VARIABLE CIRCUMSTELLAR OBSCURATION AND VARIABILITY OF EMISSION-LINES IN THE SPECTRA OF THE HERBIG AE BE STARS/

The variability of the emission lines in the spectra of the Herbig Ae/ Be stars with non-periodic Algol-type minima is considered. It is show n that the obscuration of a star and its circumstellar gas envelope by optically thick dust clouds leads to variations of the emission lines which are similar to those observed. In particular, transformation of two-component emission line into a single profile is possible due to a screening of a star by a dust cloud. Changes of the H alpha line pro file of this type were observed recently in the deep minimum of UX Ori . The model explains also the variations of the equivalent width and t he flux in this line which were observed by Kolotilov (1977), Herbst e t al. (1983) and others in the minima of UX Ori type stars and which h ave been considered up till recently as strong evidence in favour of t he surface magnetic activity of these stars.