Optical constants of cosmic carbon analogue grains — I. Simulation of clustering by a modified continuous distribution of ellipsoids

The first results on the optical constants of three different amorphous carbon samples, possible analogues of interstellar and circumstellar dust grains, are presented. They have been deduced from recent laboratory data, making use of the Kramers-Kronig approach. It is shown that the physically correct simulation of clustering by the traditional ‘CDE’ model is not applicable here. A modified CDE (MCDE) model is proposed and used in the present calculations. The MCDE model allows one to take into account the effect of percolation of the analysed amorphous carbon clusters through the parameter go, interpreted as a percolation strength. The intervals of the probable MCDE models (go) have been chosen on the basis of the relevant estimates of Stognienko, Henning & Ossenkopf for the cluster—cluster aggregation (CCA) and particle—cluster aggregation (PCA) models. The ‘optimal’ percolation strengths and optical constants have been derived by using a least-squares procedure.