A UNIFIED MODEL OF INTERSTELLAR DUST

We have simultaneously modeled both the interstellar extinction and po larization (both linear and circular) on the basis of a trimodal dust model: large silicate core-organic refractory mantle dust particles ve ry small carbonaceous particles responsible for the hump extinction an d PAH's responsible for the FUV extinction. The core-mantle particles which are the exclusive contributor to the interstellar polarization a nd the dominant contributor to the visual and NIR extinction are model ed as finite cylinders with st Gaussian size distribution in terms of perfect spinning alignment. Results for models using infinite cylinder s are presented for comparison. Our model results are in good agreemen t with such observational constraints as the average interstellar exti nction curve, the polarization law, the ratio of visual polarization. to extinction (P/A)(v), the scattering properties (albedos), the exces s NIR polarization over the extrapolation of the Serkowski law. The (P /A)(v) constraint imposed on other dust models (e.g., the silicate/gra phite model, the composite dust model) leads to either a too low (P/A) (v) value (the silicate/graphite model) or instability of particle str ucture (the composite dust model). The cosmic abundance constraints, i n particular the evidence for lower oxygen abundance in the interstell ar medium than in the solar system and the possible interstellar C/O r atios, are discussed extensively. Considering the uncertainties in the interstellar ''cosmic'' abundances, the C/O ratio and the interstella r non-dust elemental abundances, although our model requires a bit mor e carbon than the reference abundance, it is within the limit of an ac ceptable range and is a significant improvement over other models. AII the other major reference abundance (cosmic - non-dust) constraints o n O, N, Si, Mg, Fe are well satisfied.