Spectral evolution of accretion disks of dwarf novae. II. Radiative transfer models

The spectra of dwarf novae show broad absorption lines in outburst and strong emission lines during the quiescent state. Simplified calculations are presented for idealized disk models that demonstrate that these features can be attributed to radiative properties of accretion disks. Using these models, it is shown that the absorption lines are generated when the mass transfer rate through the disk is sufficiently large so that most regions of the disk are optically thick in the direction normal to the plane of the disk. In quiescence, emission lines are generated over optically thin regions with temperatures of 6000-9000 K and densities of 10 to the 14th to 10 to the 17th/cu cm. The actual detailed profiles of the lines are sensitive functions of the disk size, viscosity, and mass transfer rate. Thus, detailed analyses of spectral properties can provide useful information on disk structure and evolution. 34 references