scholarly journals SKIRT 9: Redesigning an advanced dust radiative transfer code to allow kinematics, line transfer and polarization by aligned dust grains

2020 ◽  
Vol 31 ◽  
pp. 100381 ◽  
Author(s):  
P. Camps ◽  
M. Baes
Keyword(s):  
Radiative Transfer ◽  
Dust Grains ◽  
Line Transfer

scholarly journals AGN polarization modeling with Stokes

2006 ◽  
Vol 2 (S238) ◽  
pp. 375-376 ◽  
Author(s):  
René W. Goosmann ◽  
C. Martin Gaskell ◽  
Masatoshi Shoji
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Dust Grains ◽  
Free Electrons ◽  
Wide Range ◽  
Polarization Spectra

AbstractWe introduce a new, publicly available Monte Carlo radiative transfer code, Stokes, which has been developed to model polarization induced by scattering of free electrons and dust grains. It can be used in a wide range of astrophysical applications. Here, we apply it to model the polarization produced by the equatorial obscuring and scattering tori assumed to exist in active galactic nuclei (AGNs). We present optical/UV modeling of dusty tori with a curved inner shape and for two different dust types. The polarization spectra enable us to clearly distinguish between the two dust compositions. The Stokes code and its documentation can be freely downloaded from http://www.stokes-program.info/.

Non-LTE Line Transfer with Diffusion of Excited Atoms

1977 ◽  
Vol 32 (2) ◽  
pp. 156-159
Author(s):  
D. F. Düchs ◽  
J. Oxenius
Keyword(s):  
Differential Equation ◽  
Low Temperature ◽  
Radiative Transfer ◽  
Spectral Line ◽  
Source Function ◽  
Homogeneous Medium ◽  
Classical Problem ◽  
Temperature Limit ◽  
Excited Atoms ◽  
Line Transfer

The classical problem of radiative transfer in a spectral line, due to two-level atoms, in a homogeneous medium is reconsidered. It is pointed out that the source function used up to now in the literature neglects the diffusion of the excited atoms. In many cases this assumption is not justified. In the low-temperature limit kT ≪ hv, the correct source function, allowing for diffusion of excited atoms, obeys an integro-differential equation

Non-LTE Line Transfer with Diffusion of Excited Atoms II

1978 ◽  
Vol 33 (2) ◽  
pp. 124-129
Author(s):  
D. F. Düchs ◽  
S. Rehker ◽  
J. Oxenius
Keyword(s):  
Radiative Transfer ◽  
Spectral Line ◽  
Numerical Results ◽  
Total Density ◽  
Doppler Broadening ◽  
External Radiation ◽  
Excited Atoms ◽  
Plane Parallel ◽  
Line Transfer

Non-LTE radiative transfer in a spectral line due to two-level atoms is studied taking the diffusion of excited atoms into account. Numerical results are presented for the case of a stationary, plane parallel plasma of constant total density and temperature without external radiation and without exchange of matter with the surroundings, assuming pure Doppler broadening of the spectral line.

scholarly journals Benchmarking the calculation of stochastic heating and emissivity of dust grains in the context of radiative transfer simulations

2015 ◽  
Vol 580 ◽  
pp. A87 ◽  
Author(s):  
Peter Camps ◽  
Karl Misselt ◽  
Simone Bianchi ◽  
Tuomas Lunttila ◽  
Christophe Pinte ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Dust Grains ◽  
Stochastic Heating

scholarly journals Polarimetric and radiative transfer modelling of HD 172555

2020 ◽  
Vol 499 (4) ◽  
pp. 5915-5931
Author(s):  
Jonathan P Marshall ◽  
Daniel V Cotton ◽  
Peter Scicluna ◽  
Jeremy Bailey ◽  
Lucyna Kedziora-Chudczer ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Near Infrared ◽  
Scattered Light ◽  
Position Angle ◽  
Polarization Measurement ◽  
Continuum Emission ◽  
Dust Grains ◽  
Spatially Resolved ◽  
Optical Aperture ◽  
Transfer Modelling

ABSTRACT The debris disc around HD 172555 was recently imaged in near-infrared polarized scattered light by the Very Large Telescope’s Spectro-Polarimetric High-contrast Exoplanet REsearch instrument. Here we present optical aperture polarization measurements of HD 172555 by the HIgh Precision Polarimetric Instrument (HIPPI), and its successor HIPPI-2 on the Anglo-Australian Telescope. We seek to refine constraints on the disc’s constituent dust grains by combining our polarimetric measurements with available infrared and millimetre photometry to model the scattered light and continuum emission from the disc. We model the disc using the 3D radiative transfer code hyperion, assuming the orientation and extent of the disc as obtained from the SPHERE observation. After correction for the interstellar medium contribution, our multiwavelength HIPPI/-2 observations (both magnitude and orientation) are consistent with the recent SPHERE polarization measurement with a fractional polarization p = 62.4  ±  5.2 ppm at 722.3 nm, and a position angle θ = 67°  ±  3°. The multiwavelength polarization can be adequately replicated by compact, spherical dust grains (i.e. from Mie theory) that are around 1.2 μm in size, assuming astronomical silicate composition, or 3.9 μm, assuming a composition derived from radiative transfer modelling of the disc. We were thus able to reproduce both the spatially resolved disc emission and polarization with a single grain composition model and size distribution.

