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 \sim 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 .
We lack a physical prescription for the shape of the wall , thus , here we use a simplified and unrealistic assumption : the wall is vertical .
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 .
In the context of the present model , higher eccentricities would imply that the stars are farther from the wall , the latter being too cold to explain the observed SED .
Our models suggest that the inner wall of CoKu Tau/4 is located at 1.7 a , where a is the semi-major axis of the binary system ( a \sim 8 AU ) .
A small amount of optically thin dust in the hole ( \lesssim 0.01 lunar masses ) helps to improve the fit to the 10 \mu m silicate band .
Also , we find that water ice should be absent or have a very small abundance ( a dust to gas mass ratio \lesssim 5.6 \times 10 ^ { -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 .