SPHERICAL DISKS - MOVING TOWARD A UNIFIED SOURCE MODEL FOR L1551

To predict the effects of a disk on the spectral energy distribution o f a deeply embedded protostar, we construct disk models with power-law temperature distributions (T is-proportional-to r(-q)). We then use t he spherically averaged disk emission as the central source for a sphe rical envelope, hence the term, ''spherical'' disk. We then calculate the predicted spectral energy distribution of the disk and envelope, u sing a spherically symmetric radiative transport code. Applying this p rocedure to L1551 IRS 5, we find that the predicted far-infrared flux is not very sensitive to the nature of the central source, The best so urce model is consistent with the far-infrared emission arising from t he infalling region in an ''inside-out'' collapse model, independent o f the nature of the central source. Disk models are superior to the st ar-only model when we try to match millimeter interferometer data. Whi le disks with various q can reproduce the observed 2.7 mm interferomet er flux, only an active disk (q = 0.5) can produce enough emission in a region small enough to match the observed 2.7 mm visibilities. Howev er, if the disk is backwarmed by the envelope, even purely reprocessin g disks can meet this constraint. All types of backwarmed disks are vi rtually indistinguishable in their millimeter properties. We find that all reasonable envelope models are sufficiently opaque in the mid-inf rared to attenuate any disk model to a level well below the observatio ns, unless the ratio of the mid-infrared to far-infrared dust opacitie s is similar to that of the dust opacities advocated by Mathis, Mezger , & Panagia (1983).