  EX Lup is the prototype of EXors, a subclass of low-mass pre-main sequence
stars whose episodic eruptions are attributed to temporarily increased
accretion. In quiescence the optical and near-infrared properties of EX Lup
cannot be distinguished from those of normal T Tau stars. Here we investigate
whether it is the circumstellar disk structure which makes EX Lup an atypical
Class II object. During outburst the disk might undergo structural changes. Our
characterization of the quiescent disk is intended to serve as a reference to
study the physical changes related to one of EX Lupi's strongest known
eruptions in 2008 Jan-Sep. We searched the literature for photometric and
spectroscopic observations including ground-based, IRAS, ISO and Spitzer data.
After constructing the optical-infrared spectral energy distribution (SED), we
compared it with the typical SEDs of other young stellar objects and modeled it
using the Monte Carlo radiative transfer code RADMC. A mineralogical
decomposition of the 10 micron silicate emission feature and also the
description of the optical and near-infrared spectra were performed. The SED is
in general similar to that of a typical T Tauri star, though above 7 micron EX
Lup emits higher flux. The quiescent phase data suggest low level variability
in the optical-mid-infrared domain. Integrating the optical and infrared fluxes
we derived a bolometric luminosity of 0.7 L_Sun. The 10 micron silicate profile
could be fitted by a mixture consisting of amorphous silicates, no crystalline
silicates were found. A modestly flaring disk model with a total mass of 0.025
M_Sun and an outer radius of 150 AU was able to reproduce the observed SED. The
derived inner radius of 0.2 AU is larger than the sublimation radius, and this
inner gap sets EX Lup aside from typical T Tauri stars.
