POROUS GRAINS IN THE SHELLS OF HERBIG Ae/Be STARS

                      V.B. Il'in and N.A. Krivova


Abstract.-- We simulate the polarized radiation transfer in the shells with
a spheroidal spatial distribution of fluffy dust grains. The circumstellar
dust is represented by MRN mixture of silicate and graphite particles.
The optical properties of porous grains are calculated using the EMT
approximation and Mie theory.

 For a typical Herbig Ae/Be star WW Vul with Algol-like minima, we model the
following signatures of circumstellar dust: the spectral energy distribution
from the ultraviolet to the far infrared, the colour-magnitude diagrams, the
wavelength dependence of the linear polarization degree, and intensity maps.
Effects of the porosity of grains on these data are considered. The conclusion
is made that only an intermediate porosity of grains (the volume fraction of
vacuum in the particles $p\sim$ 0.5) can satisfy the available observational
data in the frame of the model used.

 As radiation pressure should quickly blow submicron dust particles out of
the vicinities of Herbig Ae/Be stars, we briefly discuss how the grain
porosity can influence the process.