2800 MgII Doublet as an Indicator of Circumstellar Clouds

It is shown that the profiles and strengths of ultraviolet MgII doublet, k and h MgII lines, may be essentially different in the spectra of two stars of one and the same spectral and luminosity class. This fact may be explained by the presence of circumstellar clouds around the stars, particularly of B–A types. We demonstrate the possibility of the utilization of 2800 MgII doublet as an indicator of circumstellar clouds. The problem of three-scale spectral classification of stars is raised. This revised version was published online in July 2006 with corrections to the Cover Date.