scispace - formally typeset
Search or ask a question
Topic

Radiative transfer

About: Radiative transfer is a research topic. Over the lifetime, 43287 publications have been published within this topic receiving 1176539 citations.


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the authors presented a new method which sidesteps the ill conditioning, guarantees convergence to the unique best least-squares fit, gives positive coefficients, and produces fits orders of magnitude more accurate than any which have so far been published.

275 citations

Journal ArticleDOI
TL;DR: In this paper, the authors studied the pulse profiles of the accreting X-ray millisecond pulsar SAX J1808.4-3658 at different energies.
Abstract: We study the pulse profiles of the accreting X-ray millisecond pulsar SAX J1808.4-3658 at different energies. The two main emission components, the blackbody and the Comptonized tail, which are clearly identified in the time-averaged spectrum, show strong variability with the first component lagging the second one. The observed variability can be explained if the emission is produced by Comptonization in a hot slab (radiative shock) of Thomson optical depth ∼0.3-1 at the neutron star surface. The blackbody radiation is strongly beamed along the normal to the slab (a 'knife'-like or 'pencil'-like emission pattern), while the Comptonized emission has a broader angular distribution peaking at about 50°-60° from the slab normal (a 'fan'-like pattern). We construct a detailed model of the X-ray production accounting for the Doppler boosting, relativistic aberration and gravitational light bending in the Schwarzschild space-time. We present also accurate analytical formulae for computations of the light curves from rapidly rotating neutron stars using the formalism recently developed by Beloborodov. Our model reproduces well the pulse profiles at different energies simultaneously, corresponding phase lags, as well as the time-averaged spectrum. We constrain the compact star mass to be bounded between 1.2 and 1.6 M O .. By fitting the observed profiles, we determine the radius of the compact object to be R ∼11 km if M = 1.6 M O ., while for M = 1.2 M O . the best-fitting radius is ∼6.5 km, indicating that the compact object in SAX J1808.4-3658 can be a strange star. We obtain a lower limit on the inclination of the system of 65°.

274 citations

Journal ArticleDOI
TL;DR: Three major changes allowed us to improve DART accuracy by a factor of three: more accurate simulation of single and multiple scattering, use of a scheme that oversamples DART cells and a better account of the direction of radiation that gives rise to multiple scattered radiation.
Abstract: DART (Discrete Anisotropic Radiative Transfer) is a radiative transfer model that simulates remotely acquired images. It was originally developed to work in the short wavelengths (0.3–3 µm) within 3D natural scenes that are represented as matrices of rectangular cells containing trees, shrubs, grass, soil, etc. DART was recently modified to extend its domain of application and to improve its accuracy. This paper summarizes the major features of DART and presents the changes that were implemented for improving its accuracy. Presently, this model works with natural and urban landscapes, on the whole optical domain (thermal infrared included) and with a multispectral approach that uses optical data bases from 0.3 µm up to 15 µm. It simulates radiative transfer in the whole ‘atmosphere–Earth’ system and it accounts for the instrumental transfer function. Three major changes allowed us to improve DART accuracy by a factor of three: more accurate simulation of single and multiple scattering, use of a scheme tha...

