THE INVESTIGATIONS OF ZODIACAL LIGHT OF ISOLATED AE-HERBIG STARS WITH NONPERIODIC ALGOL-TYPE MINIMA

High linear polarization (up to 5-8%) discovered by our group in the deep minima of isolated AE-Herbig stars is discussed in the framework of the model of 'zodiacal light' produced by scattering matter in a circumstellar dust envelope (probably in protoplanetary discs). The numerical simulations of polarizational and colourimetrical properties of the scattered light based on the Mie theory permit to obtain from the observations some important parameters of circumstellar dust: the size distribution of grains, their rough chemical composition (silicate/graphite), the flatness of the dust envelope. Moreover, the position angle of polarization in deep minima may be used for determination of the symmetry axis projection of circumstellar disc on the sky relative to the direction of local interstellar magnetic field. The latest is important in order to understand the role of the magnetic field at the initial phase of gravitational collapse of protostellar clouds. Finally, the component of linear polarization which is due to the alignment of nonspherical circumstellar grains may be separate from the observed polarization under certain conditions.