Investigations of the dynamical evolution of protoplanetary nebulae

The spectral energy distributions (SED's) of all the known Class I (protostellar) sources in the Taurus molecular cloud were modelled. The Tereby, Shu, & Cassen (1984, TSC) density distribution for a rotating, infalling envelope was adopted. The radiative equilibrium temperature distribution from the spherical average of the TSC density distribution was calculated. The resulting spherically-symmetric temperature distribution then provides the source function to obtain the emergent spectrum at a given inclination angle i from the formal solution of the transfer equation, using the exact density (opacity) distribution. Results showed that the SED's of the protostar candidates in Taurus can be reproduced with TSC models having infall rates close to the values predicted by the theory of isothermal cloud collapse. Flat Spectrum T Tauri Stars were studied. The mid- to far-infrared fluxes of 'flat spectrum' T Tauri stars can be explained by radiative equilibrium emission from infalling dusty envelopes. This explanation indicated that models employing 'active' disks, in which the temperature distribution is a parameterized power law, should be invoked with caution. Infall also naturally explains the scattered light nebulae detected around many flat-spectrum sources. Results showed that the SED's of the protostar candidates in Taurus can be reproduced with TSC models having infall rates close to the values predicted by the theory of isothermal cloud collapse. Flattened infalling envelope models are also being studied.