On Protostellar Disks in Herbig Ae/Be Stars

The spectral shape of IR emission from Herbig Ae/Be stars has been invoked as evidence for accretion disks around high-mass protostars. Instead, we present here models based on spherical envelopes with an r-1.5 dust density profile that successfully explain the observed spectral shapes. The spectral energy distributions of eight primary candidates for protostellar disks are fitted in detail for all wavelengths available, from visual to far-IR. The only envelope property adjusted in individual sources is the overall visual optical depth, and it ranges from 0.3 to 3. In each case, our models properly reproduce the data for IR excess, visual extinction, and reddening. The success of our models shows that accretion disks cannot make a significant contribution to the radiation observed in these pre-main-sequence stars.