The vertical structure of T Tauri accretion discs IV. Self-irradiation of the disc in the FU Orionis outburst phase

Abstract

I investigate the self-irradiation of intensively accreting circumstellar discs (backwarmed discs). It is modelled using the two-layer disc approach by Lachaume et al. (2003) that includes heating by viscous dissipation and by an external source of radiation. The disc is made of a surface layer directly heated by the viscous luminosity of the central parts of the disc, and of an interior heated by viscosity as well as by reprocessed radiation from the surface. This model convincingly accounts for the infrared excess of some FU Orionis objects in the range 1-200 microns and supports the backwarmed disc hypothesis sometimes invoked to explain the mid- and far-infrared excesses whose origins are still under debate. Detailed simulation of the vertical radiative transfert in the presence of backwarming is still needed to corroborate these results and spectroscopically constrain the properties of intensively accreting discs.