Discovery of high linear polarization at brightness minima of CQ Tau

Results are presented of simultaneous UBVRI observations (carried out in Crimea during 1988/1989) of the polarization and light characteristics of an isolated Ae Herbig star CQ Tau. During this period, several decreases in light were observed, accompanied by considerable changes in the polarization parameters. It was found that, while the linear polarization of the star did not significantly differ from that of neighboring stars during the bright state (V = 9.5 mag), a considerable increase of the polarization degree was observed during the deep minimum (V = 11.2 mag), together with strong variations of the position angle.