  A few years ago, the mid-IR spectrum of a Weak Line T Tauri Star, CoKu Tau/4,
was explained as emission from the inner wall of a circumstellar disk, with the
inner disk truncated at ~10 AU. Based on the SED shape and the assumption that
it was produced by a single star and its disk, CoKu Tau/4 was classified as a
prototypical transitional disk, with a clean inner hole possibly carved out by
a planet, some other orbiting body, or by photodissociation. However, recently
it has been discovered that CoKu Tau/4 is a close binary system. This implies
that the observed mid-IR SED is probably produced by the circumbinary disk. The
aim of the present paper is to model the SED of CoKu Tau/4 as arising from the
inner wall of a circumbinary disk, with parameters constrained by what is known
about the central stars and by a dynamical model for the interaction between
these stars and their surrounding disk. In order to fit the Spitzer IRS SED,
the binary orbit should be almost circular, implying a small mid-IR variability
(10%) related to the variable distances of the stars to the inner wall of the
circumbinary disk. Our models suggest that the inner wall of CoKu Tau/4 is
located at 1.7a, where a is the semi-major axis of the binary system (a~8AU). A
small amount of optically thin dust in the hole (<0.01 lunar masses) helps to
improve the fit to the 10microns silicate band. Also, we find that water ice
should be absent or have a very small abundance (a dust to gas mass ratio
<5.6X10^{-5}). In general, for a binary system with eccentricity e>0, the model
predicts mid-IR variability with periods similar to orbital timescales,
assuming that thermal equilibrium is reached instantaneously.
