Dust grain growth and disk evolution of a set of young stellar objects

This work investigates the observed properties of a sample of young stellar systems using two computer-modeling codes, DUSTY and the Whitney TTSRE codes, to fit the spectra of many objects. The parameters of these computer models are used to attempt to answer several basic questions related to circumstellar disk evolution. Silicate band strengths and millimeter spectral indexes are related to grain growth and are found to be reasonably correlated for the group of models. Circumstellar disk self-shadowing can effect the spectral shape of far infrared data and the relation between the two are studied showing a possible correlation, however other factors can effect the shape of the far infrared data and so a firm correlation can not be confirmed. Six objects out of the nearly 50 stars fit with DUSTY are fit with the Whitney code. Chronological age estimates are compared with model parameters but no correlation could be found between either silicate band strength or millimeter spectral index and the objects' ages. This indicates that the evolutionary ages and chronological ages of this set of objects are not closely related. For two stars, HD 31648 and HD 163296, time dependent data exists showing differences in the near infrared region. To fit the differing data, the inner radius of the model disk needed to move outwards and the geometrical thickness of the model disk needed to increase. This provides a possible disk evolution scenario to explain the differing spectra.