scholarly journals AGB Stars and Their Circumstellar Envelopes. I. the VULCAN Code

Universe ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 80
Author(s):  
Sergio Cristallo ◽  
Luciano Piersanti ◽  
David Gobrecht ◽  
Lucio Crivellari ◽  
Ambra Nanni
Keyword(s):  
Radiative Transfer ◽  
Mass Loss ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Dust Grains ◽  
High Complexity ◽  
Circumstellar Envelopes ◽  
Perfect Gas ◽  
Physical Processes ◽  
Transfer Effects

The interplay between AGB interiors and their outermost layers, where molecules and dust form, is a problem of high complexity. As a consequence, physical processes like mass loss, which depend on the chemistry of the circumstellar envelope, are often oversimplified. The best candidates to drive mass-loss in AGB stars are dust grains, which trap the outgoing radiation and drag the surrounding gas. Grains build up, however, is far from being completely understood. Our aim is to model both the physics and the chemistry of the cool expanding layers around AGB stars in order to characterize the on-going chemistry, from atoms to dust grains. This has been our rationale to develop ab initio VULCAN, a FORTRAN hydro code able to follow the propagation of shocks in the circumstellar envelopes of AGB stars. The version presented in this paper adopts a perfect gas law and a very simplified treatment of the radiative transfer effects and dust nucleation. In this paper, we present preliminary results obtained with our code.

scholarly journals Revealing the dust grain size in the inner envelope of the Class I protostar Per-emb-50

2019 ◽  
Vol 623 ◽  
pp. A147 ◽  
Author(s):  
C. Agurto-Gangas ◽  
J. E. Pineda ◽  
L. Szűcs ◽  
L. Testi ◽  
M. Tazzari ◽  
...  
Keyword(s):  
Grain Size ◽  
Radiative Transfer ◽  
Grain Growth ◽  
Spectral Index ◽  
Dust Emission ◽  
Maximum Size ◽  
Interesting Case ◽  
Class I ◽  
Dust Grains ◽  
Inner Envelope

Context. A good constraint of when the growth of dust grains from sub-micrometer to millimeter sizes occurs, is crucial for planet formation models. This provides the first step towards the production of pebbles and planetesimals in protoplanetary disks. Currently, it is well established that Class II objects have large dust grains. However, it is not clear when in the star formation process this grain growth occurs. Aims. We use multi-wavelength millimeter observations of a Class I protostar to obtain the spectral index of the observed flux densities αmm of the unresolved disk and the surrounding envelope. Our goal is to compare our observational results with visibility modeling at both, 1.3 and 2.7 mm simultaneously. Methods. We present data from NOEMA at 2.7 mm and SMA at 1.3 mm of the Class I protostar, Per-emb-50. We model the dust emission with a variety of parametric and radiative-transfer models to deduce the grain size from the observed emission spectral index. Results. We find a spectral index in the envelope of Per-emb-50 of αenv = 3.3 ± 0.3, similar to the typical ISM values. The radiative-transfer modeling of the source confirms this value of αenv with the presence of dust with a amax ≤ 100 μm. Additionally, we explore the backwarming effect, where we find that the envelope structure affects the millimeter emission of the disk. Conclusions. Our results reveal grains with a maximum size no larger than 100 μm in the inner envelope of the Class I protostar Per-emb-50, providing an interesting case to test the universality of millimeter grain growth expected in these sources.

scholarly journals Circumstellar H2O in M-type AGB stars

2008 ◽  
Vol 4 (S251) ◽  
pp. 163-164
Author(s):  
Matthias Maercker ◽  
Fredrik L. Schöier ◽  
Hans Olofsson
Keyword(s):  
Radiative Transfer ◽  
Radiation Field ◽  
Central Star ◽  
Thermal Excitation ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Dust Grains ◽  
Transfer Modelling

AbstractSurprisingly high amounts of H2O have recently been reported in the circumstellar envelope around the M-type AGB star W Hya. However, substantial uncertainties remain, as the required radiative transfer modelling is difficult due to high optical depths, sub-thermal excitation and the sensitivity to the combined radiation field from the central star and dust grains.

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