Radiative transfer

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

Dust in starburst nuclei and ULIRGs: SED models for observers

Abstract: We provide a library of some 7000 SEDs (available at www.eso.org/~rsiebenm) for the nuclei of starburst and ultra luminous galaxies. Its purpose is to quickly obtain estimates of the basic parameters, such as luminosity, size and dust or gas mass and to predict the flux at yet unobserved wavelengths. The procedure is simple and consists of finding an element in the library that matches the observations. The objects may be in the local universe or at high z. We calculate the radiative transfer in spherical symmetry for a stellar cluster permeated by an interstellar medium with standard (Milky Way) dust properties. The cluster contains two stellar populations: old bulge stars and OB stars. Because the latter are young, a certain fraction of them will be embedded in compact clouds which constitute hot spots that determine the MIR fluxes. We present SEDs for a broad range of luminosities, sizes and obscurations. We argue that the assumption of spherical symmetry and the neglect of clumpiness of the medium are not severe shortcomings for computing the dust emission. The validity of the approach is demonstrated by matching the SED of seven of the best studied galaxies, including M82 and Arp220, by library elements. In all cases, one finds an element which fits the observed SED very well, and the parameters defining the element are in full accord with what is known about the galaxy from detailed studies. We also compare our method of computing SEDs with other techniques described in the literature.

Optical properties of rare earth-doped ZBLAN glasses

Abstract: An investigation has been made of the radiative and non-radiative properties of the well known ZBLAN glass composition doped with individual rare earth elements (Pr3+, Nd3+, Dy3+, Ho3+, Er3+ and Tm3+) at levels between 0.1 and 4 mol%. The optical absorption and fluorescence spectra of the samples were measured and also the lifetimes for some transitions. Using the Judd-Ofelt model, the radiative decay rates between the different levels, the lifetimes and the branching ratios were calculated. These results and comparison of calculated and measured lifetimes are discussed with respect to radiative and non-radiative rates and quantum efficiencies. The multiphonon rates below 3200 cm−1 are found to be less in ZBLAN than in other host materials (ZBLA, SiO2, YAG).

A Study on the “Runaway Greenhouse Effect” with a One-Dimensional Radiative–Convective Equilibrium Model

Abstract: A simple one-dimensional radiative–convective equilibrium model is used to investigate the relationship between the surface temperature and the outgoing infrared radiation at the top of the atmosphere. The model atmosphere has a gray infrared absorption coefficient and is composed of a radiative equilibrium stratosphere and a moist adiabat troposphere. An upper limit of the outgoing infrared radiation is found to exist. The existence of the upper limit is characterized by the radiation limits that appear when the optical depth of the entire atmosphere becomes sufficiently deep and the temperature structure around the levels where the optical depth is about unity approaches a fixed profile. This appearance of an upper limit differs from that found by Komabayashi and Ingersoll, which is obtained from the constraint of the stratospheric radiation balance. As one of those radiation limits, the outgoing infrared radiation has an asymptotic limit as the surface temperature increases. This is caused by ...

High-Ionization Emission in Metal-deficient Blue Compact Dwarf Galaxies*

Abstract: Primordial stars are expected to be very massive and hot, producing copious amounts of hard ionizing radiation. The best place to study hard ionizing radiation in the local universe is in very metal-deficient blue compact dwarf (BCD) galaxies. We have carried out a MMT spectroscopic search for [Ne V] λ3426 (ionization potential of 7.1 ryd), [Fe V] λ4227 (ionization potential of 4 ryd), and He II λ4686 (ionization potential of 4 ryd) emission in a sample of 18 BCDs. We have added data from previous work and from the Data Release 3 of the Sloan Digital Sky Survey. In total, we have assembled a BCD high-ionization sample with [Ne V] emission in four galaxies, [Fe V] emission in 15 galaxies, and He II emission in 465 galaxies. With this large sample, we have reached the following conclusions. There is a general trend of higher [Ne V], [Fe V], and He II emission at lower metallicities. However, metallicity is not the only factor that controls the hardness of the radiation. High-mass X-ray binaries and main-sequence stars are probably excluded as the main sources of the very hard ionizing radiation responsible for [Ne V] emission. The most likely source of [Ne V] emission is probably fast radiative shocks moving with velocities 450 km s-1 through a dense interstellar medium with an electron number density of several hundreds cm-3 and associated with supernova explosions of the most massive stars. These have masses of ~50-100 M☉ and are formed in very compact super-star clusters (SSCs). The softer ionizing radiation required for He II emission is likely associated with less massive evolved stars and/or radiative shocks moving through a less dense interstellar medium.

A method of calculating radiative heat diffusion in particle simulations

Abstract: A new method for solving heat diffusion in three dimensional particle simulations is described. The difficulties encounted by other authors is discussed, in particular the difficulty of including boundary conditions in particle simulations. One and three dimensional tests of the method are described.