PHOTOEVAPORATION OF PROTOSTELLAR DISKS - III - THE APPEARANCE OF PHOTOEVAPORATING DISKS AROUND YOUNG INTERMEDIATE-MASS STARS

We present theoretical continuum emission spectra (SED's), isophotal m aps and line profiles for several models of photoevaporating disks at different orientations with respect to the observer. The hydrodynamic evolution of these models has been the topic of the two previous paper s of this series. We discuss in detail the numerical scheme used for t hese diagnostic radiation transfer calculations. Our results are quali tatively compared to observed UCHII's. Our conclusion is that the high fraction of ''unresolved'' UCHII's from the catalogues of Wood & Chur chwell (1989) and Kurtz et al. (1994) cannot be explained by disks aro und massive stars. In particular, the observed infrared spectra of the se objects indicate dust temperatures which are about one order of mag nitude lower than expected. We suggest that disks around close compani ons to OB stars may be necessary to resolve this inconsistency. Altern atively, strong stellar winds and radiative acceleration could remove disk material from the immediate vicinity of luminous O stars, whereas for the lower luminosity sources considered here this will not occur. We also find that line profiles tracing the evaporated material origi nating from the disk are not influenced significantly by the existence of stellar winds over a wide range of wind velocities (400 - 1000 km s(-1)). We compare our results to the bright IRAS source MWC 349 A. Ma ny of its properties, especially its spatial appearance in high-resolu tion radio maps, can be well explained by a disk surrounding a uv lumi nous star with a high velocity stellar wind.