles show that the temperature at non-LTE conditions is lower than at LTE near the shock front. This corresponds to a higher degree of ionization for the non-LTE limit, which indicates that the neutral gas absorption is much more efficient at non-LTE than at the LTE limit. The decaying velocity under non-LTE is approximately 15% less than under LTE.
Wu, S. T.↗
Non-local thermodynamic equilibrium limb radiance from O3 and CO2 in the 9-11 micrometer spectral region
Satellite remote sensing of mesospheric and thermospheric O3 abundance in the terrestrial atmosphere often uses 9-11 micrometer thermal emission. In this paper, we apply a line-by-line non-local thermodynamic equilibrium (non-LTE) radiance model to this spectral region and investigate the conditions of LTE breakdown and the effect that this has on the limb radiance measured by an i.r. sounder. Monochromatic and band-integrated radiance calculations have been performed for limb view tangent heights between 55 and 105 km under daytime and nighttime conditions. Non-LTE emission from both O3 and CO2 are shown to be important with the divergence of radiance from LTE values and the diurnal variation being band dependent. We have shown that the contribution of the CO2 bands to the Limb Infrared Monitor of the Stratosphere O3 channel is significant for daytime conditions at tangent heights above about 60 km. A study has been made to choose O3 sounding channel spectral passbands for the High Resolution Dynamics Limb Sounder. High resolution calculations are required to determine those spectral intervals that will filter radiance from selected bands and characterize their non-LTE behavior. This will allow for improved O3 retrievals above 70 km and non-LTE studies.
Edwards, David P.↗
Rapid computation of spectrally integrated non-local thermodynamic equilibrium limb emission
The interpretation of infrared radiance measurements made by satellite-borne limb-scanning broadband radiometers requires accurate and computationally fast techniques with which to evaluate the equation of radiative transfer. This requirement is made even more stringent when analyzing measurements of non-local thermodynamic equilibrium (non-LTE) emission from the terrestrial mesosphere and lower thermosphere. In principle, line-by-line calculations which explicitly account for the departure from thermodynamic equilibrium in both the source functions and the transmittances are necessary. In this paper we extend the emissivity growth approximation (EGA) technique developed for local thermodynamic equilibrium (LTE) limb radiance for the molecular oxygen dayglow (1.27 micrometers and 762 nm), ozone and carbon dioxide in the 9- to 11-micrometer spectral interval, carbon monoxide (4.6 micrometers), nitric oxide (5.3 micrometers), and the carbon dioxide bands (15 micrometers) are presented. Using the non-LTE form of the EGA, the spectrally integrated limb emission is calculated for 35 tangent heights in the mesosphere and lower thermosphere (a total of 1200 atmospheric layers) with line-by-line accuracy in approximately 0.35 s of CPU time on readily available desktop computer hardware, while the corresponding line-by-line calculations may require several minutes. The non-LTE EGA technique will allow kinetic temperature and minor constituend retrieval algorithms to readily include non-LTE efects limited only by the a priori knowledge of the departure from LTE in the observed bands.
Mlynczak, Martin G.↗
Observations and theory of Mg II lines in early type stars. II - Theory and predicted profiles. III - The observations and a comparison with the predictions
Profiles of the UV Mg II lines in the spectra of early type stars are computed in a grid of model atmospheres with effective temperatures between 8000 and 35,000 K and log g values of 2.5 to 4.0 using the LTE and non-LTE theories of line formation. The theoretical results indicate that the line cores are strengthened by non-LTE effects over the entire temperature range, resonance-line wings are weaker in the cooler models than in the LTE case, and very large deviations from LTE occur in the hot low-gravity models. These predictions are compared with the equivalent widths of the UV Mg II lines in 106 stars and of the visual lines in 48 stars (spectral types O4 to A3). The observed equivalent widths of normal stars in luminosity classes II through V are found to agree with the predictions over the entire range from O8 to A2 if a certain Mg/H abundance is adopted. The line intensities observed in supergiants, Be, Bp, and Ap stars are discussed.
Snijders, M. A. J.↗
The effect of intermediate-scale motions on line formation
The problem of LTE and non-LTE line formation in the presence of nonthermal velocity fields with geometric scales between the microscopic and macroscopic limits is investigated in the cases of periodic sinusoidal and sawtooth waves. For a fixed source function (the LTE case), it is shown that time-averaged line profiles progress smoothly from the microscopic to the macroscopic limits as the geometric scale of the motions increases, that the sinusoidal motions produce symmetric time-averaged profiles, and that the sawtooth motions cause a redshift. In several idealized non-LTE cases, it is found that intermediate-scale velocity fields can significantly increase the surface source functions and line-core intensities. Calculations are made for a two-level atom in an isothermal atmosphere for a range of velocity scales and non-LTE coupling parameters and also for a two-level atom and a four-level representation of Na I line formation in the Harvard-Smithsonian Reference Atmosphere (1971) solar model. It is found that intermediate-scale velocity fields in the solar atmosphere could explain the central intensities of the Na I D lines and other strong absorption lines without invoking previously suggested high electron densities.
