scholarly journals The Opacity Project and the Iron Project

1996 ◽  
Vol 152 ◽  
pp. 569-576
Author(s):  
Anil K. Pradhan
Keyword(s):  
Recent Work ◽  
Thermodynamic Equilibrium ◽  
Large Scale ◽  
Local Thermodynamic Equilibrium ◽  
Atomic Data ◽  
Data Sets ◽  
Iron Ions ◽  
Theoretical Methods ◽  
Work Related ◽  
Ionization Balance

Systematic and large-scale calculation of accurate plasma opacities and atomic data by the Opacity Project and the Iron Project has applications in many areas of astrophysics. Analysis of EUVE observations using monochromatic opacities of elements calculated by the Opacity Project is described. Theoretical methods and atomic calculations are discussed briefly. Recent work related to ionization balance, photoionization and recombination, and the modeling of plasmas in local thermodynamic equilibrium (LTE) and non-LTE are discussed. New calculations for the important iron ions, under the Iron Project, are also described and their relevance to the more extensive non-LTE calculations is pointed out. The comprehensive radiative and collisional data sets from the Opacity and the Iron Projects should be applicable to a large number of sources in the EUV and other wavelength regions.

scholarly journals Non-local thermodynamic equilibrium line formation for Si i–ii–iii in A–B stars and the origin of Si ii emission lines in ι Her

2020 ◽  
Vol 493 (4) ◽  
pp. 6095-6108 ◽  
Author(s):  
Lyudmila Mashonkina
Keyword(s):  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Emission Lines ◽  
Atomic Data ◽  
Line Formation ◽  
Atmospheric Parameters ◽  
B Stars ◽  
Non Local ◽  
Effective Temperatures ◽  
Model Atom

ABSTRACT A comprehensive model atom was developed for Si i–ii–iii using the most up-to-date atomic data available so far. Based on non-local thermodynamic equilibrium (NLTE) line formation for Si i, Si ii and Si iii and high-resolution observed spectra, we determined the NLTE abundances for a sample of nine unevolved A9–B3 type stars with well-determined atmospheric parameters. For each star, NLTE reduces the line-to-line scatter for Si ii substantially compared with the LTE case and leads to consistent mean abundances from lines of different ionization stages. In the hottest star of our sample, ι Her, Si ii is subject to overionization that drives emission in the lines arising from the high-excitation doublet levels. Our NLTE calculations reproduced 10 emission lines of Si ii observed in ι Her. The same overionization effect leads to greatly weakened Si ii lines, which are observed in absorption in ι Her. Large positive NLTE abundance corrections (up to 0.98 dex for 5055 Å) were useful for achieving consistent mean abundances from lines of the two ionization stages, Si ii and Si iii. It was found that NLTE effects are overestimated for the Si ii 6347, 6371 Å doublet in ι Her, while the new model atom works well for cooler stars. At this stage, we failed to understand this problem. We computed a grid of the NLTE abundance corrections for lines of Si i, Si ii and Si iii in model atmospheres with effective temperatures and surface gravities characteristic of unevolved A–B type stars.

scholarly journals Calculation of the ionization state for LTE plasmas using analytical potentials

1999 ◽  
Vol 17 (4) ◽  
pp. 635-647 ◽  
Author(s):  
J.G. RUBIANO ◽  
R. RODRÍGUEZ ◽  
J.M. GIL ◽  
P. MARTEL ◽  
E. MÍNGUEZ
Keyword(s):  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Atomic Data ◽  
Partition Functions ◽  
Ionization State ◽  
Saha Equation ◽  
Analytical Potential ◽  
Plasma Effects

In this work, the Saha equation is solved using atomic data provided by means of analytical potentials to calculate the ionization state and ion abundances for local thermodynamic equilibrium (LTE) plasmas of Al, Fe, and Au. The plasma effects are taking into account using an analytical potential which includes plasma effects. The problem of the cut off partition functions in the Saha equation is also analyzed using three different criteria. Finally, some opacity calculations are performed.

scholarly journals Summary of the Joint Discussion: Atomic Data of Importance for Ultraviolet and X-Ray Astronomy

1971 ◽  
Vol 2 ◽  
pp. 580-583
Author(s):  
A. G. Hearn
Keyword(s):  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Ground Level ◽  
Experimental Methods ◽  
Present Knowledge ◽  
Atomic Data ◽  
The Sun ◽  
X Ray ◽  
Lyman Continuum

AbstractThis Joint Discussion is in two parts. The first part is a description of recent observations which illustrate the need for atomic data and the second part is a description of what atomic data are available or could readily be produced by the latest theoretical and experimental methods. The purpose of this summary is to highlight the immediate requirements for atomic data of current observations which are not met by our present knowledge and thereby indicate where further work is necessary in providing atomic data.Although this is a discussion of atomic data the problems of assuming local thermodynamic equilibrium have inevitably been raised. The importance of considering whether departures from LTE are significant or not in the interpretation of observations is is clearly illustrated by the work of the Harvard group on the Lyman continuum emitted by the Sun which has shown a departure coefficient as large as 200 for the ground level of hydrogen.

