  The structure of a circumstellar envelope around a young binary T Tauri star
is considered. The supersonic orbital motion of the system components in the
envelope gas leads to the formation of bow shocks around the star. Two- and
three-dimensional numerical modeling indicates an important role of these
shocks in the formation of the structure of the circumbinary envelope. In
particular, for systems with circular orbits, the size of the central region of
the envelope that is not filled with matter (the gap) is essentially determined
by the parameters of the bow shocks. These modeling results are supported by
comparisons of the obtained estimates for the gap parameters with observations.
