On the similarity of FU Orionis stars to class I protostars: evidence fromthe submillimeter

On the basis of analysis of new submillimeter maps of a sample of most know n FU Orionis stars, we confirm that these stars are extremely young, more s imilar to Class I protostars than to Class II T Tauri stars. The submillime ter maps reveal that FU Orionis stars have accretion disks that are larger and contain an order of magnitude more mass than those of T Tauri stars but are comparable in mass to those seen around Class I sources. The disks aro und the FU Orionis stars are sufficiently massive to act as reservoirs of m aterial for replenishing the mass of the disks after eruptions, in which la rge amounts of material are believed to fall onto the underlying stars. We have identified a number of FU Orionis stars that are surrounded by extende d cloud emission, and in several cases we find nearby submillimeter sources that have no optical or near-infrared counterparts. These sources most lik ely are young protostellar Class I or Class 0 sources. In at least in one c ase, V1735 Cyg, the dominant submillimeter source is the protostar, not the optically visible FU Orionis star.