Abstract
We have calculated the emergent flux for systems composed of a young star and a steady, infinitely thin, optically thick accretion disk subject to irradiation from the central star. We have found the following: (I) the emergent continuum flux is lower than calculated assuming that all the stellar energy is deposited at the bottom of the atmosphere at each annulus of the disk; thus, disks must have larger flaring, or larger accretion rates than previously thought; (2) irradiation determines the heating at large radii, producing a temperature inversion in the disk atmosphere. The disk radius where the heating to irradiation becomes more important than viscous heating increases when the mass accretion rate increases and when the stellar effective temperature decreases; (3) the the absorption strength of the CO, H20, TiO bands, and of the 10 μm silicate feature is a measure of the mass accretion rate M; (4) optically thick accretion disks can reproduce ∼ 40% of the near-infrared color observations for T Tauri stars. Large degrees of flaring and large disk sizes, Rmax ≤ 100 AU, can explain objects with fairly large far-infrared excess, but still ≈ 20% of the objects cannot be understood with the present models; (5) this study suggests that disk parameters can be determined with the following observables. M can be determined from the molecular bands of H2O, CO, and TiO; the flaring of the disk can be determined from the silicate feature, once M is known; and with these, the maximum radius of the disk can be determined from the flux at λ > 10 m. High resolution infrared spectrophotometric data are required to test these predictions.
