Amorphous carbon around carbon stars

In this paper we present the results of a simplified model to determine the flux emerging from dust envelopes around cool stars. The model proposed holds under the hypotheses of negligible scattering effects and spherical geometry of the dust cloud.The aim of this work is to compare the effects of a graphitic or amorphous composition of the carbon grains in the envelopes. To do this we have used, for the first time, experimental extinction data obtained in the laboratory for submicron amorphous carbon particles.The model has been used to fit the FIR spectral trend of 78 optically thin sources and to reproduce the full spectra of two of the most IR luminous optically-thick sources: CIT 6 and IRC+10216.Our calculations indicate clearly that solid carbon particles around these sources may be amorphous rather than crystalline.