SIMBAD references

We investigate in details the properties of the disk surrounding the 8Myr old star HR4796A, one of the few stars bringing precious clues to better understand the scenario which lead to planetary system formation. We propose a model able to reproduce all the available observations: the full spectral energy distribution from the mid-infrared to the millimeter wavelengths, resolved scattered light and thermal emission observations. We show that the circumstellar matter splits into two dust components: a cold annulus, peaked at 70AU from the star, made of ISM-like grains (amorphous composition, porosity ∼0.6) larger than 10µm and a population of hot dust close to the star (at about 9AU) made of comet-like grains (crystalline composition, porosity ∼0.97). Both dust populations are highly collisional and the grain size distribution in the cold annulus is found to be cut-off by radiation pressure. At 70AU, bodies as large as a few meters are required to fit the data leading to a minimum disk mass of a few Earth masses and to a gas to dust ratio less than 1. We discuss aftewards some implications on the disk structure and effects of larger bodies.