Radiative transfer

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

Tracing the Mass during Low-Mass Star Formation. III. Models of the Submillimeter Dust Continuum Emission from Class 0 Protostars

Abstract: Seven Class 0 sources mapped with SCUBA at 850 and 450 μm are modeled using a one-dimensional radiative transfer code. The modeling takes into account heating from an internal protostar, heating from the interstellar radiation field (ISRF), realistic beam effects, and chopping to model the normalized intensity profile and spectral energy distribution. Power-law density models, n(r) ∝ r-p, fit all of the sources; best-fit values are mostly p = 1.8 ± 0.1, but two sources with aspherical emission contours have lower values (p ~ 1.1). Including all sources, p = 1.63 ± 0.33. Based on studies of the sensitivity of the best-fit p to variations in other input parameters, uncertainties in p for an envelope model are Δp = ±0.2. If an unresolved source (e.g., a disk) contributes 70% of the flux at the peak, p is lowered in this extreme case and Δp = . The models allow a determination of the internal luminosity (Lint = 4.0 L☉) of the central protostar as well as a characteristic dust temperature for mass determination (Tiso = 13.8 ± 2.4 K). We find that heating from the ISRF strongly affects the shape of the dust temperature profile and the normalized intensity profile, but it does not contribute strongly to the overall bolometric luminosity of Class 0 sources. There is little evidence for variation in the dust opacity as a function of distance from the central source. The data are well fitted by dust opacities for coagulated dust grains with ice mantles (Ossenkopf & Henning). The density profile from an inside-out collapse model (Shu) does not fit the data well, unless the infall radius is set so small as to make the density nearly a power law.

Photodissociation of H2 in Protogalaxies: Modeling Self-Shielding in 3D Simulations

Abstract: The ability of primordial gas to cool in proto-galactic haloes exposed to Lyman-Werner (LW) radiation is critically dependent on the self-shielding of H_2. We perform radiative transfer calculations of LW line photons, post-processing outputs from three-dimensional adaptive mesh refinement (AMR) simulations of haloes with T_vir > 10^4 K at redshifts around z=10. We calculate the optically thick photodissociation rate numerically, including the effects of density, temperature, and velocity gradients in the gas, as well as line overlap and shielding of H_2 by HI, over a large number of sight-lines. In low-density regions (n 10^4 K haloes by an order of magnitude; this increases the number of such haloes in which supermassive (approx. M=10^5 M_sun) black holes may have formed.

The Spectra and Energies of Classical Double Radio Lobes

Abstract: We compare two temporal properties of classical double radio sources: (1) radiative lifetimes of synchrotron-emitting particles and (2) dynamical source ages. We discuss how these can be quite discrepant from one another, rendering use of the traditional spectral aging method inappropriate: we contend that spectral ages give meaningful estimates of dynamical ages only when these ages are 107 yr. In juxtaposing the fleeting radiative lifetimes with source ages that are significantly longer, a refinement of the paradigm for radio source evolution is required. We move beyond the traditional bulk backflow picture and consider alternative means of the transport of high Lorentz factor (γ) particles, which are particularly relevant within the lobes of low-luminosity classical double radio sources. The changing spectra along lobes are explained, not predominantly by synchrotron aging but by gentle gradients in a magnetic field frozen into a low-γ matrix that illuminates an energy distribution of particles, N(γ), controlled largely by classical synchrotron loss in the high magnetic field of the hot spot. A model of a magnetic field whose strength decreases with increasing distance from the hot spot and in so doing becomes increasingly different from the equipartition value in the head of the lobe is substantiated by constraints from different types of inverse Compton scattered X-rays. The energy in the particles is an order of magnitude higher than that inferred from the minimum energy estimate, implying that the jet power is of the same order as the accretion luminosity produced by the quasar central engine. This refined paradigm points to a resolution of the 1994 findings of Rudnick et al. and Katz-Stone & Rudnick that both the Jaffe-Perola and Kardashev-Pacholczyk model spectra are invariably poor descriptions of the curved spectral shape of lobe emission and, indeed, that for Cygnus A all regions of the lobes are characterized by a "universal spectrum."

Multiline transfer and the dynamics of stellar winds.

Abstract: A Monte Carlo technique for treating multiline transfer in stellar winds is described. With a line list containing many thousands of transitions and with fairly realistic treatments of ionization, excitation and line formation, the resulting code allows the dynamic effects of overlapping lines the investigation of and provides the means to directly synthesize the complete spectrum of a star and its wind. It is found that the computed mass loss rate for data Puppis agrees with the observed rate. The synthesized spectrum of zeta Puppis also agrees with observational data. This confirms that line driving is the dominant acceleration mechanism in this star's wind.