A-shell stars in the Geneva system

Among the various kinds of A stars having a peculiar spectrum, we find the A-shell stars. Many questions are still open concerning these stars, includ ing their evolutionary status. In the present study we have used data from the Hipparcos catalogue to examine this point. We have found that the major ity of A-shell stars are well above the main sequence. No differences could be established between A-shell stars in luminosity classes III and I and t hose in luminosity class V as regards variability, duplicity, or the import ance of the shell feature.