CIRCUMSTELLAR DUST AND CIRCUMSTELLAR EXTINCTION CURVES

We have calculated the circumstellar extinction curves produced by dus t grains which absorb and scatter the stellar radiation in the shells of pre-main-sequence stars. A Monte Carlo method was used to model the radiative transfer in non-spherical shells. The dependence on the par ticle size distribution and the dust shell parameters has been examine d. The application of the theoretical results to explain the extinctio n and polarization of the Herbig Be star ED 45677 shows that the dust shell is not disk-like and that very small grains are absent in it.