SIMBAD references

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 shown 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 Hα line profile of this type were observed recently in the deep minimum of UX Ori. The model explains also the variations of the equivalent width and the flux in this line which were observed by Kolotilov , Herbst et al. and others in the minima of UX Ori type stars and which have been considered up till recently as strong evidence in favour of the surface magnetic activity of these stars.