Interstellar extinction by porous grains

Interstellar extinction curve E(λ-V)/E(B-V) vs 1/λ is evaluated in the spectral range 3.4 μm and 0.1 μm using the extinction efficiencies of the porous silicate and graphite grains. The extinction efficiencies of the porous silicate and graphite grains are computed using the discrete dipole approximation (DDA). The model curves are compared with the average observed interstellar extinction curve. Further, we investigate the effect of porosity on the extinction in the UV in details and show that the inhomogeneity (porosity, structure) within the grains can produce shift in the central wavelength of the extinction peak in the UV, as well as variation in its width. The albedo for the porous grains in the UV and the visible spectral range is also computed and it is found to be consistent with the observations.