Modeling peculiar extinction curves

We investigate the remarkable variety of IR-through-UV extinction curves by modelling extinction profiles with core-mantle grains and a collection of single and stacked polycyclic aromatic hydrocarbons. Such a model can closely reproduce the observed curves, by simply assuming a different ratio of the molecular component to classical dust, while leaving relatively unmodified the underlying global picture. In particular, we find that for extinction curve morphologies differing significantly from the average Galactic extinction, dust grain sizes exhibit a low-end cut-off at approximately 100 nm. An additional component of very small grains of sizes around 10 nm is required to model lines of sight whose extinctions are similar to the average Galactic curve. We conclude that to be accurately described, the so-called peculiar extinction curves do not need dust grains with exotic properties.