A COMPARISON OF SOLID-STATE CARBONACEOUS MODELS OF COSMIC DUST

This is a tentative synopsis of available results from laboratories sp ecialized in solid carbon research related to cosmic dust. Differences and similarities between materials proposed as dust models are highli ghted so as to clarify the term ''amorphous carbon''. which is often u sed to designate very different products. These materials were tentati vely related to a-C:H and coals, which have been, for decades, and are still being, studied with the most sophisticated experimental methods , The physical understanding that has been reached in these fields mak es it possible now to group together some of the proposed materials in 3 classes according to their gross structural and optical properties, and, hence, to the part they may play in modelling astrophysical obse rvations, which no one of them can do entirely by itself: These are: a ) polygranular graphite; b) coals and oxidized, heal treated, f-QCC (a -C:H, HAC); c) glassy carbon grains such as carbon ari: particles (TU, AC-Ar) and annealed soot from hydrocarbon flames (XY, BE, AC-H2). The ir respective preferred fields of modelling applications seem to be: a ) the UV bump and FUV rise of IS extinction curves; b) the Unidentifie d Infrared Bands (UIBs), tile Extended Red Emission (ERE)and interstel lar (IS) IR extinction; c) the UV bump in extinction by the circumstel lar dust of a number of stars. The role of heat treatment, which is of ten used to improve the fits to astronomical observations, is discusse d. More generally, the present degree of physical understanding of car bon structure may help improving the proposed models through appropria te physical and chemical treatment.