Ionization Balance in Non-Local-Thermodynamic-Equilibrium Plasmas

2004 ◽  
Vol 21 (5) ◽  
pp. 877-880 ◽  
Author(s):  
Wu Ze-Qing ◽  
Pang Jin-Qiao ◽  
Han Guo-Xing ◽  
Yan Jun
Keyword(s):  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Non Local ◽  
Ionization Balance

scholarly journals Spectroscopic distances to late-type stars

2012 ◽  
Vol 8 (S289) ◽  
pp. 83-86
Author(s):  
Maria Bergemann ◽  
Aldo Serenelli ◽  
Gregory Ruchti
Keyword(s):  
Stellar Evolution ◽  
Large Scale ◽  
Local Thermodynamic Equilibrium ◽  
Systematic Errors ◽  
Spectroscopic Techniques ◽  
The Sun ◽  
Late Type ◽  
Non Local ◽  
Ionization Balance

AbstractA common approach to determining distances to stars without astrometric information is to compare stellar evolution models with parameters obtained from spectroscopic techniques. This method is routinely applied in the context of large-scale stellar surveys out to distances of several kpc. However, systematic errors may arise because of inaccurate spectroscopic parameters. We explore the effects of non-local thermodynamic equilibrium (NLTE) on the determination of surface gravities and metallicities for a large sample of metal-poor stars within approximately 10 kpc of the Sun. Using the improved Teff scale, we then show that stellar parameters estimated based on the widely used method of 1D LTE excitation-ionization balance of Fe results in distances which are systematically in error. For metal-poor giants, [Fe/H] ~ −2 dex, the distances can be overestimated by up to 70%. We compare the results with those from the Radial Velocity Experiment Survey catalogue (rave) for the stars in common, and find similar offsets.

Benchmark Measurements of the Ionization Balance of Non-Local-Thermodynamic-Equilibrium Gold Plasmas

2007 ◽  
Vol 99 (19) ◽  
Author(s):  
R. F. Heeter ◽  
S. B. Hansen ◽  
K. B. Fournier ◽  
M. E. Foord ◽  
D. H. Froula ◽  
...  
Keyword(s):  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Non Local ◽  
Ionization Balance

scholarly journals Review: progress in NLTE calculations and their application to large data-sets

2013 ◽  
Vol 9 (S298) ◽  
pp. 355-365 ◽  
Author(s):  
Lyudmila Mashonkina
Keyword(s):  
Large Scale ◽  
Chemical Elements ◽  
Large Data ◽  
3D Models ◽  
Atomic Data ◽  
Data Sets ◽  
Line Formation ◽  
Chemical Abundances ◽  
1D Model ◽  
Complex Term

AbstractOne of the major tasks in interpretation of data from large-scale stellar surveys is to determine the fundamental atmospheric parameters such as effective temperature, surface gravity, and metallicity. In most on-going and upcoming projects, they are derived spectroscopically, relying on classical one-dimensional (1D) model atmospheres and the assumption of LTE. This review discusses the present achievements and problems of non-local thermodynamic equilibrium (NLTE) line-formation calculations for FGK-type stars. The topics that are addressed include (i) the construction of comprehensive model atoms for the chemical elements with complex term system, (ii) possible systematic errors inherent in classical LTE spectroscopic determinations of stellar parameters and chemical abundances, (iii) the uncertainties in final NLTE results caused by the uncertainties in atomic data, and (iv) applications of the NLTE line-formation calculations coupled to the spatial and temporal average 〈3D〉 models to spectroscopic analyses.

Blackbody Radiation, Boltzmann Statistics, Temperature, and Thermodynamic Equilibrium

2017 ◽  
Author(s):  
Kelly Chance ◽  
Randall V. Martin
Keyword(s):  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Photophysical Properties ◽  
Blackbody Radiation ◽  
Boltzmann Constant ◽  
Noise Sources ◽  
Atmospheric Molecules ◽  
Tightly Coupled ◽  
Boltzmann Statistics ◽  
Planck’S Law

Blackbody radiation, temperature, and thermodynamic equilibrium give a tightly coupled description of systems (atmospheres, volumes, surfaces) that obey Boltzmann statistics. They provide descriptions of systems when Boltzmann statistics apply, either approximately or nearly exactly. These apply most of the time in the Earth’s stratosphere and troposphere, and in other planetary atmospheres as long as the density is sufficient that collisions among atmospheric molecules, rather than photochemical and photophysical properties, determine the energy populations of the ensemble of molecules. Thermodynamic equilibrium and the approximation of local thermodynamic equilibrium are introduced. Boltzmann statistics, blackbody radiation, and Planck’s law are described. The chapter introduces the Rayleigh-Jeans limit, description of noise sources as temperatures, Kirchoff’s law, the Stefan-Boltzmann constant, and Wien’s law.

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