The aim of this project is to calculate for protostellar molecular clouds with different velocity and density distributions line profiles and strengths, which can be directly compared with spatially and spectrally resolved observations, in order to derive the physical conditions of protostellar cloud cores in the first stage of star formation.
In the centre of interest is the modeling of diagnostically important rotational transitions of the CS molecule. Since NLTE (i.e. non local thermal equilibrium) effects become more important with decreasing density, the corresponding time-dependent rate equations are solved self-consistently with respect to the radiative transfer in the collapsing medium. The calculations consider both macroscopic (from rotation and accretion) and microscopic (due to turbulences) velocity fields.
Based on analytical solutions of the 1D radiative transfer equation, a method for calculating the spatially resolved molecular line intensities in a collapsing spherical medium is developed. In order to calculate the line emissions from axisymmetric, differentially rotating and collapsing clouds, as well as to test the numerical results of the spherical 1D case, the 3D transfer equation is also solved numerically by using finite differences. In order to reduce the parameter space of rotating collapsing systems in the 3D case, new analytical expressions for the density and velocity field of an isothermal cloud are derived from the basic hydrodynamic equations. One obtains these solutions as special cases of the analytical solutions for a corresponding rotating stellar wind (also derived in this paper).
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