Shine, R. A.↗
CH4 nonlocal thermodynamic equilibrium in the atmospheres of the giant planets
The present consideration of methane's vibrational relaxation in the Giant Planets' upper stratospheres employs a model for the thermalization of solar energy absorbed under non-LTE conditions, at the 1.7, 2.3. and 3.3 micron-centered CH4 band groups. On this basis, a range of model atmospheres was produced, reflecting current uncertainties concerning CH4 collisional excitation rates. At 0.1 mbar, all of the non-LTE models are within 2 K of the LTE reference models; the extreme non-LTE models steadily depart from reference LTE ones, however, and reach about + or - 20 K at 0,1 mbar.
Appleby, John F.↗
A non-local thermodynamic equilibrium, line-blanketed synthetic spectrum of Iota Herculis - C, Al, and Si lines
A non-LTE line-blanketed model stellar atmosphere is used to compute a model of I Herculis (B3 IV) with a Teff of 17,500 K and a log g of 3.75, following the conclusions of Peters and Polidan (1985). Detailed profiles of a number of lines of C, Al, and Si in the 1200-2000-A region are computed, including the resonance lines of C II, Al II, and Al III. These profiles are compared to observations obtained from the coaddition of eight IUE SWP images, using a technique developed by Leckrone and Adelman (1989). Comparison of carbon lines with a model that is underabundant in carbon by a factor of 2 relative to the sun indicates that the C abundance of Iota Her is at most one-half solar. Non-LTE effects are examined by comparing an LTE model possessing identical atmospheric parameters with the non-LTE model. Substantial differences in the populations of the model atomic states are found, but differences in the temperature structure of the two models often mask the non-LTE effects in the synthetic spectra.
Grigsby, James A.↗
Mesospheric H2O Concentrations Retrieved from SABER/TIMED Measurements
The SABER instrument on board the TIMED Satellite is a limb scanning infrared radiometer designed to measure temperature and minor constituent vertical profiles and energetics parameters in the mesosphere and lower thermosphere (MLT). The H2O concentrations are retrieved from 6.3 micron band radiances. The populations of H2O(v2) vibrational levels are in non-Local Thermodynamic Equilibrium (non-LTE) above approximately 55 km altitude and the interpretation of 6.3 micron radiance requires utilizing non-LTE H2O model that includes various energy exchange processes in the system of H2O vibrational levels coupled with O2, N2, and CO2 vibrational levels. We incorporated these processes including kinetics of O2/O3 photolysis products to our research non-LTE H2O model and applied it for the development and optimization of SABER operational model. The latter has been validated using simultaneous SCISAT1/ACE occultation measurements. This helped us to estimate CO2(020)-O2(X,v=I), O2(X,v=I)- H2O(010), and O2(X,v=1) O rates at mesopause temperatures that is critical for an adequate interpretation of non-LTE H2O radiances in the MLT. The first distributions of seasonal and meridional H2O concentrations retrieved from SABER 6.3 micron radiances applying an updated non-LTE H2O model are demonstrated and discussed.
Feofilov, A. G.↗
Consistent transport coefficients in astrophysics
A consistent theory for dealing with transport phenomena in stellar atmospheres starting with the kinetic equations and introducing three cases (LTE, partial LTE, and non-LTE) was developed. The consistent hydrodynamical equations were presented for partial-LTE, the transport coefficients defined, and a method shown to calculate them. The method is based on the numerical solution of kinetic equations considering Landau, Boltzmann, and Focker-Planck collision terms. Finally a set of results for the transport coefficients derived for a partially ionized hydrogen gas with radiation was shown, considering ionization and recombination as well as elastic collisions. The results obtained imply major changes is some types of theoretical model calculations and can resolve some important current problems concerning energy and mass balance in the solar atmosphere. It is shown that energy balance in the lower solar transition region can be fully explained by means of radiation losses and conductive flux.
Fontenla, Juan M.↗
Analysis of C II resonance lines in some main sequence early-type stars
IUE data are used to investigate C II resonance lines at 1335 A in eight main-sequence stars of spectral types from A0 to B3, and both LTE and non-LTE line profiles have been computed. In stars with low rotational velocities (such as Vega, Pi Cet, and Tau Her), logarithmic carbon abundances log N(C/H) of -3.55 to -3.45 are obtained for the non-LTE case. The LTE analysis reveals lower carbon abundances by about 0.1 dex. Significant differences among the fast rotating stars are pointed out.
Cugier, H.↗
Theoretical H II region models - The effects of stellar atmosphere models
Several grids of theoretical H II region models are computed by photoionization modeling in order to determine the extent to which the choice of the ionizing stellar atmosphere model affects the calibration of emission-line diagnostic diagrams of Evans and Dopita (1985) and the semiempirical H II region abundance sequence calibration of Evans and Dopita. Emission-line diagnostic diagrams are presented and compared for model nebulae ionized by Hummer and Mihalas (1970) unblanketed LTE atmospheres, Kurucz (1979) line-blanketed LTE atmospheres, Mihalas (1972) unblanketed non-LTE, and a truncated blackbody spectrum. The models demonstrate that for solar nebular and atmospheric abundances, there are only minor differences between H II models ionized by the Hummer and Mihalas atmospheres. The unblanketed non-LTE stellar atmosphere models of Mihalas and truncated blackbody spectra are shown to be unsuitable for general H II region modelling.
Evans, I. N.↗