The size distribution of dust grains in single clouds .1. The analysis of extinction using multicomponent mixtures of bare spherical grains

We demonstrate that the method of regularization designed to resolve inverse problems may be successfully applied in analysis of interstellar extinction. The absolute extinction curves of apparently single clouds, seen towards the stars HD 147165, 179406 and 202904, have been derived and modelled using multicomponent bare spherical dust grain mixtures containing graphite, silicates, various types of amorphous carbon, SiC and water ice. We find that the grain size distributions are essentially different from Mathis, Rumpl & Nordsieck's (MRN) power law and may be multimodal. From the recent data about reduced (similar to 2/3 solar) cosmic abundances, it has been shown that a mixture of graphite, silicate and ice grains explains quite satisfactorily the extinction towards the stars under analysis whereas a traditional mixture of graphite and silicate grains fails.