We present the results of a three-dimensional Monte Carlo radiative transfer code for starless molecular cloud cores heated by an external isotropic or non-isotropic interstellar radiation field .
The code computes the dust temperature distribution inside model clouds with specified but arbitrary density profiles .
In particular we examine in detail spherical ( Bonnor-Ebert ) clouds , axisymmetric and non-axisymmetric toroids , and clouds heated by an external stellar source in addition to the general interstellar field .
For these configurations , the code also computes maps of the emergent intensity at different wavelengths and arbitrary viewing angle , that can be compared directly with continuum maps of prestellar cores .
In the approximation where the dust temperature is independent of interactions with the gas and where the gas is heated both by collisions with dust grains and ionization by cosmic rays , the temperature distribution of the gas is also calculated .
For cloud models with parameters typical of dense cores , the results show that the dust temperature decreases monotonically from a maximum value near the cloud ’ s edge ( 14–15 K ) to a minimum value at the cloud ’ s center ( 6–7 K ) .
Conversely , the gas temperature varies in a similar range , but , due to efficient dust-gas coupling in the inner regions and inefficient cosmic-ray heating in the outer regions , the gradient is non-monotonic and the gas temperature reaches a maximum value at intermediate radii .
The emission computed for these models ( at 350 \mu m and 1.3 mm ) shows that deviations from spherical symmetry in the density and/or temperature distributions are generally reduced in the simulated intensity maps ( even without beam convolution ) , especially at the longer wavelengths .
adiative transfer ; ISM : clouds , dust , extinction