We present mid-infrared Spitzer-IRS spectra of the well-known UX Orionis star
VV Ser. We combine the Spitzer data with interferometric and spectroscopic data
from the literature covering UV to submillimeter wavelengths. The full set of
data are modeled by a two-dimensional axisymmetric Monte Carlo radiative
transfer code. The model is used to test the prediction of (Dullemond et al.
2003) that disks around UX Orionis stars must have a self-shadowed shape, and
that these disks are seen nearly edge-on, looking just over the edge of a
puffed-up inner rim, formed roughly at the dust sublimation radius. We find
that a single, relatively simple model is consistent with all the available
observational constraints spanning 4 orders of magnitude in wavelength and
spatial scales, providing strong support for this interpretation of UX Orionis
stars. The grains in the upper layers of the puffed-up inner rim must be small
(0.01-0.4 micron) to reproduce the colors (R_V ~ 3.6) of the extinction events,
while the shape and strength of the mid-infrared silicate emission features
indicate that grains in the outer disk (> 1-2 AU) are somewhat larger (0.3-3.0
micron). From the model fit, the location of the puffed-up inner rim is
estimated to be at a dust temperature of 1500 K or at 0.7-0.8 AU for small
grains. This is almost twice the rim radius estimated from near-infrared
interferometry. A best fitting model for the inner rim in which large grains in
the disk mid-plane reach to within 0.25 AU of the star, while small grains in
the disk surface create a puffed-up inner rim at ~0.7-0.8 AU, is able to
reproduce all the data, including the near-infrared visibilities. [Abstract
abridged]Comment: 12 pages, accepted for publication in Ap