274 citations

Journal ArticleDOI
TL;DR: Using a significantly revised non-LTE radiative transfer code that allows for the effects of line blanketing by He, C, O, Si, and Fe, a detailed analysis of the Galactic Wolf-Rayet (W-R) star HD 165763 (WR 111, WC5) was performed in this article.
Abstract: Using a significantly revised non-LTE radiative transfer code that allows for the effects of line blanketing by He, C, O, Si, and Fe, we have performed a detailed analysis of the Galactic Wolf-Rayet (W-R) star HD 165763 (WR 111, WC5) Standard W-R models consistently overestimate the strength of the electron scattering wings, especially on strong lines, so we have considered models where the wind is both homogeneous and clumped The deduced stellar parameters for HD 165763 are as follows: The stellar parameters deduced for HD 165763 are significantly different from earlier analyses The deduced luminosity is a factor of 2 larger, and a smaller core radius is found The smaller radius is in better agreement with expectations from stellar evolution calculations Both of these changes can be attributed to the effects of line blanketing The deduced C/He abundance is similar to earlier calculations, and the O/He abundance had not previously been determined The observed iron spectrum, principally due to Fe V and Fe VI, is well reproduced using a solar iron mass fraction, although a variation of at least a factor of 2 about this value cannot be precluded In particular, the models naturally produce the Fe V emission feature centered on 1470 A and the complex Fe emission/absorption spectrum at shorter wavelengths Also, Fe strongly modifies the line strengths and profile shapes shortward of 1800 A and must be taken into account if we are to successfully model this region The reddening toward HD 165763 does not follow the mean Galactic extinction law We determine the reddening law toward HD 165763 by comparing our model continuum levels to observations In order to simultaneously match the UV, optical, and particularly the infrared fluxes, we used the parameterized reddening law of Cardelli, Clayton, and Mathis with EB-V = 03 and R = 45, where R = AV/EB-V Based on both observational and theoretical suggestions we have considered models in which the wind is still accelerating at large radii In particular, we discuss models in which the velocity law can be characterized by β = 1 for r < 10R* but that undergo a substantial velocity increase (~600 km s-1) beyond 10R* These models appear to give slightly better fits to the line profiles, but the improvements are small, and it is difficult to gauge whether observational data require such a velocity law We cannot yet determine whether the winds of W-R stars are driven by radiation pressure, because we neglect many higher levels of iron in our model ions, and we do not include important elements such as cobalt and nickel However, the wind problem in W-R stars is less severe than previously assumed if clumping occurs For our clumped model, the single scattering limit is only exceeded by a factor of 10 compared to 3 times this value for a homogeneous wind Clumping appears to be the key to explaining the apparent high mass-loss rates determined for W-R stars and is extremely important in understanding how or even whether W-R winds are driven by radiation pressure A reduction in W-R mass-loss rates has important implications for stellar evolution calculations

274 citations

Journal ArticleDOI
TL;DR: In this article, the size distributions of dust particles from Africa were measured using a variety of aerodynamic, optical, and geometric means, and compared with the literature, comparisons of these size distributions showed quite dissimilar results.
Abstract: [1] A multitude of sensitivity studies in the literature point to the importance of proper chemical and morphological characterization of particles when the radiative impacts of airborne dusts are modeled. However, the community data set is based on heterogeneous measurement methods relying on varying aerodynamic, chemical, morphological, and optical means. During the Puerto Rico Dust Experiment, size distributions of dust particles from Africa were measured using a variety of aerodynamic, optical, and geometric means. Consistent with the literature, comparisons of these size distributions showed quite dissimilar results. “Measured” volume median diameters varied from 2.5 to 9 μm for various geometric, aerodynamic, optical, and optical inversion methods. Aerodynamic systems showed mixed performance. Column integrated size distributions inverted from AERONET Sun/sky radiance data produced somewhat reasonable results in the coarse mode when given proper constraints and taken in the proper context. The largest systematic errors were found in optical particle counters due to insensitivities to particle size in the 4–10 μm region with further complications due to dust particle morphology and index of refraction issues. As these methods can produce quite dissimilar size distributions, considerable errors in calculated radiative properties can occur if incorrectly modeled into dust parameters. None of the methods compared in this study can adequately reproduce the measured mass extinction or mass scattering efficiency of the dust using spherical geometry methods. Given all of the uncertainties in the sizing methods, we promote the use of fundamental and quantifiable descriptors of particles such as mass as a function of aerodynamic diameter.

274 citations


Network Information
Related Topics (5)
Scattering
152.3K papers, 3M citations
85% related
Magnetic field
167.5K papers, 2.3M citations
84% related
Turbulence
112.1K papers, 2.7M citations
82% related
Dark matter
41.5K papers, 1.5M citations
82% related
Electron
111.1K papers, 2.1M citations
81% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,706
20223,291
20211,335
20201,335
20191,429
20181,409