CIRCUMPROTOSTELLAR ENVIRONMENTS .2. ENVELOPES, ACTIVITY, AND EVOLUTION

We have obtained 800 and 1100 mu m photometric observations of a complete, flux-limited, IRAS-selected sample of cold sources in Taurus, whose infrared and molecular properties indicate them to be low-mass protostars which are younger than T Tauri stars. The goal of this study is to understand the role of the circumstellar envelope and disk during low-mass star formation and to search for signs of evolution. We find a good correlation between the submillimeter flux density (as well as of envelope mass) with both the mechanical luminosity of the molecular outflow and with the far-infrared luminosity, presumably produced by accretion onto the protostar. This suggests that the mass of the disk/envelope may be linked to the rate of accretion onto the protostar and to the generation of outflows. However, in contrast to the results of Cabrit & Andre (1991) we see no evidence for a lower limit to the disk/envelope mass which can produce outflows. We also find a significant difference between the spectral energy distributions at submillimeter wavelengths of embedded protostars compared to optically visible T Tauri stars. The more evolved (T Tauri) objects tend to have shallower spectral indices than embedded sources, suggesting (1) an evolution of dust grains, and/or (2) a more compact envelope and optically thick disk in the older objects.