J.C. Correia 1, M. Griffin 1, & P. Saraceno 2
1 Physics Dept., Queen Mary & Westfield College, Mile End Road, London E1 4NS, UK
2 Istituto di Fisica dello Spazio Interplanetario - CNR - Roma, Italy
We present ISO-LWS and JCMT continuum observations of a sample of young stellar objects representing different protostellar stages. These observations are complemented with IRAS data and other data available in the literature in order to construct complete spectral energy distributions. A spherical envelope+disk model is used to characterize the circumstellar matter around these objects and to derive relevant physical parameters. Special attention is given to the envelopes density profiles and to the dust emissivity. The results presented here emphasize the importance of the LWS data in giving us acess to the region of the spectrum where the youngest objects have their peak emission. They also show the need for submillimetre mapping with instruments like SCUBA in order to constrain some of model parameters.