- THz RADIATIVE TRANSFER BASICS AND LINE RADIATION

AbstractWe consider the propagation of spectral-line radiation in a correlated turbulent atmosphere. The ensembles of turbulent velocities u(r,t) and optical depths, τν, are assumed to be Gaussian. We investigate the explicit analytical solution of the stochastic radiative transfer equation for the intensity Iν of radiation. The scattering term is not taken into account. It is shown that, in addition to the usual Doppler broadening of the spectral line, correlated turbulent motions of atoms and molecules give rise to considerable changes in the shape of a spectral line. We find that the mean intensity I(0)ν (Iν=I(0)ν+I′ν, I′ν = 0) obeys the usual radiative transfer equation with renormalized extinction factor αeffν if the correlation length R0 of the turbulence is small as compared to a photon free path. A simple analytical expression for αeffν is given. This expression integrally depends on the two-point correlation function of the turbulent velocity field.

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Collisions Between High Latitude Clouds: Theory Meets Observations

International Astronomical Union Colloquium ◽

10.1017/s025292110002426x ◽

1989 ◽

Vol 120 ◽

pp. 460-460

Author(s):

J.C. Lattanzio ◽

E.R. Keto

Keyword(s):

Radiative Transfer ◽

High Latitude ◽

Energy Content ◽

Three Dimensional ◽

External Pressure ◽

Line Radiation ◽

Particle Hydrodynamics ◽

Smoothed Particle ◽

Simulated Source ◽

The Stability

We report on fully three-dimensional hydrodynamic and radiative transfer simulations of collisions between high latitude clouds. Our model uses the smoothed particle hydrodynamics code described by Lattanzio and Henriksen (1988) to compute the velocity, temperature, and density fields in the impacted clouds and a recently developed radiative transfer code to compute 13 CO line radiation from the simulated source. By including the instrumental effects involved in a particular observations we can make detailed comparisons with the observations. The model shows that: 1) The previously unexplained energy source for the broad CO line wings reported by Blitz, Magnani, and Wandel (1988) derives from the collisions. 2) Collisions can induce rapid gravitational collapse and star formation in these clouds which are otherwise supported against gravitational contraction via their internal energy content. 3) The external pressure due to intercloud HI, firts proposed for these objects by Keto and Myers (1986), plays a significant role in the stability and evolution of the high latitude clouds.

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