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Radiative transfer
About: Radiative transfer is a research topic. Over the lifetime, 43287 publications have been published within this topic receiving 1176539 citations.
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TL;DR: In this article, the authors present an approach for constructing detailed atmospheric models and synthetic spectra for hot luminous stars, which takes into account the effects of NLTE and radiation driven winds properly.
Abstract: Spectral analysis of hot luminous stars requires adequate model atmospheres which take into account the effects of NLTE and radiation driven winds properly. Here we present significant improvements of our approach in constructing detailed atmospheric models and synthetic spectra for hot luminous stars. Moreover, as we regard our solution method in its present stage already as a standard procedure, we make our program package WM- basic available to the community (download is possible from the URL given below). The most important model improvements towards a realistic description of stationary wind models concern: (i) A sophisticated and consistent description of line blocking and blanketing. Our solution concept to this problem renders the line blocking influence on the ionizing fluxes emerging from the atmospheres of hot stars - mainly the spectral ranges of the EUV and the UV are affected - in identical quality as the synthetic high resolution spectra representing the observable region. In addition, the line blanketing effect is properly accounted for in the energy balance. (ii) The atomic data archive which has been improved and enhanced considerably, providing the basis for a detailed multilevel NLTE treatment of the metal ions (from C to Zn) and an adequate representation of line blocking and the radiative line acceleration. (iii) A revised inclusion of EUV and X-ray radiation produced by cooling zones which originate from the simu- lation of shock heated matter. This new tool not only provides an easy-to-use method for O-star diagnostics, whereby physical constraints on the properties of stellar winds, stellar parameters, and abundances can be obtained via a comparison of observed and synthetic spectra, but also allows the astrophysically important information about the ionizing fluxes of hot stars to be determined automatically. Results illustrating this are discussed by means of a basic model grid calculated for O-stars with solar metallicity. To further demonstrate the astrophysical potential of our new method, we first provide a detailed spectral diagnostic determination of the stellar parameters, the wind parameters, and the abundances by an exemplary application to one of our grid-stars, the O9.5Ia O-supergiant α Cam. Our abundance determinations of the light elements indicate that these deviate considerably from the solar values.
517 citations
TL;DR: In this article, the solar spectral absorption optical depth of atmospheric aerosols for specific case studies during several field programs (three cases have been reported previously; two are new results) was determined.
Abstract: We have determined the solar spectral absorption optical depth of atmospheric aerosols for specific case studies during several field programs (three cases have been reported previously; two are new results). We combined airborne measurements of the solar net radiant flux density and the aerosol optical depth with a detailed radiative transfer model for all but one of the cases. The field programs (SAFARI 2000, ACE Asia, PRIDE, TARFOX, INTEX-A) contained aerosols representing the major absorbing aerosol types: pollution, biomass burning, desert dust and mixtures. In all cases the spectral absorption optical depth decreases with wavelength and can be approximated with a power-law wavelength dependence (Absorption Angstrom Exponent or AAE). We compare our results with other recent spectral absorption measurements and attempt to briefly summarize the state of knowledge of aerosol absorption spectra in the atmosphere. We discuss the limitations in using the AAE for calculating the solar absorption. We also discuss the resulting spectral single scattering albedo for these cases.
516 citations
01 Jan 2002
TL;DR: In this paper, the authors provide a primer on radiative transfer: absorption and scattering opacity, Stokes parameters, Poincare sphere, and the Mueller matrix, as well as the principle of reciprocity for the bidirectional reflectance.
Abstract: Preface 1. Basic properties of radiation, atmospheres and oceans 2. Basic state variables 3. Interaction of radiation with matter 4. Formulation of radiative transfer problems 5. Approximate solutions of prototype problems 6. Accurate numerical solutions of prototype problems 7. Emission-dominated radiative processes 8. Radiative transfer in spectrally-complex media 9. Solar radiation driving photochemistry and photobiology 10. The role of radiation in climate Appendix 1. A primer on radiative transfer: absorption and scattering opacity Appendix 2. Stokes parameters, Poincare sphere, and the Mueller matrix Appendix 3. Nomenclature: glossary of symbols Appendix 4. Principle of reciprocity for the bidirectional reflectance Appendix 5. Isolation of the azimuth-dependence Appendix 6. The streaming term in spherical geometry Appendix 7. Reflectance and transmittance of the invariant intensity (I n2) Appendix 8. Scaling transformation for anisotropic scattering Appendix 9. Reciprocity, duality and effects of surface reflection Appendix 10. Removal of overflow problems in the intensity formulas.
515 citations
TL;DR: In this article, the bow-shock models of HH objects are used to predict the line ratios and line profiles expected from HH objects, and a simple analytic formula is presented that can be used to estimate the shock velocity and bow-shaking orientation from a single high-resolution observation of a low-excitation line.
Abstract: The bow-shock models of HH objects presently constructed from a collection of 43 radiative-planar-shock models are used to predict the line ratios and line profiles expected from HH objects. It is found that a radiating-bow-shock model formed around a 'bullet' of dense gas plowing into the ambient medium accounts for existing observations sufficiently well to constitute a unifying model. For particular bow-shock orientations, double-peaked profiles are predicted in spatially unresolved spectra. A simple analytic formula is presented that can be used to estimate the shock velocity and bow-shock orientation from a single high-resolution observation of a low-excitation line. 63 references.
514 citations
TL;DR: The CHIANTI database as mentioned in this paper provides a set of atomic data for the interpretation of astrophysical spectra emitted by collisionally dominated, high temperature, optically thin sources.
Abstract: Aims. The goal of the CHIANTI atomic database is to provide a set of atomic data for the interpretation of astrophysical spectra emitted by collisionally dominated, high temperature, optically thin sources. Methods. A complete set of ground level ionization and recombination rate coefficients has been assembled for all atoms and ions of the elements of H through Zn and inserted into the latest version of the CHIANTI database, CHIANTI 6. Ionization rate coefficients are taken from the recent work of Dere (2007, A&A, 466, 771) and recombination rates from a variety of sources in the literature. These new rate coefficients have allowed the calculation of a new set of ionization equilibria and radiative loss rate coefficients. For some ions, such as Fe viii and Fe ix, there are significant differences from previous calculations. In addition, existing atomic parameters have been revised and new atomic parameters inserted into the database. Results. For each ion in the CHIANTI database, elemental abundances, ionization potentials, atomic energy levels, radiative rates, electron and proton collisional rate coefficients, ionization and recombination rate coefficients, and collisional ionization equilibrium populations are provided. In addition, parameters for the calculation of the continuum due to bremsstrahlung, radiative recombination and two-photon decay are provided. A suite of programs written in the Interactive Data Language (IDL) are available to calculate line and continuum emissivities and other properties. All data and programs are freely available at http://wwwsolar.nrl.navy.mil/ chianti
513 citations