On the validity of grey radiation transfer in dusty envelopes

Thomas Preibisch, Cordula Sonnhalter & Harold W. Yorke

Astronomy and Astrophysics 299, 144, (1995)


Radiative transfer calculations in dusty protostellar envelopes have been performed to test the validity of the grey approximation which is often used in radiation hydrodynamic calculations. In the spherical symmetric (1D) case we compare grey calculations with the frequency dependent exact solution of radiation transport. In the 2D case we use the flux-limited diffusion approximation to solve the radiation transport equation in grey and frequency dependent form. In all cases the dust temperature distributions are determined self-consistently.

Model envelopes are considered with a density peaked structure and with different total optical depths in the 1D case. In the 2D case we use the density distributions of various disk models. A dust model consisting of amorphous carbon and silicate grains, partially coated with `dirty ice', is assumed. We find that the dust temperatures are generally underestimated in the grey approximation (by factors up to three) and that the radiative acceleration can be underestimated by orders of magnitude. The importance of efficient but more accurate algorithms than the usual grey approximation is stressed.

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