Statistics – Computation
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000esasp.456..303o&link_type=abstract
ISO beyond the peaks: The 2nd ISO workshop on analytical spectroscopy. Eds. A. Salama, M.F.Kessler, K. Leech & B. Schulz. ESA-SP
Statistics
Computation
Radiative Transfer, Molecular Data, Line: Formation, Line: Profiles
Scientific paper
Radiative transfer computations are the basic tool to derive the physical parameters of the interstellar medium from astronomical observations. However, many computations are still hindered by severe problems. The uncertainties start with the input data where the dust scattering functions, the line frequencies in the infrared and the collision rates are poorly known. They continue with problems in the treatment of coherent radiation, partial redistribution, and the representation of maser spots. Nevertheless, numerical simulations of radiative transfer experienced a tremendous progress over the last years. Molecules with hundreds of levels including rotational-vibrational transitions are simulated. The codes start to include the correct treatment of continuum pumping and overlapping lines, and first steps are made to deal with maser beaming, polarisation and partial coherence. We get a better feeling which approximations are to be applied in certain situations allowing rapid data reduction but acknowledging that there is no standard way. Growing experience from the simulations shows, however, that a large part of the former knowledge on the interpretation of measurements has to be revised. In the analysis of molecular line data ambiguity of the solutions is the rule, not the exception. The results confirm the general wisdom that numerical models can explain many observations but do not necessarily lead to a true physical and intuitive understanding of radiative transfer in the interstellar medium.
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