Source function approximations and their impact on the shape of self-reversed atomic lines

The shape of optically thick atomic lines emitted from inhomogeneous plasmas is calculated using both a heuristic one-parameter approximation (OPA) for the source function and the Bartels approximation. The results are compared with those obtained from solving the radiation transfer equation using selected trial source functions. The accuracy of the OPA is proved to be higher than that of the Bartels, particularly within the central line region, and independent of the equilibrium conditions in the plasma. The results open up the possibility of a realistic analysis of self-reversed lines and their application to plasma diagnostics.