35 research outputs found
Time-dependent Monte Carlo continuum radiative transfer
Aims. We present an implementation of an algorithm for 3D time-dependent
Monte Carlo radiative transfer. It allows one to simulate temperature
distributions as well as images and spectral energy distributions of the
scattered light and thermal reemission radiation for variable illuminating and
heating sources embedded in dust distributions, such as circumstellar disks and
dust shells on time scales up to weeks.
Methods. We extended the publicly available 3D Monte Carlo radiative transfer
code POLARIS with efficient methods for the simulation of temperature
distributions, scattering, and thermal reemission of dust distributions
illuminated by temporally variable radiation sources. The influence of the
chosen temporal step width and the number of photon packages per time step as
key parameters for a given configuration is shown by simulating the temperature
distribution in a spherical envelope around an embedded central star. The
effect of the optical depth on the temperature simulation is discussed for the
spherical envelope as well as for a model of a circumstellar disk with an
embedded star. Finally, we present simulations of an outburst of a star
surrounded by a circumstellar disk.
Results. The presented algorithm for time-dependent 3D continuum Monte Carlo
radiative transfer is a valuable basis for preparatory studies as well as for
the analysis of continuum observations of the dusty environment around variable
sources, such as accreting young stellar objects. In particular, the combined
study of light echos in the optical and near-infrared wavelength range and the
corresponding time-dependent thermal reemission observables of variable, for
example outbursting sources, becomes possible on all involved spatial scales.Comment: Accepted for publication in Astronomy & Astrophysics. 15 pages, 18
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Xâray imaging of a highâtemperature furnace applied to glass melting
The dynamics of sodaâlimeâsilica glass grain melting is investigated experimentally using a nonintrusive technique. A cylindrical alumina crucible is filled with glass cullet and placed into a furnace illuminated by an Xâray source. This glass granular bed is gradually heated up to 1100°C, leading to its melting and the generation of a sizeâdistributed population of bubbles rising in the molten glass. An image processing algorithm of Xâray images of the cullet bed during melting allows the characterization of bubbles size distribution in the crucible as well as their velocity. The introduction of tin dioxide ÎŒâparticles in the glass matrix before melting enhances the texture of the images and makes possible the determination of the bubbleâinduced molten glass velocity field by an optical flow technique. The bubble size distribution can be fitted by a logânormal law, suggesting that it is closely related to the initial size distribution in the cullet bed. The liquid motion induced by the bubbles in Stokes' regime is strongly affected by the flow confinement and the determination of bubble rising velocity along its trajectory unveils the existence of local tiny temperature fluctuations in the crucible. Overall, the measuring techniques developed in this work seem to be very promising for the improvement of models and optimization of industrial glass furnaces
VLTI-MATISSE L- and N-band aperture-synthesis imaging of the unclassified B[e] star FS Canis Majoris
Stars and planetary system
MATISSE, the VLTI mid-infrared imaging spectro-interferometer
GalaxiesStars and planetary systemsInstrumentatio
Muster zur Aufstellung von Umweltschutz-Berichten in den Kommunen Vorstudie
Technische Informationsbibliothek Hannover: RN 8908 (78-002) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman