Non-LTE Monte Carlo radiative transfer. II. Nonisothermal solutions for viscous Keplerian disks

We discuss the basic hydrodynamics that determines the density structure of the disks around hot stars. Observational evidence supports the idea that these disks are Keplerian (rotationally supported) gaseous disks. A popular scenario in the literature, which naturally leads to the formation of Keplerian disks, is the viscous decretion model. According to this scenario, the disks are hydrostatically supported in the vertical direction, while the radial structure is governed by the viscous transport. This suggests that the temperature is one primary factor that governs the disk density structure. In a previous study we demonstrated, using three-dimensional non-LTE Monte Carlo simulations, that viscous Keplerian disks can be highly nonisothermal. In this paper we build on our previous work and solve the full problem of the steady state nonisothermal viscous diffusion and vertical hydrostatic equilibrium. We find that the self-consistent solution departs significantly from the analytic isothermal density, with potentially large effects on the emergent spectrum. This implies that nonisothermal disk models must be used for a detailed modeling of Be star disks.

Radiative capture of nucleons at astrophysical energies with single-particle states

Radiative capture of nucleons at energies of astrophysical interest is one of the most important processes for nucleosynthesis. The nucleon capture can occur either by a compound nucleus reaction or by a direct process. The compound reaction cross sections are usually very small, especially for light nuclei. The direct capture proceeds either via the formation of a single-particle resonance or a non-resonant capture process. In this work we calculate radiative capture cross sections and astrophysical S-factors for nuclei in the mass region A < 20 using single-particle states. We carefully discuss the parameter fitting procedure adopted in the simplified two-body treatment of the capture process. Then we produce a detailed list of cases for which the model works well. Useful quantities, such as spectroscopic factors and asymptotic normalization coefficients, are obtained and compared to published data. (C) 2010 Elsevier Inc. All rights reserved.

Excited Electronic States, Transition Probabilities, and Radiative Lifetimes of CAs: A Theoretical Contribution and Challenge to Experimentalists

High-level CASSCF/MRCI calculations with a quintuple-zeta quality basis set are reported by characterizing for the first time a manifold of electronic states of the CAs radical yet to be investigated experimentally. Along with the potential energy curves and the associated spectroscopic constants, the dipole moment functions for selected electronic states as well as the transition dipole moment functions for the most relevant electronic transitions are also presented. Estimates of radiative transition probabilities and lifetimes complement this investigation, which also assesses the effect of spin-orbit interaction on the A (2)Pi state. Whenever pertinent, comparisons of similarities and differences with the isovalent CN and CP radicals are made.

2-Aminopurine non-radiative decay and emission in aqueous solution: A theoretical study

The minimum energy path along the lowest-lying pi pi* excited state of 2-aminopurine was calculated to elucidate the mechanisms of radiationless decay and emission in water. The sequential Monte Carlo quantum mechanics approach with a multiconfigurational and perturbative description of the wave function was employed to compute the minimum, transition state, and conical intersection. It was found that the barrier in the potential energy surface to access the conical intersection funnel increases in aqueous environment, making the system prone to enlarge the emission yield. These results rationalize the observed enhancement of emission in 2-aminopurine upon increasing of the solvent polarity. (c) 2008 Elsevier B.V. All rights reserved.

Challenges in Radiative Transfer Modeling - W3 IRS5

By modeling the spectral energy distribution (SED) of the W3 IRS5 high-mass star formation region and matching this model to observed data, we can constrain the physical parameters of the basic system geometry and cloud mass distribution. From these parameters, we hope to add to the understanding of high-mass star formation processes. In particular, we hope to determine if the geometries associated with lowmass star formation carry over into the high-mass regime.

Atomic radiative transitions in thermo field dynamics

In this work we rederive the Lamb-Retherford energy shift for an atomic electron in the presence of a thermal radiation. Using the Dalibard, Dupont-Roc and Cohen-Tannoudji (DDC) formalism, where physical observables are expressed as convolutions of suitable statistical functions, we construct the electromagnetic field propagator of thermo field dynamics in the Coulomb gauge in order to investigate finite temperature effects on the atomic energy levels. In the same context, we also analyze the problem of the ground state stability.

Operator ordering in quantum radiative processes

In this work we reexamine quantum electrodynamics of atomic electrons in the Coulomb gauge in the dipole approximation and calculate the shift of atomic energy levels in the context of Dalibard, Dupont-Roc and Cohen-Tannoudji formalism by considering the variation rates of physical observable. We then analyze the physical interpretation of the ordering of operators in the dipole approximation interaction Hamiltonian in terms of field fluctuations and self-reaction of atomic electrons, discussing the arbitrariness in the statistical functions in second-order bound-state perturbation theory. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Radiative Omega(-)->Xi(-)gamma decay and physics beyond the standard model

We investigate the impact of new physics beyond the Standard Model to the s --> d gamma process, which is responsible for the short-distance contribution to the radiative decay Omega-( )--> Xi(-) gamma. We study three representative extensions of the Standard Model, namely a one-family technicolor model, a two Higgs doublet model and a model containing scalar leptoquarks. When constraints arising from the observed b --> s gamma transition and the upper limit on D-0-(D) over bar(0) mixing are taken into account, we find no significant contributions of new physics to the s --> d gamma process.

Silicon monosulphide radiative association

Rate coefficients for radiative association of silicon and sulphur atoms to form silicon monosulphide (SiS) molecule are estimated. The radiative association is due mainly to approach in the E(1)Sigma(+) and A(1)Pi states of SiS. For temperatures ranging from similar to 1000 to similar to 14 000 K, the rate coefficients are found to vary from 8.43 x 10(-17) to 2.69 x 10(-16) cm(3) s(-1). Our calculated rate coefficient is higher than the values used in modelling the chemistry of Type Ia supernovae.

The formation of CN and CN+ by direct radiative association

Rate coefficients for direct radiative association of carbon and nitrogen atoms to form CN, and of carbon ions and nitrogen atoms to form CN+ ions, are calculated for temperatures in the range of 300 to 14,700 K. For the CN molecule, the rate coefficients can be represented by the standard expression, k(CN)(T) = 7.87 x 10(-19)(T/300)(0.056) exp (-96.0/T) cm(3) s(-1) for temperatures between 300 and 2700 K and k(CN)(T) = 1.37 x 10(-18)(T/300)-0.128 exp (-520.1/T) cm(-3) s(-1) at T > 2700 K. For the CN+ ion, the corresponding expression is k(CN+)(T) = 1.08 x 10(-18)(T/300)(0.071) exp (-57.5/T) cm(-3) s(-1) for the temperature range studied. Calculated rate coefficients k(CN) are about 2 orders of magnitude lower than the canonical value used in the modeling of the chemistry of various astrophysical environments.

Formation of SO, SO+, and S-2 by radiative association

Rate coefficients for radiative association of SO, SO+, and S-2 are estimated. For temperatures ranging from 300 to 14,000 K, the direct radiative association rate coefficients are found to vary with temperature from 1.73 x 10(-19) to 7.29 x 10(-19) cm(3) s(-1) and from 1.49 x 10(-21) to 3.70 x 10(-19) cm(3) s(-1) for S-2 and SO, respectively. The rate coefficients for formation through the inverse predissociation for S-2 are found to vary from 3.59 x 10(-18) to 1.44 x 10(-20) cm(3) s(-1). For SO+, the direct rate coefficient varies rapidly with temperature from 3.62 x 10(-27) cm(3) s(-1) at 2000 K to 2.34 x 10(-20) cm(3) s(-1) at 14,000 K. The direct radiative association rate coefficients increase with the increase in temperature, but the inverse predissociation rate coefficients decrease with the increase in temperature.

Radiative association of C and P, and Si and P atoms

The rate coefficients for the formation of carbon monophosphide (CP) and silicon monophosphide (SiP) by radiative association are estimated for temperatures ranging from 300 to 14 100 K. In this temperature range, the radiative association rate coefficients are found to vary from 1.14 x 10(-18) to 1.62 x 10(-18) cm(3) s(-1) and from 3.73 x 10(-20) to 7.03 x 10(-20) cm(3) s(-1) for CP and SiP, respectively. In both cases, rate coefficients increase slowly with the increase in temperature.

Formation of SiC by radiative association

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Radiative association of Ti and O atoms

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

QED(3) RADIATIVE-CORRECTIONS IN THE HEISENBERG PICTURE

We evaluate the vacuum polarization tensor for three-dimensional quantum electrodynamics (QED3) via Heisenberg equations of motion in order to clarify the problem arising from the use of different regularization prescriptions in the interaction picture. We conclude that the photon does acquire physical mass of topological origin when such contribution is taken into account for the photon propagator.