  EX Lup is the prototype of the EXor class of eruptive young stars. These
objects show optical outbursts which are thought to be related to runaway
accretion onto the star. In a previous study we observed in-situ crystal
formation in the disk of EX Lup during its latest outburst in 2008, making the
object an ideal laboratory to investigate circumstellar crystal formation and
transport. This outburst was monitored by a campaign of ground-based and
Spitzer Space Telescope observations. Here we modeled the spectral energy
distribution of EX Lup in the outburst from optical to millimeter wavelengths
with a 2D radiative transfer code. Our results showed that the shape of the SED
at optical wavelengths was more consistent with a single temperature blackbody
than a temperature distribution. We also found that this single temperature
component emitted 80-100 % of the total accretion luminosity. We concluded that
a thermal instability, the most widely accepted model of EXor outbursts, was
likely not the triggering mechanism of the 2008 outburst of EX Lup. Our
mid-infrared Spitzer spectra revealed that the strength of all crystalline
bands between 8 and 30 um increased right after the end of the outburst. Six
months later, however, the crystallinity in the 10 um silicate feature complex
decreased. Our modeling of the mid-infrared spectral evolution of EXLup showed
that, although vertical mixing should be stronger during the outburst than in
the quiescent phase, fast radial transport of crystals (e.g., by stellar/disk
wind) was required to reproduce the observed mid-infrared spectra.
