On the origin of the azimuthal asymmetry in pole-on protoplanetary disks: The case of LkHα 101

Abstract

The model of a protoplanetary disk of a star with a low-mass companion ($M_2:M_1 \le 0.1$), moving on a circular orbit, which slightly inclined to the disk plane ($\le 10^{\circ}$), is considered. The SPH-method is used to calculate gas-dynamic ows. The motion of the companion on the orbit leads to the inhomogeneous distribution of the matter in the disk: there are a cleared gap, density waves and streams of matter. Because of the disturbances the inner part of the disk is tilted to its periphery and also do not coincides with the orbit plane of the companion. It leads to anisotropic illumination of the disk by the star and, as a consequence, to the appearance of large-scale inhomogeneity on the disk image: it has a bright area in the form of a \horseshoe" and a small shadow zone located asymmetric with respect to the line of nodes. The asymmetry of the disk image is clearly visible even if it is observed pole-on. The motion of the companion on the orbit does not lead to the synchronous movement of the shadow and bright areas: they only make small oscillations relative to the some direction. By using the proposed model we an fairly accurately reproduce the asymmetric image of the disk of star LkH$\alpha$ 101, observed almost pole-on. The study of such asymmetric disks opens up new opportunity for searching massive bodies around young stars.