  The model of an young star with a protoplanetary disk and a low-mass
companion, which is moving on a circular orbit, inclined to the disk plane, is
considered. The hydrodynamic models of such a system were calculated by SPH
method. It was shown the distortions in the disk, caused by the orbital motion
of the companion, lead to the strong dependence of illumination conditions of
the disk on the azimuth (because of extinction between the star and the disk
surface) and, therefore, it leads to the appearance of large-scale asymmetry in
images of disks. The calculations showed the dependence of the illumination on
the azimuth was stronger in the central part of the disk than on the periphery.
Bright and dark domains are located not symmetry with respect to the line of
nodes. The sizes and locations of the domains are depended on the model
parameters as well as on the phase of the orbital period. The bright and dark
domains do not follow the companion, but they make small amplitude oscillations
with respect to some direction. The properties of the model, which were written
above, open new opportunities of searching low-mass companions in the vicinity
of young stars. The stars with protoplanetary disks, which are observed face-on
or under the small inclination angle i, are the best ones for this purpose.
