Radiative Transfer in Protoplanetary Disk : vertical energy structure modelling and disk chemistry effects

Protoplanetary disks are the precursors of planetary systems. All building materials needed to assembly the planetary systems are supplied by these reservoirs, including many organic molecules [1-2]. Thus, the physical and chemical properties in protoplanetary disks set the boundary conditions for the formation and evolution of planets and other solar system bodies. The structure and chemistry of protoplanetary disks depend strongly on the nature of central star around which they have formed. The dust temperature is manly set by the stellar luminosity, while the chemistry of the whole disk depends on the UV and X ray fluxes. Therefore, a knowledge, as accurate as possible, of the radiative transfer inside disks is a prerequisite for their modelling. In a passive accretion disk the mass accretion processes, the viscous dissipative heating, and the reprocessing of stellar radiation by the flared disk atmospheres, may play a primary role in structuring the various radial regions at different evolutionary epochs making difficult to provide a "standard model" for this scenario. On the other hand, our current knowledge of the star-forming regions and the more evolved debris disks let us to attempt a disk-star environment modelling. During the last 10 years many authors suggested various numerical and analytical techniques to resolve the disk temperature structure and provide vertical temperature profiles and disk SED reconstruction. [3-6]. In this work we have solved the radiative transfer problem in separate interesting disk regions: 1) Disk atmospheres at large radius, r > 10 AU. 2) Equatorial plane regions spanned over 1 < r < 10 AU and 10 < r < 100 AU. The effects of different dust compositions [7-8] and ranges of star luminosity in UV and X rays have been compared. We solved the equatorial plane problem in cylindrical symmetry modelling the disk as an internal high density cloud region heated primarily by viscous processes and X-UV star radiation from upper atmosphere. In that region we applied the P-N approximation [9] obtaining a rapid convergent solution and customizable accuracy at boundaries. As complementary task we investigate more complex atmosphere models where the diffuse gas-dust medium, the direct high energy X-UV star flux and the geometry of the disk impose a more accurate treatment. We propose a simplified analytical approach based on P-N approximation as parallel plane problem (suitable for limited range of r) and a more accurate Monte Carlo integration with specifically designed numerical code solving the RT in the 4 Stokes radiation field components. The resulting radiation fluxes of non reprocessed UV and X rays provide initial boundary conditions for the inner equatorial region. Some preliminary results are presented.